Developmental Enhancement And Mechanism Of C₄ Photosynthesis In Salsola Ferganica

Salsola is a genus with the most abundant types of photosynthetic pathways in desert plants,most of which belong to the C₄ species,the others are the C₃ and C₃-C₄intermediate types.In recent years,studies on the types of photosynthetic pathway have received wide attention.Since the developmental enhancement of C₄ photosynthesis was uncovered in Chenopodiaceae,Cleomaceae and other plants,this phenomenon has been reported in many C₄ plants.However,few reports were documented on this aspect in Salsola species.Salsola ferganica is an annual C₄ plant in Salsola of Chenopodiaceae,which is extremely resistant to stress.In the previous work,we found that the C₄anatomic structure of S.ferganica changed significantly with development.Therefore,in the present study,we analyzed the leaf anatomic structure,photosynthetic enzyme localization,and the expression of photosynthetic enzyme genes at the transcriptional and translational levels,and expected to reveal the developmental enhancement of the C₄ photosynthetic system,which should provide a theoretical basis for understanding the evolutionary mechanism of photosynthesis carbon assimilation pathways.The main results are as follows:(1)The developmental changes of the C₄ anatomic structure of leaf were analyzed.The anatomic structures of the young and intermediate leaf of S.ferganica presented significant differences,which were mainly reflected in the size and arrangement of mesophyll cells(MC)and vascular bundle sheath cells(BSC)as well as the distribution of the chloroplasts;whereas,the anatomic structures of mature leaf among different parts were not significantly different.With the development of the leaves,a complete"Salsoloid"leaf anatomy is gradually formed.The longitudinal anatomic structure of the intermediate leaf showed that MC and BSC differentiated from the base to the tip of the leaf,and developed into two types of cells with significantly different morphological structures,indicating that a gradient enhancement of the characteristics of C₄ photosynthetic structure is present in a single leaf with the development progression.(2)The changes in the localization of C₄ photosynthetic enzymes(PE)with development were further detected.The expression of Ribulose-1,5 diphosphate carboxylase(RUBPC)during the leaf development of S.ferganica was visualized in the early stage and was located in BSC;the significant expression of phosphoenolpyruvate carboxylase(PEPC)was occurred later than that of RUBPC and was early located in both MC and BSC.As the leaf developing,the RUBPC was specifically localized in BSC,and PEPC was in MC.The localization of these two PE showed a stage-by-stage change with leaf development and was significantly enhanced in mature leaf.(3)The expression characteristics of C₄ PE genes at the transcriptional and translational levels were analyzed.The expression patterns of RUBPC,PEPC,NAD-malic enzyme(NAD-ME),and Pyruvate,Pi dikinase(PPDK)genes at m RNA and protein levels showed a significant enhancement trend with development in the leaf of S.ferganica in different development stages;the expression level also gradually increased,showing an increasing longitudinal development gradient.In conclusion,our results showed that C₄ photosynthetic structure and the location and expression of PE of S.ferganica were gradually increased with the development of leaf,and eventually presented a fully-developed complete C₄ photosynthesis system.