physiological response of sunflower seedlings to salinity and potassium supply

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Physiological responseof sunflower seedlingsto salinity and potassiumsupplyIsabel C. Delgado a & A. Juan Sánchez‐Raya b

a Departamento de Biología Vegetal,Producción Vegetal y Ecología, EscuelaPolitécnica Superior, Universidad de Almería,Almería, E‐04120, Spainb Departamento de Agroecología y ProtecciónVegetal, Estación Experimental del Zaidín,C.S.I.C., Apdo. 419, Granada, 18080, SpainPublished online: 11 Nov 2008.

To cite this article: Isabel C. Delgado & A. Juan Sánchez‐Raya (1999)Physiological response of sunflower seedlings to salinity and potassium supply,Communications in Soil Science and Plant Analysis, 30:5-6, 773-783, DOI:10.1080/00103629909370245

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COMMUN. SOIL SCI. PLANT ANAL., 30(5&6), 773-783 (1999)

Physiological Response of SunflowerSeedlings to Salinity and Potassium Supply

Isabel C. Delgadoa and A. Juan Sánchez-Rayab

a Departamento de Biología Vegetal, Producción Vegetal y Ecología, EscuelaPolitécnica Superior, Universidad de Almería, E-04120 Almería, Spainb Departamento de Agroecología y Protección Vegetal, Estación Experimentaldel Zaidín, C.S.I.C. Apdo. 419, 18080 Granada, Spain

ABSTRACT

Sunflower seeds (Helianthus annutis L. cv. Dwarf) were grown only withincreasing saline solutions [0, 50, and 100 mM sodium chloride (NaCl)] andpotassium (K) supply to determine how salinity and K supply will affectplant germination and growth. Potassium supply under highly salineconditions (100 mM) or nonsaline conditions had a beneficial effect onsunflower seedlings germination which was not significantly altered withmoderate salt concentrations (50 mM). During the stage studied, K supply inthe absence of salinity increased significantly seedling biomass which reflectswhat is happening in the aerial part and root. This increase was proportionallyhigher in the stem than in the leaf with no variations in the foliar surface. Ina saline environment, K supply did not markedly alter plant dry matterproduction, but increased foliar surface with moderate salt concentrations(50 mM) in the root environment.

773

Copyright © 1999 by Marcel Dekker, Inc. www.dekker.com

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774 DELGADO AND SÁNCHEZ-RAYA

INTRODUCTION

Potassium is an important plant nutrient element that plays a biophysical role incell hydration and a biochemical role in a great variety of metabolic processes,such as protein synthesis (Hsiao and Läuchli, 1986). According to Chow et al.(1990), the maintenance of K levels into the cytoplasm, which is critical formetabolism, is essential for surviving in a saline environment where thepredominant cation, sodium (Na), is present when salt (NaCl) concentrations arehigh. In a saline environment, plants take up large amounts of Na, even if thataffects negatively K and calcium (Ca) acquisition. Potassium like Ca is requiredin an external milieu to maintain cell membrane selectivity and integrity(Muhammed et al., 1987).

It seems that K and Na absorption occurs in two separate ways, and with differenttransporters, mainly in case of low K availability. Under these conditions, a highlyspecific mechanism is triggered which may lead to a sufficient supply of K to theplant even in the presence of other cations (Bernstein et al., 1974). But the Cadisplacement due to high Na concentrations alters some aspects of the membranestructure which are critical for the selective absorption of K (Chow et al., 1990).On the other hand, Kafkafi (1984) stated that competition between the twomonovalent cations takes place in the root. According to Israeli et al. (1986),increased concentrations of Na in the root result in a decrease in K concentration.The replacement of K by Na is likely to be possible by nonspecific processeswhen cell turgor increases due to antagonism between both elements. That iswhy an adequate K supply is so important in the presence of high Na levels (Cerdaet al., 1995). Bernstein et al. (1974) proved that, in saline soils, increasingfertilization with K is required to counteract the competitive effects of high Naconcentrations. Such is the case of carrot where high Ca and Na concentrationsinterferes with appropriate K nutrition. The resultant biomass of the plant washigher at 'low' than 'high' salt concentrations and increased when increasingconcentrations of K were applied to the root environment. Spinach plant stemgrowth requires larger amounts of K under 'high' salt conditions than 'low' saltconditions. The reduction of plant biomass due to an increase in salinity may bemitigated by increasing the K supply in the root environment (Chow et al., 1990).Kafkafi (1984) reported that even if K is added constantly to the culture solution,the accumulation of this cation by the root is depressed when the proportion of Naincreases.

