| Maize is one of the most important feed crops and is the major source of starch. Starch is the most significant carbon reserve in higher plant. Many researches about the biosynthesis and accumulation of starch of wheat, rice grain have been done, however, further research to address the starch synthesis net-work is necessary. The production of starch in higher plant is orchestrated by four major types of enzymes, named ADP-glucose pyrophosphorylase (AGPase), starch synthase (SSs), starch branching enzymes (SBEs) and starch-debranching enzymes (DBEs). The regulatory and rate-limiting step of starch biosynthesis is the synthesis of the ADP-glucose, catalysised by ADP-glucose pyrophosphorylase, which could affect the final starch content directly in higher plant for that low AGPase activity was observed in AGPase genes deficient mutant. This enzyme in higher plant is a heterotetrameric (α2β2), consisting of two "regulatory" subunits (AGPL) and two slightly smaller "catalytic" subunits (AGPS). In higher plant, each subunit of AGPase is encoded by distinct genes. In maize, six gene encoding AGPase can be found in the database, three of which encode for large subunit, AGPL1, AGPL2 and AGPL3; and the others of which encode for small subunit, AGPS1, AGPS2 and AGPS3. Therefore, study on the expression patterns of maize AGPase genes can help us better understand the relationship between AGPase genes and starch biosynthesis, and also can improve starch content quality.The expression patterns of six maize AGPase genes in different organ and different developmental stage of maize were studied by using Quantitative Real-time RT-PCR in this work. The results showed that:1).The expression profillings of AGPase genes in maize were tissue-specific and developmental stage-specific.2).As the expression level of cytoplasmic AGPase gene increased in 10d to 16d after pollination, AGPase activity was also significantly enhanced. When the AGPase enzyme accumulated to a certain level, starch accumulation rate also began to grow significantly and had the same change trends.3).The different influence of day and night cycles on the exppression of AGPase genes may relate to the different tissues. The influence of day and night cycles on the exppression of AGPase genes in old leaf, young leaf and sheath were less than the influence of day and night cycles on the exppression of AGPase genes in developed leaf. In developed leaf, the expression level of agpl1, agpl2, agpl3, agps1 and agps2 gene in the night was far more than in the day.4).Our data showed significant difference in response to sugar or hormone among differenct AGPase isoforms. In this work, we presented that both agps1 and agps2 are nearly identical and similarly induced by hormone. On the other hand, tissue-specific expression profilling and different response to sugar of the two genes were observed. These facts support the functional divergence between the two genes and that sugar may be one of the impact factors.5).Glucose had greater effect on the expression of maize AGPase gene than sucrose, PEG6000 and manitol. However, minor changes were observed for trancripts of agps2 was observed. The amount of endogenous surcose in developing grain reached max at approximately 13 days after pollination and then decreased, but the expression level of AGPase genes did not appear 13 days after pollination. It seemed that the data of the endogenous sucrose, expression level of AGPase genes and exdogenous sucrose did not consist with each other. The most suitable explanation for this discrepancy was that many signal factors effect the complicated starch metabolism together for that more obvious changs of transcript for AGPase genes in ABA and sucrose treatment than sucrose alone treatment were observed.
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