pectin solubility and water relations during vase life of cut flowers

Pectin Solubility and Water Relations during Vase Life of Cut Flowers

Maria Helena Teixeira Gomes1, Susana Maria Pinto de Carvalho1, and Domingos Paulo Ferreira de Almeida1,2*

1CBQF, Escola Superior de Biotecnologia, Universidade Católica Portuguesa, Rua Dr. António Bernardino de Almeida, 4200-072 Porto, Portugal

2Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, s/n, 4169-007, Porto, Portugal

Abstract. Pectic polymers are major components of primary cell walls having a high water-binding ability. Pectin levels and solubility were quantified in stems and petals of rose (Rosa hybrida L.), chrysanthemum (Chrysanthemum morifoliumRamat.), carnation (Dianthus caryophyllus L.), and snapdragon (Anthirrhinum majus L.) and related to the rate of solution uptake and to the rate of fresh weight increase during the vase life of these cut flowers. Total pectins in stems ranged from 176 μg･mg-1 in chrysanthemum to 203 μg･mg-1 in carnation. Water soluble pectin accounted for only 1.9 to 3.6% of total stem pectins, in rose and snapdragon, respectively, whereas chelator-soluble pectins ranged from 3.8% of total in chrys-anthemum to 10.1% in snapdragon. Petals of each species had a higher proportion of water- and chelator-soluble pectins than stems. Water uptake rate during vase life was 0.16 g･g-1･day-1 for carnation, 0.35 g･g-1･day-1 for chrysanthemum, 0.52 g･g-1･day-1 for rose, and 0.62 g･g-1･day-1 for snapdragon. In the absence of salts, maximum fresh weight increase in relation to the initial value varied from 15% in carnation to 33% in chrysanthemum. Addition of KCl or CaCl2 to the vase solution depressed the uptake rate but prolonged the period of increasing fresh weight and delayed the fresh weight decline. Significant positive linear relationships were found between the solubility of stem pectins and the rate of fresh weight increase in the four cut flowers and between the solution uptake rate and the amount of CDTA-soluble pectins present in the petals. These results provide correlative evidence for a role of pectins in the water relations of cut flowers.

Additional key words: Anthirrhinum majus, apoplast, carnation, cell wall, Chrysanthemum morifolium, Dianthus cary-ophyllus, polyuronides, Rosa hybrida, rose, snapdragon

Hort. Environ. Biotechnol. 51(4):262-268. 2010.

*Corresponding author: [email protected] November 26, 2009; accepted May 3, 2010.

Introduction

Water relations play a critical role in the postharvest life of cut flowers, water imbalances within the cut flower resulting in wilting, one of the major causes for the termination of vase life (Halevy and Mayak, 1981; van Doorn, 1997). According to the cohesion-tension theory, long-distance water movement through the stem is driven by a water potential gradient, and is made possible by the small diameter and thick walls of xylem vessels, the hydration properties of cell walls, and the internal cohesion of the water column (Tyree, 1997). Despite the ongoing debate around the shortcomings of this theory (Tyree, 1997; Zimmermann et al., 2000), its principles are useful to explain long-distance water movement in cut flowers. Water evaporation occurs from the apoplast of the substomatal cells, both in the leaves and petals. The adhesion of water to the cell walls in the evaporating surfaces and in the xylem ves-sels provide the anchoring points to sustain the water column. By affecting water adhesion via hydrogen bonding, the nature of cell walls in the evaporating surfaces and in the xylem conduits interferes with long-distance water transport in cut flowers.

Pectins are major components of the primary cell wall ac-counting for ca. one-third of the cell wall material of dicoty-

ledonous plants (Brett and Waldron, 1996). Pectic polysaccharides are likely to affect water movement and water retention in plant organs in a number of ways. Pectins present in the xylem pit membranes regulate the lateral movement of water within the xylem vascular bundles by shrinking or swelling depending on the solution ionic content (Gascó et al., 2006; Zwieniecki et al., 2001). In fact, in stem segments, the hydraulic resistance of xylem is reduced by the presence of K+ or Ca2+ in the so-lution (Gascó et al., 2006; van Ieperen et al., 2000; Zwieniecki et al., 2001) and tap water containing salts provides a better water balance to cut flowers than de-ionized or distilled water (van Meeteren et al., 1999). These findings can be partially ex-plained by the salt-induced shrinkage of the pectins in the xylem conduit-to-conduit connections, which favors water flow, whereas pectin swelling induced by distilled water increases hydraulic resistance (van Ieperen, 2007; Zwieniecki et al., 2001).

