Huang Wei, Zhang Shi-Bao, Hu Hong
Key Laboratory of Economic Plants and Biotechnology, Kunming Institute of Botany, Chinese Academy of Sciences Kunming, China.
Front Plant Sci. 2014 Dec 3;5:688. doi: 10.3389/fpls.2014.00688. eCollection 2014.
The greater rate of CO2 assimilation (A n) in sun-grown tobacco leaves leads to lower intercellular and chloroplast CO2 concentrations and, thus, a higher rate of oxygenation of ribulose-1,5-bisphosphate (RuBP) than in shade-grown leaves. Impairment of the photorespiratory pathway suppresses photosynthetic CO2 assimilation. Here, we hypothesized that sun leaves can up-regulate photorespiratory pathway to enhance the A n in tobacco. To test this hypothesis, we examined the responses of photosynthetic electron flow (J T) and CO2 assimilation to incident light intensity and intercellular CO2 concentration (C i) in leaves of 'k326' tobacco plants grown at 95% sunlight (sun plants) or 28% sunlight (shade plants). The sun leaves had higher photosynthetic capacity and electron flow devoted to RuBP carboxylation (J C) than the shade leaves. When exposed to high light, the higher Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) content and lower C i in the sun leaves led to greater electron flow devoted to RuBP oxygenation (J O). The J O/J C ratio was significantly higher in the sun leaves than in the shade leaves under strong illumination. As estimated from CO2-response curves, the maximum J O was linearly correlated with the estimated Rubisco content. Based on light-response curves, the light-saturated J O was linearly correlated with light-saturated J T and light-saturated photosynthesis. These findings indicate that enhancement of the photorespiratory pathway is an important strategy by which sun plants maintain a high A n.
在阳光充足环境下生长的烟草叶片中，二氧化碳同化率（An）较高，导致细胞间和叶绿体二氧化碳浓度较低，因此，与在遮荫环境下生长的叶片相比，核酮糖-1,5-二磷酸（RuBP）的氧化速率更高。光呼吸途径受损会抑制光合二氧化碳同化。在此，我们假设阳生叶可以上调光呼吸途径以提高烟草的An。为了验证这一假设，我们检测了在95%光照（阳生植株）或28%光照（遮荫植株）下生长的‘k326’烟草植株叶片中光合电子流（JT）和二氧化碳同化对入射光强和细胞间二氧化碳浓度（Ci）的响应。阳生叶比遮荫叶具有更高的光合能力和用于RuBP羧化的电子流（JC）。当暴露于强光下时，阳生叶中较高的Rubisco（核酮糖-1,5-二磷酸羧化酶/加氧酶）含量和较低的Ci导致用于RuBP氧化的电子流（JO）更大。在强光照射下，阳生叶的JO/JC比值显著高于遮荫叶。根据二氧化碳响应曲线估算，最大JO与估算的Rubisco含量呈线性相关。基于光响应曲线，光饱和JO与光饱和JT和光饱和光合作用呈线性相关。这些发现表明，增强光呼吸途径是阳生植物维持高An的重要策略。
