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Measurement of the Leakage of CO2 from Bundle-Sheath Cells of Leaves during C4 Photosynthesis.

机译:C4光合作用期间叶片束鞘细胞中CO2泄漏的测量。

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摘要

During C4 photosynthesis, CO2 is released in bundle-sheath cells by decarboxylation of C4 acids and then refixed via ribulose-1,5-bisphosphate carboxylase. In this study we examined the efficiency of this process by determining the proportion of the released CO2 that diffuses back to mesophyll cells instead of being refixed. This leak of CO2 was assessed by determining the amount of 14CO2 released from leaves during a chase in high [12CO2] following a 70-s pulse in 14CO2. A computer-based analysis of the time-course curve for 14CO2 release indicated a first-order process and provided an estimate of the initial velocity of 14CO2 release from leaves. From this value and the net rate of photosynthesis determined from the 14CO2 fixed in the pulse, the CO2 leak rate from bundle-sheath cells (expressed as a percentage of the rate of CO2 production from C4 acids) could be deduced. For nine species of Gramineae representing the different subgroups of C4 plants and two NAD-malic enzyme-type dicotyledonous species, the CO2 leak ranged between 8 and 14%. However, very high CO2 leak rates (averaging about 27%) were recorded for two NADP-malic enzyme-type dicotyledonous species of Flaveria. The results are discussed in terms of the efficiency of C4 photosynthesis and observed quantum yields.
机译:在C4光合作用期间,CO2通过C4酸脱羧而在束鞘细胞中释放,然后通过1,5-双磷酸核糖羧化酶固定。在这项研究中,我们通过确定释放回扩散到叶肉细胞而不是固定在叶肉细胞中的CO2的比例来检查此过程的效率。通过确定在追赶高[12CO2]过程中从叶子中释放的14CO2的量(在14CO2中产生70秒的脉冲后)来评估CO2的泄漏情况。基于计算机的14CO2释放时程曲线的分析表明是一阶过程,并提供了从叶片释放14CO2的初始速度的估计。根据该值和由固定在脉冲中的14CO2确定的光合作用的净速率,可以推导出束鞘细胞的CO2泄漏率(表示为C4酸产生的CO2的百分比)。对于代表C4植物不同亚组的9种禾本科植物和2种NAD-苹果酸酶型双子叶植物,CO2泄漏的范围为8%至14%。但是,黄褐藻的两种NADP-苹果酸酶型双子叶物种记录到很高的CO2泄漏率(平均约27%)。根据C4光合作用的效率和观察到的量子产率讨论了结果。

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