Department of Botany, University of Illinois, Urbana, Illinois 61801.
Plant Physiol. 1970 May;45(5):612-5. doi: 10.1104/pp.45.5.612.
Chloroplasts were isolated from pea and sunflower leaves having various water potentials. Oxygen evolution by the chloroplasts was measured under identical conditions for all treatments with saturating light and with dichloroindophenol as oxidant. Evolution was inhibited when leaf water potentials were below -12 bars in pea and -8 bars in sunflower and the inhibition was proportional to leaf water potential below these limits. Inhibition was more severe in sunflower than in pea chloroplasts. In sunflower, it could be detected after 5 minutes of leaf desiccation, and, up to 1 hour, the effect was independent of the duration of low leaf water potential.In high light, the reduction in activity of sunflower chloroplasts paralleled the reduction in CO(2) fixation by intact sunflower plants having low leaf water potentials. Stomatal apertures and transpiration rates were also reduced under these conditions and were probably limiting. In low light, intact sunflowers required more light per unit of CO(2) fixed when leaf water potentials were low than when they were high. This increased light requirement in the intact system was of a magnitude which could be predicted from the reduced oxygen evolution by the isolated chloroplasts. It was concluded that moderately low leaf water potential affects photosynthesis in at least two ways: first, through an inhibition of oxygen evolution by chloroplasts and, second, by closure of stomata in intact leaves.
从具有不同水势的豌豆和向日葵叶片中分离出叶绿体。在所有处理中，用饱和光和二氯靛酚作为氧化剂，在相同条件下测量叶绿体的氧气释放。当豌豆叶片水势低于-12 巴和向日葵叶片水势低于-8 巴时，光合作用受到抑制，并且这种抑制与叶片水势低于这些极限值成正比。在向日葵叶绿体中，抑制作用比在豌豆叶绿体中更为严重。在向日葵中，在叶片干燥 5 分钟后就可以检测到，并且在 1 小时内，该效应与低叶片水势的持续时间无关。在高光下，具有低叶片水势的完整向日葵植物的 CO(2)固定活性的降低与向日葵叶绿体活性的降低平行。在这些条件下，气孔开度和蒸腾速率也降低，可能是限制因素。在低光下，当叶片水势较低时，完整的向日葵植物每固定单位 CO(2)所需的光量比水势较高时要多。完整系统中的这种光需求增加的幅度可以从分离的叶绿体中氧气释放的减少来预测。结论是，适度低的叶片水势至少以两种方式影响光合作用：首先，通过叶绿体氧气释放的抑制，其次，通过完整叶片中气孔的关闭。
