Chitinase: Differential induction of gene expression and enzyme activity by drought stress in the wild (Lycopersicon chilense Dun.) and cultivated (L-esculentum Mill.) tomatoes

We have previously reported the isolation of a drought: and abscisic acid ( ABA)-induced chitinase gene from Lycopersicon chilense, a drought tolerant wild tomato (Chen et al., 1994. Mol. Gen. Genet. 245: 195-202). We have the refore carried out a comparative study in order to examine chitinase gene e xpression and enzyme activity in Lycopersicon chilense (LA2747 and LA1930) and L. esculentum (cultivar Starfire) during water stress. Both enzyme assa y and northern blot analysis revealed that chitinase expression was differe ntially induced by drought in the two species. Higher induction of chitinas e occurred in tolerant species compared to the sensitive one. Among the gen otypes examined, L. chilense LA2747 which is the most drought tolerant, pre sented the highest level of chitinase induction, while the lowest level was found in L. esculentum, Starfire. Similar results were obtained using cell suspensions treated with ABA and mannitol. Both ABA treatment and osmotic stress induced chitinase gene expression in the cell suspensions and this i nduction was more pronounced in the wild tomato compared to the cultivated one. Drought induced accumulation of chitinase mRNA was investigated in L. chilense, LA2747 leaves, stems and roots. The results revealed that the chi tinase gene was organ specifically expressed during drought stress. Leaves of drought stressed plants showed the highest expression and roots showed t he lowest. The accumulation of chitinase during drought stress was also con firmed by in situ hybridization. Leaf water potentials (LWP) were determine d in the three genotypes during drought stress. A correlation was found bet ween the chitinase gene expression and leaf water potential during drought stress. The highest level of leaf water potential was maintained in L. chil ense LA2747 which also demonstrates the highest level of chitinase expressi on among the three genotypes. Our results suggest that the L. chilense chit inase gene might be involved in drought tolerance of this species.