[Effects of high- and low temperature stresses on ascorbic acid metabolism system in potato leaves].

In order to investigate the responses of ascorbic acid (AsA) metabolism system in potato leaves to high and low temperature stresses, a pot experiment was conducted with potato plants exposed to 40 degrees C or 5 degrees C, with the leaf AsA content, mRNA expression level of GalLDH and DHAR genes, activities of GalLDH, DHAR, APX, MDHAR and GR, and contents of hydrogen peroxide (H2O2) and malondialdehyde (MDA) determined. Under the exposure to 40 degrees C, the leaf AsA content increased rapidly and reached the highest (43.7% higher than the control) at 6 h, followed by a rapid decrease. Under the exposure to 5 degrees C, the AsA content also increased first, reached the highest (27.7% higher than the control) at 9 h, and then decreased. Under the two temperature regimes, the activities of leaf GalLDH, DHAR, APX, MDHAR and GR decreased after an initial increase, the mRNA expression level of GalLDH and DHAR genes showed the similar changes with their corresponding enzyme activities, and the leaf MDA and H2O2 contents increased remarkably after 24 h. All the results suggested that the AsA metabolism system in potato leaves was stimulated in the early period of high- and low temperature stresses, but its function declined gradually with the duration of the stresses.