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Scientia Horticulturae 159 (2013) 41–51

Contents lists available at SciVerse ScienceDirect

Scientia Horticulturae

journa l homepage: www.e lsev ier .com/ locate /sc ihor t i

egulatory effects of exogenous gibberellic acid (GA3) on waterelations and CO2 assimilation among grapevine (Vitis vinifera L.)ultivars

éter Teszláka,∗, Marianna Kocsisb, Krisztián Gaála, Martin Pour Nikfardjamc

Department of Viticulture and Technology Development, University of Pécs, Pázmány Péter 4, 7634 Pécs, HungaryDepartment of Plant Physiology, University of Pécs, Ifjúság 6, 7624 Pécs, HungaryState Research Institute for Viticulture and Pomiculture, Traubenplatz 5, 74189 Weinsberg, Germany

r t i c l e i n f o

rticle history:eceived 11 December 2012eceived in revised form 29 April 2013ccepted 30 April 2013

eywords:ibberellic acid (GA3)ell wall elasticitysmotic adjustmentet CO2 assimilation

a b s t r a c t

Different impacts of exogenous gibberellic acid (GA3) on water relation and CO2 gas exchange in grapevineleaves were studied on four varieties belong to various ecogeographical groups. GA3 treatment resultedin increasing cell wall rigidity in some cultivars and affected the linear correlation between elastic-ity modulus (‘ε’) and relative water content at the turgor loss point (RWCTLC). The response of cultivar‘Riesling’ agreed with the hypothesis; GA treatment resulted in increasing ‘ε’ values (‘ε’ > 12 MPa), indi-cating decreased cell wall elasticity. According to pressure–volume analysis, osmotic potential at fullturgor (˘100) in treated ‘Sauvignon Blanc’ vines was higher compared to the controls. Results of analy-sis demonstrated that the four varieties showed a negative linear correlation between apoplastic watercontent (AWSD%) and leaf water potential at the turgor loss point (� TLP) and a positive linear correlation

ater use efficiencyrapevine (Vitis vinifera L.)

between AWSD% and RWCTLP. Values of Ci and PN showed a positive exponential correlation; Ci valuesincreased parallel with increasing net CO2 assimilation in a range between 10 and 24 Pa of Ci both incontrol and treated vines. In each cultivar, intrinsic water use efficiency (WUEi) increased at reducedstomatal conductance. GA3 treatment resulted in favourable values of WUEi as expected for cultivar‘Kadarka’ (group of convarietas pontica). WUEi was significantly (P < 0.05) lower in the GA3 treated vinescompared to the controls in most of the varieties irrespective of different ecogeographical groups.

. Introduction

Gibberellic acid (GA) plays an important role in many essen-ial plant growth and development processes, including seedermination, stem elongation, leaf expansion and reproductiveevelopment. GA is widely regarded as a growth-promoting com-

ound that positively regulates processes such as seed germination,tem elongation, leaf expansion, flower and fruit development andoral transition (Razem et al., 2006).

Abbreviations: AWSD%, apopalstic water content; Ci , sub-stomatal CO2 concentra-ion; E, transpiration rate; ‘ε’, modulus of cell wall elasticity; GA3, gibberellic acid;s, stomatal conductance to water vapour; ‘KA’, Vitis vinifera L. cultivar ‘Kadarka’;

LE’, Vitis vinifera L. cultivar ‘Lemberger’ (syn. ‘Kékfrankos’); PCA, principal compo-ents analysis; PN, net CO2 assimilation; ˘100, osmotic potential at full turgor; ‘RI’,itis vinifera L. cultivar ‘Riesling’; RWCTLP, relative water content at turgor loss point;

SB’, Vitis vinifera L. cultivar ‘Sauvignon Blanc’; WUEi, intrinsic water use efficiencyPN/gs); � PD, predawn leaf water potential (leaf water potential at stomatal closure);

TLP, leaf water potential at turgor loss point.∗ Corresponding author. Tel.: +36 30 846 7557; fax: +36 72 517 936.

E-mail address: teszlak.peter@pte.hu (P. Teszlák).

304-4238/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.scienta.2013.04.037

© 2013 Elsevier B.V. All rights reserved.

The GAs have long been used in horticultural practice as growthregulators for crop improvement. Insignificant effects and lack oftoxicity allows a wide range of applications in several cultivatedspecies, e.g. increasing stem elongation and bract size or coloriza-tion (Blanchard and Runkle, 2008) and seedless fruit production(Retamales et al., 1998). In woody angiosperms flowering is gener-ally associated with reduced stem elongation. It may be proposedthat the role of GAs in flowering of different plant groups reflect therelationship between stem elongation and flowering (Goldschmidt,1998).

GA has also been used in viticulture as a regulatory compound.Early experiments have shown that different concentrations ofGA3 delay bud-break in cultivars ‘Riesling’ and ‘Velteliner Grün’,as well as some rootstock varieties (Alleweldt, 1959, 1961). Pre-bloom GA3 treatment leads to bunch expansion resulting in a looserarchitecture of clusters. This impact of GA3 is now used in tablegrape production (Van der Merwe et al., 1991; Williams and Ayars,

2005). The impact of GA treatment on the grape cluster dependslargely on the concentration and development stage when used.Adverse effects could include the inhibition on inflorescence pri-mordia development.

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GA is required for the formation and growth of the inflores-ence axis. At an early stage, GA promotes flowering, while laterA inhibits of flowering because it directs the Anlagen to form ten-rils (Mullins et al., 1992). In general, it has a positive impact oneedless table grapes, while it can exert positive or negative effectsn quality of seeded grapes. In practice, seeded varieties are moreensitive to GA3 treatment than seedless grapes. Using 20 mg L−1

f GA results in a significant decrease of yield, because increasedower-abscission has a negative effect on successful fertilizationBaydar and Harmankaya, 2005). In the case of wine grapes, posi-ive effects are earlier ripening, higher Brix◦, and increased rate oferry skin/berry flesh. Furthermore, a recent study reported thatA3 significantly increased potassium content in grape berries of aitis vinifera L. × Vitis labrusca L. hybrid (Niu et al., 2008), which cane important for production of quality grapes and wine.

GA3 treatment also has an impact on stomatal movement (Viciaaba, Fritillaria imperialis), where it induces transient opening oftomata in the dark (Göring et al., 1990; Pospisilova, 2003). Inroad bean (V. faba) GA3 increased stomatal conductance, net CO2ssimilation and Rubisco activity (Yuan and Xu, 2001). Neverthe-ess, many studies can be found, which report inconsistent effectsAshraf et al., 2002) or decreasing effects on stomatal conductancend transpiration rate (Bishnoi and Krishnamoorthy, 1993; Singht al., 1999).

