U. van Meeteren

Reconsideration of the use of deionized water as vase water in postharvest experiments on cut flowers

Abstract The relevance of deionized water as a control treatment in vase life experiments and the effects of major tap water components on cut flower water balance were investigated. Chrysanthemum ( Dendranthema x grandiflorum Tzvelev cv. Cassa) was used in all experiments. Deionized water gave a sharp decrease in fresh weight of the cut flowers after 1–3 days. This decrease was absent in tap water. After 4 days in deionized water, hydraulic resistance in the basal part of the stem was ∼50 times the value of fresh cut flowers and seven times the value in tap water. Change in fresh weight during vase life in a solution containing combinations of CaCl 2 , NaHCO 3 and Cu 2+ at concentrations commonly present in tap water was similar to that in tap water. However, none of the minerals tested by themselves gave fresh weight results similar to those from using tap water. In the combined solution, hydraulic resistance in the basal part of the stem after 4 days was comparable to that in tap water. A minimal amount of Cu 2+ (>0.30 mg·l −1 ) enhanced fresh weight, probably by reducing bacterial growth in the cut open vessels. Calcium chloride (>0.7 mM) delayed the increase in hydraulic resistance in the stem (not including the basal 3 cm) compared to deionized water, and at a high concentration (10.7 mM), substantially decreased the transpiration rate. Sodium bicarbonate (1.5 mM) neither affected hydraulic resistance nor transpiration rate, but positively influenced fresh weight change during vase life when combined with CuSO 4 and as compared to deionized water. Results strongly question the appropriateness of deionized water as a control solution in vase life experiments.

Role of air embolism and low water temperature in water balance of cut chrysanthemum flowers.

Abstract The water balance of cut chrysanthemum flowers (Chrysanthemum morifolium cultivar ‘Cassa’) which had been dry stored and dehydrated did not recover, but deteriorated from the first day of the vase period. During the vase period, the water balance was affected to a greater extent by a preceding dry-storage period (with a minimal loss of water) than by preceding water loss. The water balance could be restored by vacuum rehydration or by placing the stems for 2 h in cold water (0–5°C). Low water temperature also improved the water balance of flowers immediately after cutting, but any influence of low water temperature was absent when flowering stems were previously fully hydrated. It is concluded that there could be two separate mechanisms for water uptake in cut chrysanthemum flowers; one of them is blocked by air (or other gasses) coming into the stems and the other one by a period of dry storage. Air blocking the water uptake seems to be removed by placing the stems in cold water.

Embolism repair in cut flower stems: a physical approach

Abstract The role of xylem anatomical properties on air embolism removal and xylem hydraulic conductance recovery from cut flower stems during the first hours of vase life was studied from a physical point of view. A model based on physical processes was developed and tested using chrysanthemum ( Dendranthema × grandiflorum Tzvelev) cut flowers. The model predicts that the repair process takes place in two major phases. During the first few seconds after replacing in water, initially air-filled vessels at the cut surface partly refill with water. Consequently, reconnections are established between the vase water and the non-cut water-filled xylem vessels just above the cut surface and hydraulic conductance is partly recovered. During the following hours, air partly or completely dissolves into the surrounding water in the stem and hydraulic conductance recovery gradually takes place. The results of the model agreed well with dynamic measurements of hydraulic conductance recovery on chrysanthemum stem segments after aspiration of air. Visual detection of air emboli by cryo-scanning electron microscopy showed that after 1.5 h of repair, air was only present in large-diameter vessels at a position relatively distant from the cut surface of the stem. According to the model, hydraulic conductance repair occurs more readily in stems with smaller diameter vessels. Model calculations and experiments showed that the height of water in the vase influences recovery of water uptake more in stems with large-diameter vessels than in stems with small-diameter vessels. It is concluded that the anatomical structure of the xylem plays an important role in the rehydration capability of cut flowers.

Effect of time since harvest and handling conditions on rehydration ability of cut chrysanthemum flowers

