Involvement of GTP-binding protein in the induction of phytoalexin biosynthesis in cultured carrot cells

Biosynthetic activity of carrot phytoalexin 6-methoxymellen was induced in cell suspension culture by the treatment with oligogalacturonide elicitor; however, the elicitor-induced activity appreciably reduced in the presence of suramin, a potent inhibitor of GTP-binding proteins. In contrast. additi on of G-protein activators, such as mastoparan or GTP-gamma -S. to carrot c ell culture triggered 6-methoxymellein production even in the absence of ur onide elicitor. An appreciable GTPase activity was found in purified plasma membrane of cultured carrot cells, and the hydrolytic activity was signifi cantly increased by the addition of elicitor. Carrot plasma membrane was ca pable of associating with GTP-gamma -S, and the binding ability was markedl y increased in the presence of elicitor. However, the binding activity mark edly decreased when the membrane preparation was pre-incubated with GTP but not with ATP. These observations strongly suggest that a certain GTP-bindi ng protein located at plasma membrane of cultured carrot cells plays an imp ortant role in the oligogalacturonide elicitor-induced 6-methoxymellein pro duction. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.