In some cases GA3 treatment changes lignin deposition (reducedignin content in Asparagus), which plays an important role in theegulation of water content through changes in cell wall elastic-ty (Liu and Jiang, 2006). GA3 reduces the threshold of cell wallxpansion, thus minimum levels of turgidity can induce cell wallxpansion, and can influence the osmotic and turgor pressure of therowing zone through translocation of osmotically active solutesBehringer et al., 1990).

Little is known about how GA3 can change elastic and osmoticegulation of water content and alter CO2 assimilation in leaves ofrapevines (Williams and Ayars, 2005). GA3 has a significant role inhe formation of primary bud necrosis (physiological disorder) inhe case of vigorously growing cultivars such as ‘Shiraz’ (Collins andawnsley, 2008). In practice it is used for synchronizing maturationf grape berry, making homogeneous berries and bunches and issed to enhance veraison and ripening process (Pagay and Cheng,008).

GA3 not only increases the size of the berries and clusters, butlso reduces compactness of bunches, and leads to a thicker berrykin, which greatly improves the favourable microclimate withinlusters and reduces Botrytis infection and bunch-rot (Reynoldst al., 2006). Recent experiment have shown that GA3 treatment20 mg L−1 at bloom, 40 mg L−1 post-bloom) significantly increaseshe colour and anthocyanin content, results in a sweeter fruityaste, and improved flavour with more persistence (Reynolds et al.,006). GA3 is useful for reducing the effects of trunk girdling effectenhanced abscisic acid accumulation) on photosynthesis via anncrease in stomatal conductance (Harrell and Williams, 1987;

illiams and Ayars, 2005). In grapevines a number of bioactive gib-erellins (GA1, 3, 17, 19) can be found both in seeded and in seedlessarieties (Perez et al., 2000). Today, research continues in the areaf GA application in relation to grape and wine production as wells precision viticulture. It is very important as a cost-effective tech-ology for viticulture, just as with “minimal pruning”, where GA3an improve must quality (higher Brix◦) and balance the delayingffect of “minimal pruning” on ripening date (Weyand and Schultz,005). The outlined strategy seems promising for the production ofuality fruit in an economically driven viticultural system.

The aim of this study was to demonstrate the effect of exogenousibberellic acid on the regulation of water relations, osmotic andlastic acclimation mechanisms in leaves through correlation anal-sis and multiple statistics, as well as to examine how GA3 can affect

lturae 159 (2013) 41–51

CO2 assimilation and intrinsic water use efficiency of differentgrapevine cultivars. The research was carried out on four grapevinevarieties under field conditions. Unique to these experiments is thefact that we report about well-known cultivars (‘Sauvignon Blanc’and ‘Riesling’) in addition to important local and autochthonousvarieties (‘Lemberger’ and ‘Kadarka’) of Hungary, which are com-pletely uncharacterized in the field of physiological responses toGA3 treatment.

2. Materials and methods

2.1. Experimental site and plant material

The study was carried out at the St. Nicholas Hill ResearchStation of the Institute of Viticulture and Oenology, University ofPécs, Hungary. We studied four grapevine (V. vinifera L.) cultivars:‘Sauvignon Blanc’ (SB) and ‘Riesling’ (RI) (convarietas occidentalis);‘Lemberger’ (LE) (convarietas orientalis) and ‘Kadarka’ (KA) (convari-etas pontica), which have different origins and taxonomic positionsaccording to ampelographic classifications (Németh, 1967). Eachvariety was grafted on a generally used rootstock (‘Teleki 5C’, Vitisberlandieri × Vitis riparia hybrid).

Five-year-old vines were grown on south-facing slopes andterraces of the Mecsek Hills (latitude: 46◦07′ N, longitude: 18◦17′

E, 200 m elevation) in non-irrigated field conditions. The soil wasa Ramann-type brown forest soil mixed with clay, formed onPannonian red sandstone. Vines were trained to an umbrella sys-tem with 2.0 m × 1.0 m row by vine spacing. Row direction wasNorth–South on steep slopes and East–West on micro terraces.Steep slopes are typically characterized as severely eroded siteswith shallow soil layer. Representative leaf samples for measure-ments originated from homogeneous plantings with 100 vinesof each cultivar. The site is situated within the Praeillyricum(plant geographical district), which on average receives 782 mmof precipitation per year, 2021 h of sunshine annually and withan annual mean temperature of 11.6 ◦C. However, the mesocli-matic characteristics of the site show significant extremes inprecipitation events (344–1140 mm), in amount of sunshine hours(1986–2548 h) and in annual mean temperature (9.3–14.0 ◦C)according to data collected between 1950 and 2005 (IVO, 2010).

The research was conducted on two different plots with var-ious soil conditions in 2004 and 2005. One of the plots was aneroded steep-slope, and was more exposed to drought stress thanthe other plot, which had a deeper soil layer. Two of the studiedcultivars are used worldwide (‘SB’, ‘RI’) with a well-known per-formance based on their high-level ecological plasticity and weregrown under eroded shallow soil conditions (steep-slope). The twoother cultivars (‘LE’, ‘KA’) have high significance as autochthonousand regional grapevines, and were grown in more favourable, con-ditions with deeper soil (terraces). ‘Lemberger’ is a red wine variety,and is the most widely grown cultivar in the Carpathian Basin.‘Kadarka’ is a typical Hungarian autochthonous red wine varietybefore the 20th century, but has become more and more impor-tant again and has a great marketing value. So far, only preliminaryresults are available about the physiological behaviour (water rela-tion and photosynthetic activity) of this variety (Teszlák et al.,2004). Treatment effects were not influenced by the two differ-ent soil conditions, because all GA3 treated and control vines werewithin the same plot of the given variety.

All measurements of the study were based on fifty specimensof control and treated vines that were situated in different rows of

each variety. The separation distance between treated and controlvines was sufficient to excluded hormone drift during GA applica-tion. In order to evaluate combined data of two consecutive years,in the second year a different set of fifty vines was treated with

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A3, because it is known that GA3 treatment can have some post-reatment effects on differentiation of inflorescence primordia andhus, may have influenced the mean principles of our experimentalesign.

.2. Flower treatment with GA3

Grapevine flowers were sprayed at full bloom to the drip pointith an aqueous 20 ppm gibberellic acid (GA3) solution (containing

.2% Tween 20®). All reagents used were of analytical grade unlesstherwise stated. GA3 and Tween 20® were from Fluka (Buchs,witzerland). Freshly made hormone solutions were used for eachreatment. The solutions were kept in the dark before spraying,ecause the gibberellic acid decays rapidly in direct sunlight. Thereatments were conducted between 10th and 15th of June in 2004nd between 13th and 18th of June in 2005. The growth cycles ofhe varieties differed (different ripening dates), however, the flow-ring period was finished after 7 (‘RI’, ‘LE’) and 8 (‘SB’, ‘KA’) days in004, respectively. In 2005 this period took about 11 (‘LE’, ‘KA’) and2 (‘SB’, ‘RI’) days. In the case of each variety, GA3 treatment wasarried out at full bloom in both years.

