Limitations to leaf photosynthesis in field-grown grapevine under drought — metabolic and modelling approaches

Abstract

Abstract. 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, Ψ PD = -0.13 ± 0.01 MPa), drought-stressed plants (Ψ PD = -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 CO 2 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 CO 2 (100 Pa) for drought-stressed plants were decreased relative to well-watered plants, as well as maximum photosynthetic rates measured at light and CO 2 saturating conditions (three times ambient CO 2 levels). Although stomatal closure was a strong limitation to CO 2 assimilation under drought, comparable reductions in electron transport, CO 2 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.

Partial rootzone drying: regulation of stomatal aperture and carbon assimilation in field-grown grapevines (Vitis vinifera cv. Moscatel)

“…1). These results are in accordance with reports of high tolerance of the photochemical apparatus of grapevine leaves under environmental stress (Gamon and Pearcy 1990;Chaumont et al 1995), including drought (Flexas et al 1999a(Flexas et al , 1990bMaroco et al 2002). The major process involved in protection against photodamage during water stress is probably the increase of non-photochemical energy dissipation, as we observed in NI vines (Fig.…”

“…However, Rubisco activity seems to be more resistant to water stress than photophosphorylation, with significant effects occurring only for severe drought. In studies with grapevine, Escalona et al (1999) did not observe a significant reduction in Rubisco carboxylation efficiency for Ψ L of -0.5 ± 0.04 MPa, while Maroco et al (2002) observed a significant reduction of V Cmax for Ψ L of -0.95 ± 0.01 MPa in the same cultivar. In contrast, TPU capacity was significantly reduced in both NI and PRD vines compared with FI vines.…”

“…Response curves of net photosynthesis to internal CO 2 (A-C i ) were obtained with the same equipment with the leaf chamber temperature kept at 25°C, photosynthetic photon flux density (PPFD) of 1200 µmol photons m -2 s -1 and relative humidity at 60-70%. The maximum rate of Rubisco carboxylation (V Cmax ), mitochondrial respiration (R d ), maximum electron transport capacity at saturating light (J max ) and the rate of triose-P utilization (TPU) were obtained by fitting the model of Farquhar et al (1980) with modifications by Sharkey (1985) to A-C i response curves, as described by Maroco et al (2002) using the NONLIN procedure of SAS (version 8.0; SAS Institute, Cary, NC, USA). The limitation to photosynthesis imposed by closed stomatal conductance in treatments was estimated through the relative stomatal limitation (RSL, in percent) calculated from A-C i response curves using the equation:…”

“…This effect may prevent the metabolic inhibition of CO 2 assimilation that otherwise would occur if stress under field conditions was allowed to develop extensively (e.g. Escalona et al 1999;Maroco et al 2002). The aim of the present work was to analyse the effects of PRD on photosynthesis, stomatal conductance and water use efficiency (both in the short and long term) in field-grown grapevines.…”

“…occur when vines are subjected to drought under field conditions (Escalona et al 1999;Maroco et al 2002).…”