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 stress-induced 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.
Original language | English (US) |
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Pages (from-to) | 725-735 |
Number of pages | 11 |
Journal | Plant, Cell and Environment |
Volume | 27 |
Issue number | 6 |
DOIs | |
State | Published - Jun 2004 |
Keywords
- Adenosine 5′-triphosphate
- Heat stress
- NADP-malate dehydrogenase
- Photosynthesis
- Rubisco activation
ASJC Scopus subject areas
- Physiology
- Plant Science