.3. Soil water content

Soil water content was evaluated gravimetrically according tolack (1965), and expressed as the percent of water mass per totaleight. A soil borer (0.03 m in diameter) was used to collect a sam-le through to a depth of 10 cm. Water mass was determined byeighing the soil sample before and after drying (n = 4 for each

reatment and each collection date). Soil samples were collected todepth of 0.5 m. Soil moisture was examined four times during therowing season (bud-break, flowering, pea size berry and veraison)n 2004 and 2005. The samples were transported in a hermeticallyealed glass jar. The gravimetric method was used to determine theater content of the samples, and dried at 105 ◦C in an oven (KKanz, Hungary). Fresh weight and dry weight of soil samples wereetermined in glass jars using an analytical balance (±0.1 mg) (Met-lerToledo, Switzerland). For determination of soil moisture values,he following formula was used:

oil water content (%) = fresh weight − dry weightfresh weight

× 100.

Predawn leaf water potential (� PD) (Scholander et al., 1965)easurements were performed as supplementary data to soil mois-

ure values in the first year. � PD was determined using fullyxpanded, mature leaves in a pressure chamber with nitrogen ashe pressurizing gas. The readings were taken beginning at 03:30nd commencing before sunrise. It has been assumed that beforeunrise the vine is in equilibrium with the soil’s water potential,herefore making � PD a very sensitive indicator of soil water avail-bility (van Zyl, 1987). The � PD values were obtained from threeeplicates.

.4. Pressure–volume analysis

Fully expanded, healthy sun-adapted detached leaves were usedrom randomly chosen individual vines. Samples (n = 3) were col-ected in polyethylene bags from the 8–12th nodes in the afternoon.irectly after the leaf removal, their fresh weight was determined,nd then their complete rehydration to full turgor was startedvernight in the dark for 12 h in a plastic bowl filled with distilled

ater. After rehydration, leaves were removed from the water totable to allow dehydration due to free transpiration. Leaf waterotential (� ) (pressure) and leaf weight (volume) were determined0 times in each leaf under continuous dehydration with a pressure

lturae 159 (2013) 41–51 43

chamber and analytical balance (±0.1 mg). At the end of this proce-dure, leaves were completely dried in a drying oven (at 105 ◦C) andweighed to determine dry mass. The relative water content (RWC)in each leaf was calculated according to the following formula:

RWC(%) = FW − DWTW − DW

× 100,

where FW, fresh weight from the first measurement before fullsaturation; DW, dry weight; and TW, turgid weight, followed byactual water potential measurement. This allowed as to relate leafweights to relative water content. Using these data, we plottedpressure–volume curves (Höfler diagrams), which rely on balanc-ing pressures and relative water content or water saturation deficit(WSD) (WSD = 1 − RWC) to extrapolate cell properties (Tyree andJarvis, 1982). Linear regression of data (1/� , RWC) was carried outusing Excel® (Microsoft Corp., Redmond, USA). Between six andeight data points were used to fit the “osmotic line”. Outliers wereexcluded from regression analyses. The fitted regressions explainedbetween 77 and 100% (average 92%) of the variance in 1/� dataon the linear portion of the curve (Pallardy et al., 1991). Resid-ual plots indicated that a linear regression was appropriate for allgraphs (Andersen et al., 1991; Urban et al., 1993). The turgor losspoint (RWCTLP), osmotic potential at full turgor (˘100), apoplasticwater fraction at full turgor (AWSD%) and cell wall elasticity (ε) werederived from the PV curves (Pallardy et al., 1991). The turgor dataof each leaf was estimated by interpolation of the “osmotic line” tothe WSD of the leaf. The pressure–volume analysis was performed4 times, between 14 and 19th of July and between 10 and 16th ofAugust in 2004; and between 04 and 13th of July and between 20and 28th of September in 2005, respectively.

2.5. Gas exchange measurements

The gas exchange measurements were conducted on attachedleaves using an infrared open-system portable LCA-4 gas analyser(ADC BioScientific Ltd., Hoddesdon, UK) with three replicates persample. Mature and healthy sun-adapted leaves from the 8–12thnode were used for the analysis. Measurements were carried outunder the maximum photosynthetic activity of leaves, between10:00 and 11:30 h local time, at 1500–1700 �mol m−2 s−1 PPFDunder normal atmospheric CO2 concentration, at 25 ◦C (2004)and at 22 ◦C (2005) leaf surface temperature under 0.17–0.83 kPavapour pressure deficit. We determined the net CO2 assimilationrate (PN), the rate of transpiration (E), the stomatal conductance(gs), the value of partial pressure of intercellular CO2 (mesophyllconductance) (Ci) and WUEi (PN/gs). The PPFD incidence on leaveswas always higher than 1500 �mol m−2 s−1, which is considered tobe above photosynthesis saturation in the grapevine (Flexas et al.,2002). PN, E, gs and Ci were calculated using the equations of vonCaemmerer and Farquhar (1981). The PN/gs ratio was used to indi-cate intrinsic water use efficiency, according to Iacono et al. (1998).Gas exchange measurements of the first experimental year wereperformed on 24th of June and 12th of July (n = 3) during the pre-harvest period, and in the following year on 10th of October (n = 5)after harvest.

2.6. Statistical analysis

Statistical analysis was carried out using Excel® (MicrosoftCorp., Redmond, USA), SPSS® (SPPS Corp., Chicago, USA), and S-PLUS® (MathSoft Inc., Cambridge, USA). Paired sample t-tests wereperformed on all data sets with 99% confidence interval. Prin-

cipal component analysis (PCA) was performed on normalizeddata sets of pressure–volume analysis and gas exchange mea-surements (Fig. 7). Correlation analysis of linear and non-linearregression was performed (r = correlation coefficient, DF = degree

44 P. Teszlák et al. / Scientia Horticulturae 159 (2013) 41–51

Table 1Seasonal dynamics of soil water content (%) measured gravimetrically in 2004 and in 2005 at different growing stages of ‘Sauvignon Blanc’ (SB), ‘Riesling’ (RI), ‘Lemberger’(LE) and ‘Kadarka’ (KA). SB and RI are cultivated together on N–S directed steep slope with eroded shallow soil layer and LE and KA are cultivated together on E–W directedterraces with deeper soil layer.

