Causes of decreased photosynthetic rate and metabolic capacity in water-deficient leaf cells: a critical evaluation of mechanisms and integration of processes

Abstract

With progressive WD, A decreases as g(s) falls. Under low light during growth and WD, A is stimulated by elevated CO(2), showing that metabolism (A(pot)) is not impaired, but at high light A is not stimulated, showing inhibition. At a given intercellular CO(2) concentration (C(i)) A decreases, showing impaired metabolism (A(pot)). The C(i) and probably chloroplast CO(2) concentration (C(c)), decreases and then increases, together with the equilibrium CO(2) concentration, with greater WD. Estimation of C(c) and internal (mesophyll) conductance (g(i)) is considered uncertain. Photosystem activity is unaffected until very severe WD, maintaining electron (e(-)) transport (ET) and reductant content. Low A, together with photorespiration (PR), which is maintained or decreased, provides a smaller sink for e(-)(,) causing over-energization of energy transduction. Despite increased non-photochemical quenching (NPQ), excess energy and e(-) result in generation of reactive oxygen species (ROS). Evidence is considered that ROS damages ATP synthase so that ATP content decreases progressively with WD. Decreased ATP limits RuBP production by the Calvin cycle and thus A(pot). Rubisco activity is unlikely to determine A(pot). Sucrose synthesis is limited by lack of substrate and impaired enzyme regulation. With WD, PR decreases relative to light respiration (R(L)), and mitochondria consume reductant and synthesise ATP. With progressing WD at low A, R(L) increases C(i) and C(c). This review emphasises the effects of light intensity, considers techniques, and develops a qualitative model of photosynthetic metabolism under WD that explains many observations: testable hypotheses are suggested.

Reduced plant water status under sub-ambientpCO2limits plant productivity in the wild progenitors of C3and C4cereals

“…Wong et al (1979) showed that P i remained constant whilst A and g s varied together, and that stomatal aperture is determined by the capacity of the mesophyll tissue to fix carbon. Our results could therefore be a reflection of direct effects of leaf water status on A mediated via non-stomatal (metabolic) limitations that are independent of P i (Lawlor & Tezara, 2009). Furthermore, it has been demonstrated that C 4 plants are sensitive to non-stomatal limitations mediated via plant water status, and the effect was greater than in C 3 leaves (Ripley et al, 2007;Taylor et al, 2011).…”

“…This response limits transpiration rates and also CO 2 supply to the mesophyll which, in turn, can reduce A (Bunce, 2006). Photosynthesis is also very sensitive to the direct effects of leaf water deficits measured as more negative W leaf (Lawlor and Tezara, 2009). Therefore, improvements in W leaf at post-glacial compared to glacial pCO 2 in this study indicate that plant water status was more favourable for carbon assimilation, and are consistent with studies finding that leaf W leaf and A are improved under elevated pCO 2 in both C 3 and C 4 plants under water deficits (Wall, 2001;Wall et al, 2001;LeCain et al, 2003;Robredo et al, 2006).…”

Stress-Induced Cytokinin Synthesis Increases Drought Tolerance through the Coordinated Regulation of Carbon and Nitrogen Assimilation in Rice

“…In the initial stages of water stress, a decrease in stomatal conductance mediated by ABA can limit the internal CO 2 concentration used in C assimilation (Zhang and Davies, 1990;Tardieu and Davies, 1993). As the stress progresses, the decrease in photosynthetic activity and the continuation of respiration both contribute to the maintenance (or increase) of internal CO 2 in plants subjected to stress (Lawlor and Tezara, 2009). Our results support this concept.…”

Analysis of biochemical variations and microRNA expression in wild (Ipomoea campanulata) and cultivated (Jacquemontia pentantha) species exposed to in vivo water stress

“…Decreased chlorophyll is recognized to directly affect photosynthesis which plays a vital role in plant growth and development (Chaves et al 2009;Flexas et al 2004;Lawlor and Tezara 2009). Larger fall in the chlorophyll content of J. pentantha may depict its susceptibility to water deficit.…”