JXB Advance Access originally published online on March 21, 2005
Journal of Experimental Botany 2005 56(415):1269-1276; doi:10.1093/jxb/eri111
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RESEARCH PAPER |
Up-regulation of the mitochondrial alternative oxidase pathway enhances photosynthetic electron transport under drought conditions
1Plant Physiology Institute (INFIVE), Schools of Agronomy and of Natural Sciences, National University of La Plata, cc 327 1900 La Plata, Argentina
2Physical Chemistry-PRALIB, School of Pharmacy and Biochemistry, University of Buenos Aires, Buenos Aires, Argentina
* To whom correspondence should be addressed. Fax: +54 221 4233698. E-mail: carlos.bartoli{at}ceres.agro.unlp.edu.ar
The aim of this study was to explore the role of the mitochondrial alternative oxidase (AOX) in the protection of photosynthesis during drought in wheat leaves. The relative water contents of water-replete and drought-exposed wheat plants were 97.2±0.3 and 75±2, respectively. Drought increased the amount of leaf AOX protein and also enhanced the rate of AOX-dependent O2 uptake by the respiratory electron transport chain. The amount of the reduced, active form of the AOX protein was specifically increased by drought. The AOX inhibitor salicylhydroxamic acid (1 mM; SHAM) inhibited 70% of AOX activity in vivo in both water-replete and drought-exposed plants. Plants treated with SHAM were then exposed to low (100), high (350), or excess light (800 µmol photons m–2 s–1) for 90 min. SHAM did not modify chlorophyll a fluorescence quenching parameters in water-replete controls after any of these treatments. However, while the maximal quantum yield of photosystem II (PSII) electron transport (Fv/Fm) was not affected by SHAM, the immediate quantum yield of PSII electron transport (
PSII) and photochemical quenching (qP) were gradually reduced by increasing irradiance in SHAM-treated drought-exposed plants, the decrease being most pronounced at the highest irradiance. Non-photochemical quenching (NPQ) reached near maximum levels in plants subjected to drought at high irradiance. However, a combination of drought and low light caused an intermediate increase in NPQ, which attained higher values when AOX was inhibited. Taken together, these results show that up-regulation of the respiratory AOX pathway protects the photosynthetic electron transport chain from the harmful effects of excess light.
Key words: Alternative oxidase, chlorophyll fluorescence, drought, photoprotection, respiration, wheat
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