Department of Horticulture & Forestry, Cook College, Rutgers University, New Brunswick, New Jersey 08903.
Plant Physiol. 1985 Sep;79(1):189-93. doi: 10.1104/pp.79.1.189.
The relationship between leaf K(+) concentration, in vitro dehydration, and nonstomatal-controlled photosynthesis was investigated using leaf slices that were vacuum infiltrated with media containing varying sorbitol concentrations. The leaf slices were from plants either supplied with complete or K(+)-deficient medium throughout a 35-day growth period. During this time, leaf K(+) concentration, water potential, osmotic potential, and turgor pressure were monitored. Leaf K(+) concentration averaged 239 micomoles per gram (fresh weight) in control plants, and dropped to 74.3 micromoles per gram (fresh weight) in K(+)-deficient plants. Less negative osmotic potentials and resultant turgor loss in K(+)-deficient plants indicated that the osmotically active pool of cellular K(+) was lower in those plants.The decrease in leaf K(+) concentration enhanced the dehydration inhibition of photosynthesis. For example, increasing sorbitol from 0.33 to 0.5 molar during incubation inhibited photosynthesis in the controls by 14% or less. This same protocol resulted in an inhibition of photosynthesis by as much as 41% in K(+)-deficient tissue. In contrast to the data obtained with leaf slices, dehydration inhibition of isolated chloroplast photosynthesis was not affected by K(+) status of parent plant material. These data are consistent with the hypothesis that one effect of leaf K(+) deficiencies on photosynthetic response to dehydration may be mediated by extra-choloroplastic factors.Ammonium ions, which facilitate stromal alkalinization, reversed the increased sensitivity of K(+)-deficient leaf slice photosynthesis to cell dehydration. However, NH(4) (+) had no effect on photosynthesis of K(+)-deficient leaf slices under nonhypertonic conditions. These data suggest that endogenous extra-chloroplastic K(+) may modulate dehydration inhibition of photosynthesis, possibly by facilitating stromal alkalinization.
使用真空渗透含有不同山梨糖醇浓度的介质的叶片切片研究了叶片 K(+)浓度、体外脱水和非气孔控制光合作用之间的关系。叶片切片来自于在 35 天生长期间用完整或 K(+)-缺乏培养基供应的植物。在此期间，监测了叶片 K(+)浓度、水势、渗透势和膨压。对照植物叶片 K(+)浓度平均为 239 微摩尔/克（鲜重），K(+)-缺乏植物叶片 K(+)浓度降至 74.3 微摩尔/克（鲜重）。K(+)-缺乏植物中较低的负渗透势和由此产生的膨压损失表明细胞 K(+)的渗透活性池较低。叶片 K(+)浓度的降低增强了光合作用对脱水的抑制作用。例如，在孵育过程中，将山梨糖醇从 0.33 增加到 0.5 摩尔，对照植物光合作用的抑制作用不超过 14%。在 K(+)-缺乏组织中，相同的方案导致光合作用的抑制作用高达 41%。与叶片切片获得的数据相反，原生植物材料 K(+)状态不影响分离叶绿体光合作用的脱水抑制作用。这些数据与以下假设一致，即叶片 K(+)缺乏对脱水后光合作用反应的影响之一可能是由质外体因素介导的。铵离子促进基质碱化，逆转了 K(+)-缺乏叶片切片光合作用对细胞脱水的敏感性增加。然而，在非高渗条件下，NH(4) (+)对 K(+)-缺乏叶片切片的光合作用没有影响。这些数据表明，内源性质外体 K(+)可能通过促进基质碱化来调节光合作用对脱水的抑制作用。