Besides their role in regulating water flow through xylem pits, pectins have the potential to influence the hydration ability and the water retention capacity of the apoplast, since these polymers have a high water-binding capacity and the ability to form hydrogels (Thakur et al., 1997). Since cut flowers have their stems continuously immersed in water the possibility arises that radial water movement through the stem may contribute to the overall hydration status of the cut flower. The observed slow lateral movement of water out of the xylem into the

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surrounding cortex of asparagus spears (Heyes and Clark, 2003) can be explained by the hydrophilic nature of the pectins present in the parenchyma cell walls, and hints at a putative role for pectin in the hydration and water retention ability of cut flower stems.

It is our hypothesis that close relationships are likely to exist (1) between the content or the solubility of stem pectins and the fresh weight increase in a cut flower during vase life, and (2) between the pectins in petals and the water uptake rate. The reason for the first hypothesis is that pectins, owing to their high water-absorption capacity and their ability to form hydrogels, can affect the hydration status of the cut flower stem immersed in vase solution. Therefore, a stem continuously immersed can retain water either absorbed via the stem surface or via radial movement of xylem sap. The second hypothesis is based on the fact that the negative charges in demethylated pectins on petals, a major evaporating surface of cut flowers, affect the adhesion of water molecules interfering with long-distance water movement.

Despite their potential effect in water relations, pectic poly-mers remain very poorly characterized in cut flowers, although senescence-related changes in petal pectins have been reported for carnation (De Vetten and Huber, 1990) and Sandersonia aurantiaca (O’Donoghue et al., 2002). Moreover, in spite of the findings that ions enhance the internal flow regime in the xylem vessels of stem segments, there is still lacking evidence of this phenomenon in planta (van Ieperen, 2007).

The objective of this study was to determine the pectin con-tent in stems and petals of four dicotyledonous species and explore the putative relationship between the amount and solu-bility of pectic polymers in cut flowers and their water relations. In addition, since the presence of salts in the vase solution is known to improve the water balance of cut flowers (van Meeteren et al., 1999), and interfere with pectin hydration (Gascó et al., 2006; Zwieniecki et al., 2001), water relations and vase life were examined in distilled water and in the presence of the inorganic salts KCl and CaCl2.

Materials and Methods

Plant material

Rose (Rosa hybrida L. ‘Starlet’), spray chrysanthemum (Chrys-anthemum morifolium Ramat. ‘Sunny Elite Reagan’), carnation (Dianthus caryophyllus L. ‘Liberty’), and snapdragon (Anth-irrhinum majus L. ‘Winter Euro White’) were grown under plastic tunnels in Vila do Conde (41º 21' N; 8º 44' W), North-western Portugal. Flower stems were harvested at commercial maturity, immediately placed in water and transported to the laboratory. The lower leaves were removed and the stems were cut to a uniform length of 55 cm from the base of the flower calyx in rose and carnation, or a total length of 70 cm in chrysanthemum and snapdragon.

Assay conditions and vase solutions

Within 90 min. of harvest, flower stems were prepared and individually placed in glass cylinders containing 100 mL of solution. During the vase period, the solution was replenished daily, approximately at the same time, to the initial volume. Flower stems were maintained in a room at 20 ± 1℃, 70 ± 5% relative humidity and 11 μmol･m-2･s-1 of PAR irradiance by cool-white fluorescent lamps, with a 12-h photoperiod.

