Photoprotection During Winter Stress

对于那些在冬季产叶或留叶的植物来说，暴露在高水平阳光下的潜在危险会增加。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可能进行得更慢。不能通过光合作用利用的被吸收的光能会增强叶片中危险和有害的反应。然而，叶片具有光保护机制来抵消这种损害潜力，最显著的是通过类胡萝卜素玉米黄质和黄质促进的过程将多余的光能无害地消散为热。在无压力的环境条件下，这些类胡萝卜素只有在强光存在时(例如中午)才会大量存在并活跃。然而，在冬季，PI发现玉米黄质+黄质可以被保留并持续进行光保护过程，即使在晚上也是如此。这项建议的主要目的是检验一种假设，即与类胡萝卜素结合的特定蛋白质的磷酸化参与了这一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对这一机制进行了不同的修改。对于在冬季继续生长并保持活跃的光合作用机构的植物物种，玉米黄质+黄质在温暖的日子里会脱离并迅速消失。与夏季相比，在冬季停止生长并缩小其光合作用装置的植物物种，玉米黄质+黄质被保留下来，并在过渡到更温暖的条件后保持数天。PI将检验这样一种假设，即色素结合蛋白的磷酸化模式的差异伴随着不同物种在光保护过程中的使用差异，这些物种对冬季胁迫表现出非常不同的适应模式。这项研究不仅对了解植物如何能够在严酷的冬季条件下保留功能叶片(对耐寒作物品种，如冬季谷物、菠菜等具有明显的影响)具有重要意义，而且还可以作为理解持续光保护机制的指南，这些光保护机制涉及类胡萝卜素玉米黄质+紫质黄质，这些物质发生在面临许多其他胁迫的植物叶片中，包括干旱胁迫、养分供应不足、盐度或重金属水平过高等。

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.