Department of Agricultural Sciences, University of California, Los Angeles, California 90024.
Plant Physiol. 1970 Mar;45(3):300-3. doi: 10.1104/pp.45.3.300.
Cycloheximide drastically reduced the rate of root pressure exudation in detopped tobacco (Nicotiana tabacum L.), and the effect was more pronounced for nitrate salts in the external solution than for some other salts or when the roots were in water. Diurnal periodicity was greatly decreased, and its phase was changed. Effects began within an hour. Cation uptake was reduced by relatively low levels of cycloheximide. The effects of cycloheximide seemed to be reversible. Mild phosphorus deficiency resulted in decreased exudation rates from detopped tobacco and in no response to nitrate. Periodicity of exudation was not greatly affected by phosphorus deficiency, however. Gamma ray irradiation with a (60)Co source at levels (up to 40-50 kiloroentgens) which are considered disruptive of moderately large molecules had relatively little effect on the exudation rate. Higher levels of irradiation, which disrupt most protein molecules, decreased exudation and obscured periodicity. The results indicate either that new protein (or peptide) synthesis is needed for the rapid nitrate transport or that the deficiency and inhibitor disrupt cellular membranes. Phosphorus deficiency increased the sensitivity of the plants to inhibition by irradiation of the exudation process.
环己亚胺能大大降低去顶烟草（Nicotiana tabacum L.）的根压渗出率，而且这种效应在外液中硝酸盐盐比其他盐类或根系在水中时更为明显。昼夜周期性大大降低，相位也发生了变化。这种作用在 1 小时内就开始显现。环己亚胺的浓度相对较低时就会减少阳离子的吸收。环己亚胺的作用似乎是可逆的。轻度磷缺乏会导致去顶烟草的渗出率降低，并且对硝酸盐没有反应。然而，渗出的周期性并没有受到磷缺乏的很大影响。用（60）Co 源进行伽马射线照射（高达 40-50 千伦琴），被认为会破坏中等大小的分子，对渗出率的影响相对较小。更高水平的照射会破坏大多数蛋白质分子，从而减少渗出并使周期性变得模糊。结果表明，快速的硝酸盐转运需要新的蛋白质（或肽）合成，或者缺乏和抑制剂破坏了细胞膜。磷缺乏会增加植物对辐射抑制渗出过程的敏感性。
