Simpson S F
Biological Laboratories, Harvard University, Cambridge, Massachusetts 02138.
Plant Physiol. 1977 Jan;59(1):4-9. doi: 10.1104/pp.59.1.4.
The hormonal control of DNA and protein syntheses in cortical explants taken at 10 to 11 mm from the tip of 3-day-old seedling roots (Pisum sativum cv. Little Marvel) was examined. On the auxin medium, S2M, the cortical cells began to enlarge at day 4 in culture, with no DNA synthesis or cell division throughout the 7-day culture period. With the addition of kinetin to this medium, S2M + K, the DNA content of the explants increased about three times by day 3, with further increases thereafter. This DNA increase was followed by cell division activity and subsequent tracheary element differentiation initiated at day 5. At least two divisions per parent cortical cell were required prior to this cytodifferentiation. The absolute hormonal requirements for the DNA synthesis and cell division responses were substantiated by the lack of either response in explants cultured on basal (S2M medium minus auxins) or basal + K medium for 7 days. On the auxin medium, there was no protein accumulation in the cortical explants over the 7-day period. On S2M + K medium, protein accumulation began after day 2 with a steady rate of increase until day 4, and some fluctuation thereafter. The pattern of increasing uptake of (14)C-leucine was similar for days 0 to 4 in explants on either medium. After day 4 on S2M, the uptake continued to increase coincident with cell enlargement initiation, whereas on S2M + K there was a decline. Incorporation of (14)C-leucine into trichloroacetic acid-precipitates of the total buffered homogenate from explants on both media exhibited a similar pattern, i.e. an increase during days 0 to 3 and then a decline to a level about three times higher than day 0. Incorporation into the homogenate soluble fraction also showed a similar pattern in explants cultured with or without kinetin. From the differences in net protein accumulation and the incorporation data, speculation on a cytokinin effect on protein synthesis and degradation rates is presented.
研究了取自3日龄豌豆（Pisum sativum cv. Little Marvel）幼苗根尖10至11毫米处的皮层外植体中DNA和蛋白质合成的激素调控。在生长素培养基S2M上，皮层细胞在培养第4天开始增大，在整个7天的培养期内没有DNA合成或细胞分裂。向该培养基中添加激动素后，即S2M + K，外植体的DNA含量在第3天增加了约三倍，此后进一步增加。DNA的增加之后是细胞分裂活动，随后在第5天开始进行管状分子分化。在此细胞分化之前，每个亲本皮层细胞至少需要进行两次分裂。通过在基础培养基（不含生长素的S2M培养基）或基础 + K培养基上培养7天的外植体中缺乏任何一种反应，证实了DNA合成和细胞分裂反应对激素的绝对需求。在生长素培养基上，皮层外植体在7天内没有蛋白质积累。在S2M + K培养基上，蛋白质积累在第2天后开始，以稳定的速率增加直至第4天，此后有一些波动。两种培养基上的外植体在第0至4天，（14）C-亮氨酸摄取增加的模式相似。在S2M上第4天后，摄取随着细胞增大的开始而继续增加，而在S2M + K上则下降。两种培养基上外植体的总缓冲匀浆中，（14）C-亮氨酸掺入三氯乙酸沉淀中呈现出相似的模式，即在第0至3天增加，然后下降到比第0天高约三倍的水平。掺入匀浆可溶部分在有或没有激动素培养的外植体中也表现出相似的模式。根据净蛋白质积累和掺入数据的差异，对细胞分裂素对蛋白质合成和降解速率的影响进行了推测。
