C3和C4植物光合途径的适应性变化和进化

 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。

A REVIEW OF ADAPTABLE VARIATIONS AND EVOLUTION OF PHOTOSYNTHETIC CARBON ASSIMILATING PATHWAY IN C3 AND C4 PLANTS

Three photosynthetic pathways are used by plants: C₃, which most plants use, C₄ and crassulacean acid metabolism (CAM). C₃ 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 C₃ 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 C₃ 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 C₃ 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 biosphere. It is possible that C₄ photosynthesis can be used to resist adversity and increase the yield of C₃ 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.