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首页> 外文期刊>Journal of Experimental Botany >Bundle-sheath leakiness in C-4 photosynthesis: a careful balancing act between CO2 concentration and assimilation
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Bundle-sheath leakiness in C-4 photosynthesis: a careful balancing act between CO2 concentration and assimilation

机译：C-4光合作用中的鞘鞘渗漏：CO2浓度与同化之间的谨慎平衡作用

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摘要

Crop species with the C-4 photosynthetic pathway are generally characterized by high productivity, especially in environmental conditions favouring photorespiration. In comparison with the ancestral C-3 pathway, the biochemical and anatomical modifications of the C-4 pathway allow spatial separation of primary carbon acquisition in mesophyll cells and subsequent assimilation in bundle-sheath cells. The CO2-concentrating C-4 cycle has to operate in close coordination with CO2 reduction via the Calvin-Benson-Bassham (CBB) cycle in order to keep the C-4 pathway energetically efficient. The gradient in CO2 concentration between bundle-sheath and mesophyll cells facilitates diffusive leakage of CO2. This rate of bundle-sheath CO2 leakage relative to the rate of phosphoenolpyruvate carboxylation (termed leakiness) has been used to probe the balance between C-4 carbon acquisition and subsequent reduction as a result of environmental perturbations. When doing so, the correct choice of equations to derive leakiness from stable carbon isotope discrimination (Delta C-13) during gas exchange is critical to avoid biased results. Leakiness responses to photon flux density, either short-term (during measurements) or long-term (during growth and development), can have important implications for C-4 performance in understorey light conditions. However, recent reports show leakiness to be subject to considerable acclimation. Additionally, the recent discovery of two decarboxylating C-4 cycles operating in parallel in Zea mays suggests that flexibility in the transported C-4 acid and associated decarboxylase could also aid in maintaining C-4/CBB balance in a changing environment. In this paper, we review improvements in methodology to estimate leakiness, synthesize reports on bundle-sheath leakiness, discuss different interpretations, and highlight areas where future research is necessary.
机译：具有C-4光合作用途径的农作物通常具有高生产力的特点，特别是在有利于光呼吸的环境条件下。与祖先的C-3途径相比，C-4途径的生化和解剖学修饰允许在空间上分离叶肉细胞中初级碳的采集并随后在束鞘细胞中进行同化。浓缩二氧化碳的C-4循环必须与通过Calvin-Benson-Bassham（CBB）循环进行的二氧化碳减排密切配合，以保持C-4途径在能量上高效。束鞘和叶肉细胞之间的CO2浓度梯度促进了CO2的扩散泄漏。相对于磷酸烯醇丙酮酸羧化的速率（称为泄漏性），束鞘式CO2泄漏率已被用来探测C-4碳的获取与随后由于环境扰动而减少之间的平衡。这样做时，正确选择方程式以在气体交换过程中从稳定的碳同位素判别（Delta C-13）得出渗漏是至关重要的，以避免产生偏差的结果。短期（测量过程中）或长期（生长和发育过程中）对光子通量密度的渗漏响应可能会对底层光条件下的C-4性能产生重要影响。但是，最近的报告显示泄漏会受到相当大的适应。另外，最近在玉米中并行运行的两个脱羧C-4循环的发现可能表明，在不断变化的环境中，运输的C-4酸和相关脱羧酶的柔韧性也有助于维持C-4 / CBB平衡。在本文中，我们将对方法的改进进行评估，以评估泄漏率，综合有关束鞘泄漏的报告，讨论不同的解释，并重点指出需要进行进一步研究的领域。

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