The Effect Of Artificial Ageing Treatment On Metabolism Of The Soluble Sugar And Their Relative Gene Expressions At The Early Stage In Maize Seed Germination

Aging lead to the reduction of the capacity to supply energy and material at the late stage of seed germination.However,the effect of seed aging on the mobilization and metabolism of reserved material during the initial stage of seed germination remains rarely reported.In this paper we used the seeds of the maize "Dabaitou" as the material,to study the effects of artificial aging on the soluble sugar,the key enzyme activities and the relevant gene expression of glycolytic pathway,tricarboxylic acid cycle and pentose phosphate pathway.The ATP content was studied,in order to improve the recognition of the mechanism of maize aging.The main results are as follows:1)The effects of seed aging on the water absorption during initial germinating The water absorption curve of unaged seeds(the control)showed a fast-slow pattern during the 0-24 h imbibition,when the first 8h was the a fast stage,follow by the slower one the 8-24 h.After 24h-imbibition the embryo was about to extrude throuth the seed coat.The water absorption rate in artificially aged seeds showed no difference from the control,indicating that artificial aging had no significant effect on the water uptake at the early stage of maize seed germination2)The effects of seed aging on the soluble sugar content during initial germinatingNinety-one percent of total soluble sugar in the maize seeds embryo were tested bu UPLCto be sucrose,indicating that it is the main soluble sugar in maize embryo.In the control seed,the sucrose content decreased gradually and the fructose and glucose content increased during the imbibitions.In artificially aged seeds,the content of sucrose decreased and then increased during the imbibition,and the content of fructose increased extent gradually reduced.Indicating that artificial aging treatment might inhibited the transformation from sucrose to fructose and glucose,and also the further utilization of fructose and glucose.3)The effects of seed aging on the key enzyme activities of the metabolism of soluble sugar during initial germinationIn the control seed,the hexokinase,pyruvate kinase,citrate synthase,glucose-6-phosphate dehydrogenase activities incresed and phosphofructokinase activity decreased with prolonged imbibition.The artificially aged seeds showed the same trend as the control during imbibition,but the time to reach significant differences was delayed with redued rangeability.The results suggested that aging inhibited the glycolysis and the pentose phosphate pathways,and enhanced the tricarboxylic acid cycle,which could disrupt the coordination of various metabolic pathways.4)The effects of aging on the in-process products of soluble sugar metabolismThe content of the in-process products of glucose metabolism in aged seeds were determined through target metabolic analysis.The results suggested that these products were significantly affected by artificial aging treatment,but the changes varied in different metabolic pathways,indicating that the production and utilization of these products was affected by aging.5)The effects of seed aging on the energy production during initial germinatingThe control seeds reserved a small amount of ATP,which increased significantly after 16 himbibition,and finally increased by 21.51 times at the 24 h.In the aged seeds,the ATP content was significantly decreased,which was only 33.3% of the control in the 10 d aged seeds.And the increase range of ATP content of the aged seeds was significantly lower than that of the control seeds.The results showed that artificial aging treatment inhibited the production of ATP during maize seed imbibition.6)The analysis of the expression of the key enzyme genes of soluble sugar metabolismIn order to further study the effects of artificial aging on soluble sugar metabolism,the expression of key enzyme genes of sugar metabolism in the early stage of germination after artificial aging was determined by q RT-PCR.The results showed that there were differences in the expression patterns of different genes during the process of seed aging,and most of the genes were down-regulated at the later stage of seed aging,indicating that aging affected gene expressions of glucose metabolism.7)A probable mechanism of for maize seed agingAt the early stage of seed germination(8h-imbibition),the transformation of soluble sugar and the metabolism of glucose and fructose might initiate at the 8h-imbibition.However,the aging treatment had a significant negative effect on the mobilization of soluble sugar and its metabolic regulation in the early stage of seed germination,which could lead to metabolic disorder,and then lead to insufficient supply of energy and intermediate products.These may lead to the block of radicle protrusion,and ultimately result in germination failure.