Jasmonic acid stimulates the expression of nod genes in Rhizobium

Jasmonates and salicylic acid are considered to be signal molecules that in duce a variety of plant genes involved in wound or defence response, as wel l as affecting nos promoter activity. In this paper we examined whether the se chemicals could also affect nod genes from isogenic rhizobia strains. Is ogenic strains contain the Rhizobium leguminosarum nodA promoter fused to t he lacZ gene of Escherichia coli and differ only in the source of the regul atory nodD gene. Naringenin, jasmonic acid and methyl jasmonate induced exp ression of nod genes in strain RBL 1284 and salicylic acid showed no activi ty alone or when used in combination with other compounds; addition of nari ngenin + jasmonic acid produced a synergistic effect. Results obtained with strain RBL5284 were similar to those for RBL1284 albeit the combination of naringenin with the other compounds markedly inhibited nod gene expression . Whereas RBL5283 responded to naringenin with a strong induction, jasmonic acid, methyl jasmonate or salicylic acid showed no significant responses. The inhibitory effect of salicylic acid on nod gene expression indicates th at the induction mechanism of jasmonic acid, methyl jasmonate, N-propyldihy drojasmonate and naringenin is probably different from that of salicylic ac id.