Inhibition of photosynthesis by high temperature in oak (Quercus pubescensL.) leaves grown under natural conditions closely correlates with a reversible heat‐dependent reduction of the activation state of ribulose‐1,5‐bisphosphate carboxylase/oxygenase
Year: 2004
Type: article
Abstract: ABSTRACT Inhibition of the net photosynthetic CO2assimilation rate (Pn) by high temperature was examined in oak (Quercus pubescensL.) leaves grown under natural conditions. Combined measurements of gas exchange and chlorophyll (Chl)afluorescence were employed to differentiate between inhibition originating from heat effects on components of the thylakoid membranes and that resulting from effects on photosynthetic carbon metabolism. Regardless of whether temperature was increased rapidly or gradually,Pndecreased with increasing leaf temperature and was more than 90% reduced at 45 °C as compared to 25 °C. Inhibition ofPnby heat stress did not result from reduced stomatal conductance (gs), as heat‐induced reduction ofgswas accompanied by an increase of the intercellular CO2concentration (Ci). Chl afluorescence measurements revealed that between 25 and 45 °C heat‐dependent alterations of thylakoid‐associated processes contributed only marginally, if at all, to the inhibition ofPnby heat stress, with photosystem II being remarkably well protected against thermal inactivation. The activation state of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) decreased from about 90% at 25 °C to less than 30% at 45 °C. Heat stress did not affect Rubiscoper se, since full activity could be restored by incubation with CO2and Mg2+. Western‐blot analysis of leaf extracts disclosed the presence of two Rubisco activase polypeptides, but heat stress did not alter the profile of the activase bands. Inhibition ofPnat high leaf temperature could be markedly reduced by artificially increasingCi. A highCialso stimulated photosynthetic electron transport and resulted in reduced non‐photochemical fluorescence quenching. Recovery experiments showed that heat‐dependent inhibition ofPnwas largely, if not fully, reversible. The present results demonstrate that inQ. pubescensleaves the thylakoid membranes in general and photosynthetic electron transport in particular were well protected against heat‐induced perturbations and that inhibition ofPnby high temperature closely correlated with a reversible heat‐dependent reduction of the Rubisco activation state.
Source: Plant Cell & Environment
Authors: P. HALDIMANN, U. FELLER
Institution: University of Bern
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: bronze
OpenAlex ID: W1978823766