A Role for Ca2+ in the Elicitation of Rishitin and Lubimin Accumulation in Potato Tuber Tissue

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Abstract
Calcium and strontium ions enhanced rishitin but not lubimin accumulation in tuber tissue of potato (Solanum tuberosum cv Kennebec) treated with arachidonic acid (AA). The same cations in the presence of poly-L-lysine (PL) enhanced the accumulation of lubimin more than rishitin. In contrast, Mg2+ did not affect AA-elicited rishitin and lubimin accumulation and inhibited the accumulation of these compounds following application of PL. AA-elicited potato tuber tissue remained sensitive to the stimulatory effects of Ca2+ and Sr2+ up to 24 h after application of AA, but PL-elicited tuber tissue was sensitive to Ca2+ and Sr2+ for only 6 hours after PL application. Ethyleneglycol-bis (.beta.-aminoethyl ether)-N,N''-tetraacetic acid and La3+ both inhibited rishitin and lubimin accumulation elicited by AA. The inhibition by either agent was overcome by the addition of Ca2+. Calcium was more effective in overcoming lanthanum inhibition when applied simultaneously than when applied 12 hours later. Lanthanum was only effective in inhibiting rishitin and lubimin accumulation when applied within 3 hours of the application of AA. Inhibition of phytoalexin accumulation was greater when La3+ was applied simultaneously with AA compared to La3+ application after AA application to discs. These observations suggest that the mobilization of calcium may play a central regulatory role in the expression of phytoalexin accumulation following elicitation in potato tissue.