Muhammed et al. (1987) stated that a high Na/K ratio in a saline growthenvironment may alter the selectivity of the root membrane resulting in a passiveaccumulation of Na in the root and stem. On the other hand, a low Na/K ratio isvery important for stomata movement, photosynthesis, and transpiration controlunder normal conditions. According to Kafkafi (1984), cell capacity to retain Kat high external concentrations of Na may be an important mechanism in the

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RESPONSE OF SUNFLOWER SEEDLINGS TO SALINITY AND K 775

TABLE 1. Series of treatments applied throughout theexperiment.

C-SO Control with distilled waterC-S50 Control with moderate salinity (50mM NaCl)C-S100 Control with high salinity ( 1 OOmM NaCl)K-SO Salinity-free + 4.4mEq/l K as K2 SO4

K-S50 Moderate salinity + 4.4mEq/l K as Kj SO4

K-S100 High salinity + 4.4mEq/l K as K2 SO4

"C=control, S= salinity, K=potassium.

regulation of salt-tolerant species. In these studies, the effects of salinity on theabsorption and transport of nutrient elements overlapped.

The aim of our study was to investigate the effects of the Na-K interaction onthe transport of the other elements, indirectly, through its influence on sunflowerseed germination and the early stages of seedling growth. In order to isolate thesalinity effects on transport, we used an artifice consisting of germinating seedsand growing seedlings in distilled water alone or with treatment solutions in orderthat the seedlings would have to grow exclusively on the seed's own reserves. Inprevious studies, no visual symptoms of nutrient element deficiency were observedduring the experiment.

MATERIALS AND METHODS

Sunflower seeds were germinated and grown on quartz sand in plastic 2,000-mL capacity truncated cone-shaped pots with a perforated base. The pots werefilled with 2,500 g quartz sand with 500-mL nutrient solution of each treatmentbeing applied.

A randomized block design with two different treatments (control plants, andK-treated plants), three levels of salinity (0, 50, and 100 mM NaCl), and sixreplications for each treatment was used.

The nutrient solutions corresponding to both treatments used for pot irrigationwere prepared with A.R. quality salts as given in Table 1. The experimentconducted in a controlled growth chamber with a 14-hour light period at 28°Cand a 10-hour dark period at 20°C, and with constant relative humidity of 70%.

Germination and growth were in distilled water alone for the controls, and withK or NaCl solutions for the corresponding treatments, avoiding the overlap of theabsorption and transport mechanisms, attempting to isolate the latter for the otherelements.

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The experiment lasted for 25 days after sowing. At the end of the experiment,the following growth parameters were determined: leaf dry weight, stem dryweight, root dry weight, stem length, and foliar surface. Afterwards, shoot andseedling dry weight, and leaf dry weight/foliar surface ratio, shoot/root dry weightratio, and percentage of germination were also determined. Foliar surface wasdetermined with a LI-COR, LI-3000 meter.

Significant differences between the values obtained after treatments weredetermined using standard analysis of variance (ANOVA) at a 0.05% confidencelevel.

