Department of Plant Biology, Carnegie Institution of Washington, 94305, Stanford, CA, USA.
Planta. 1984 Nov;161(6):490-504. doi: 10.1007/BF00407081.
When the shrub Nerium oleander L., growing under full natural daylight outdoors, was subjected to water stress, stomatal conductance declined, and so did non-stomatal components of photosynthesis, including the CO2-saturated rate of CO2 uptake by intact leaves and the activity of electron transport by chloroplasts isolated from stressed plants. This inactivation of photosynthetic activity was accompanied by changes in the fluorescence characteristics determined at 77 K (-196°C) for the upper leaf surface and from isolated chloroplasts. The maximum (F M) and the variable (F V) fluorescence yield at 692 nm were strongly quenched but there was little effect on the instantaneous (F O) fluorescence. There was a concomitant quenching of the maximum and variable fluorescence at 734 nm. These results indicate an inactivation of the primary photochemistry associated with photosystem II. The lower, naturally shaded surfaces of the same leaves were much less affected than the upper surfaces and water-stress treatment of plants kept in deep shade had little or no effect on the fluorescence characteristics of either surface, or of chloroplasts isolated from the water-stressed leaves. The effects of subjecting N. oleander plants, growing in full daylight, to water stress are indistinguishable from those resulting when plants, grown under a lower light regime, are exposed to full daylight (photoinhibition). Both kinds of stress evidently cause an inactivation of the primary photochemistry associated with photosystem II. The results indicate that water stress predisposes the leaves to photoinhibition. Recovery from this inhibition, following restoration of favorable water relations, is very slow, indicating that photoinhibition is an important component of the damage to the photosynthetic system that takes place when plants are exposed to water stress in the field. The underlying causes of this water-stress-induced susceptibility to photoinhibition are unknown; stomatal closure or elevated leaf temperature cannot explain the increased susceptibility.
当生长在户外全日照环境下的夹竹桃（Nerium oleander L.）受到水分胁迫时，气孔导度下降，光合作用的非气孔成分也随之下降，包括完整叶片 CO2 饱和时的 CO2 吸收速率和从胁迫植物中分离出的叶绿体的电子传递活性。这种光合作用活性的失活伴随着在 77K（-196°C）下测定的荧光特性的变化，这些特性是针对上叶面和从分离的叶绿体进行的。最大（F M）和可变（F V）荧光在 692nm 处的荧光产率强烈猝灭，但对瞬时（F O）荧光几乎没有影响。734nm 处的最大和可变荧光也伴随着猝灭。这些结果表明与光系统 II 相关的原初光化学失活。同一叶片的较下面，自然阴影表面受影响比上面小得多，而在深阴影下保存的植物进行水分胁迫处理对任一面的荧光特性或从水分胁迫叶片中分离出的叶绿体几乎没有或没有影响。将全日照下生长的夹竹桃植物置于水分胁迫下的影响与在较低光照条件下生长的植物暴露于全日照下（光抑制）的结果无法区分。这两种胁迫显然都会导致与光系统 II 相关的原初光化学失活。结果表明，水分胁迫使叶片容易受到光抑制。在恢复有利的水分关系后，从这种抑制中恢复非常缓慢，这表明光抑制是植物在田间暴露于水分胁迫时发生的光合作用系统损伤的一个重要组成部分。这种由水分胁迫引起的对光抑制的敏感性的潜在原因尚不清楚；气孔关闭或叶片温度升高不能解释这种敏感性增加的原因。
