Department of Agricultural Sciences, University of Copenhagen, 2765 Taastrup, Denmark.
Pest Manag Sci. 2010 May;66(5):536-42. doi: 10.1002/ps.1904.
Changes in chlorophyll fluorescence have often been advocated as a sensitive biomarker of plant stress, assuming that any kind of plant stress serious enough to affect plant growth will also affect photosynthesis. Glyphosate affects photosynthetic electron transport indirectly by inhibiting sink processes. The question is how fast this inhibition can be observed on CO(2) assimilation and ultimately on chlorophyll fluorescence?
Experiments measuring CO(2) assimilation, conductance and chlorophyll fluorescence using four Kautsky curve parameters on barley (Hordeum vulgare L.) exposed to increasing doses of glyphosate showed a total cessation of CO(2) fixation and conductance without significant changes in chlorophyll fluorescence. The decrease in CO(2) fixation and conductance was significant 1 day after spraying and corresponded well to the decrease in biomass 5-7 days after spraying.
A total cessation of CO(2) assimilation can take place without affecting chlorophyll fluorescence. Hypotheses concerning what happens to the energy from the photosynthetic apparatus that is not used for CO(2) assimilation are discussed. The results question the use of chlorophyll fluorescence as a universal indicator of stress on photosynthetic processes. Also, they demonstrate that changes in gas-exchange parameters are more sensitive biomarkers for glyphosate toxicity compared with chlorophyll fluorescence.
叶绿素荧光变化常被认为是植物胁迫的敏感生物标志物，因为任何严重到足以影响植物生长的胁迫都会影响光合作用。草甘膦通过抑制汇过程间接影响光合作用电子传递。问题是这种抑制作用在 CO2 同化和最终在叶绿素荧光上能多快被观察到？
使用四种 Kautsky 曲线参数对暴露于草甘膦递增剂量的大麦（Hordeum vulgare L.）进行的 CO2 同化、导度和叶绿素荧光实验表明，CO2 固定和导度完全停止，而叶绿素荧光没有明显变化。喷药后 1 天 CO2 固定和导度的下降非常显著，与喷药后 5-7 天生物量的下降相吻合。
CO2 同化的完全停止可以在不影响叶绿素荧光的情况下发生。讨论了关于未用于 CO2 同化的光合作用装置的能量去向的假说。研究结果质疑将叶绿素荧光作为光合作用过程应激的通用指标的使用。此外，它们表明与叶绿素荧光相比，气体交换参数的变化是草甘膦毒性的更敏感生物标志物。
