期刊
JOURNAL OF EXPERIMENTAL BOTANY
卷 63, 期 3, 页码 1445-1459出版社
OXFORD UNIV PRESS
DOI: 10.1093/jxb/err386
关键词
Malate valve; NADP-malate dehydrogenase; oxidative stress; poising mechanisms; redox homeostasis
资金
- Deutsche Forschungsgemeinschaft [EM166/1]
- Department of Science and Technology-Deutscher Akademischer Austauschdienst (DAAD)
- DAAD-Finland
- DFG
- Academy of Finland [118637, 8133293, 130075, 130595]
- Academy of Finland (AKA) [130595, 130075, 130595] Funding Source: Academy of Finland (AKA)
The nuclear-encoded chloroplast NADP-dependent malate dehydrogenase (NADP-MDH) is a key enzyme controlling the malate valve, to allow the indirect export of reducing equivalents. Arabidopsis thaliana (L.) Heynh. T-DNA insertion mutants of NADP-MDH were used to assess the role of the light-activated NADP-MDH in a typical C-3 plant. Surprisingly, even when exposed to high-light conditions in short days, nadp-mdh knockout mutants were phenotypically indistinguishable from the wild type. The photosynthetic performance and typical antioxidative systems, such as the Beck-Halliwell-Asada pathway, were barely affected in the mutants in response to high-light treatment. The reactive oxygen species levels remained low, indicating the apparent absence of oxidative stress, in the mutants. Further analysis revealed a novel combination of compensatory mechanisms in order to maintain redox homeostasis in the nadp-mdh plants under high-light conditions, particularly an increase in the NTRC/2-Cys peroxiredoxin (Prx) system in chloroplasts. There were indications of adjustments in extra-chloroplastic components of photorespiration and proline levels, which all could dissipate excess reducing equivalents, sustain photosynthesis, and prevent photoinhibition in nadp-mdh knockout plants. Such metabolic flexibility suggests that the malate valve acts in concert with other NADPH-consuming reactions to maintain a balanced redox state during photosynthesis under high-light stress in wild-type plants.
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