Adams W W, Díaz M, Winter K
Lehrstuhl für Botanik II, Universität Würzburg, Mittlerer Dallenbergweg 64, D-8700, Würzburg, Federal Republic of Germany.
Centro de Investigaciones en Ecologia y Zonas Aridas, Universidad Francisco de Miranda, P.O. Box 7506, Coro, Falcón, Venezuela.
Oecologia. 1989 Sep;80(4):553-561. doi: 10.1007/BF00380081.
Diurnal measurements of chlorophyll a fluorescence from cacti (Nopalea cochenillifera, Opuntia ficus-indica, and Opuntia wentiana) growing in northern Venezuela were used to determine photochemical fluorescence quenching related to the reduction state of the primary electron acceptor of PS II as well as non-photochemical fluorescence quenching which reflects the fraction of energy going primarily into radiationless deexcitation. The cladodes used in this study were oriented such that one surface received direct sunlight in the morning and the other one during the afternoon. Both surfaces exhibited large increases in radiationless energy dissipation from the photochemical system accompanied by decreases in PS II photochemical efficiency during direct exposure to natural sunlight. During exposure to sunlight in the morning, dissipation of absorbed light energy through photosynthesis and radiationless energy dissipation was sufficient to maintain Q, the primary electron acceptor for PS II, in a low reduction state. During exposure to sunlight in the afternoon, however, the reduction state of Q rose to levels greater than 50%, presumably due to a decrease in photosynthetic electron transport as the decarboxylation of the nocturnally accumulated malic acid was completed. Exposure to direct sunlight in the afternoon also led to more sustained increases in radiationless energy dissipation. Furthermore, the increases in radiationless energy dissipation during exposure of a water-stressed cladode of O. wentiana to direct sunlight were much greater than those from other well-watered cacti, presumably due to sustained stomatal closure and decreased rates of photosynthetic electron transport. These results indicate that the radiationless dissipation of absorbed light is an important process in these CAM plants under natural conditions, and may reflect a protective mechanism against the potentially damaging effects of the accumulation of excessive energy, particularly under conditions where CO availability is restricted.
对生长在委内瑞拉北部的仙人掌（胭脂掌、印度榕仙人掌和温氏仙人掌）进行叶绿素a荧光的日间测量，以确定与PS II初级电子受体还原状态相关的光化学荧光猝灭以及反映主要进入无辐射去激发的能量分数的非光化学荧光猝灭。本研究中使用的仙人掌茎片的摆放方向是，一个表面在上午接受直射阳光，另一个表面在下午接受直射阳光。在直接暴露于自然阳光期间，两个表面的光化学系统无辐射能量耗散都大幅增加，同时PS II光化学效率下降。在上午暴露于阳光期间，通过光合作用和无辐射能量耗散对吸收光能的耗散足以使PS II的初级电子受体Q维持在低还原状态。然而，在下午暴露于阳光期间，Q的还原状态升至50%以上，这可能是由于夜间积累的苹果酸脱羧完成后光合电子传递减少所致。下午暴露于直射阳光还导致无辐射能量耗散持续增加。此外，水分胁迫的温氏仙人掌茎片暴露于直射阳光期间，无辐射能量耗散的增加幅度远大于其他水分充足的仙人掌，这可能是由于气孔持续关闭和光合电子传递速率降低所致。这些结果表明，在自然条件下，吸收光的无辐射耗散是这些景天酸代谢植物中的一个重要过程，可能反映了一种针对过量能量积累潜在破坏作用的保护机制，特别是在CO2可用性受限的条件下。
