ISHS Acta Horticulturae 543: VII International Symposium on Postharvest Physiology of Ornamental Plants
THE EFFECT OF TRANSIENT WATER STRESS ON SUGAR METABOLISM AND DEVELOPMENT OF CUT FLOWERS |
| Authors: | S. Mayak, S. Meir, H. Ben-Sade |
| Abstract:
Transient water stress is an integral part of postharvest handling of cut flowers. It was therefore of interest to study how it influences the further development of the flowers once placed in water. An expansion of petal cells is central in growth of petals and thus opening of flowers. Among the processes involved are an increase in the osmotic pool, loosening and synthesis of cell wall components. In response to transient water stress a marked rise in the concentration of soluble sugars and reduction in starch has occurred in rose petals Rosa hybrida L. cv. Mercedes at the same time the growth of the flower was substantially inhibited. The rise in sugar content in rose petals was due to transport of sugars from the leaves to the flowers and to hydrolysis of starch within the petals. The contribution of the latter seems to be smaller by comparison. A similar study was conducted with wax flowers Chamelaucium unicatum. In response to transient water stress, A marked rise in soluble sugars coupled with marked enhancement of opening of the flowers has occurred. Fructans and starch are the source for the rise in soluble sugars. By inference we suggest that the difference between the flowers seem to stem from the effect transient waster stress may have on the processes occurring in the cell wall. It was hypothesized that in rose petals, loosening and synthesis of cell wall were negatively influenced by water stress, resulting in growth inhibition of the petals. In contrast, wax flowers that were introduced to culture from arid environment, are more immune to the adverse effect of transient water stress. Hence in response to water stress, osmotic adjustment occurs and in cooperation with cell expansion leads to growth stimulation of the petals. Transient water stress is an integral part of postharvest handling of cut flowers in the channels of marketing. The water transpired is replaced by air disrupting water column continuity and impeding water movement. Consequently water availability is reduced and hence turgor pressure is lowered. The question arise, will the flowers regain turgor pressure if replaced in water ? Will the flowers resume growth processes in the petals ? Does osmotic adjustment occurs and is it part of the recovery mechanism ? The driving force for water uptake is the difference in water potential, the osmotic potential in the plant cells is one of its components. It was estimated that in rose petals sugars are about 55% of the osmotic pool(Acock and Nichols 1979). Since photosynthetic activity is low in petals (Weiss et al., 1988), the petals depend on import carbon metabolites to support their growth. Starch is accumulating in petals and as it degrade it may serve as a source to supplement the osmotic pool, the maintenance of which is important in assuring a favorable water status. In response to water stress in plants, the concentration of a variety of common solutes, including sugars, organic acids and ions had been observed. This response however has not been adequately studied in petals. A cut flower provides an interesting plant model for studying the influence of stress in relation to tissue growth. First there are no roots to affect the osmotic adjustment to stress. Second, water stress can be quickly imposed and relieved. Third, growth is primarily restricted to the petals, that if were not exposed to stress would have undergone an intensive expansion processes. Note that growth of rose petals is primarily due to expansion of cells (Siegelman et al., 1958). In the present study we demonstrated that in response to water stress a rise in soluble sugars has occurred. A reduction in the content of carbohydrate polymers has been measured. But the reduction in starch could not account for the rise in the sugar content. The rise in the content of sugars seem to derive from import from the adjacent leaves. | |
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