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Low light conditions not only induce leaf senescence, but also photosynthetic acclimation. This study aimed to determine whether plants exhibit photosynthetic acclimation during low-light-induced leaf senescence. The influences of shading on leaf senescence and photosynthetic acclimation were explored in post-anthesis maize plants. The results showed that whole shading (WS) of maize plants accelerated leaf senescence, whereas partial shading (PS) slowed leaf senescence. WS led to larger decreases in the photosynthetic rate (P n ) and stomatal conductance (G s ) compared to those of the PS treatment. Interestingly, chlorophyll a fluorescence (ChlF) demonstrated that the absorption flux (ABS/CS o ) and trapped energy flux (TR o /CS o ) per cross section in leaves remained relatively stable under WS, whereas significant decreases in the active PSII reaction centers (RC/CS o ) resulted in considerable increases in absorption (ABS/RC) and trapped energy flux (TR o /RC) per reaction center. ABS/CS o , TR o /CS o , ABS/RC, and TR o /RC increased markedly under PS, whereas there were slight decreases in RC/CS o and electron transport activity. These results suggest that the PS treatment resulted in obvious improvements in the absorption and capture of light energy in shaded leaves. Further analysis demonstrated that both the WS and PS treatments resulted in a greater decrease in the activity of Rubisco compared to that of phosphoenolpyruvate carboxylase (PEPC). Moreover, PEPC activity in PS was maintained at a high level. Consequently, the current study proposed that the improvement of the absorption and capture of light energy and the maintenance of PEPC activity of mesophyll cells were due to photosynthetic acclimation of low-light-induced leaf senescence in maize plants. In addition, the rate of senescence of vascular bundle cells in maize leaves exceeded that of mesophyll cells under low light, showing obvious tissue specificity., (© 2021. The Author(s), under exclusive licence to Springer Nature B.V.)

Plants in their natural environment are often exposed to fluctuating light because of self-shading and cloud movements. As changing frequency is a key characteristic of fluctuating light, we speculated that rapid light fluctuation may induce rapid photosynthetic responses, which may protect leaves against photoinhibition. To test this hypothesis, maize seedlings were grown under fluctuating light with various frequencies (1, 10, and 100 cycles of fluctuations/10 h), and changes in growth, chlorophyll content, gas exchange, chlorophyll a fluorescence, and P700 were analyzed carefully. Our data show that though the growth and light-saturated photosynthetic rate were depressed by rapidly fluctuating light, photosynthesis induction was clearly speeded up. Furthermore, more rapid fluctuation of light strikingly reduced the chlorophyll content, while thermal dissipation was triggered and enhanced. The chlorophyll a fluorescence induction kinetics and P700 absorption results showed that the activities of both photosystem II and photosystem I decreased as the frequency of the fluctuating light increased. In all treatments, the light intensities of the fluctuating light were kept constant. Therefore, rapid light fluctuation frequency itself induced the acceleration of photosynthetic induction and the enhancement of photoprotection in maize seedlings, which play important roles in protecting photosynthetic apparatus against fluctuating high light to a certain extent., (© 2020. Springer Nature B.V.)