Arabidopsis plants were exposed to high light or sulphur depletion alone or in combination for 6 d, and changes of photosynthetic parameters and metabolite abundances were quantified. Photosynthetic electron transport rates (ETRs) of plants exposed to sulphur depletion and high light decreased strongly at day 2 of the acclimation period. After 3 d of treatment, the photosynthetic capacity recovered in plants exposed to the combined stresses, indicating a short recovery time for re-adjustment of photosynthesis. However, at metabolic level, the stress combination had a profound effect on central metabolic pathways such as the tricarboxylic acid (TCA) cycle, glycolysis, pentose phosphate cycle and large parts of amino acid metabolism. Under these conditions, central metabolites, such as sugars and their phosphates, increased, while sulphur-containing compounds were decreased. Further differential responses were found for the stress indicator proline accumulating already at day 1 of the high-light regime, but in combination with sulphur depletion first declined and after a recovery phase reached a delayed elevated level. Other metabolites such as raffinose and putrescine seem to replace proline during the early combinatorial stress response and may act as alternative protectants. Our findings support the notion that plants integrate the selectively sensed stress factors in central metabolism.
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