2004 2005

Budbreak Anthesis Pea size Veraison Budbreak Anthesis Pea size Veraison

SB, RI 14.02 ± 0.63 12.05 ± 1.61 8.63 ± 1.08 9.80 ± 0.73 13.30 ± 1.28 13.37 ± 0.65 11.29 ± 1.55 13.60 ± 1.12LE, KA 14.87 ± 1.91* 15.48 ± 1.14** 12.94 ± 2.35** 15.43 ± 1.77** 15.57 ± 1.74** 16.89 ± 1.72** 15.12 ± 1.38** 14.46 ± 1.18*

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f freedom, r0.05 = critical value of correlation coefficient at P < 0.05evel) in two highlighted varieties (‘SB’ and ‘LE’), and these vari-ties were reported by correlation analysis of pressure–volumeata (Figs. 1 and 4). In the Ci–PN, gs–WUEi relationships (non-linearorrelation) were based on cumulated gas exchange data of eachariety (Figs. 5 and 6).

. Results and discussion

.1. Soil water availability

Since the plots were located in two different soil types within thexperimental sites, it is important to measure the soil water contentharacteristics of each location. The ‘SB’ and ‘RI’ were grown on anroded site, while the ‘KA’ and ‘LE’ were on a plot with deeper soil,ut treated and control vines of all cultivars were grown within theame plot. The values of soil water content by ‘SB’ and ‘RI’ graduallyecreased from bud-break to the “pea size berry” stage in 2004Table 1). The cultivars showed the lowest values on this soil by theea size berry stage in both years. The year 2004 was a rather rainyintage, but there was a period with moderate drought stress inuly, which also marked a decline of the soil water content betweenhenological stages of flowering and pea size berry. During thiseriod, the soil water content decreased by 28% in ‘SB’ and ‘RI’ andy 16% in ‘KA’ and ‘LE’ between the stages of anthesis and pea sizeerry. Data of soil water content established the fact that we couldnd moderate drought stress only at the site of ‘SB’ and ‘RI’.

During the vegetation period and the four phenological stages,he values of soil water content were significantly higher by ‘LE’nd ‘KA’ than by ‘SB’ and ‘RI’ [budbreak (P < 0.05), anthesis, veraisonnd pea berry size (P < 0.01)]. The year 2005, was characterized byood precipitation, in most cases the values were higher than in therevious year in both plots. There were no significant differencesmong phenological stages. However, between both plots thereere also significant differences in this year [budbreak, anthesis,ea berry size (P < 0.01) and veraison (P < 0.05)], better soil watertates were recorded for ‘LE’ and ‘KA’ than for ‘SB’ and ‘RI’.

In addition to soil water measurements, predawn leaf waterotential (� PD) was recorded according to Richter (1997). Theesults show no significant difference between treated and con-rol vines (P < 0.05) regardless of cultivar (data not shown). The

PD values between −0.07 MPa and −0.12 MPa indicated a posi-ive water-status in each cultivar, so the treatment did not alterhe effect of moderate and severe drought stress. The high � PD val-es indicate favourable plant water status in most of the cultivarsvan Zyl, 1987). The non-significant deviations of the � PD valuesuggest the same water-status in both plots of treated and controlines (Table 1). Significant differences of � PD values could onlye found between the different cultivars, both in the GA3 treated

nd the control vines, which arise from the different physiologicalroperties determined by different genotypes. Anyway, the GA3reatment did not have a significant impact upon the � PD changesith any of the investigated cultivars.

rse and favourable soil conditions at P < 0.05 level (n = 4).rse and favourable soil conditions at P < 0.01 level (n = 4).

3.2. GA3 affects on RWC-correlated cell wall elasticity

The relative water content at turgor loss point (RWCTLP) of ‘SB’showed a linear correlation with the alteration of cell wall elasticitymodulus (‘ε’) by control plants. Parallel with the decreasing elastic-ity modulus, the leaves lost their turgor by lower RWC (Fig. 1). Thisrefers to the fact that the ‘SB’ increases cell wall elasticity to regu-late its water content. Generally, in higher plants the RWCTLP showslinear correlation with the modulus of cell wall elasticity and theincreasing ‘ε’ value indicates a higher cell wall rigidity. By chang-ing the ‘ε’ value, the control leaves of ‘SB’ showed typical behaviourof this cultivar during water deficiency (Teszlák, 2008), but the GAtreated plants did not show a similar linear correlation (P > 0.05,r = 0.47, DF = 10, r0.05 = 0.57).

The GA treatment decreased the capacity of the elastic watercontent regulation and altered the ‘ε’ range; however, it did notinfluence RWCTLP values of leaves. The effect of GA3 treatment on‘SB’ probably did not manifest in cumulative lignifications and cellwall rigidity, but may have reduced rigidity through the accumu-lation of lignin precursors. It has been reported that GA3 treatmentin green asparagus (Asparagus officinalis L.) may reduce depositionof lignin (Liu and Jiang, 2006). Lignin precursors (e.g. coumaricacid, caffeic acid, ferulic acid) play a critical role in regulation ofmembrane fluidity, because the activity of several enzymes (e.g.phenylalanine ammonia-lyase) is influenced by the effect of GA3(Stephane et al., 1992).

Values of elastic modulus increased significantly in case of GA3treated ‘RI’ compared to the other cultivars, and indicated a lossof cell wall elasticity in leaves. This experimental result is in accor-dance with a known effect, which was already described in numberof woody plants: GA3 increases the incorporation of lignin in thecell wall and, consequently, reduces the flexibility of cell walls(Cheng and Marsh, 1968; Liu and Jiang, 2006). Presumably, GA3can influence cell wall elasticity through an indirect way to regulatephenylalanine ammonia-lyase enzyme (PAL) activity. The increas-ing enzyme activity of PAL is well-known under drought and otherabiotic stresses (Liu and Jiang, 2006), therefore a relationship canbe assumed between the acclimation mechanisms of drought tol-erance and some responses to GA3 treatment at the cell or tissuelevel, as well, in grapevine.

The ‘LE’ showed the same difference between control andtreated vines. The correlation was significant in leaves of controlvines (r = 0.85), but this linkage between ‘ε’ and RWCTLP disap-peared in the treated plants (Fig. 2). Both cultivars, ‘SB’ and ‘LE’,showed remarkable differences: ‘ε’ values (8–12 MPa, in controlvines even higher values) and RWCTLP ranges of ‘LE’ were signif-icantly higher than in ‘SB’. Under treatment, the ‘ε’ values of ‘LE’decreased. The range of RWCTLP was between 85% and 98% in con-trol and treated plants. This suggests that ‘LE’ is a bit less droughttolerant than is ‘SB’. Since ‘LE’, compared with ‘SB’, loses turgor ear-

lier at higher RWC; ‘LE’ is able to tolerate only a small loss of water tothe turgor loss point. GA has a known effect on the synthesis of thecell wall plugged material and on the genetic regulation of enzymeproduction regulating lignin synthesis (Liu and Jiang, 2006).

