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Abstract(s)
The effects of a slowly-imposed drought stress on gas-exchange, chlorophyll a fluorescence,
biochemical and physiological parameters of Vitis vinifera L. leaves (cv. Aragonez, syn. Tempranillo) growing in a
commercial vineyard (South Portugal) were evaluated. Relative to well-watered plants (predawn water potential,
ΨPD = –0.13 ± 0.01 MPa), drought-stressed plants (ΨPD = –0.97 ± 0.01 MPa) had lower photosynthetic rates
(ca 70%), stomatal conductance, and PSII activity (associated with a higher reduction of the quinone A pool and
lower efficiency of PSII open centres). Stomatal limitation to photosynthesis was increased in drought-stressed
plants relative to well-watered plants by ca 44%. Modelled responses of net photosynthesis to internal CO2
indicated that drought-stressed plants had significant reductions in maximum Rubisco carboxylation activity
(ca 32%), ribulose-1,5-bisphosphate regeneration (ca 27%), and triose phosphate (triose-P) utilization rates
(ca 37%) relative to well-watered plants. There was good agreement between the effects of drought on modelled
biochemical parameters, and in vitro activities of key enzymes of carbon metabolism, namely Rubisco,
glyceraldehyde-3-phosphate dehydrogenase, ribulose-5-phosphate kinase and fructose-1,6-bisphosphate
phosphatase. Quantum yields measured under both ambient (35 Pa) and saturating CO2 (100 Pa) for
drought-stressed plants were decreased relative to well-watered plants, as well as maximum photosynthetic rates
measured at light and CO2 saturating conditions (three times ambient CO2 levels). Although stomatal closure was
a strong limitation to CO2 assimilation under drought, comparable reductions in electron transport, CO2
carboxylation, and utilization of triose-P capacities were also adaptations of the photosynthetic machinery to
dehydration that slowly developed under field conditions. Results presented in this study confirm that modelling
photosynthetic responses based on gas-exchange data can be successfully used to predict metabolic limitations to
photosynthesis.
Description
Keywords
Drought Enzymes of carbon metabolism Gas exchange Modelling Photosynthesis Vitis vinifera
Citation
Functional Plant Biology, 29, 451-459