RESULTS AND DISCUSSION

Increasing concentrations of NaCl produced a decrease in the germinationpercentage (Figure 1) which was significant after adding the two levels of NaClused in this experiment. According to the studies of Van der Moezel and Bell(1987) and Ramagopal (1990), germination impairment may be due to a decreaseor delay in water absorption which may facilitate the entry of toxic concentrationsofions. In our experiment, 'moderate' (50mMNaCl)and'high' (lOOmMNaCl)salt concentrations significantly depressed germination percentage. Addition ofK to the culture medium enhanced germination percentage of sunflower seedling,the enhancement being significant with 'high' (100 mM NaCl) salt concentrations.Caro et al. (1974) reported that it is during the first phase of the plant's life whenthe effects of salinity are critical, the affect on plant development may occur. Onthe other hand, Dudeck and Peacock (1985) showed that several cultivare ofryegrass are most salt-sensitive during this phase of germination. Later Ungar(1996) stated that an increase in salinity significantly decreased Atriplex patulagermination. Salinity impairs the development of all the seedling components asNaCl concentrations increase in the culture medium.

Under our experimental conditions, K supply, in the absence of salinity,enhanced significantly the accumulation of organic matter by the seedling (Figure2) which was reflected in the root, and specially in the aerial part (Figure 3).Potassium supply, in the presence of NaCl (Figure 2), altered seedling developmentpositively (at 50 mM) or negatively (at 100 mM), albeit not significantly in anycase.

In our experiment, only the highest concentration of NaCl (100 mM) decreasedthe accumulation of dry matter by the seedling aerial part. This negative influenceis due to a similar effect produced on the leaf dry matter, but not on the stem(Figure 4), whose dry matter was increased with 'moderate' salinity levels (50mM). This increase may be an example of the Arndt-Schulz law, according towhich 'low' concentrations of toxins tend to stimulate biological processes,whereas 'high' concentrations depress them (Tingery, 1980). At 'moderate'salinity, K supply increased significantly aerial part dry weight while that of theroot did not change. At the highest salinity level, aerial part dry weight was not

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100

80

60

50

NaCI(mM)

I Control fZ2K-supply

100

I L.S.D.

FIGURE 1. Percentage of germination in sunflower seedlings grown with differentconcentrations of NaCl and K supply. Significance level 5%.

•5 c n¿DU

200

150

100

50

n

mg/plant

1Jl50

NaCI(mM)100

Control seedling X¿Zá K-treated seedling E H L.S.D.

FIGURE 2. Dry weight of sunflower seedlings (mg/plant) grown with differentconcentrations of NaCl and K supply. Significance level 5%.

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mg/plant160

140

120

100

80

60

40

20

n

peon

iliI188U

0

• i Control root

S 3 Control shoot

IS1 i150

NaCl (mM)

E223 K-treated root

^ 3 K-treated shoo

1_ n100

^ L.S.D. root

• L.S.(). shoo

FIGURE 3. Root and shoot dry weight of sunflower seedlings grown with differentconcentrations of NaCl and K supply. Significance level 5%.

mg/plant

I B Control leal

K\\l Control stem

50

NaCl (mM)

EZ3 K-treated leaf

E23 K-treated stem

ES3 L.S.D. leaf

CH L.S.D. stem

FIGURE 4. Leaf and stem dry weight (mg/plant) of sunflower seedlings grown withdifferent concentrations of NaCl and K supply. Significance level 5%.

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altered, and that of the root was decreased, albeit not significantly (Figure 3).This suggests that K supply, under our experimental conditions, enhances thetransport of the other elements from the seed to the aerial part rather than to theroot in the presence of salinity.

This seems to be confirmed by an increase, after K supply, of the ratio betweenthe dry weight of the aerial part and that of the root (Figure 5) which is increasedin all cases, albeit not significantly in the presence of salinity. The needs of K forthe growth of the aerial part increased under saline conditions. Some authorshave shown that the addition of K to the culture medium alleviates the reductionof salt-induced biomass (Chow et al , 1990). This response is probably due to theinhibition of the salt effects by K (El-Haddad and O'Leary, 1994). The decreasein the growth of sunflower seedlings under saline conditions may be explained bythe fact that this crop does not limit Na accumulation and/or by a water shortagein the leaf. Both effects may be mitigated by adding K to the saline environment,but, on the other hand, K plays an important role in the osmotic adjustment(Marschner, 1995).