P. Teszlák et al. / Scientia Horticulturae 159 (2013) 41–51 45

Fig. 1. Cell wall elasticity ‘ε’ and osmotic potential at full turgor (˘100) in relation to relative water content at turgor loss point (RWCTLP) and apoplastic water content (AWSD%)in leaves of GA3 treated (T-SB) and control (C-SB) ‘Sauvignon Blanc’. Correlation analysis of scatter diagrams shows significant relationships at or above: r0.05 = 0.57 (R2 = 0.32),d.f. = 10. The GA treatment decreased the capacity of the elastic water content regulation and altered the ‘ε’ range. GA did not increase cell wall rigidity, but only affectedt n Blat %, sigo

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he significant linear correlation between ε and RWCTLC. Leaves of treated ‘Sauvignohe controls. The treatment resulted in a significant correlation between P100–AWSD

smotic potential with decreasing AWSD% values.

We assumed that GA treatment resulted in increasing cell walllasticity, which could be indicate by decreasing values of ‘ε’ mod-lus. Our study ascertained that the treatment did not have aignificant effect on the ‘ε’ modulus by ‘SB’, ‘LE’ and ‘KA’. The GAreatment did not enhance the cell wall rigidity directly, but only

ffected the significant linear correlation between ‘ε’and RWCTLC.hereas, response of ‘RI’ agreed with the basic hypothesis; GA

reatment resulted in increasing ‘ε’ values (‘ε’ > 12 MPa), indicat-ng decreased cell wall elasticity. The ‘KA’ showed the lowest ‘ε’

ig. 2. Cell wall elasticity (ε) and osmotic potential at full turgor (˘100) in relation to relatin leaves of GA3 treated (T-LE) and control (C-LE) ‘Lemberger’. Correlation analysis of sc.f. = 10. The GA treatment decreased the capacity of the elastic water content regulationly affected the significant linear correlation between ε and RWCTLC. The treatment didorrelation between P100–AWSD%, and significant ˘100–AWSD% correlation indicates that thecrease of AWSD% values indicates that water volume increases in apoplastic spaces whe

nc’ lost their turgor by lower RWC with decreasing elasticity modulus compared tonificant ˘100–AWSD% correlation indicates that the treatment affects the change of

value (min = 2.13 MPa), the ‘ε’–RWCTLC linear correlation was sig-nificant in the control (r = 0.88) and treated (r = 0.75) vines as well(data not shown). Unfortunately, the regulatory mechanisms con-trolling water content in autochthonous cultivars, like ‘KA’, are lessknown.

Previous investigations confirm its remarkably lower modulusof cell wall elasticity – even under severe drought stress – in pro-portion to other cultivars (not published). The group of “ponticaproles” contains some cultivars with weak (e.g. ‘Hárslevelu’) and

ve water content at turgor loss point (RWCTLP) and apoplastic water content (AWSD%)atter diagrams shows significant relationships at or above: r0.05 = 0.57 (R2 = 0.32),n and altered the ‘ε’ range. GA did not significantly increase cell wall rigidity, butnot significantly reduce ˘100 values in ‘Lemberger’, but it resulted in a significante treatment affects the change of osmotic potential with decreasing AWSD% values.n osmotic potential turns into more negative in control plants.

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6 P. Teszlák et al. / Scientia H

lso good-moderate (‘Kövidinka’) drought tolerance. The results ofKA’ and ‘LE’ refer to the fact that increasing cell wall elasticity couldlay an important role in the conservation of favourable water sta-us by V. vinifera L. cultivars of both the “convarietas pontica” andorientalis” groups.

.3. Effect of GA3 on osmotic potential and osmotic adjustment

In the treated vines of ‘SB’, osmotic potential at full turgor (˘100)as higher compared to the control vines. In the case of other vari-

ties, treatments had no significant effect on the change of ˘100.he changes of ˘100 values correlated negatively with changes inhe apoplastic water content (AWSD%) in the majority of grape vari-ties (Patakas et al., 2005). Our results were in agreement withhis, but control leaves of ‘SB’ did not show a significant correla-ion (r = 0.33, DF = 10, r0.05 = 0.57) according to the analysis of AWSD%nd ˘100 relationship (Fig. 1). The AWSD% values of control leavesaried between 30 and 60%, and between 40 and 70% in the GA3reated vines. The GA3 treatment resulted in a significant corre-ation between AWSD% and ˘100 (r = 0.73). However, a significantWSD%–˘100 correlation indicates that the treatment affects thehange of osmotic potential with decreasing AWSD% values.

The treatment did not significantly reduce ˘100 values in ‘LE’.he osmotic potential of the treated plants showed greater fluctu-tions as a function of AWSD% changes. The ˘100 values of treatedeaves varied between −0.60 and −1.40 MPa, and the range amongontrol plants was between −1.00 and −1.40 MPa. In the casef treated vines, AWSD% values did not drop below 40%, and the

100–AWSD% correlation was not significant (r = 0.53) (Fig. 2). Inontrast, we found a significant correlation (r = 0.88) in controlines of ‘LE’, and the AWSD% values fell below 40% parallel withecreasing ˘100 values below −1.00 MPa. Significant decrease ofWSD% values indicates that water volume increases in apoplasticpaces when osmotic potential becomes increasingly negative. Thishange may be closely related to the change in cell wall elasticityaused by different regulatory mechanisms of the cell wall.

Both varieties showed that GA3 treatment caused an increasinguctuation of osmotic potential compared to the control leaves.ased on a generally used determination of osmotic adjustmentOA = ˘100 control − ˘100 treated) (Turner, 2004) we could not detectctive osmotic adjustment anywhere (OA = close to zero). But wideange of ˘100 values can indicate an advanced capacity of osmoticegulation in treated plants. In case of ‘RI’ the treated and controlines showed significant (r = 0.73, r = 0.83) correlations between

100 and AWSD% (data not shown). We found the highest range ofWSD% values in this variety, which changed between 20 and 80%

n control, and 20–60% in treated vines, and ‘RI’ fluctuated muchess in osmotic potential values of treated vines compare to ‘SB’ orthers. It is known that ‘RI’ has only a weak ability to adjust osmot-cally to drought (Düring, 1987), and our results are in accordance

ith this based on a comparison of ‘RI’ with ‘SB’.Presumably, there is a relationship between the activity of

smotic regulation and the chemical composition of wines madey standard technology in the case of each cultivar. Other ana-

ytical experiments demonstrated that GA3 treatment induced aignificantly higher residual sugar content, fructose content andolyphenol content in wine of ‘SB’ compared to ‘RI’ (Nikfardjamt al., 2005). It is well known that changes in carbohydrate con-ent have a high contribution towards the osmotic regulatory

echanisms of grapevine (Patakas and Noitsakis, 1999; Patakast al., 2002). ‘RI’ has a significant role in German and also Hun-

arian viticulture, where a number of studies relate to this varietye.g. “minimal pruning” experiments) (Schultz and Weyand, 2005;

eyand and Schultz, 2006). The researchers used GA3 applica-ion as complementation of this special viticultural technology

lturae 159 (2013) 41–51

to improve grape quality (e.g. to increase sugar content), and toachieve earlier ripening (Schultz and Weyand, 2005).

