BIOSYNTHESIS AND METABOLISM OF ABSCISIC-ACID IN TOMATO LEAVES INFECTED WITH BOTRYTIS-CINEREA

Two virulent strains of Botrytis cinera Pers., one of them (Bc 6) prod ucing abscisic acid (ABA) via 1',4'-trans-diol-ABA in defined liquid c ulture, and a second strain (Bc 9) without the ability to form ABA or its fungal precursor, and two near-isogenic lines of tomato were used to study the biosynthesis and metabolism of ABA in infected isolated l eaves. The tomato plants used were Lycopersicon esculentum Mill. cv. A ilsa Craig (wild type) and the ABA-deficient mutant flacca. The level of 1',4'-trans-diol-ABA increased in Ailsa Craig and flacca leaves in a similar pattern to about 4 mu g .(g DW)(-1) after conidiospore infec tion with Be 6, but not after infection with Bc 9. Pulse-feeding exper iments showed that [2-C-14]-1 ',4'-trans-diol-ABA was metabolised to A BA and to further plant metabolites of ABA (phaseic acid, dihydrophase ic acid and polar compounds) in both uninfected and infected leaves. F ollowing infection, the turnover of 1',4'-trans-diol-ABA was reduced. The level of endogenous ABA in leaves infected with the ABA-producing strain Be 6 rose more than tenfold in Ailsa Craig and twofold in flacc a, respectively. Infection of Ailsa Craig leaves with Bc 9 caused a fi vefold increase in ABA, and no increase of ABA in flacca. It is conclu ded that at least four processes control the level of ABA in wild-type tomato leaves infected with Botrytis cinerea: stimulation of fungal A BA biosynthesis by the host; release of ABA or its precursor by the fu ngus; stimulation of biosynthesis of plant ABA by the fungus; inhibiti on of its metabolism by the fungus. Application of ABA together with f ungal spores to tomato leaves caused a faster development of necrotic leaf area than spore inoculation only.