DIFFERENTIAL ACCUMULATION OF TRANSCRIPTS OF 1-AMINOCYCLOPROPANE-1-CARBOXYLATE SYNTHASE GENES IN TOMATO PLANTS INFECTED WITH PHYTOPHTHORA-INFESTANS AND IN ELICITOR-TREATED TOMATO CELL-SUSPENSIONS

The activity of 1-aminocyclopropane-1-carboxylate synthase (ACC-S, EC 4.4.1.14) increases in tomato leaves infected with Phytophthora infest ans (Mont.) de Bary and in tomato cell suspension cultures treated wit h fungal elicitors. cDNA probes corresponding to three different ACC-S genes were used to analyze the levels of different mRNAs encoding ACC -S in infected and elicitor-treated tomato. The level of mRNA hybridiz ing with Ben17, a specific probe for the LE-ACC2 gene, increased in to mato leaves following infection and in cells treated with elicitors. T here was no detectable mRNA hybridizing with Ben 18, a specific probe for the fruit ripening-induced gene LE-ACC4, in any of the samples fro m leaves or cell cultures. The level of mRNA hybridizing to pBTAS3, a cDNA probe for a third ACC-S gene, rapidly increased in elicitor-treat ed cell cultures, even when RNA synthesis was blocked by cordycepin. T hese data support the view that the expression of the genes for ACC-S is differentially regulated by diverse stimuli and that the regulation of ACC-S activity occurs both by modulation of expression of the diff erent genes and by subsequent, post-transcriptional processes.