The ˘100 values of ‘KA’ varied between −0.60 and −1.40 MPa intreated and also in control vines. The AWSD% values varied between40 and 80% in the control leaves, but GA3 treatment decreasedAWSD% below 40% as with ‘SB’ (Fig. 1). Control plants showed nosignificant correlation between ˘100 and AWSD% (r = 0.41), but thetreatment set up a significant correlation (r = 0.80). Based on thissimilarity, it is assumable that ‘KA’ and ‘SB’ have an approximatelyequivalent capability for osmotic adjustment. From viticulturalstudies we can give only poor information about water relationcharacteristics of this autochthonous variety, despite the fact that‘KA’ is a fashionable/rediscovered type for quality red wine mak-ing in the Carpathian Basin. Results of present experiments aboutwater relations in ‘KA’ are supported by previous results from phys-iological pilot measurements (seasonal variability of � PD), whichhas already been published (Teszlák et al., 2004).

The results confirmed that GA3 treatment could increaseosmotic potential of grapevine leaves even during a favourable nonwater-stressed vintage. It may indicate active osmotic adjustmentin leaf tissue and support the results of the first correlation anal-ysis (Figs. 1 and 2), since the change in water content of apoplastspaces is closely linked to capability to osmotically regulate in theinvestigated cultivars.

Relevant plant hormone studies show a positive correlationbetween GA content and the amount of nutrients (e.g. N, P and K)absorbed by different plant tissues (Famiani et al., 1997; Gao et al.,2001; Niu et al., 2008). The higher nutrient content contributes tothe active osmotic adjustment of grapevine leaves (Patakas et al.,2002). The GA3 treatment triggered the same response in groupsof different origins (‘LE’, convarietas orientalis and ‘KA’, convarietaspontica). However, there was an opposite response in the whitegrape cultivars, despite the fact that both ‘SB’ and ‘RI’ belong to thesame taxonomic group of convarietas occidentalis.

3.4. Apoplastic water content in relation to turgor loss point

Each variety has demonstrated a significant linear relationshipbetween the changes in apoplastic water content (AWSD%) and RWCat turgor loss point (RWCTLP). However, this correlation has to bedivided into two main parts: on the one hand TLP at the given RWC,and on the other hand TLP at the given values of water poten-tial (� ). The results demonstrated that the V. vinifera L. cultivarstested showed a negative linear correlation between AWSD% and� TLP and a positive linear correlation between AWSD% and RWCTLP(Figs. 3 and 4). Values of � TLP in ‘SB’ could be defined in a widerange (−1.00 and −1.70 MPa) during recording of pressure volumecurves after hypothetically complete saturation. Lower AWSD% val-ues were found in the control plants compared to the treated. Thecontrol leaves did not show a significant correlation between theAWSD% and � TLP (Fig. 3).

The effect of GA3 treatment resulted in a significant correlationbetween AWSD% and RWCTLP (r = 0.57, DF = 10, r0.05 = 0.57); the tur-gor loss of cells occurred after a 20% reduction of AWSD% values witha corresponding decrease in leaf water potential by 0.20 MPa. TheRWCTLP change is closely linked to the � TLP change, but the rela-tionship between the RWCTLP and AWSD% is no longer clear-cut. GA3treated ‘SB’ showed a significant correlation (r = 0.77); turgor losswas at 60% of AWSD% value and 87% of RWC, but in the control vinesAWSD% values were below 60%. Based on regression analysis, it isascertainable that turgor loss of control plants is already possibleover 95% at 60% of AWSD% (Fig. 3). In ‘LE’ we found similar results

like in ‘SB’. Control vines did not show significant changes (r = 0.52)in correlation between AWSD% and � TLP values (Fig. 4).

In treated ‘LE’ the linear correlation was higher (r = 0.78) thanin treated ‘SB’. Leaves of ‘LE’ lost their turgor if leaf water

P. Teszlák et al. / Scientia Horticulturae 159 (2013) 41–51 47

Fig. 3. Apoplastic water content (AWSD%) and water potential at turgor loss point (� TLP) in relation to relative water content at turgor loss point (RWCTLP) and apoplasticwater content (AWSD%) in leaves of GA3 treated (T-SB) and control (C-SB) ‘Sauvignon Blanc’. Correlation analysis of scatter diagrams shows significant relationships at ora AWSD

o curredc

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bove: r0.05 = 0.57 (R2 = 0.32), d.f. = 10. There is a negative linear correlation betweenf GA3 treatment resulted in a significant correlation, the turgor loss of cells has ocorrelation between the AWSD% and � TLP.

otential reached −1.40 MPa, while in contrast, ‘SB’ already hadurgor loss close to −1.20 MPa at 60% of AWSD%. In both vari-ties, the control leaves suffered turgor loss at 60% of AWSD% near1.40 MPa. The linear relationship between AWSD% and RWCTLPas characterized by a significantly greater slope in ‘LE’ than in

SB’.Consequently, the significant difference between the two GA3

reated varieties was that ‘SB’ responded with a decline of RWCTLProm 6% to 20% decrease of AWSD% and in ‘LE’ this decrease wasnly 3% (Figs. 3 and 4). This major difference between the varieties

ig. 4. Apoplastic water content (AWSD%) and leaf water potential at turgor loss point (� TL

ater content (AWSD%) in leaves of GA3 treated (T-LE) and control (C-LE) ‘Lemberger’. Co0.5 = 0.57 (R2 = 0.32), d.f. = 10. There is a negative linear correlation between AWSD% and �reatment resulted in a significant correlation, the turgor loss of cells has occurred after 20%etween the AWSD% and � TLP.

% and � TLP and a positive linear correlation between AWSD% and RWCTLP. The effectafter 20% reduction of AWSD% values. The control leaves did not show a significant

suggests that ‘SB’ is able to tolerate a significantly greater RWCdecrease to TLP in a 60–40% of AWSD% range than is ‘LE’. However,an interesting observation was that GA3 treated ‘SB’ lost its turgorat higher LWP with wider fluctuation of RWCTLP range compared tothe ‘LE’. Based on comparison of different responses in control andtreated vines it can be concluded that the effect of GA3 treatmentresults in an earlier turgor loss of ‘SB’ in contrast to the control vines.