All solutions were made with distilled water containing 1.03 mM of 8-hydroxiquinoline sulfate to reduce bacterial growth (van Doorn and Perik, 1990). According to the treat-ment, the solutions also contained 10 mM KCl, 20 mM KCl, 10 CaCl2, or 20 mM CaCl2, and there was a control without the added salts. Electrical conductivity of the vase solution was measured with a HI-991301 conductivity meter (Hanna Instruments, UK). Freshly made solutions had pH 3.9 and electrical conductivity of 0.1, 1.5, 3.0, 2.5, and 4.6 dS･m-1 for the control, 10 mM KCl, 20 mM KCl, 10 mM CaCl2, and 20 mM CaCl2, respectively.

Determination of fresh weight, solution uptake,

and vase life

To evaluate changes in the water status of the cut flowers, the fresh weight (FW) of each flower stem was determined daily at ca. 11:00 h. Weight measurements were converted to relative FW, expressed as percentage of the initial FW of each flower stem. Maximum FW during vase life and the number of days to achieve it were determined by interpo-lation. The rate of FW increase was calculated as the quotient between these two variables.

Solution uptake was calculated from daily measurements of the weight of the solution in the cylinders, corrected for the direct evaporation from cylinders containing no flower stem. The slope of the cumulative solution uptake curve was used as the rate of solution uptake.

The developmental stage of the flower was daily assessed measuring the maximum diameter of rose and carnation flowers, or the number of open flowers in spray chrysanthemum and in the snapdragon spike. The vase life terminated upon petal wilting for carnation, wilting or bent-neck for rose, and when > 50% of the flowers wilted in spray chrysanthemum or snapdragon.

Preparation of ethanol insoluble solids and

pectin determination

At harvest, petals and basal 15-cm stem segments were excised from the cut flowers and frozen at –20℃ until pre-paration. Ethanol insoluble solids (EIS) were prepared by homogenizing 10 g of frozen tissue in 80% ethanol and wash-ing the residue with acetone as described in Pinheiro and Almeida (2008). Total uronic acids in the EIS were determined following the method of Ahmed and Labavitch (1977). Pectin

Maria Helena Teixeira Gomes, Susana Maria Pinto de Carvalho, and Domingos Paulo Ferreira de Almeida264

Table 1. Total, CDTA-, and water-soluble pectins in stems and petals of four cut flower species.

Cut flowerPectins in stems (μg･mg-1) Pectins in petals (μg･mg-1)

Total CSP WSP Total CSP WSP

Rose 179.4bz

(100)13.5b(7.5)

3.4d(1.9)

154.9dz

(100)29.8d(19.2)

5.1c(3.3)

Chrysanthemum 175.8b(100)

6.7c(3.8)

6.0b(3.4)

227.4b(100)

40.2b(17.7)

34.8b(15.3)

Carnation 203.1a(100)

12.6b(6.2)

4.2c(2.1)

200.9c(100)

20.9d(10.4)

26.7c(13.3)

Snapdragon 191.1ab(100)

19.3a(10.1)

6.8a(3.6)

242.4a(100)

53.5a(22.1)

70.2a(29.0)

P-value 0.025* 0.000*** 0.000*** 0.000*** 0.000*** 0.000***z Values are means of five replications. Mean separation within columns by Duncan’s multiple range test at P ≤ 0.05. Within parenthesis are the percentages of total pectins. CSP, CDTA-soluble pectins; WSP, water-soluble pectins.

NS,*,**,*** Nonsignificant or significant at P ≤ 0.05, 0.01, or 0.001, respectively.

solubility was determined in water and in the calcium-chelating agent trans-1,2-cyclohexanediaminetetraacetic acid (CDTA). Water- and CDTA-soluble pectins were extracted by suspending 20 mg of EIS in 7 mL of distilled water or 50 mM sodium acetate, 50 mM CDTA, pH 6.5, respectively. The suspensions were incubated in a shaker for 6 h at 20℃, then filtered through a glass fiber filter (Whatman GF/C), and soluble uronic acid in the filtrate was determined using the m-phenylphenol method (Blumenkrantz and Asboe-Hansen, 1973).

