Grams Thorsten E E, Thiel Stephan
GSF-National Research Center for Environment and Health, Institute of Soil Ecology, Department of Environmental Engineering, Ingolstädter Landstrasse, D-85764 Neuherberg, Germany.
J Exp Bot. 2002 Jun;53(373):1475-83.
The high light-induced switch in Clusia minor from C(3)-photosynthesis to Crassulacean acid metabolism (CAM) is fast (within a few days) and reversible. Although this C(3)/CAM transition has been studied intensively, the nature of the photoreceptor at the beginning of the CAM-induction signal chain is still unknown. Using optical filters that only transmit selected wavelengths, the CAM light induction of single leaves was tested. As controls the opposite leaf of the same leaf pair was studied in which CAM was induced by high unfiltered radiation (c. 2100 micromol m(-2) s(-1)). To evaluate the C(3)-photosynthesis/CAM transition, nocturnal CO(2) uptake, daytime stomatal closure and organic acid levels were monitored. Light at wavelengths longer than 530 nm was not effective for the induction of the C(3)/CAM switch in C. minor. In this case CAM was present in the control leaf while the opposite leaf continued performing C(3)-photosynthesis, indicating that CAM induction triggered by high light conditions is wavelength-dependent and a leaf internal process. Leaves subjected to wavelengths in the range of 345-530 nm performed nocturnal CO(2) uptake, (partial) stomatal closure during the day (CAM-phase III), and decarboxylation of citric acid within the first 2 d after the switch to high light conditions. Based on these experiments and evidence from the literature, it is suggested that a UV-A/blue light receptor mediates the light-induced C(3)-photosynthesis/CAM switch in C. minor.
小克鲁西亚木（Clusia minor）中由高光诱导的从C(3)光合作用向景天酸代谢（CAM）的转变迅速（在几天内）且可逆。尽管对这种C(3)/CAM转变已进行了深入研究，但CAM诱导信号链起始处光受体的性质仍不清楚。使用仅透射选定波长的光学滤光片，对单叶的CAM光诱导进行了测试。作为对照，研究了同一叶对中相对的叶片，其中通过高未过滤辐射（约2100微摩尔·米-2·秒-1）诱导CAM。为了评估C(3)光合作用/CAM转变，监测了夜间CO(2)吸收、白天气孔关闭和有机酸水平。波长大于530纳米的光对小克鲁西亚木中C(3)/CAM转换的诱导无效。在这种情况下，对照叶中存在CAM，而相对的叶片继续进行C(3)光合作用，这表明高光条件触发的CAM诱导是波长依赖性的且是叶片内部过程。暴露于345 - 530纳米波长范围内的叶片在切换到高光条件后的头2天内进行夜间CO(2)吸收、白天（CAM第三阶段）（部分）气孔关闭以及柠檬酸脱羧。基于这些实验和文献证据，表明UV - A/蓝光受体介导了小克鲁西亚木中光诱导的C(3)光合作用/CAM转换。
