Thylakoid membrane responses to moderately high leaf temperature in Pima cotton

Abstract

Photosynthesis is inhibited by high temperatures that plants are likely to experience under natural conditions. Both increased thylakoid membrane ionic conductance and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) deactivation have been suggested as the primary cause. The moderately heat-tolerant crop Pima S-6 cotton ( Gossypium barbadense ) was used to examine heat stressinduced inhibition of photosynthesis. Previous field-work indicated that moderate heat stress ( T = 35-45 ∞ ∞ ∞ ∞ C) is associated with very rapid leaf temperature changes. Therefore, a system was devised for rapidly heating intact, attached leaves to mimic natural field heat-stress conditions and monitored Rubisco activation, carbon-cycle metabolites, thylakoid ionic conductance, and photosystem I activity. As a proxy for NADPH and stromal redox status the activation state of NADP-malate dehydrogenase (NADP-MDH) was measured. In dark-adapted cotton leaves, heating caused an increase in thylakoid permeability at temperatures as low as 36 ∞ ∞ ∞ ∞ C. The increased permeability did not cause a decline in adenosine 5 ¢ ¢ ¢ ¢ -triphosphate (ATP) levels during steady-state or transient heating. Rapid heating caused a transient decline in ribulose 1,5-bisphosphate without a decrease in Rubisco activation. Sustained heating caused a decline in Rubisco activation and also oxidized the stroma as judged by NADP-MDH activation and this is hypothesized to result from increased cyclic photophosphorylation, explaining the maintenance of ATP content in the face of increased thylakoid membrane ion leakiness.

Increased Thermostability of Thylakoid Membranes in Isoprene-Emitting Leaves Probed with Three Biophysical Techniques

“…Increased permeability has been found to occur particularly at high temperatures, concurrently with denaturation of membrane lipids (Bukhov et al, 1999;Schrader et al, 2004;). The increased membrane permeability of heat-treated samples can be due to conformational changes of membrane lipids, opening of ion channels, or changes in lipid-lipid interactions (Santarius, 1980).…”

“…The oldest and most widely accepted idea is that isoprene stabilizes chloroplast membranes (Sharkey and Singsaas, 1995). Thylakoid membranes become leaky at high temperature (Pastenes and Horton, 1996;Bukhov et al, 1999;Schrader et al, 2004;. It was suggested that the positive effect of isoprene might be due to the hydrophobic nature of the molecule, the localization of isoprene synthase enzyme near the thylakoid membranes (Wildermuth and Fall, 1998;Schnitzler et al, 2005), and the high octanol/water partitioning coefficient (Copolovici and Niinemets, 2005).…”

The Roles of ATP Synthase and the Cytochrome b 6/f Complexes in Limiting Chloroplast Electron Transport and Determining Photosynthetic Capacity

“…We also observed decreases in 12qL and NADP-MDH activation at high temperature (Figs. 3 and 4), implying that the heat-induced decline in photosynthesis would be also affected by, at least, the redox status of the stroma (Schrader et al, 2004;Sharkey, 2005).…”

Photosynthetic performance of Salvinia natans exposed to chromium and zinc rich wastewater

“…Salvinia exposed to Cr and Zn did not exhibit a significant increase in NADP-MDH activity indicating that metal stress does not affect stromal status as adequate levels of NADPH and other reducing equivalents are maintained for CO 2 assimilation. It is supposed that closure of the malate valve under stress also prevents drainage of excess reducing equivalents from the chloroplast, hence preventing the oxidation of stroma (Scheibe and Stitt, 1988;Schrader et al, 2004). The effect of ARC and redox state on the enzyme activation has also been reported (Backhausen et al, 2000).…”