Adams W W, Volk M, Hoehn A, Demmig-Adams B
Department of Environmental, Population and Organismic Biology, University of Colorado, 80309-0334, Boulder, CO, USA.
Oecologia. 1992 Jun;90(3):404-410. doi: 10.1007/BF00317698.
Leaves from two species, Euonymus kiautschovicus and Arctostaphylos uva-ursi, with a variety of different orientations and exposures, were examined in the field with regard to the xanthophyll cycle (the interconversion of three carotenoids in the chloroplast thylakoid membranes). East-, south-, and west-facing leaves of E. kiautschovicus were sampled throughout the day and all exhibited a pronounced and progressive conversion of violaxanthin to zeaxanthin, followed by a reconversion of zeaxanthin to violaxanthin later in the day. Maximal levels of zeaxanthin and minimal levels of violaxanthin were observed at the time when each leaf (orientation) received the maximum incident light, which was in the morning in east-facing, midday in southfacing, and in the afternoon in west-facing leaves. A very slight degree of hysteresis in the removal of zeaxanthin compared to its formation with regard to incident light was observed. Leaves with a broader range of orientations were sampled from A. uva-ursi prior to sunrise and at midday. All of the examined pigments (carotenoids and chlorophylls) increased somewhat per unit leaf area with increasing total daily photon receipt. The sum of the carotenoids involved in the xanthophyll cycle, violaxanthin + antheraxanthin + zeaxanthin, increased more strongly with increasing growth light than any other pigment. In addition, the amounts of zeaxanthin present at midday also increased markedly with increasing total daily photon receipt. The percentage of the xanthophyll cycle that was converted to zeaxanthin (and antheraxanthin) at peak irradiance was very large (approximately 80%) in the leaves of both E. kiautschovicus and A. uva-ursi. The daily changes in the components of the xanthophyll cycle that paralleled the daily changes in incident light in the leaves of E. kiautschovicus, and the increasing levels of the xanthophyll cycle components with total daily photon receipt in the leaves of A. uva-ursi, are both consistent with the involvement of zeaxanthin (i.e. the xanthophyll cycle) in the photoprotection of the photosynthetic apparatus against damage due to excessive light.
对卫矛和熊果这两个物种的叶片进行了研究，这些叶片具有各种不同的朝向和光照条件，研究内容涉及叶黄素循环（叶绿体类囊体膜中三种类胡萝卜素的相互转化）。全天采集了卫矛朝东、朝南和朝西的叶片样本，所有样本都呈现出紫黄质向玉米黄质的显著且渐进的转化，随后在当天晚些时候玉米黄质又重新转化为紫黄质。在每片叶子（不同朝向）接收到最大入射光时，观察到玉米黄质达到最高水平，紫黄质达到最低水平，其中朝东的叶子在早晨、朝南的叶子在中午、朝西的叶子在下午接收到最大入射光。观察到与入射光相比，玉米黄质在形成和去除过程中存在非常轻微的滞后现象。在日出前和中午从熊果采集了具有更广泛朝向的叶片样本。随着每日总光子接收量的增加，所有检测的色素（类胡萝卜素和叶绿素）每单位叶面积都有所增加。参与叶黄素循环的类胡萝卜素总和，即紫黄质 + 环氧玉米黄质 + 玉米黄质，随着生长光照的增加比其他任何色素增加得都更强烈。此外，中午时玉米黄质的含量也随着每日总光子接收量的增加而显著增加。在卫矛和熊果的叶片中，在峰值辐照度下转化为玉米黄质（和环氧玉米黄质）的叶黄素循环百分比都非常大（约80%）。卫矛叶片中叶黄素循环成分的每日变化与入射光的每日变化平行，以及熊果叶片中叶黄素循环成分随着每日总光子接收量增加而增加，这两者都与玉米黄质（即叶黄素循环）参与光合机构免受过量光损伤的光保护作用一致。
