Departments of Botany and Agronomy, University of Illinois, Urbana, Illinois 61801.
Plant Physiol. 1973 Jun;51(6):993-7. doi: 10.1104/pp.51.6.993.
Electron transport in chloroplasts isolated from desiccated sunflower (Helianthus annuus L. cv. Russian Mammoth) leaves was compared with electron transport in sunflower chloroplasts in sorbitol-containing media having various osmotic potentials. In media having low osmotic potentials and dichloroindophenol as electron acceptor, the activity for electron transport was inhibited, but the inhibition was much less than that due to comparable desiccation in vivo. The inhibition at low osmotic potentials was rapidly reversed by returning the chloroplasts to media having high osmotic potentials, but the activity of chloroplasts from desiccated tissue showed no reversal when the chloroplasts were placed in media having high osmotic potentials. Nevertheless, the inhibition of chloroplast activity due to desiccation in vivo was basically reversible, because chloroplasts recovered quickly when they were rehydrated in vivo. The large differences between desiccation in vivo and exposure to low osmotic potential in vivo indicate that osmotic solutions did not reproduce the effects of tissue desiccation. It is concluded that decreases in the Gibbs free energy of water due to decreased osmotic potentials probably have only a small effect on electron transport in chloroplasts from desiccated tissue and do not account for the major effects of leaf desiccation on electron transport.
从脱水向日葵（Helianthus annuus L. cv. Russian Mammoth）叶片中分离出的叶绿体的电子传递与含有不同渗透势的山梨醇介质中的向日葵叶绿体的电子传递进行了比较。在低渗透势和二氯靛酚作为电子受体的介质中，电子传递活性受到抑制，但抑制作用远小于体内类似脱水引起的抑制作用。将叶绿体返回高渗透压介质可迅速逆转低渗透压下的抑制，但从脱水组织中分离出的叶绿体在高渗透压介质中无活性逆转。然而，由于体内脱水引起的叶绿体活性抑制基本上是可逆的，因为当它们在体内重新水合时，叶绿体很快恢复。体内脱水和体内低渗透势暴露之间的巨大差异表明，渗透溶液并未复制组织脱水的效果。因此，由于渗透势降低导致的水吉布斯自由能降低可能对脱水组织叶绿体的电子传递只有很小的影响，并且不能解释叶片脱水对电子传递的主要影响。