The increase of � TLP (less negative) would adversely affect droughttolerance in ‘SB’, and thereby impair the performance of vines aswell.

P) in relation to relative water content at turgor loss point (RWCTLP) and apoplasticrrelation analysis of scatter diagrams shows significant relationships at or above:TLP and a positive linear correlation between AWSD% and RWCTLP. The effect of GA3

reduction of AWSD% values. The control leaves did not show a significant correlation

48 P. Teszlák et al. / Scientia Horticulturae 159 (2013) 41–51

Fig. 5. Relationship between partial pressure of intercellular CO2 (Ci) and net CO2 assimilation in leaves of GA3 treated (T) and control (C) ‘Sauvignon Blanc’, ‘Riesling’,‘Lemberger’ and ‘Kadarka’ (summarized data of varieties). Correlation analysis of scatter diagrams shows significant relationships at or above: r0.01 = 0.39 (R2 = 0.15), d.f. = 42.V ionsht CO2 a

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ariances of Ci and PN values between the two vintages did not affect the Ci–PN relathis correlation we can conclude that Ci values increase parallel with increasing net

As a result it can be assumed that when GA3 treatment is accom-anied with moderate or severe drought stress, it may significantlyeduce yield and quality and exacerbate the deterioration relatedo water deficiency. In the case of ‘LE’, GA3 treatment did not affect

TLP increase at 40–60% of AWSD% range. It follows that droughtolerant ability of ‘LE’ is not significantly influenced by exogenousA3, or it can be assumed that there is no adverse impact on vineerformance.

In ‘RI’ and ‘KA’ a significant correlation was detected betweenWSD% and � TLP changes, GA3 treated leaves suffered turgor lossnly below 60% of AWSD% in ‘RI’ and already above 60% of AWSD% in

KA’ (data not shown). According to linear regression, turgor loss ofRI’ and ‘KA’ can occur at 60% of AWSD% and close to −1.4 MPa of � inoth treated and control vines. In contrast, a significant differenceas found between the two varieties with regard to RWC valuesetermined on the basis of TLP, whereas control leaves of ‘RI’ wereble to tolerate less than 10% decrease of RWC to the turgor lossoint at 60% of AWSD%, and control samples of ‘KA’ lost their turgornly below 87% of RWC.

The results of principal component analysis (PCA) showed thatA3 treatment caused opposite effects in ‘SB’ and ‘RI’ and more-ver, had a significantly reduced effect on ‘LE’ and ‘RI’ (Fig. 7). It islso interesting because ‘SB’ and ‘RI’ can be classified in the sameaxonomic group (convarietas occidentalis) within the V. vinifera L.pecies. Relevant studies in the field of grapevine water relationsid not describe significant differences between cultivars belong-

ng to the same convarietas (Bota et al., 2001; Medrano et al., 2003;chultz, 2003; Alsina et al., 2007).

Results of PCA suggested that a change in values of AWSD% washe most important phenomenon to indicate a GA3 effect in eachultivar. AWSD% contributed with the highest proportion to theevelopment of both a vintage effect as well as GA3 influence in

SB’, ‘RI’, ‘LE’ and ‘KA’ (Fig. 7).

.5. Intercellular CO2 concentration related to net CO2ssimilation

Distinct values are defined by partial pressure of intercel-ular CO2 (Ci) in comparison between GA3 treated and controlines, however, there was no difference between varieties in 2004.reated ‘LE’ showed significantly (P < 0.5) lower values of Ci thanid the control vines. In both years Ci values ranged between 10nd 30 Pa, however varieties showed significantly lower Ci in 2005ompared to the previous vintage. This discrepancy was in correla-ion with the difference of leaf surface temperature, whose average

alues were lower (close to 22 ◦C) at sampling in 2005 than in 2004close to 25 ◦C). However, higher leaf surface temperature did notegatively affect the net CO2 assimilation (PN), maximum valuesf PN (>16 �mol m−2 s−1), which were significantly higher in the

ip, in both years Ci–PN changes showed a positive exponential correlation. Based onssimilation in a range between 10 and 24 Pa of Ci both in control and treated vines.

first year than in 2005 (<13 �mol m−2 s−1). In each variety, signifi-cant (P < 0.05) differences were registered in Ci values between GA3treated and control vines in 2005 (data not shown).

Leaves of GA3 treated ‘SB’ and ‘RI’ (on an eroded steep slope)showed significantly higher values of Ci compared to the control.In contrast, control leaves of ‘LE’ and ‘RI’ (on a favourable soil type)were characterized by higher Ci values compared to the treatedvines. Variances of Ci and PN values between the two vintagesdid not affect the Ci–PN relationship; in both years Ci–PN changesshowed a positive exponential correlation. Based on this correlationwe can conclude that Ci values increase in parallel with increasingnet CO2 assimilation in a range between 10 and 24 Pa of Ci both incontrol and treated vines (Fig. 5). Down regulation of PN occurredwhen Ci level reached values between 24 and 30 Pa.

As verified by comparison of the Ci–PN curves in treated andcontrol vines, the GA3 treatment resulted in a closer significant cor-relation (r = 0.66) compared to the control (r = 0.45) at P < 0.01 levelof significance (Fig. 5). Increasing effect of GA3 treatment on CO2assimilation and stomatal conductance in a seedless table grapevariety was reported earlier (Williams and Ayars, 2005). In somevintages, but in most cases, some seasonal measurements did notshow significant differences between treated and control vines.According to our experiment, there was a significant negative effectof GA3 treatment on stomatal conductance (gs) in ‘SB’, ‘RI’ and ‘LE’(data not shown).

In ‘RI’ higher Ci values were registered at lower gs in GA3 treatedplants compared to the controls. The relationship suggests the pre-dominance of non-stomatal limitation to CO2 assimilation (Flexasand Medrano, 2002) in GA3 treated ‘Riesling’ vines. However, it cor-responds to the basic finding that leaves have higher Ci values atdrought stress reduced gs (<50 mmol m−2 s−1) than at a relativelyhigh gs (>50 mmol m−2 s−1) range (Harrell and Williams, 1987;Medrano et al., 2002). Relevant studies based on gene expressionanalysis have shown in woody plants (Citrus limon L.) that the effectof higher GA content on gene regulation is very similar to the abioticstress responses and gene regulation pathway (Huerta et al., 2008).Our experimental results with four grape varieties also suggest thatGA3 treatment may be associated with photosynthetic responsesevolving under drought stress conditions in seeded grape varieties,and it is opposed to the results of other gas exchange studies (PNand gs) in seedless varieties (Williams and Ayars, 2005).

