Proc. VII Int.Symp. on Postharvest Physiology Ornamentals Eds. T.A.& D.G.Clark Acta Hort. 543, ISHS 2001 345 CALCIUM IN REGULATION OF POSTHARVEST LIFE OF FLOWERS A.H. Halevy, S. Torre, A. Borochov and R. Porat The Hebrew University of Jerusalem Department of Horticulture Rehovot 76100, Israel S. Philosoph-Hadas, S. Meir and H. Friedman Volcani Center Department of Postharvest Science of Fresh Produce Bet Dagan 50250, Israel Keywords : rose, Phalaenopsis, senescence, sensitivity to ethylene, gravitropic bending, LaCl 3 , Ca-chelators. Abstract Calcium is involved in regulation of many processes during plant growth and senescence. Calcium influences cell-wall and membrane structure and function. Cytosolic calcium is considered as second messenger in regulation of important cellular events. We present three cases in which calcium was shown to regulate processes of postharvest life of flowers. 1.Rose petal senescence In whole rose cut flowers and in detached petals, CaCl 2 treatment promoted bud opening and delayed senescence. The treated flowers stayed turgid and continued their initial postharvest growth for longer periods of time. Calcium treatment delayed the decrease in membrane proteins and phospholipids (PL) with time and increased ATPase activity in the aging petals. Electrolyte leakage was postponed in calcium treated flowers. We suggest that the calcium-induced delay in rose petal senescence involves the protection of membrane proteins and PLs from degeneration. 2.Pollination-induced senescence of Phalaenopsis . Pollination increased ethylene production and sensitivity to ethylene. Treatment of both pollinated and unpollinated flowers with calcium ions increased the sensitivity of the flowers to ethylene and promoted ethylene production and senescence, while EGTA - a chelator of calcium, decreased these processes. 3.Gravitropic bending of flowers . Calcium chelators and the calcium channel blocker LaCl 3 inhibited the gravitropic bending of several flower stalks. These modulators had no deleterious effect on the flowering shoots, indicating that they inhibit the gravitropic bending by interfering specifically with the gravitropism related processes. An ethylene gradient was developed across the flowering shoot prior to the bending response, with high levels of ethylene production at the lower side. This ethylene gradient was abolished by treatment with the calcium antagonists. Abbreviations: BAPTA = 1,2-bis (2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; CDTA = trans-1,2-cyclohexan dinitro-N,N,N',N'-tetraacetic acid; EGTA = ethylene glycol bis (β -amino- ethylether) N,N,N',N'-tetraacetic acid; FW = fresh weight; PL = phospholipids. 1. Introduction Calcium has been known for many years as an important component of plant cells and an essential macro plant nutrient. Extracellular Ca 2+ plays a major role in cell wall structure and in maintenance of membrane function and structure. In recent years it became clear that cytosolic Ca 2+ act as a secondary messenger transducing a wide range of external stimuli into metabolic events, some of which lead to regulation of plant