Effects of organic fertilizer applications on starch changes in tobacco (Nicotiana tabacum L.) leaves during maturation
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Starch is a major feedstock for biofuel production. To meet growing fuel demands, the starch yields of energy crops need to be improved. In this study, the effects of the application of an organic fertilizer composed of cotton cake, oil cake and wheat straw at different concentrations (3000, 6000 and 9000 kg ha−1) were investigated in order to optimize the yield of tobacco (Nicotiana tabacum L.) leaves. To analyze the effects of the application of organic fertilizers on starch biosynthesis, we compared the phenotypic index, starch content, ultrastructure and starch granule volume during maturation. The results revealed that application of the organic fertilizer markedly promoted the accumulation of starch in tobacco leaves, and the concentration of organic fertilizer required for optimal yield in yellow loam areas was 6000 kg hm−2. Analysis of starch synthesis-related gene expression patterns revealed that the transcript levels of adenosine diphosphate-glucose pyrophosphorylase (AGPase), starch synthase (SS) and starch branching enzyme (SBE) increased gradually as leaf growth progressed, attained a maximum value at the mature stage, and then declined as leaves progressed toward maturity and senescence. The expression levels of these genes were higher in plants treated with the organic fertilizer than in those grown under normal conditions. Notably, AGPS3, AGPSL, GBSS1 and SS1 were highly expressed, indicating that these genes play crucial roles in starch synthesis in leaf tissue. The results provide insights into the molecular regulation of starch biosynthesis in tobacco leaves.