The studies of Satti and López (1994) and López and Satti (1996) showed moresignificant effects of K addition under such circumstances, but in these cases,there is an additional and direct intervention of K on the absorption of the othernutrient elements which was avoided in our case, and when overlapped to theeffect on transport, may make the action of K more evident.

In the absence of salinity, K supply enhanced significantly the acquisition ofdry matter by leaf and stem, whereas at moderate salinity, this enhancement wassignificant in the stem, but not in the leaf (Figure 4). At high salinities, K increasedleaf dry matter and decreased that of the stem. These changes were not significant,but can account for the behavior mentioned above of the seedling aerial part.Stem length grew as it acquired dry matter (Figure 6). Salt had a drastic effect onthe accumulation of dry matter by the leaf (Figure 4), but it was even more dramaticon the foliar surface (Figure 6) resulting in an increase of dry matter per unit offoliar surface (Figure 7) similar to that observed by Katerj i et al. ( 1996) as salinityacts primarily on initial cell extension rather than on cell division (Papp et al.,1983). The consequence is an increase in leaf thickness (Bhivare andNimbalkar,1984). Intervention of K improves somewhat the acquisition of dry matter.

The addition of K increased significantly the foliar surface of seedlings grownwithout NaCl and those grown under 'moderate' salinity, whereas those grown at'high' salinity had a nonsignificant decrease in their foliar surface. This wasreflected in the leaf dry weight/foliar surface ratio (Figure 7) which decreasedsignificantly under conditions of 'moderate' salinity.

CONCLUSIONS

Salinity decreased germination and the development of sunflower seedlings asa result of several physiological responses, such as the modification of K absorption

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1

0,8

0,6

0,1

0,2

n

wm m

Üi 1111111

I Control shoot/root

50 10D

NaCl (mM)

K-treated shoot/root 5 Ü L.S.D.

FIGURE 5. Shoot/root dry weight ratio of sunflower seedlings grown with differentconcentrations of NaCl and K supply. Significance level 5%.

cmi/planM/cm/plant10

8

6

4

50

NaCl (mM)

• I Control F. surface EZ3 K-lreated F. surface EM L.S.D. F. surface

ES3 Control stem length E 3 K-ltealed s . length C U L.S.O. stem length

FIGURE 6. Foliar surface (cmVplant) and stem length (cm/plant) of sunflower seedlingsgrown with different concentrations of NaCl and K supply. Significance level 5%.

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mg/cm2

\

1mm WEIIIIIIU ^^m//////

50

NaCI (mM)

I Control E2Z2K-treated

100

L.S.D.

FIGURE 7. Leaf dry weight (mg/plant)/foliar surface (cmVplant) ratio of sunflowerseedlings grown with different concentrations of NaCI and K supply. Significance level5%.

owing to the alteration of cell membrane permeability as a consequence of Naaccumulation, and a subsequent water shortage in plant tissues which is inagreement with Schreiner and Ltldders (1996). This was mitigated, however, bythe presence of larger amounts of K in the culture medium. Obviously, theintervention of K under saline conditions is more significant in terms of absorptionthan transport. But it is important to understand from our data that the accumulationof dry matter by the aerial parts and roots points to a preferential intervention of Kwhich improves the transport of nutrient elements to the aerial parts of the plantwhich benefits both leaf and stem development. In the case of leaves, interventionof K is even greater, thus benefiting growth extension of the leaf surface.

ACKNOWLEDGMENTS

The authors want to thank Mrs. E. Velasco for widely revising the English styleof the manuscript.

REFERENCES

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physiological response of sunflower seedlings to salinity and potassium supply

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