Experimental design and statistical analyses

Experiments were conducted in a completely randomized design with five replicate flower stems per treatment. The data were subjected to one-way analysis of variance (ANOVA) followed by mean separation using the Duncan’s multiple range test at 5% level, whenever a significant F-value was found. The relationships between pectins and the water were tested using linear regression analysis. All analyses were per-formed with the software package SPSS 16.0 for Windows (SPSS Inc., Chicago, IL, USA).

Results and Discussion

Pectin content and solubility in stems and

petals

Total pectins and their fractions soluble in water or soluble in a calcium chelator (CDTA) were analyzed in the stems and petals of the cut flowers at harvest. The total amount of pectins in stems and petals was species-dependent (Table 1). In rose and carnation, stems and petals had similar amounts of pectins, whereas in chrysanthemum and snapdragon stems had less pectin than petals (Table 1). Only a small fraction of stem pectins were water-soluble (2 to 4%). The proportion of CDTA- soluble pectin was more variable among the flower species, accounting for only 4% of the total stem pectins in chrysan-themum or up to 10% of the total pectins in snapdragon stem. In the four studied cut flowers the solubility of pectins was

higher in petals than in stems, and soluble petal pectins varied over a wider range among species. Water-soluble pectin ranged from 3% of total petal pectin in rose to 29% in snapdragon. The CDTA-soluble fraction ranged from 10% of total petal pectin in carnation to 22% in snapdragon. Our findings con-cerning the higher content of soluble pectins in the petals as compared to the stem, partly explain why petals have been described as having the capacity to apparently remove water from other plant organs. This phenomenon was observed in several species leading to the conclusion that once the flowers are formed, they get priority for water over the vegetative tissue (reviewed by van Doorn and van Meeteren, 2003). For instance, in cut chrysanthemum it was found that the leaves often wilt whereas the flowers remain turgid for a much longer period.

Solution uptake

Electrical conductivity was monitored throughout the vase period to ascertain possible changes in solute concentration. Electrical conductivity of the solutions remained stable through-out the vase life, as shown in Fig. 1 for cut roses. The same was observed in chrysanthemums, carnations, and snapdragons (data not shown). These results indicate that solution uptake occurred via mass flow with no exclusion of the dissolved salts.

The four species used in this study covered a wide range of solution uptake rates. In the absence of salts, the average solution uptake rate during vase life, was 0.16 g･g-1･day-1 for carnation, 0.35 g･g-1･day-1 for chrysanthemum, 0.52 g･g-1･day-1 for rose, and 0.62 g･g-1･day-1 for snapdragon (Fig. 2). Salts had a significant (P<0.05) effect on the cumulative solution uptake throughout the vase period in all studied cut flowers, but in rose this only became visible after day 4 . Both KCl and CaCl2 reduced the solution uptake rate, but this effect was more pronounced for CaCl2 and its magnitude depended on the species: minimal in carnation and stronger in snapdragon and rose, the two species exhibiting higher uptake rates (Fig.


Fig. 1. Electrical conductivity of the vase solutions during vase period of cut roses. Vase solutions contained no salts (○), 10 mM KCl (□), 20 mM KCl (■), 10 mM CaCl2 (△) or 20 mM CaCl2 (▲).Values are means ± S.D. (n = 5). When not seen error bars fall within the symbol.

Fig. 2. Cumulative solution uptake during vase life of four cut flower species held in water (○), 10 mM KCl (□), 20 mM KCl (■), 10 mM CaCl2 (△) or 20 mM CaCl2 (▲). Values are means ±S.D. (n = 5).

Fig. 3. Relative fresh weight during vase life of four cut flower species held in water (○), 10 mM KCl (□), 20 mM KCl (■), 10 mM CaCl2(△) or 20 mM CaCl2 (▲). Values are means ± S.D. (n=5).

2). Similar effects of these cations on the uptake rate of cut chrysanthemum were previously described (van Meeteren et al., 1999). Though these results seem conflicting with the ob-servations that KCl or CaCl2 increase the hydraulic conductivity of stem segments (van Ieperen et al., 2000; Zwieniecki et al., 2001), due to the shrinkage of pectins present in the xylem pit membranes (Zwieniecki et al., 2001). However, the movement of water in a multiorgan cut flower depends on factors that are absent in artificial experiments that use stem segments to study hydraulic conductivity (van Ieperen, 2007).

