THE ROLE OF CA2-CULTURE OF ONION (ALLIUM-CEPA L)( IN ELICITATION OF PHYTOALEXIN SYNTHESIS IN CELL)

Treatment of Allium cepa L. cell-suspension cultures with a biotic eli citor derived from the fungus Botrytis cinerea, resulted in phytoalexi n synthesis. Two phytoalexins, 5-octyl-cyclopenta-1,3-dione and 5-hexy l-cyclopenta-1,3-dione, were accumulated in cultured onion cells. Remo val of extracellular Ca2+ by the calcium chelator ethylene glycol bis( b-aminoethyl ether) N,N'-tetraacetic acid abolished the elicitor-media ted phytoalexin synthesis. The calcium channel blockers, verapamil and -N,N-(dimethylamino)octyl-3,4,5-trimethoxybenzoate caused similar eff ects, whereas the addition of the Ca2+ ionophore A23187 enhanced the a ccumulation of phytoalexins in the absence of the elicitor. Increase i n the cytoplasmic Ca2+ concentration in elicitor-treated onion cells w as observed as monitored by the fluorescent calcium indicator indo-1. These observations suggest that Ca2+ acts as a second messenger in the regulation of phytoalexin synthesis in cultured onion cells.