Metabolite control overrides circadian regulation of phosphoenolpyruvate carboxylase kinase and CO2 fixation in Crassulacean acid metabolism
Metabolite control overrides circadian regulation of phosphoenolpyruvate carboxylase kinase and CO2 fixation in Crassulacean acid metabolism
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DOI：
10.1104/pp.121.3.889
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发表时间：
1999-11-01
期刊：
影响因子：
7.4
通讯作者：
Nimmo, HG
中科院分区：
文献类型：
--
作者：
Borland, AM;Hartwell, J;Nimmo, HG
磷酸烯醇丙酮酸羧化酶 (PEPc) 催化景天酸代谢植物中 CO2 的初级固定。通过酶的通量由可逆磷酸化调节。 PEPc 激酶由其可翻译 mRNA 水平的变化来控制，以响应昼夜节律。通过将长寿花叶子置于夜间厌氧条件下以调节苹果酸积累的程度，或在夜间升高温度以增加苹果酸从液泡到细胞质的流出，研究了 PEPc 激酶可翻译 mRNA 水平变化以及代谢物参与激酶控制的生理意义。 CO2 固定和 PEPc 激酶活性的变化反映了激酶 mRNA 的变化。在前半夜进行厌氧处理然后转移到环境空气中的叶子中观察到最高的 CO2 固定率和激酶 mRNA 水平。在经过过夜厌氧处理并在一天开始时转移到环境空气中的叶子中，在光照期的前 3 小时，PEPc 激酶可翻译的 mRNA 和活性、PEPc 的磷酸化状态以及大气 CO2 的固定显着高于对照叶子。夜间温度从 19 摄氏度升高到 27 摄氏度会导致激酶 mRNA 和活性迅速降低；然而，在通过厌氧处理阻止苹果酸积累的叶子中没有观察到这一点。这些数据与高浓度苹果酸减少激酶 mRNA 和激酶本身积累的假设一致。
Phosphoenolpyruvate carboxylase (PEPc) catalyzes the primary fixation of CO2 in Crassulacean acid metabolism plants. Flux through the enzyme is regulated by reversible phosphorylation. PEPc kinase is controlled by changes in the level of its translatable mRNA in response to a circadian rhythm. The physiological significance of changes in the levels of PEPc-kinase-translatable mRNA and the involvement of metabolites in control of the kinase was investigated by subjecting Kalanchoe daigremontiana leaves to anaerobic conditions at night to modulate the magnitude of malate accumulation, or to a rise in temperature at night to increase the efflux of malate from vacuole to cytosol. Changes in CO2 fixation and PEPc kinase activity reflected those in kinase mRNA. The highest rates of CO2 fixation and levels of kinase mRNA were observed in leaves subjected to anaerobic treatment for the first half of the night and then transferred to ambient air. In leaves subjected to anaerobic treatment overnight and transferred to ambient air at the start of the day, PEPc-kinase-translatable mRNA and activity, the phosphorylation state of PEPc, and fixation of atmospheric CO2 were significantly higher than those for control leaves for the first 3 h of the light period. A nighttime temperature increase from 19 degrees C to 27 degrees C led to a rapid reduction in kinase mRNA and activity; however, this was not observed in leaves in which malate accumulation had been prevented by anaerobic treatment. These data are consistent with the hypothesis that a high concentration of malate reduces both kinase mRNA and the accumulation of the kinase itself.