Relative fresh weight

During vase life relative FW increased for a period of time, after which it started declining (Fig. 3). This common trend has been previously observed in several cut flowers including chrysanthemum (van Meeteren et al., 1999) and rose (Doi et al., 2000). The timing when the FW starts to decline marks the beginning of the senescence phase (Mayak and Halevy, 1980), and this can be delayed by the presence of substances in the vase water solution that reduce bacterial growth (van Meeteren et al., 1999). The studied cut flowers differed in the maximum relative FW increase and in the timing of starting to decrease the FW. In the absence of salts, maximum FW increase in relation to the initial value was 15% in carnation (day 6), 20% in rose (day 5), 30% in snapdragon (day 5), and 33% in chrysanthemum (day 15). Interestingly, although KCl and CaCl2 depressed solution uptake (Fig. 2), the presence of salts in the vase solution increased the maximum relative FW and delayed its decline (Fig. 3), indicating an enhancement of the water status of the cut flower. As shown by van Meeteren et al. (1999), the reason behind this FW increase is a lower transpiration rate observed in plants held in vase solutions containing KCl and CaCl2, which compensates for the lower uptake rates.

Postharvest flower development and vase life

The species studied had different rates of postharvest flower development (Fig. 4). Rose flower opening was completed at day 6 for all treatments, while in carnation, maximum flower diameter was achieved in day 4 (Fig. 4A and 4C). In chrys-anthemum and snapdragon, opening of flower buds continued


Fig. 4. Postharvest flower development of four cut flower species held in water (○), 10 mM KCl (□), 20 mM KCl (■), 10 mM CaCl2(△) or 20 mM CaCl2 (▲). Values are means ± S.D. (n = 5).

Table 2. Vase life of four cut flower species in solutions containing different concentrations of KCl or CaCl2.

Vase solutionVase life (days)

Rose Chrysanthemum Carnation Snapdragon0 mM 12.6 abz 24.2 a 12.2 11.610 mM KCl 12.4 b 24.8 a 12.0 11.420 mM KCl 13.4 ab 19.2 b 11.6 11.410 mM CaCl2 14.6 a 25.8 a 11.8 11.820 mM CaCl2 11.4 b 22.4 ab 12.4 12.0P-value 0.033* 0.009** 0.976NS 0.827NS

z Values are means of five replicates. Mean separation in columns by Duncan’s multiple range test at P ≤ 0.05.NS,*,**,*** Nonsignificant or significant at P ≤ 0.05, 0.01, or 0.001, respectively.

throughout the vase period (Fig. 4B and 4D). Flower opening in rose and carnations was slightly slower in water than in salt-containing solutions, but that effect was not present in the other two cut flowers (Fig. 4).

Under the conditions used in this study, the average vase life of chrysanthemum was double than that of the other three species (Table 2). Vase life duration was significantly affected by the vase solutions in rose and chrysanthemum, but not in carnation and snapdragon (Table 2). Even in rose and chrysan-themum, no clear tendency can be established regarding the effect of salts on vase life.

Relationship between pectins and water relations

in cut flowers

The four dicotyledonous cut flower species analyzed dif-fered in their pectin content, solution uptake rate, and relative

FW increase during the vase life, enabling the analysis of the putative relationships between the amount and solubility of pectic polymers in cut flowers and their water relations.

Consistent with our hypotheses that overall stem and petal pectins interfere with water relations of cut flowers, significant positive linear regressions were found between the solubility of stem pectins and the rate of FW increase in the four cut flowers studied (Fig. 5) as well as between the rate of solution uptake and the amount of CDTA-soluble pectins present in the petals (Fig. 6).

Although these results provide only correlative evidence for the relationship between pectins and water relations in cut flowers, these findings can be interpreted on the basis of the hydrophilic nature of pectic polymers.

