Photosynthetic acclimation strategies in response to intermittent exposure to high light intensity in wheat (Triticum aestivum L.)

Plants are intermittently exposed to high intensity light; however, it is unknown how the photosynthetic apparatus of cultivated crops, such as wheat (Triticum aestivum L.), acclimatizes to intermittent high light conditions. To address this question, we grew wheat plants under constant high light (800 mu mol m(-2)s(-1); 100%H), constant low light (100 mu mol m(-2)s(-1); 0%H), 1 day high light followed by 3 days low light (25%H), or 1 day high light followed by 1 day low light (50%H) for 4 weeks. We analyzed seedling growth and the activity and photosensitivity of the photosynthetic apparatus in leaves. Compared with 0%H plants, there was no difference in photosynthetic electron transfer rate or thylakoid membrane protein levels in 25%H plants, but the Rubisco protein levels and photosynthetic carbon fixing capacity were higher. A higher proportion of exposure to high light (50%H) did not further improve the photosynthetic carbon fixing capacity, but it increased the photosynthetic electron transfer rate and photosynthetic protein levels in thylakoid membranes and enhanced the tolerance of the photosynthetic apparatus to high light. Therefore, the acclimation of photosynthesis to intermittent high light exposure depends on the proportion and duration of the high light exposure. Furthermore, during intermittent high light exposure, wheat preferentially invested in photosynthetic carbon assimilation vs the electron transfer reaction and photoprotection. This photosynthetic acclimation strategy maximizes carbon assimilation under intermittent high light conditions.