C_3和C_4植物光合途径的适应性变化和进化

A REVIEW OF ADAPTABLE VARIATIONS AND EVOLUTION OF PHOTOSYNTHETIC CARBON ASSIMILATING PATHWAY IN C_3 AND C_4 PLANTS

高等植物大多为C3植物,C4植物和景天酸代谢(Crassulacean acid metabolism,CAM)植物是由C3植物进化而来的。C4途径的多源进化表明,光合途径由C3途径向C4途径的转变相对简单。该文分析研究了植物光合途径的进化前景,指出C4植物是从C3植物进化而来的高光效种类,且地质时期以来降低的大气CO2浓度和升高的大气温度以及干旱和盐渍化是C4途径进化的外部动力。C3植物的C4途径的发现说明植物的光合途径并非是一成不变的,C3和C4植物的光合特征具有极大的可塑性,某些环境的变化会引起植物光合途径在C3和C4途径之间转变。C3植物具有的C4途径是环境调控的产物,是对逆境的适应性进化结果,因而光合途径的转变也适用于干旱地区植被的适应性生存机理研究。该文还利用国外最新的C4光合进化模型介绍了植物在进化C4途径中所经历的7个重要时期(从分子基础到形态基础、结构基础,再到物质代谢水平、光合酶活水平,直到C3和C4途径协调运转时期,最后达到形态与功能最优化阶段),并结合全球气候变化的特点对国内外相关领域的研究进行了分析,总结了植物光合途径的适应性转变和进化的研究成果,为今后的相关工作提出建议。

Three photosynthetic pathways are used by plants： C3, which most plants use, C4 and crassulacean acid metabolism （CAM）. Ca is the ancestral pathway, with C4 and CAM representing recently diverged forms. We conclude that the variation and evolution of photosynthetic pathway of C3 and C4 are adaptations to environmental stresses. First, we discuss the evolutional future of photosynthetic pathways. It has been suggested that low atmosphere CO2, enhanced temperatures, drought and salinity are external drivers of C4 photosynthetic evolution. Second, we analyze the possibility of evolution from Ca to C4. The polyphyletic evolution of the C4 pathway suggests that the transition from C3 to C4 was relatively simple. This suggestion is supported by the observation that both Ca and C4 plants possess inherent plasticity in their photosynthetic characteristics. The stress causing the shift from C3 to C4 was involved in the environmental regulation of plants, and the C4 pathway in C3 plants evolved as an adaptation. The environmental stresses may have involved plant capacities for survivorship and competition in arid areas. Third, we present a simplistic model of the main phases of C4 photosynthetic evolution and discuss the variation and evolution of Ca and C4 photosynthetic carbon assimilating pathways. Evolution was not directly to C4 photosynthesis, so each step had to be stable, beginning with numerous preconditions needed for an evolutionary lineage to begin evolving C4 characteristics. A current complication of C4 photosynthetic evolution is global climate change and human manipulation of the bio- sphere. It is possible that C4 photosynthesis can be used to resist adversity and increase the yield of Ca crops. In conclusion, study of the evolution of photosynthetic pathway in plants provided insight into the photosynthetic physiology of plants under stress and provided new theory to reconstruct vegetation, enhance crop yield, and explain adaptation of C3 species in arid areas.