Photoprotection During Winter Stress

对于那些在冬季产生或保留叶子的植物来说，暴露在高水平阳光下的潜在危险增加了。 绿色色素叶绿素负责吸收光能并将其传递用于光合作用。 光合作用的生化反应在冬季普遍存在的低温下不能进行或进行得更慢。 无法通过光合作用利用的吸收光能可能会加剧叶子中的危险和破坏性反应。 然而，叶子具有光保护机制来抵消这种破坏性的潜力，最值得注意的是通过类胡萝卜素玉米黄质和花药黄质促进的过程将多余的光能无害地耗散为热量。 在无压力的环境条件下，这些类胡萝卜素仅在高光存在时（例如中午）才大量存在和活跃。 然而，在冬季，PI发现玉米黄质+花药黄质可以保留并持续参与光保护过程，即使在夜间。 该提议的主要目的是检验这样的假设，即与这些类胡萝卜素结合的特定蛋白质的磷酸化参与了这种光保护过程的持续激活。 PI还将评估具有不同生命形式的植物物种是否采用该机制的不同修饰。 对于在冬季保持生长并维持活跃的光合装置的植物物种，玉米黄质+花药黄质在温暖的日子里变得脱离并迅速消失。 对于与夏季相比在冬季停止生长并缩小其光合机构的植物物种，玉米黄质+花药黄质被保留并在过渡到较温暖的条件时保持参与数天。 PI将测试的假设，在磷酸化模式的色素结合蛋白的差异伴随着这些差异，在就业的光保护过程中表现出这些非常不同的模式，适应冬季胁迫的物种之间。 这项研究不仅对了解植物如何在冬季的恶劣条件下保持功能性叶片很重要（对冬季耐寒作物物种，如冬季谷物，菠菜等具有明显的影响），而且还应该作为理解持续光保护机制的指导，所述持续光保护机制涉及类胡萝卜素玉米黄质+花药黄质，所述持续光保护发生在面临许多其它胁迫的植物的叶子中，所述其它胁迫包括干旱胁迫、营养物的可用性不足、盐或重金属的过量水平等。

For those plants that produce or retain leaves during the winter, the potential hazards of being exposed to high levels of sunlight are increased. The green pigment chlorophyll is responsible for absorbing light energy and passing it on for use in photosynthesis. The biochemical reactions of photosynthesis cannot proceed or proceed more slowly at the low temperatures prevalent during winter. Absorbed light energy that cannot be utilized through photosynthesis can potentiate dangerous and damaging reactions in the leaves. However, leaves possess photoprotective mechanisms to counteract this damaging potential, most notably the harmless dissipation of excess light energy as heat through a process that is facilitated by the carotenoids zeaxanthin and antheraxanthin. Under nonstressful environmental conditions these carotenoids are present and active in large quantities only when high light is present (e.g. at midday). During the winter, however, the PIs have found that zeaxanthin + antheraxanthin can be retained and continually engaged for the photoprotective process even during the night. The main objective of this proposal is to test the hypothesis that phosphorylation of particular proteins to which those carotenoids are bound are involved in the sustained activation of this photoprotective process. The PI's will furthermore evaluate whether plant species with different lifeforms employ different modifications of this mechanism. For plant species that keep growing and maintain an active photosynthetic apparatus during the winter, zeaxanthin + antheraxanthin become disengaged and disappear rapidly on warm days. For plant species that cease growth and downsize their photosynthetic apparatus during the winter compared to the summer, zeaxanthin + antheraxanthin are retained and remain engaged for days upon transition to warmer conditions. The PIs will test the hypothesis that differences in the phosphorylation patterns of the pigment-binding proteins accompany these differences in the employment of the photoprotective process between species exhibiting these very different patterns of acclimation to winter stress. This study is not only important to understanding how plants are able to retain functional leaves during the harsh conditions of winter (with the obvious implications for winter-hardy crop species such as winter cereals, spinach, etc.), but should also serve as a guide in understanding the mechanism of sustained photoprotection involving the carotenoids zeaxanthin + antheraxanthin that occurs in the leaves of plants facing many other stresses, including drought stress, insufficient availability of nutrients, excessive levels of salinity or heavy metals, etc.