Physiological Characteristics Of Different Genotypes Of Mung Bean At The Flowering And Pods Formation Stage

Mung bean plays an important role in restructuring of crop production and high-efficiency and high quality development of agriculture.As Chinese people change their food compositions and strengthen their health awareness,mung bean as a medicinal and edible crop is rapidly becoming more and more important in the development of functional food development.However,because mung bean research had a late start,its basic research has been very weak,especially in physiological characteristics of the metabolisms in its plants after flowering,which play a determining role in its yield and quality formation;as a result,the field production of mung bean lacks proper varieties in addition to extensive field managements and farming practices and thus low yields of mung bean are common.Therefore,it has become an urgent problem that need being solved to increase the yield and quality of mung bean in production.The study determined physiological parameters related to plant metabolisms of different varieties (lines) or regionally adopted varieties of mung bean developed in various regions—leaf transpiration rate,net photosynthetic rate,chlorophyll,solvable protein and malondialdehyde (MDA) contents,and superoxide dismutase (SOD),catalase (CAT) and peroxidase (POD) activities—at the flowering and pods formation stage , the key yield-formation time of mung bean.In the meantime,it anatomically examined structural differences and dynamics of functional leaves of different mung bean varieties at the flowering and pods formation stage by paraffin sectioning.It got the following main conclusions:1.In different varieties (lines),the net photosynthetic rates (Pn),transpiration rates (Tr),stomatal conductance (Gs),and chlorophyll and solvable protein contents of the leaves of main stems at the flowering nodes appeared to decline at the flowering and pods formation stage and the photosynthetic capabilities of the leaves at different flowring nodes decreased in the order of the 9th leaf,8th leaf,7th leaf and 6th leaf from ground at the same growth stages.Different varieties of mung bean significantly differed in their photosynthetic capabilities.The net photosynthetic rates of the leaves of high-yield varieties(lines) were 16.1-21.3% higher than those of low-yield varieties (lines) at the flowring nodes of the main stems from flowering to maturing;and high-yield varieties (lines) were able to keep a relatively high net photosynthetic rate at the late stage of growth,indicating their remarkably high photosynthetic efficiencies.2.In different varieties (lines),the leaves of main stems at different flowering nodes senesced one by one from bottom to top at the flowering and pods formation stage;in the meantime,their SOD and CAT activities appeared to decline and their POD activities and MDA contents continued to rise,resulting in their membrane structures and physiological capability being damaged and thus their photosynthetic capabilities being lowered.Different varieties (lines) significantly differed in leaf senescence and active oxygen species metabolism.In high-yield varieties (lines) the SOD and CAT activities of the leaves were higher and that declined more slowly at the late stage of growth;their average declining rates were 28.6 U·g-1·d-1,18.6 U·g-1·d-1 in high yield varieties (lines) and 28.6 U·g-1·d-1,18.6 U·g-1·d-1 in low yield varieties (lines).At the late stage of growth,high-yield varieties (lines) were still able to keep higher SOD and CAT activities thus effectively prolonging their leaf senescences.3.Different varieties (lines) tended to decrease the thicknesses and palisade parenchyma thicknesses of the leaves of their main stems at the flowering nodes after they flowerd;their leaf structures gradually senesced,mesophyll cells disintegrated and palisade parenchyma tending to be disorganized,after the peak flowering to maturing stage.Different genotypes of mung bean significantly differed in leaf and palisade parenchyma thicknesses and leaf structure.The aveage leaf thickness of high-yield varieties (lines) ranged within 224.2-235.3μm and that of low yield varieties (lines) ranged within 211.8-223.0μm;high yield varieties had better developed palisade parenchyma and their palisade parenchyma thickness to leaf thickness ratios averaged 53.8%,4.7% higher than the average of low-yield varieties (lines).High yield varieties (lines) had the leaf structures that senesced slowly and the mesophyll cells that contained more chloroplasts,and thus they were able to keep high chlorophyll contents and high net photosynthetic rates thereby leading to higher photosynthetic productivities.Correlation analysises indicate that at the flowering and pods formation stage,the leaf thickenesses and the palisade parenchyma thicknesses were significantly and positively correlated with the chlorophyll contents and the net photosynthetic rates.This further proved that the morphologyies and structures of mung bean plants matched with their physiological functions.4.After the varieties (lines) began to flower,their root bleeding intensities appeared to vary regularly.Their root vigors began to rise at the early flowering stage,peaked at the peak flowering and pods formation stage and then rapidly declined.Their root vigors tended to vary basically in the same way as the photosynthetic capabilities of the leaves of the their main stems at the flowering nodes did,but the root vigors began to decline later than the leaf vigors;the leaves of the main stems at the flowring nodes began to decline in vigor 15 days after flowering and the roots were able to keep their vigors for 30 days after flowering and then decreased them rapidly.Different genotypes of mungbean significantly differed in their root vigors.High yield varieties (lines) whose leaves senesced slowly has a stronger root bleeding intensity and then their root vigors declined slowly after the peak flowering and pods formation stage.5.At the flowering and pods formation stage,the dry matter accumulations of different varieties (lines) aboveground all tended to increase at first and then decrease and the dry matter accumulations in their seeds appeared to vary in a S-shaped way,indicating that the 16-31 days after flowering was the key time for the formation of biomass and seed sinks of mung bean.In the varieties (lines),the dry matter accumulations of their leaves,stalks,and pod shells as the photosynthate sources of seed formation varied in a single-peak curve and the leaves of their main stems at flowering nodes were the major organs of seed filling.Different genotypes of mung bean differed significantly in dry matter accumulation and transport.High yield varieties presenting strong capabilities of different organs in dry matter accumulation and transport after flowering,and the leaves of their main stems at flowering nodes were able to accumulate more dry matter functioning as larger"sources"and their transportation ratio and amount of transportation of dry matter appeared higher at late growth,the amount of transportation of high-yield varieties (lines) averaged at 2.85 g per plant and those of low yield varieties (lines) averaged 1.94 g per plant.Because of their high numbers of pods high-yield varieties (lines) had large sink sizes so as to form high harvesting indexes and seed yields.