Photoprotection During Winter Stress

对于那些在冬季长出或保留叶子的植物来说，暴露在高强度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给光合作用。在冬季普遍存在的低温下，光合作用的生化反应不能进行或进行得更慢。吸收的光能不能通过光合作用被利用，可能会在叶子中产生危险和破坏性的反应。然而，叶片具有光保护机制来抵消这种破坏潜力，最明显的是通过类胡萝卜素玉米黄质和花青素促进的无害的热量消耗多余的光能。在无压力的环境条件下，这些类胡萝卜素只有在强光下（例如中午）才会大量存在和活跃。然而，在冬季，pi发现玉米黄质+花青素可以保留并持续参与光保护过程，即使在夜间也是如此。这项提议的主要目的是验证这样一种假设，即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将进一步评估具有不同生命形式的植物物种是否采用这种机制的不同修改。对于在冬季保持生长和保持活跃光合机构的植物物种，玉米黄质+花青素在温暖的日子里脱离并迅速消失。与夏季相比，在冬季停止生长和减少光合作用装置的植物物种，玉米黄质+花青素在过渡到更温暖的条件时被保留并保持数天。pi将测试这样一种假设，即色素结合蛋白磷酸化模式的差异伴随着物种之间光保护过程的使用差异，这些物种对冬季压力的适应模式非常不同。这项研究不仅对了解植物如何在严酷的冬季条件下保持功能叶片具有重要意义（对冬季谷物，菠菜等耐寒作物物种具有明显的影响），而且还可以作为理解持续光保护机制的指南，该机制涉及类胡萝卜素玉米黄质+花青素，发生在面临许多其他胁迫的植物叶片中，包括干旱胁迫，营养物质供应不足、盐度或重金属含量过高等。

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.