Abstract Fresh cut chrysanthemum (Dendranthema x grandiflorum ‘Cassa’) flowers rehydrated fully after rapid water loss over 1 h at 20°C, 60% relative humidity (RH), and 14 μmol·m−2·s−1 light, the water loss being 5% of their fully saturated fresh weight. For rehydration after desiccation, it proved important that flowers were cut at a minimum distance above soil level. The water status of cut flowers dry-stored in darkness for 24 h at 20°C with minimal water loss (∼1%) decreased sharply during the first days of subsequent vase life. Flowers stood for 3–4 h in 20°C water and at low light intensity (14 μmol·m−2·s−1) followed by ‘desiccation’ did not rehydrate after the desiccation, but decreased further in fresh weight when returned to water. Rehydration ability of these flowers was restored, however, when the stem ends were trimmed by 7 cm under water after desiccation. Recutting in air did not restore rehydration ability. After periods of 4 or 24 h at 20°C in 5°C water at low light intensity followed by desiccation, flowers regained their water status during subsequent vase life. Flowers stood for 24 h in 20°C water and at high light intensity (187 μmol·m−2·s−1) followed by desiccation rehydrated almost fully when returned to water. It is proposed that an undefined ‘rehydration-inhibiting’ process starts after harvest, which is not due to dehydration of xylem walls or other stem tissue, or to the growth of microorganisms.

The existence of a critical period for the abscission and a non-critical period for blasting of flower-buds of Lilium ‘Enchantment’; influence of light and ethylene

Abstract Flower-bud blasting and abscission, 2 dissimilar phenomena occurring in buds of Lilium ‘Enchantment’, can both be evoked by darkness or ethylene (C2H4). Flower-bud abscission is influenced more strongly than bud blasting by short light periods and C2H4. Flower-bud blasting can occur through out inflorescence development, abscission only during a critical stage of development of the flower-buds, which proved to coincide with a peak in the endogenous production of C2H4 by the buds and with the end of the meiotic phase of the stamens. Both C2H4 production by the buds and the occurrence of flower-bud abscission were influenced by the length of time the bulbs had been stored before planting.

Reconsideration of the use of deoonized water as vase water in postharvest experiments on cut flowers (corrected version)

The relevance of deionized water as a control treatment in vase life experiments and the effects of major tap water components on cut flower water balance were investigated. Chrysanthemum (Dendranthema x grandiflorum Tzvelev cv. Cassa) was used in all experiments. Deionized water gave a sharp decrease in fresh weight of the cut flowers after 1–3 days. This decrease was absent in tap water. After 4 days in deionized water, hydraulic resistance in the basal part of the stem was ∼50 times the value of fresh cut flowers and seven times the value in tap water. Change in fresh weight during vase life in a solution containing combinations of CaCl2, NaHCO3 and Cu2+ at concentrations commonly present in tap water was similar to that in tap water. However, none of the minerals tested by themselves gave fresh weight results similar to those from using tap water. In the combined solution, hydraulic resistance in the basal part of the stem after 4 days was comparable to that in tap water. A minimal amount of Cu2+ (>0.30 mg·l−1) enhanced fresh weight, probably by reducing bacterial growth in the cut open vessels. Calcium chloride (>0.7 mM) delayed the increase in hydraulic resistance in the stem (not including the basal 3 cm) compared to deionized water, and at a high concentration (10.7 mM), substantially decreased the transpiration rate. Sodium bicarbonate (1.5 mM) neither affected hydraulic resistance nor transpiration rate, but positively influenced fresh weight change during vase life when combined with CuSO4 and as compared to deionized water. Results strongly question the appropriateness of deionized water as a control solution in vase life experiments.

Water relations and keeping-quality of cut Gerbera flowers. V. Role of endogenous cytokinins☆

Abstract The objective of the present work was to investigate if differences in internal water relations, due to differences in membrane permeability, between Gerbera petals of inflorescences ageing in a vase and on the plant could be ascribed to differences in cytokinin activities. Moreover, cytokinin activities in petal-extracts of 3 cultivars, differing in their keeping-quality, were compared. Cytokinin activities (“free” and “bound”) in petals decreased during the first 6 days of the experiment (both in the vase and on the plant). On Day 8, a very high activity was found in almost all the R f -fractions of the chromatogram. After Day 8, the activity decreased again. For young inflorescences, developing on the plant, a peak level was reached for “free” cytokinins at a very early bud stage and for “bound” cytokinins when the petals were just fully expanded. There were no correlations between petal-cytokinin activities at day of harvest of 3 Gerbera cultivars and their keeping-quality. It is concluded that changes in membrane permeability, which occur during ageing of petals of cut Gerbera inflorescences, are not triggered by changes in cytokinin activities.

Water relations and keeping quality of cut Gerbera flowers. VI. Role of pressure potential

Abstract The increase of ion leakage (I.L.) of Gerbera petal cells during ageing was hastened by lowering the pressure potential of excised petals. Increasing pressure potential by placing flower stems in KNO 3 -solutions delayed the increase of I.L. It is suggested that differences in time curves of I.L. for cut and intact flowers are initiated by differences in pressure potential. The theory that determinations of pressure potential, water content per dry weight and dry weight per area of petals will give a good indication of potential keeping-quality is discussed.