EARLY RESPONSES OF DROUGHT-RESISTANT AND DROUGHT-SUSCEPTIBLE TOMATO PLANTS SUBJECTED TO WATER-STRESS

Three-week-old seedlings of one drought-susceptible tomato cultivar (Lycopersicon esculentum cv. "New Yorker") and two drought-resistant species of tomato (Solanum pennellii and Lycopersicon chilense) were subjected to various degrees of PEG 8000-induced water stress from -0.017 to -1.0 MPa for a duration of 24 h so that their early responses to water stress could be compared. Such a comparison would determine if there was a relationship to root cytokinin levels following sudden induction of water stress in the drought-resistant species. Transpiration rates of leaves were monitored throughout the 24-h period, shoots were evaluated for leaf water potential (LWP), and roots were extracted for levels of t-zeatin riboside (t-ZR) and dihydrozeatin riboside (DHZR) using a monoclonal antibody enzyme immunoassay. Transpiration rates were evaluated gravimetrically by difference every 6 h up to 24 h. Transpiration rate decreased with increasing PEG levels and passage of time in all three species, measured at 6 and 12 h, logarithmically in the case of the two Lycopersicon species and linearly in the case of Solanum. From 12-18 h (while plants were in darkness), transpiration rate was a function of the level of PEG only and not time in all three species. When light resumed from 18-24 h, only 5. pennellii showed no further decrease in transpiration rate over time with increasing PEG. Drought-susceptible L. esculentum had a stronger linear decrease in LWP with increasing PEG 8000 concentration than the other two species. L. esculentum also had a higher initial transpiration rate than did either of the drought-resistant species. The two drought-resistant species showed less change in LWP with 5. pennellii having a small decrease and L. chilense having little change. Only S. pennellii exhibited a decrease in root t-ZR levels, which may imply a role for root cytokinin within the first 24-h exposure to water stress in this species. L. esculentum exhibited no change in root t-ZR. The levels of t-ZR in L. chilense were less than that of L. esculentum but showed only a slight decrease with increasing PEG. S. pennellii and L. chilense, although both drought-resistant tomato species, showed different patterns of response with respect to pattern of decline in transpiration rate, LWP, and root t-ZR levels. © 1990 Springer-Verlag New York Inc.