Department of Biology, University of Dayton, Dayton, Ohio 45469-0001.
Plant Physiol. 1987 Oct;85(2):365-9. doi: 10.1104/pp.85.2.365.
The mechanism responsible for the inhibition of net carbon exchange (NCE) which was reported previously (DR Geiger et al. 1986 Plant Physiol 82: 468-472) was investigated by applying glyphosate [N-(phosphonomethyl)glycine] to exporting leaves of sugar beet (Beta vulgaris L.). Leaf internal CO(2) concentration (C(i)) remained constant despite decreases in stomatal conductance and NCE following glyphosate treatment, indicating that the cause of the inhibition was a slowing of carbon assimilation rather than decreased conductance of CO(2). Throughout a range of CO(2) concentrations, NCE rate at a given C(i) declined gradually, with the time-series of response curves remaining parallel. Gas exchange measurements revealed that disruption of chloroplast carbon metabolism was an early and important factor in mediating these glyphosate effects, perhaps by slowing the rate of ribulose bisphosphate regeneration. An increase in the CO(2) compensation point accompanied the decrease in NCE and this increase was hastened by stepwise lowering of the ambient CO(2) concentration. Eventually the CO(2) compensation point approached the CO(2) level of air and the difference between internal and external CO(2) concentrations decreased. In control and in glyphosate-treated plants, both carbon assimilation and photorespiration at atmospheric CO(2) level were inhibited to a similar extent of air level of O(2). Maintaining leaves in low O(2) concentration did not prevent the decline in NCE rate.
先前有报道称（DR Geiger 等人，1986 年，《植物生理学》82：468-472），有一种机制可以抑制净碳交换（NCE），本研究通过向出口叶片的糖甜菜（Beta vulgaris L.）喷洒草甘膦[N-（膦酸甲基）甘氨酸]来探究这种机制。尽管草甘膦处理后气孔导度和 NCE 下降，但叶片内部 CO2 浓度（C(i)）保持不变，这表明抑制的原因是碳同化速度减慢，而不是 CO2 导度降低。在一系列 CO2 浓度下，给定 C(i)下的 NCE 速率逐渐下降，响应曲线的时间序列保持平行。气体交换测量表明，叶绿体碳代谢的破坏是介导这些草甘膦效应的早期和重要因素，可能是通过减缓核酮糖二磷酸的再生速率。随着 NCE 的下降，CO2 补偿点增加，而环境 CO2 浓度的逐步降低则加速了这种增加。最终，CO2 补偿点接近空气的 CO2 水平，内部和外部 CO2 浓度之间的差异减小。在对照和草甘膦处理的植物中，在大气 CO2 水平下，碳同化和光呼吸都受到类似程度的抑制，达到空气水平的 O2。将叶片维持在低 O2 浓度下并不能阻止 NCE 速率的下降。
