Wednesday, February 6, 2008

Postharvest longevity of flowers

Keeping flowers beautiful for as long as possible is crucial to the floriculture industry, since consumers would probably buy less of the really old-looking, wilted flowers, than they do of the pretty, fresh flowers. This is the topic of installment 4 of the makita-prepares-for-exam

Part 1-Plant growth medium
Part 2-Nutritional deficiencies
Part 3-Plant growth regulators
Part 5-Legal protection of cultivar propagation

Many factors influence flower longevity, and they differ from one plant species to another. More than simply a question of more revenue for growers, flower longevity increases the chances of cross-pollination by insects (Primack, 1985). In many plants, senescence (wilting and dying) of flowers is enhanced by the plant hormone ethylene (hence the use of plant growth regulators to remove flowers from the plant, see part 3).

An interesting paper by Torre et al. (1999) linked low relative humidity during rose production, with higher calcium (Ca) content and delay of senescence. They propose that Ca protects membrane proteins and phospholipids from degradation. This prevents the cell membranes from breaking down and releasing ethylene, which results in continued transport of water nutrients and keeps the cells alive longer. Cool! Could you feed your roses calcium (you know, put some chalk shavings into the vase)? Well, I haven't tried chalk shavings, but apparently calcium chloride does the job, at least according to these scientists.

Application of carbohydrates (sugars), cytokinins, and gibberellins also seems to increase flower longevity (Leonard & Nell, 2004; Wingler et al, 1998). In Alstroemeria (the flowers at my wedding, hi honey!!!), which is normally classified as insensitive to ethylene for induction of senescence, a very small, but consistent amount of ethylene is produced just before the flower falls off (Wagstaff et al., 2005). It looks as if the flower is normally insensitive, but becomes sensitive to ethylene just before this abscission, and that ethylene is produced right at that time.

Leonard, R.T., and Nell, T.A. (2004) Short-term pulsing improves postharvest leaf quality of cut oriental lilies. HortTechnology, 2004. Vol 14, pp. 405-411.

Primack, Richard B. (1985) Longevity of individual flowers. Ann. Rev. Ecol. Syst. Vol 16, pp.15-37.

Torre, S., Borochov, A., and Halevy, A.H. (1999) Calcium regulation of senescence in rose petals. Physiologia Plantarum. Vol 107, pp. 214-219.

Wagstaff C., Chanasut, U., Harren, F.J.M., Laarhove, L, Thomas, B., Rogers, H.J., and Stead, A.D. (2005) Ethylene and flower longevity in Alstroemeria: relationship between tepal senescence, abscission and ethylene biosynthesis. J. Exp. Botany. Vol 56, pp. 1007-1016.

Wingler, A., von Schaewen, A., Leegood, R.C., Lea, P.J., and Quick, W.P. (1998) Regulation of leaf senescence by cytokinin, sugars, and light. Plant Physiol. Vol 166, pp. 329-335.

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