While several genes associated with the preparatory steps in starch synthe­sis are up-regulated in the — N case, the genes encoding for key enzymes AGPase and starch synthase were repressed (Table 1). The degradative side of starch metabolism, specifically a-amylase which hydrolyzes starch to glucose, was also strongly repressed during nitrogen limitations. When coupled to the increased but still overall low starch contents in the — N case (Table 3), these findings suggest that the -N cells accumulated starch by repressing starch degradation. It is also notable that pyruvate kinase (log2FC = -0.21) and the three-enzyme pyruvate dehydrogenase complex for converting glucose to acetyl-CoA (to supply fatty acid synthesis) were up-regulated during nitrogen limitation (Figure 5D).

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