The apoplast constitutes a continuum throughout a plant organ (Canny, 1995) allowing the equilibrium between the dilute solution flowing in the xylem-lumen apoplast and the water free-space of the apoplast of parenchyma cells in the stem cortex. Mass flow of water in the apoplast of the cortical parenchyma has been demonstrated in roots from dicotyledonous species (Aloni et al., 1998) and provides evidence for the possibility of bi-directional water movement between the cortex and the vascular tissue. The cell wall composition of the vas-cular tissue is similar to that of parenchyma, with similar amounts of pectins, at least in the flowering stem of broccoli (Muller et al., 2003). Therefore, given their high water-binding capacity, pectins in the cortex parenchyma may affect the overall hydration properties of the cut flower immersed in a vase solution. Direct absorption of vase water to the cell walls of cortical parenchyma and apoplastic continuity in the stem can create a ‘sponge effect’ by which water accumulates in the immersed portion of the stem. Data from fruit, where a close relationship between pectin solubilization and cell wall swelling has been documented (Redgwell et al., 1997), support the idea that pectins affect the hydration properties of cell walls. This ‘sponge effect’ can partly explain why cut flowers held in a vase with higher water height (resulting in a larger position of the stem immersed) showed higher relative FW increase (van Doorn, 1994; van Ieperen et al., 2002).

Pectins can also play an important role in sap flow, pro-


Fig. 5. Relationship between soluble stem pectins (water- + CDTA- soluble) and the rate of fresh weight increase in four cut flower species. Regression line: y = 0.704x - 2.964; R2 = 0.965; P = 0.018; n = 4.

Fig. 6. Relationship between CDTA-soluble petal pectins and the average solution uptake rate in four cut flower species. Regression line: y = 0.039x - 0.270; R2 = 0.936; P = 0.032; n = 4.

viding anchor points for the water molecules. Adhesion of the xylem sap to the negative charges of petal pectins would sus-tain the water column during transpiration. This role of pectins provides a possible explanation for the relationship between the negatively charged chelator-soluble pectins in petals and the rate of solution uptake.

Conclusions

Pectin content and solubility in petals and stems can vary substantially among cut flower species, and differences in chelator-solubility of petal pectin among four dicotyledonous cut flowers can be related to the differences in their water up-take rates. In addition, the proportion of soluble stem pectins is positively related to the increase in cut flower FW. These findings provide correlative evidence for a role of pectins in the water relations of cut flowers beyond the regulation of porosity on pit membranes in the vessel-to-vessel junctions. Further studies will be needed to confirm these relationships in other plant species and to ascertain the actual mechanism behind the observed relationships. However, the possibility that pectins, owing to their water-binding ability, may influ-ence the hydration status of a cut flower stem continuously immersed in vase solution and the possibility of short-distance radial movement of water from the vase solution to the stem cortex and even to the vascular bundles, warrants detailed study in cut flowers with differing pectic contents and compositions.

Literature Cited

Ahmed, A.E.R. and J.M. Labavitch. 1977. A simplified method for ac-curate determination of cell wall uronide content. J. Food Biochem. 1:361-365.

Aloni, R., D.E. Enstone, and C.A. Peterson. 1998. Indirect evidence for bulk water flow in root cortical cell walls of three dicotyledonous

species. Planta 207:1-7.Blumenkrantz, N. and G. Asboe-Hansen. 1973. New method for quan-

titative determination of uronic acids. Anal. Biochem. 54:484-489.Brett, C.T. and K.W. Waldron. 1996. Physiology and Biochemistry

of Plant Cell Walls. 2nd ed. Chapman & Hall, London.Canny, M.J. 1995. Apoplastic water and solute movement: new rules

for an old space. Ann. Rev. Plant Physiol. Plant Mol. Biol. 46:215- 236.

De Vetten, N.C. and D.J. Huber. 1990. Cell wall changes during the expansion and senescence of carnation (Dianthus caryophyllus L.) petals. Physiol. Plant. 78:447-454.