The GA3 treatment had a significant effect on the CO2 assim-ilation rate (PN) in each cultivar, but the difference betweentreated and control vines did not appear in two consecutive years.There was a favourable growing season with adequate soil mois-

ture in 2005, which provided a precise monitoring of GA3 effectsunder field conditions. Values of PN ranged between 5.05 and10.26 �mol m−2 s−1 in ‘SB’; 3.38 and 6.86 �mol m−2 s−1 in ‘RI’; 7.41and 12.84 �mol m−2 s−1 in ‘LE’; 3.70 and 11.54 �mol m−2 s−1 in ‘KA’

P. Teszlák et al. / Scientia Horticulturae 159 (2013) 41–51 49

Fig. 6. Relationship between stomatal conductance of water vapour and intrinsic water use efficiency (WUEi) in leaves of GA3 treated (T) and control (C) ‘SauvignonBlanc’, ‘Riesling’, ‘Lemberger’ and ‘Kadarka’ (summarized data of varieties). Correlation analysis of scatter diagrams shows significant relationships at or above: r0.001 = 0.48(R2 = 0.23), d.f. = 42. A general correlation was found in each cultivar that water use efficiency increases at reduced stomatal conductance. The gs values reached between 0.01and 0.32 mol m−2 s−1 in GA3 treated vines. GA3 treatment results in favourable water use efficiency in most of the cultivars.

Fig. 7. Principal component analysis of untreated and GA3 treated ‘Sauvignon Blanc’ (a), ‘Riesling’ (b), ‘Lemberger’ (c) and ‘Kadarka’ (d). On the diagrams numerals indicatethe control (1–6) and GA3 treated (13–18) vines in 2004 and control (7–12) and GA3 treated (19–24) vines in 2005; only the three important components [cell wall elasticity(ε), apoplast water content (AWSD%) and net CO2 assimilation (PN)] are shown. In case of each cultivar AWSD% was the most important component with the longest vectors ofPCA. Separated sets of C-2004, T-2004 and C-2005, T-2005 indicate differences between untreated (C) and GA3 treated (T) vines.

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n 2005. The treatment increased PN significantly (P < 0.05, P < 0.01)n red grapevine cultivars (‘LE’, ‘KA’), respectively, but we foundeduced PN values in the white cultivars (‘SB’, ‘RI’). In 2004 thereas a significant difference between the treated and control vines

‘SB’ (P < 0.01), ‘RI’ (P < 0.05), ‘LE’ (P < 0.05), ‘KA’ (P < 0.01)] duringhe period of rapid berry development, but at the second mea-urement date of the year, the cultivars did not show such clearesponses to the treatment. The PN values ranged between 5.26nd 15.21 �mol m−2 s−1 in ‘SB’; 1.55 and 13.53 �mol m−2 s−1 in ‘RI’;.39 and 14.51 �mol m−2 s−1 in ‘LE’; 9.17 and 16.24 �mol m−2 s−1

n ‘KA’.

.6. GA3 influence on intrinsic water use efficiency

The varieties showed different responses to GA3 treatment inhe case of intrinsic water use efficiency (WUEi = PN/gs) values.ignificant difference could not be detected in any variety, withhe exception of ‘LE’, in which the treatment caused significantlyP < 0.05) higher WUEi values in 2004. It can be concluded that ‘LE’as a more sensitive response to exogenous GA3 during the grow-

ng season, when the water supply is limited (mild or moderaterought) compared to the others. In addition, this variety can be atdisadvantage, because of the high value of WUEi in treated vines,hen water stress is severe.

Significant differences were recorded between the treated andontrol vines of each variety in 2005 (more humid vintage). Valuesf WUEi were significantly (P < 0.05) lower in the GA3 treated vinesompared to the controls in ‘SB’, ‘RI’ and ‘LE’. In contrast, a higher

UEi was recorded in ‘KA’. The correlation analysis of aggregatedata (each cultivar, all measurement dates) demonstrated a closeorrelation (P < 0.001, R2 = 0.23) between WUEi and gs both in thereated (r = 0.56) and control (r = 0.64) vines (Fig. 6).

A general correlation was found in each cultivar that water usefficiency increases with reduced stomatal conductance. The gs

alues reached between 0.01 and 0.32 mol m−2 s−1 in GA3 treatedines, and between 0.03 and 0.76 mol m−2 s−1 in the controls. Sig-ificant differences were found between treated and control vinesased on a correlation analysis of combined data, the R-value ofurvilinear relationship in GA3 treated vines was smaller com-ared to the control (Fig. 6). At higher levels of stomatal closurehe increase of WUEi stopped close to 160 �mol CO2 mol−1 H2On GA3 treated plants, while in the controls it increased further to

maximum value of 230 �mol CO2 mol−1 H2O. From this differ-nce it can be suggested that GA3 treatment results in favourableater use efficiency in most of the cultivars under the described

ircumstances.Commonly, the members of the eastern variety group showed a

eaker transpiration activity compared to the occidentalis or pon-ica groups under moderate water stress conditions (Bisson, 1995),nd they have also lower frost tolerance (Zunic et al., 1989). Today,t is not clear what kind of physiological differences exists betweenhe 3 ecogeographical groups of V. vinifera L. in Hungary. In thisopic, further studies are needed involving more cultivars withinhese high priority groups.

. Conclusion

The exogenous GA3 treatment had significant effects on waterelation in grapevine leaves, alter the positive correlation betweenell wall elasticity and relative water content significantly, and havegreat impact on the osmotic regulation and changes of apoplas-

ic water content in the leaves. In the majority of the cultivars,he treatment induced changes in turgor loss point; leaves lostheir turgor at higher relative water content and at significantlyigher leaf water potential compared to the untreated plants. The

lturae 159 (2013) 41–51

extent and magnitude of responses showed a high variance amongtreatments with respect to different ecogeographical groups. Wecan conclude that there is no uniform effect of GA3 on the wholeleaf water status, but cannot ignore the subtle differences of mainwater relation and gas exchange parameters. Influence of exoge-nous hormone treatment may be associated with already describedacclimation mechanisms of grapevines developed under mild ormoderate drought conditions. Conversely, cultivars with a differ-ent tolerance to drought have different responses to gibberellic acidbased on our two-year investigation. GA3 has been in use for manyyears in table grape growing, but its influence on grapevines (winegrapes) is less known. Since GA3 can also provoke an opposite effecton the regulation of water balance and photosynthesis between thedifferent cultivars, therefore only prudent use is recommended.

Acknowledgements

The authors are grateful to Ms. Maria Kun-Czibere for her tech-nical assistance and control of viticultural management on theexperimental plots of field-grown grapevines. The authors grate-fully acknowledge Professor Bruce I. Reisch (Cornell University) forproofreading of English manuscript. This work has been developedwith financial support from the Hungarian Ministry of Agricultureand Rural Development “Research and Development” Project Nos.30918 and 30601 (2005/2006).

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