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Effects of Various Levels of CO2 on the Induction of Crassulacean Acid Metabolism in Portulacaria afra (L.) Jacq.

机译:不同水平的二氧化碳对马齿Port马齿Port中新陈代谢的诱导作用。

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摘要

In response to water stress, Portulacaria afra (L.) Jacq. (Portulacaceae) shifts its photosynthetic carbon metabolism from the Calvin-Benson cycle for CO2 fixation (C3) photosynthesis or Crassulacean acid metabolism (CAM)-cycling, during which organic acids fluctuate with a C3-type of gas exchange, to CAM. During the CAM induction, various attributes of CAM appear, such as stomatal closure during the day, increase in diurnal fluctuation of organic acids, and an increase in phosphoenolpyruvate carboxylase activity. It was hypothesized that stomatal closure due to water stress may induce changes in internal CO2 concentration and that these changes in CO2 could be a factor in CAM induction. Experiments were conducted to test this hypothesis. Well-watered plants and plants from which water was withheld starting at the beginning of the experiment were subjected to low (40 ppm), normal (ca. 330 ppm), and high (950 ppm) CO2 during the day with normal concentrations of CO2 during the night for 16 days. In water-stressed and in well-watered plants, CAM induction as ascertained by fluctuation of total titratable acidity, fluctuation of malic acid, stomatal conductance, CO2 uptake, and phosphoenolpyruvate carboxylase activity, remained unaffected by low, normal, or high CO2 treatments. In well-watered plants, however, both low and high ambient concentrations of CO2 tended to reduce organic acid concentrations, low concentrations of CO2 reducing the organic acids more than high CO2. It was concluded that exposing the plants to the CO2 concentrations mentioned had no effect on inducing or reducing the induction of CAM and that the effect of water stress on CAM induction is probably mediated by its effects on biochemical components of leaf metabolism.
机译:为了响应水分胁迫,Portulacaria afra(L.)Jacq。 (马齿ae科)将其光合作用碳代谢从卡尔文-本森循环转变为CO2固定(C3)光合作用或Crassulacean酸代谢(CAM)循环,在此期间有机酸随着C3型气体交换而波动。在CAM诱导过程中,出现CAM的各种属性,例如白天的气孔关闭,有机酸的昼夜波动增加以及磷酸烯醇丙酮酸羧化酶活性的增加。据推测,由于水分胁迫而导致的气孔关闭可能会引起内部CO2浓度的变化,而这些CO2的变化可能是CAM诱导的一个因素。进行实验以检验该假设。在实验开始时,浇水良好的植物和从中抽水的植物在白天受到低(40 ppm),正常(约330 ppm)和高(950 ppm)的CO2的影响,并具有正常的CO2浓度在夜间16天。在缺水和水分充足的植物中,通过总可滴定酸度的波动,苹果酸的波动,气孔导度,CO2吸收和磷酸烯醇丙酮酸羧化酶活性确定的CAM诱导不受低,正常或高CO2处理的影响。然而,在水分充足的植物中,低和高浓度的CO2都倾向于降低有机酸浓度,低浓度的CO2比高浓度的二氧化碳更能减少有机酸。得出的结论是,使植物暴露于上述CO2浓度对诱导或减少CAM的诱导没有影响,而水分胁迫对CAM诱导的影响可能是由其对叶片代谢生化成分的影响介导的。

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