The Cytological Mechanism Of Brassinosteroid And Strigolactone Regulate Rice Mesocotyl Elongation

In recent years,with the transforming of rural labor force to urban,direct sowing cultivation techniques are widely spread because of their time-saving,labor-saving,land-saving and water-saving.Direct sowing cultivation success largely depends on seeds germinating ability,while the length of mesocotyl is one of the important factors,which affects the ability of seeds germination,but the study of its cytology structure and molecular mechanism is still unclear,so we want to know the mechanism of rice mesocotyl elongation.BRs are sterols compounds,which are endogenous hormone in plants,acting unique roles in the regulation of plant growth and development,it has been reported that BR can promote rice mesocotyl elongation;SLs are new kinds of terpenoids endogenous hormone in plants,recent studies show that SL can inhibit rice mesocotyl elongation,but the mechanism of how BR and SL regulate rice mesocotyl elongation is unknown.To reveal how BR and SL regulate rice mesocotyl elongation in cytological level,we did cross section and longitudinal section by using BR and SL related mutants and transgene lines,we divided every of these mesocotyl into three parts according to previous studies,which named top part,middle part and basal part respectively,after cross section of seven days' mesocotyl,we found that the lower part of the mesocotyl,the programmed cell death phenomenon is more serious,so we could not observe cytological structure clearly when using longitudinal section.Than we did their growth dynamic curve,and found that mesocotyl stop elongation after five days,so we use five days' mesocotyl for section to avoid severe PCD.After longitudinal section of these material,we found that cell number and cell length of BR signal amplification transgene lines and SL related mutants were increased compared with the wide type every part,while the cell number and cell length of BR insensitive mutant and negative elements were decreased compared with the wide type each part.To further reveal which factor affects mesocotyl elongation,we calculated the contribution rate of these factors and drew a conclusion: rice mesocotyl elongation mainly results from cell division.These results can provide cytological basis for further study of molecular mechanism in mesocotyl elongation,and provide theoretical basis for improving rice mesocotyl elongation trait to adapt direct sowing cultivation techniques.