Photoprotection During Winter Stress

拟议的研究将检验低温驯化的光保护过程，促进植物在冬季保留叶片的多余激发能的无害耗散。过量的激发能可以在叶绿素/类胡萝卜素结合的色素复合物内直接去除，这一过程需要类胡萝卜素玉米黄质和叶绿体膜内的低pH。在温暖的日子里，在其他有利的条件下，玉米黄质在中午光线充足的时候积累起来，在一天结束的时候，光线变得不过量，玉米黄质就会重新转化为其前体。在冬季，大量的玉米黄质可以在寒冷的夜晚保留下来，准备在早晨叶绿素吸收光的瞬间进行能量消耗。在拟议的研究中，这种色素夜间滞留的机制，以及它继续参与能量耗散，将被检查。第一种机制涉及到在冬季条件下叶片光合膜上维持pH梯度的假设，这导致玉米黄质持续参与能量耗散，主要是在次要的、近端叶绿素结合蛋白中。第二种有待测试的机制涉及假设的玉米黄质由核心天线蛋白中的β -胡萝卜素合成，这可能伴随着对冬季过度光照条件的适应。为了验证这一假设，将从适应夏季有利温度和冬季低温的叶片中确定特定叶绿体蛋白质的类胡萝卜素成分。最终，通过这些研究收集到的信息可能有助于提高种植在比植物在其进化史中所经历的温度更低的地区的农业物种的耐受性。

9631064 Adams The proposed studies will examine the low temperature acclimation of a photoprotective process facilitating the harmless dissipation of excess excitation energy in plants that retain leaves during the winter. Excess excitation energy can be removed directly within the chlorophyll/carotenoid-binding pigment complexes in a process requiring the carotenoid zeaxanthin and a low pH within the chloroplast membrane. On warm days, under otherwise favorable conditions, zeaxanthin accumulates during midday when light is excessive and is reconverted to its precursor by the end of the day as light levels become nonexcessive. During the winter large amounts of zeaxanthin can be retained throughout cold nights, ready to become engaged in energy dissipation the instant chlorophyll absorbs light in the morning. In the proposed studies the mechanisms underlying the nocturnal retention of this pigment, and its continued engagement for energy dissipation, will be examined. The first mechanism involves the hypothesized maintenance of a pH gradient across the photosynthetic membrane of leaves exposed to winter conditions which results in the sustained engagement of zeaxanthin in energy dissipation, primarily in the minor, proximal chlorophyll-binding proteins. The second mechanism to be tested involves the hypothesized synthesis of zeaxanthin from beta-carotene in the core antenna proteins that may accompany acclimation to the conditions of excess light during the winter. To test this hypothesis the carotenoid composition of specific chloroplast proteins will be determined from leaves acclimated to favorable temperatures in the summer as well as low temperatures in the winter. Ultimately the information gleaned through these studies may prove useful in improving the tolerance of agricultural species planted in areas th at experience lower temperatures than those experienced by the plants during their evolutionary history.