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.
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