Carbon and nitrogen metabolism in arbuscular mycorrhizal maize plants under low-temperature stress

Effects of the arbuscular mycorrhizal (AM) fungus Glomus tortuosum on carbon (C) and nitrogen (N) metabolism of Zea mays L. grown under low-temperature stress was investigated. Maize plants inoculated or not inoculated with AM fungus were grown in a growth chamber at 25 degrees C for 4 weeks and subsequently subjected to two temperature treatments (15 degrees C, low temperature; 25 degrees C, ambient control) for 2 weeks. Low-temperature stress significantly decreased AM colonisation, plant height and biomass. Total N content and activities of glutamate oxaloacetate transaminase and glutamate pyruvate transaminase of AM plants were higher than those of non-AM plants. AM plants had a higher net photosynthetic rate (Pn) than non-AM plants, although low temperature inhibited the Pn. Compared with non-AM plants, AM plants exhibited higher leaf soluble sugars, reducing sugars, root sucrose and fructose contents, and sucrose phosphate synthase and amylase activities at low temperature. Moreover, low-temperature stress increased the C : Nratio in the leaves of maize plants, and AM colonisation decreased the root C : N ratio. These results suggested a difference in the C and N metabolism of maize plants at ambient and low temperature regimes. AM symbiosis modulated C metabolic enzymes, thereby inducing an accumulation of soluble sugars, which may have contributed to an increased tolerance to low temperature, and therefore higher Pn in maize plants.