Doi, M., Y. Hu, and H. Imanishi. 2000. Water relations of cut roses as influenced by vapor pressure deficits and temperatures. J. Japan. Soc. Hort. Sci. 69:584-589.

Gascó, A., A. Nardini, E. Gortan and S. Salleo. 2006. Ion-mediated increase in the hydraulic conductivity of laurel stems: role of pits and consequences for the impact of cavitation on water transport. Plant, Cell Environ. 29:1946-1955.

Halevy, A.H. and S. Mayak. 1981. Senescence and postharvest physiology of cut flowers - Part 2. Hortic. Rev. 3:59-143.

Heyes, J.A. and C.J. Clark. 2003. Magnetic resonance imaging of water movement through asparagus. Functional Plant Biol. 30:1089-1095.

Mayak, S. and A.H. Halevy. 1980. Flower senescence, p. 131-156. In: Thimann, K.W. (ed.). Senescence in Petals. CRC Press, Boca Raton, FL.

Muller, S., W.G. Jardine, B.W. Evans, R.J. Vietor, C.E. Snape, and M.C. Jarvis. 2003. Cell wall composition of vascular and parenchyma tissues in broccoli stems. J. Sci. Food Agric. 83:1289-1292.

O'Donoghue, E.M., S.D. Somerfield, and J.A. Heyes. 2002. Organization of cell walls in Sandersonia aurantiaca floral tissue. J. Exp. Bot. 53:513-523.

Pinheiro, S.C.F. and D.P.F. Almeida. 2008. Modulation of tomato pericarp firmness through pH and calcium: Implications for the texture of fresh-cut fruit. Postharvest Biol. Technol. 47:119-125.

Redgwell, R.J., E. MacRae, I. Hallett, M. Fischer, J. Perry, and R. Harker. 1997. In vivo and in vitro swelling of cell walls during fruit ripening. Planta 203:162-173.

Thakur, B.R., R.K. Singh, and A.K. Handa. 1997. Chemistry and uses of pectin – a review. Critical Rev. Food Sci. Nutr. 37:47-73.

Tyree, M.T. 1997. The Cohesion-Tension theory of sap ascent: current controversies. J. Exp. Bot. 48:1753-1765.

van Doorn, W. and R.R.J. Perik. 1990. Hydroxyquinoline citrate and


low pH prevent vascular blockage in stems of cut rose flowers by reducing the number of bacteria. J. Amer. Soc. Hort. Sci. 115:979- 981.

van Doorn, W.G. 1994. Vascular occlusion in cut flowering rose stems exposed to air: role of xylem wall pathway for water. Physiol. Plant. 90:45-50.

van Doorn, W.G. 1997. Water relations of cut flowers. Hort. Rev. 18: 1-85.

van Doorn, W.G. and U. van Meeteren. 2003. Flower opening and closure: a review. J. Exp. Bot. 54:1801-1812.

van Ieperen, W. 2007. Ion-mediated changes of xylem hydraulic resistance in planta: fact or fiction? Trends Plant Sci. 12:137-142.

van Ieperen, W., U. van Meeteren, and H. van Gelder. 2000. Fluid ionic

composition influences hydraulic conductance of xylem conduits. J. Exp. Bot. 51:769-776.

van Ieperen, W., U. van Meeteren, and J. Nijsse. 2002. Embolism repair in cut flower stems: a physical approach. Postharvest Biol. Technol. 25:1-14.

van Meeteren, U., H. van Gelder, and W. van Ieperen. 1999. Recon-sideration of the use of deionized water as vase water in postharvest experiments on cut flowers. Postharvest Biol. Technol. 17:175-187.

Zimmermann, U., H.J. Wagner, H. Schneider, M. Rokitta, A. Haase, and F.W. Bentrup. 2000. Water ascent in plants: the ongoing debate. Trends Plant Sci. 5:145-146.

Zwieniecki M.A., P.J. Melcher, and N.H. Holbrook. 2001. Hydrogel control of xylem hydraulic resistance in plants. Science 291:1059- 1062.

pectin solubility and water relations during vase life of cut flowers

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