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.