Elicitation of Pisatin in Pea (Pisum sativum L.) By Copper-Asparagine Complexes

Abstract

The early events in the mode-of-action of CuCl2 solutions in relation to pisatin elicitation were examined. Cu2+ ions were rapidly adsorbed to or taken up by pea endocarp tissue from CuCl2 solutions and large quantities of amino acids and sugars were rapidly released from the plant cells into the external solutions. Asparagine accounted for 56% of the amino-nitrogen while glucose represented 58% of the sugars. The concentration increases of asparagine and glucose relative to the water controls were approximately 140- and 180-fold respectively. The enhanced pisatin elicitor activity of pea-Cu2+ -leachates (4 h, 20°C) obtained following the topical application of CuCl2 solutions to endocarp tissues was primarily due to the formation in the external solutions of Cu2+ -asparagine complexes. This was demonstrated by their isolation, identification and bioassay, and by the bioassay of synthetic Cu2+ -asparagine complexes. Cu2+ - complexes with other amino acids also present in pod leachates were prepared and their differential pisatin elicitor activity compared to asparagine. Only aspartic acid-complexes exhibited higher elicitor activity (109%) than Cu2+-asparagine. The other amino acids used resulted in pisatin concentrations 64 (homoserine) to 78% (glutamine) of that induced by asparagine.