Comparative Study On Sucrose Accumulation And Transport In Maize B73 And Dongtian 4 In Grain Filling Stage

Sweet corn is loved by people for its unique flavor,which is mainly determined by the sucrose content in the grain.At the same time,sucrose is also the main form of the sythesis,transportation and distribution of photosynthetic products in corn.Its accumulation and translocation play an important role in the formation of different types of maize yield and quality.In this experiment,the common maize inbred line B73 and the sweet corn inbred line Dongtian 4 were used as materials to compare the photosynthetic characteristics at the grain filling stage and the differences in accumulation of sucrose,fructose,and glucose in the source and sink organs.Based on bioinformatics analysis of maize ZmSWEETs members,combined with expression analysis of key members of the maize ZmSWEET family?ZmSWEET13a,ZmSWEET13,and ZmSWEET13c?.The changes in sugar content of common corn and sweet corn were analyzed from the perspective of sucrose accumulation and translocation.the reason.The main results are as follows:?1?At the filling stage,the photosynthetic rate of the two cultivars showed similar trends,which were stable in the early period and decreased significantly in the later period.The photosynthetic rate of Dongtian 4 was higher than that of B73 in the early stage of filling,and it was significantly different on the 7th day.It decreased rapidly at the late stage and was lower than that of B73.Compared with B73,Dongtian 4 had a high stomatal conductance in the early filling stage and a low late stage,whereas the intercellular CO₂concentration was opposite.This showed that Dongtian 4 had ample supply of CO₂,high assimilation efficiency,and low intercellular CO₂ concentration during the early grain filling period,accumulating more assimilation products and transporting to the sink organ.B73 maintained relatively high stomatal conductance at the late filling stage to meet the CO₂ supply,and the net photosynthetic rate decreased slowly,which provided sufficient material for the later grain development.?2?The change trend of photosynthetic pigments in B73 and Dongtian 4 at filling stage was different.The contents of photosynthetic pigments in Dongtian 4 decreased gradually;B73 increased first,reached the maximum after 14 days of grouting,coincided with the maximum net photosynthetic rate,and then decreased.In the early filling stage,the contents of chlorophyll a and carotenoids in Dongtian 4 were significantly higher than those in B73and were lower than B73 in the later period.The higher content of chlorophyll a in early stage made Dongxue 4 more photochemically active and could synthesize more assimilation force for the assimilation of CO₂ with higher net photosynthetic rate.In the later period,the higher photosynthetic pigment content in B73 also provided energy guarantee for maintaining higher photosynthetic rate.?3?The contents of three soluble sugars in leaves,stems and grains at the filling position of B73 and Dongtian 4 during filling stage were different.In leaf,the sucrose content of B73 was higher than that of Dongtian 4,but the glucose and fructose content was lower than that of Dongtian 4.However,the total amount of the three sugars was higher than thatof the B73 in the early filling stage,which was related to the higher net photosynthetic rate.In stems,the three soluble sugar contents in B73 were higher than those in Dongtian 4.In the grains,except for 7 days after pollination,the sucrose content of Dongtian 4 was higher than that of B73,and the difference was significant.It was related to the low activity of SS and CWINV and high activity of SPS.The content of starch in the two varieties was opposite,B73 was significantly higher than Dongtian 4,which resulted in a higher filling rate.?4?Through the alignment of amino acid conserved sequences,23 named ZmSWEET gene family members and 2 unnamed members were identified in the maize genome database,and bioinformatics analysis was performed.The transcriptome data published by S.C.Stelpflug showed that ZmSWEET13a,13b,and 13c had the highest expression levels in the leaves and stems during corn grain filling.ZmSWEET13a,13b,13c may participate in sugar transport during grain filling.?5?The expression levels of key members in B73 and Dongtian 4 ZmSWEETs at filling stage were different.ZmSWEET13a,13b,13c expressed the highest in 14th day after B73 filling and 21 days after Dongtian 4 filling in the spike leave.At this time,the sucrose content in leaves of both varieties reached the highest.Compared with B73,the high-level expression of three genes in leaves and stems of Dongtian 4 was long-lasting,which was conducive to the loading and unloading of sucrose at the source end.Among them,ZmSWEET13b expressed higher in leaves than ZmSWEET13a and ZmSWEET13c,suggesting that it plays an important role in source loading.In summary,compared with B73,Dongtian 4 had high photosynthetic pigment content,adequate CO₂ supply,high net photosynthetic rate and soluble sugar content in leave at the early filling stage,and high expression of key members of the ZmSWEET gene family had a long duration.For a long time in leave and stem,the assimilate could be transported from the source to the grain bank timly.At the same time,the activities of SS and CWINV werw low and the SPS was high in the grain,resulting the sucrose content was high,and the starch content was low.In B73,the expression levels of ZmSWEET13a,13b,13c were low,and sucrose could not be transported to the grain in time and accumulated in leaves and stems.However,the starch content in grains rapidly increased,and the photosynthetic pigment content in B73 was also higher in the later period.The photosynthetic rate provides energy assurance with a high grouting rate.