Pflanzenphysiologisches Institut und Botanischer Garten der Universität Göttingen, Untere Karspüle 2, 3400 Göttingen, West Germany.
Plant Physiol. 1990 Jan;92(1):246-53. doi: 10.1104/pp.92.1.246.
We investigated whether the reductive pentose phosphate path in guard cells of Pisum sativum had the capacity to contribute significantly to the production of osmotica during stomatal opening in the light. Amounts of ribulose 1,5-bisphophate carboxylase/oxygenase (Rubisco) were determined by the [(14)C]carboxyarabinitol bisphosphate assay. A guard cell contained about 1.2 and a mesophyll cell about 324 picograms of the enzyme; the ratio was 1:270. The specific activities of Rubisco in guard cells and in mesophyll cells were equal; there was no indication of a specific inhibitor of Rubisco in guard cells. Rubisco activity was 115 femtomol per guard-cell protoplast and hour. This value was different from zero with a probability of 0.99. After exposure of guard-cell protoplasts to (14)CO(2) for 2 seconds in the light, about one-half of the radioactivity was in phosphorylated compounds and <10% in malate. Guard cells in epidermal strips produced a different labelling pattern; in the light, <10% of the label was in phosphorylated compounds and about 60% in malate. The rate of solute accumulation in intact guard cells was estimated to have been 900 femto-osmol per cell and hour. If Rubisco operated at full capacity in guard cells, and hexoses were produced as osmotica, solutes could be supplied at a rate of 19 femto-osmol per cell and hour, which would constitute 2% of the estimated requirement. The capacity of guard-cell Rubisco to meet the solute requirement for stomatal opening in leaves of Pisum sativum is insignificant.
我们研究了豌豆保卫细胞中的还原戊糖磷酸途径在光下气孔开放时是否有能力大量生成渗透物。通过 [(14)C]核酮糖 1,5-二磷酸羧化酶/加氧酶（Rubisco）的比色法来确定核酮糖 1,5-二磷酸羧化酶/加氧酶（Rubisco）的含量。一个保卫细胞中大约含有 1.2 个和一个叶肉细胞中大约含有 324 个微克的酶；比例为 1:270。保卫细胞和叶肉细胞中 Rubisco 的比活相等；保卫细胞中没有 Rubisco 的特定抑制剂。Rubisco 活性为每 guard-cell 原生质体 115 飞摩尔/小时。这个值的概率为 0.99，非常接近零。将保卫细胞原生质体暴露在光下的 [(14)CO2]中 2 秒钟后，大约一半的放射性物质在磷酸化合物中，<10%在苹果酸中。表皮条带中的保卫细胞产生了不同的标记模式；在光下，<10%的标记物在磷酸化合物中，大约 60%在苹果酸中。完整的保卫细胞中溶质的积累速率估计为每细胞和小时 900 飞摩尔。如果 Rubisco 在保卫细胞中满负荷运转，并且六碳糖作为渗透物产生，溶质可以以每细胞和小时 19 飞摩尔的速度供应，这将构成估计需求的 2%。豌豆保卫细胞 Rubisco 满足叶片气孔开放的溶质需求的能力是微不足道的。
