Sunlight represents the energy source for photosynthesis and plant growth. When growing in the field, plant photosynthesis has to manage strong fluctuations in light intensities. Regulation based on the thio- redoxin ...Sunlight represents the energy source for photosynthesis and plant growth. When growing in the field, plant photosynthesis has to manage strong fluctuations in light intensities. Regulation based on the thio- redoxin （Trx） system is believed to ensure light-responsive control of photosynthetic reactions in the chlo- roplast. However, direct evidence for a role of this system in regulating dynamic acclimation of photosyn- thesis in fluctuating conditions is largely lacking. In this report we show that the ferredoxin-dependent Trxs ml and m2 as well as the NADPH-dependent NTRC are both indispensable for photosynthetic acclimation in fluctuating light intensities. Arabidopsis mutants with combined deficiency in Trxs ml and m2 show wild- type growth and photosynthesis under constant light condition, while photosynthetic parameters are strongly modified in rapidly alternating high and low light. Two independent trxmlm2 mutants show lower photosynthetic efficiency in high light, but surprisingly significantly higher photosynthetic efficiency in low light. Our data suggest that a main target of Trx ml and m2 is the NADP-malate dehydrogenase involved in export of excess reductive power from the chloroplast. The decreased photosynthetic efficiency in the high-light peaks may thus be explained by a reduced capacity of the trxm lm2 mutants in the rapid light acti-vation of this enzyme. In the ntrc mutant, dynamic responses of non-photochemical quenching of excita- tion energy and plastoquinone reduction state both were strongly attenuated in fluctuating light intensities, leading to a massive decrease in PSII quantum efficiency and a specific decrease in plant growth under these conditions. This is likely due to the decreased ability of the ntrc mutant to control the stromal NADP（H） redox poise. Taken together, our results indicate that NTRC is indispensable in ensuring the full range of dynamic responses of photosynthesis to optimize photosynthesis and maintain growth in fluctu- ating light, while Trxs ml and m2 are indispensable for full activation of photosynthesis in the high-light pe- riods but negatively affect photosynthetic efficiency in the low-light periods of fluctuating light.展开更多
文摘Sunlight represents the energy source for photosynthesis and plant growth. When growing in the field, plant photosynthesis has to manage strong fluctuations in light intensities. Regulation based on the thio- redoxin （Trx） system is believed to ensure light-responsive control of photosynthetic reactions in the chlo- roplast. However, direct evidence for a role of this system in regulating dynamic acclimation of photosyn- thesis in fluctuating conditions is largely lacking. In this report we show that the ferredoxin-dependent Trxs ml and m2 as well as the NADPH-dependent NTRC are both indispensable for photosynthetic acclimation in fluctuating light intensities. Arabidopsis mutants with combined deficiency in Trxs ml and m2 show wild- type growth and photosynthesis under constant light condition, while photosynthetic parameters are strongly modified in rapidly alternating high and low light. Two independent trxmlm2 mutants show lower photosynthetic efficiency in high light, but surprisingly significantly higher photosynthetic efficiency in low light. Our data suggest that a main target of Trx ml and m2 is the NADP-malate dehydrogenase involved in export of excess reductive power from the chloroplast. The decreased photosynthetic efficiency in the high-light peaks may thus be explained by a reduced capacity of the trxm lm2 mutants in the rapid light acti-vation of this enzyme. In the ntrc mutant, dynamic responses of non-photochemical quenching of excita- tion energy and plastoquinone reduction state both were strongly attenuated in fluctuating light intensities, leading to a massive decrease in PSII quantum efficiency and a specific decrease in plant growth under these conditions. This is likely due to the decreased ability of the ntrc mutant to control the stromal NADP（H） redox poise. Taken together, our results indicate that NTRC is indispensable in ensuring the full range of dynamic responses of photosynthesis to optimize photosynthesis and maintain growth in fluctu- ating light, while Trxs ml and m2 are indispensable for full activation of photosynthesis in the high-light pe- riods but negatively affect photosynthetic efficiency in the low-light periods of fluctuating light.
