Up-regulation of the mitochondrial alternative oxidase pathway ameliorates photosynthetic electron transport under drought conditions

CARLOS G. BARTOLI; FACUNDO GOMEZ; GUSTAVO GERGOFF; JUAN J. GUIAMET; SUSANA PUNTARULO

JOURNAL OF EXPERIMENTAL BOTANY

OXFORD UNIV PRESS

Lugar: Oxford; Año: 2005 vol. 56 p. 1269 - 1276

0022-0957

This work tested the possible role of the mitochondrial alternative oxidase (AOX) pathway in the protection of chloroplasts against excess energy in wheat leaves under water stress. The relative water contents of control and droughted plants were 97.260.3 and 7562, respectively. Drought increased AOX-dependent O2 uptake and the amount of AOX protein in wheat leaves. In particular, the content of the reduced, active form of AOX increased dramatically under stress conditions. Supplying 1mM salicilhydroxamic acid (SHAM) through the cut leaf tip inhibited 70% of in vivo AOX capacity in either control or droughted plants. After SHAM treatment, plants were exposed to three levels of irradiance (100, 350, and 800 lmol photons m22 s21) for 90 min. Under good irrigation and at any light regime, SHAM did not affect any of the chlorophyll fluorescence parameters measured. While the potential quantum yield of PSII (Fv/Fm) was not affected, actual quantumyield (UPSII) and photochemical quenching (qP) were progressively reduced by drought and increasing irradiance. The addition of AOX inhibitor to droughted leaves caused a drop of UPSII and qP, with a more pronounced effect at higher irradiances. Non-photochemical quenching operated at near maximum levels in plants subjected to drought under the two higher irradiances. However, the combination of drought and lower irradiance caused an intermediate increase in non-photochemical quenching, with a higher value when AOX was inhibited. These results show that up-regulation of the AOX pathway protects the photosynthetic electron transport chain from the excess reducing power generated in chloroplasts of wheat plants under drought.