The Adaptive Evolution Of Photosynthetic Carbon Assimilating Pathway In Salsola Abrotanoides

The chang of global climate aggravates the degradation of natural vegetation in arid areas and the selection of plants with strong drought resistance to improve vegetation coverage was regarded as the most effective strategy to alleviate land desertification problem.At present,the research on the drought resistance of plants mainly focused on illuminating the drought resistance characteristics,the view from the perspective of the transformation of photosynthetic pathways to enhance plant drought resistance has made an important contribution to revel the mechanism of plant drought resistance in essence.In the process of photosynthetic evolution from C3 to C4 under the stimulation of the arid environment,the anatomical characteristics of the assimilation organs,the activity of photosynthetic key enzymes and their distribution,carbon isotope fractionation,photosynthetic rate and some another characters will change significantly.In order to further explore the mechanism of the development of C4 pathway in xerophytic plants,we selected a typical C3 species Salsola abrotanoides that widely distributed in the desert area as the material,and chose the C3-C4 intermediate S.laricifolia and the C4 species S.arbuscula as controls,and three research pots alone with the natural precipitation gradient was designed and plotted as experiment sites.To provide the basis to illuninate the theory that C3 plants would improve the adaptability of drought stress through the development of C4 pathway,the determination of the expression level of photosynthetic enzymes,photosynthetic enzyme activity,anatomical structure of the assimilation organ,and the photosynthetic rate were processed to investigate whether S.abrotanoides would change their photosynthetic pathway to adapt to the harsh environment.The main experimental results are as follows:(1)The gene expression level of pepc and rbc L of S.abrotanoides increased with increased water deficit conditions and the variation of pepc was very significant(P<0.001),but acts below C3-C4 intermediate species S.laricifolia and C4 species S.arbuscula.The result of Western blotting indicated that the expression level of PEPC and Rubisco were increased with drought stress,and the expression of PEPC was very significant(P<0.001).The expression of NAD-ME was down-regulated and PEPCK expression was not significant(P>0.05),and NADP-ME was not detected in S.abrotanoides.(2)The results of scanning electron microscope showed that the density of trichome acts higher,the stomatal density became larger and the opening degree became smaller,and the epidermis wax was more abundant with the increase of drought.The observation of anatomical structure of the leaves showed that with the increase of drought,the density of veins(P<0.001),the area of water storage tissue,and the number of small vascular bundles increased,and the area of vascular bundles and vascular sheath cells became larger and larger,and the area ratio of chloroplasts and mitochondria in vascular bundle sheath cells increased.The results indicated that S.abrotanoides was developing structural features compatible with C4 pathway.(3)By observing the photosynthetic products and measuring the parameters of gas exchange,it was found that the number of starch granules in the vascular sheath cells of S.abrotanoides increased gradually with the increase of drought stress,the photosynthetic efficiency and the water use efficiency increased gradually,the intercellular CO2 concentration became smaller.It is suggested that the typical C3 plant of S.arbuscula can improve the photosynthetic rate and the high efficiency of carbon sequestration by developing C4 pathway in the arid environment.(4)By measuring the stable carbon isotope ?13C value,it was found that S.arbuscula was a typical C4 species(?13C value was-10.29‰),The ?13C value of S.abrotanoides increased with the decrease of precipitation and the difference was very significant(P<0.001),which provided a strong evidence for the improvement of water use efficiency in the development of C4 photosynthetic pathway of S.abrotanoides.Based on the above results,one of the most important survival mechanisms of C3 S.abrotanoides was to increase the expression level of C4 photosynthetic key enzymes genes and gradually developed the structural characteristics of the C4 pathway.and improve carbon accumulation efficiency in the more arid environment.