Abstract

A pot culture experiment of nitrogen forms (NO₃^¯:NH₄⁺) with four ratios (100:0, 75:25, 50:50, and 25:75) in nutrient solutions was conducted to examine the effects of nitrogen forms on the growth, ascorbate-glutathione (ASC-GSH) cycleand lipid peroxidation in developing seeds of vegetable soybean. Results showed that the best plant growth vigor was observed in NO₃^¯ (75%), and then in NH₄⁺(50%). The contents of ASC and dehydro-ascorbate (DHA), and DHA/ASC ratio in NO₃^¯ (75%) and NH₄⁺ (50%) maintained stable values, but obvious increases were observed in NO₃^¯ (100%) and NH₄⁺ (75%). The GSH contents exhibited increasing trends, while the increases in oxidized glutathione (GSSG) contents were only observed in NO₃^¯ (100%) and NH₄⁺ (75%), in which high GSSH/GSH ratios were observed. In NO₃^¯ (100%) and NH₄⁺ (75%), the enzymes activities in ASC-GSH cycle, including ascorbate peroxidase (APX, EC 1.11.1.11), dehydro-ascorbate reductase (DHAR, EC 1.8.5.1) and glutathione reductase (GR, EC 1.6.4.2), expressed increasing trends. Significant increases in lipid peroxidation and hydrogen peroxide (H₂O₂) generation were also observed in NO₃^¯ (100%) and NH₄⁺ (75%) as against NO₃^¯ (75%) and NH₄⁺ (50%). It was shown that the degree of oxidative damage was relatively low when the ratio of nitrogen forms was 75:25, and this could be a good guidance on the nitrogen application in the cultivation of vegetable soybean.

Key words: Nitrogen forms, seed development, ascorbate-glutathione cycle, vegetable soybean.