The role of Ca(2+) in elicitation of phytoalexin synthesis in cell culture of onion (Allium cepa L.).

Treatment of Allium cepa L. cellsuspension cultures with a biotic elicitor derived from the fungus Botrytis cinerea, resulted in phytoalexin synthesis. Two phytoalexins, 5-octylcyclopenta-1,3-dione and 5-hexyl-cyclopenta-1,3-dione, were accumulated in cultured onion cells. Removal of extracellular Ca(2+) by the calcium chelator ethylene glycol bis(b-aminoethyl ether) N,N'-tetraacetic acid abolished the elicitor-mediated phytoalexin synthesis. The calcium channel blockers, verapamil and 8-N,N-(dimethylamino)octyl-3,4,5-trimethoxybenzoate caused similar effects, whereas the addition of the Ca(2+) ionophore A23187 enhanced the accumulation of phytoalexins in the absence of the elicitor. Increase in the cytoplasmic Ca(2+) concentration in elicitor-treated onion cells was observed as monitored by the fluorescent calcium indicator indo-1. These observations suggest that Ca(2+) acts as a second messenger in the regulation of phytoalexin synthesis in cultured onion cells.