Department of Plant Biology, Carnegie Institution of Washington, 94305, Stanford, CA, USA.
Planta. 1984 Nov;161(6):505-18. doi: 10.1007/BF00407082.
Damage to primary photosynthetic reactions by drought, excess light and heat in leaves of Macroptilium atropurpureum Dc. cv. Siratro was assessed by measurements of chlorophyll fluorescence emission kinetics at 77 K (-196°C). Paraheliotropic leaf movement protected waterstressed Siratro leaves from damage by excess light (photoinhibition), by heat, and by the interactive effects of excess light and high leaf temperatures. When the leaves were restrained to a horizontal position, photoinhibition occurred and the degree of photoinhibitory damage increased with the time of exposure to high levels of solar radiation. Severe inhibition was followed by leaf death, but leaves gradually recovered from moderate damage. This drought-induced photoinhibitory damage seemed more closely related to low leaf water potential than to low leaf conductance. Exposure to leaf temperatures above 42°C caused damage to the photosynthetic system even in the dark and leaves died at 48°C. Between 42 and 48°C the degree of heat damage increased with the time of exposure, but recovery from moderate heat damage occurred over several days. The threshold temperature for direct heat damage increased with the growth temperature regime, but was unaffected by water-stress history or by current leaf water status. No direct heat damage occurred below 42°C, but in water-stressed plants photoinhibition increased with increasing leaf temperature in the range 31-42°C and with increasing photon flux density up to full sunglight values. Thus, water stress evidently predisposes the photosynthetic system to photoinhibition and high leaf temperature exacerbates this photoinhibitory damage. It seems probable that, under the climatic conditions where Siratro occurs in nature, but in the absence of paraheliotropic leaf movement, photoinhibitory damage would occur more frequently during drought than would direct heat damage.
干旱、过量光照和热量对紫花苜蓿叶片初级光合作用的破坏，通过在 77K（-196°C）下测量叶绿素荧光发射动力学来评估。拟向光性叶片运动保护水分胁迫下的 Siratro 叶片免受过量光照（光抑制）、热和过量光照与高叶片温度相互作用的破坏。当叶片被限制在水平位置时，会发生光抑制，并且光抑制损伤的程度随着暴露于高水平太阳辐射的时间而增加。严重的抑制会导致叶片死亡，但叶片会从中度损伤中逐渐恢复。这种由干旱引起的光抑制损伤似乎与低叶片水势的关系比与低叶片导度的关系更密切。暴露在 42°C 以上的叶片温度下，即使在黑暗中也会对光合作用系统造成损伤，叶片在 48°C 时死亡。在 42 到 48°C 之间，热损伤的程度随着暴露时间的增加而增加，但中度热损伤的恢复需要数天时间。直接热损伤的阈值温度随生长温度制度而增加，但不受水分胁迫历史或当前叶片水分状况的影响。在 42°C 以下不会发生直接热损伤，但在水分胁迫下，光抑制会随着叶片温度在 31-42°C 范围内的升高以及在全阳光值下的光子通量密度的增加而增加。因此，水分胁迫显然使光合作用系统易受光抑制的影响，而高叶片温度会加剧这种光抑制损伤。在 Siratro 自然发生的气候条件下，但不存在拟向光性叶片运动的情况下，干旱期间光抑制损伤可能比直接热损伤更频繁地发生，这似乎是很有可能的。
