Physiological Mechanisms Of Nutritional Quality And Antioxidant Activity Influenced By Nitrogen, Sulphur And Selenium Application In Leaf Mustard (Brassica Juncea Coss.)

With enormous increase of vegetable output in recent years, focus of our efforts in vegetable production has been changed from high yield to high quality. People gradually pay more attention to the nutritional quality and healthy functions of vegetables with the increase of living standard. Leaf mustard (Brassica juncea Coss.) is a member of the cruciferae family, commonly known as the mustard family. It has been widely used and processed as delicious and nutritional food, and is particularly popular in China. Nitrogen and sulphur are essential nutrient elements for growth and development of vegetable, being concerned with photosynthesis, respiration and the metabolism of protein and carbohydrate in plant. Selenium is essential microelement for human and animal, being associated with health such as antioxidative, anticarcinogenic activities, promoting immunity and so on.The effects of nitrogen, sulphur and selenium on quality and antioxidant activity in leaf mustard were studied in this paper, the objectives are to know how nitrogen, sulfur and selenium affect the nutritional quality and antioxidant activity in leaf mustard. The results are summarized as follows:1. Effects of nitrogen and sulphur treatments with four levels of nitrogen (10, 100, 200 and 300 kg/ha) and two levels of sulphur (0 and 50 kg/ha) on the growth and nutritional quality in two cultivars of leaf mustard (cv. Xuelihong and cv. Baobaoqingcai) were studied in field trials. The results showed that increasing nitrogen application increased the shoot height, shoot fresh weight, yield, and the contents of chlorophyll, free amino acids, total N and S in shoots of both cultivars of leaf mustard and the nitrate content in cv. Xuelihong, but decreased the dry matter content and the soluble sugar content in both cultivars. The soluble protein content in two cultivars of leaf mustard was significantly increased when the low dose of nitrogen ( < 100 kg/ha) was applied. The nitrate content in cv. Baobaoqingcai was not significantly influenced by increasing applied nitrogen when KCl (non-sulfur) was applied,, however, significantly increased when K2SO4 (sulfur) was applied. Sulphur application significantly promoted the soluble protein content in cv. Xuelihong, the nitrate content in cv. Baobaoqingcai and the shoot S content in both cultivars of leaf mustard, but did not affect other tested indexes in leaf mustard. Effects of nitrogen and sulphur on the shoot P, K, Ca, Mg, Fe and Zn content are respectively different.2. Effects of nitrogen and sulphur treatments on the antioxidant substances in two cultivars of leaf mustard (cv. Xuelihong and cv. Baobaoqingcai) were studied by field trials. The results showed that the ascorbic acid (AsA) content in leaf mustard firstly increased then decreasedwith increasing nitrogen supply, however, the glutathione (GSH) content in leaf mustard were significantly increased. The AsA and GSH content in leaf mustard were significantly increased by sulphur application. The chlorophyll a, chlorophyll b, β-carotene, lutein and vitamin A content in two cultivars of leaf mustard were significantly promoted by increasing nitrogen supply, but when the dose of nitrogen was higher than 200 kg/ha, their contents were stable. Effects of the sulphur treatments on the pigments and vitamin A content were not significant, but the genotype significantly influenced the antioxidant substances in leaf mustard.3. Effects of nitrogen and sulphur treatments on the phenolic compounds and antioxidant acitivity in two cultivars of leaf mustard (cv. Xuelihong and cv. Baobaoqingcai) were studied in field trials. The results showed that total phenolics content in leaf mustard decreased with increasing nitrogen application, but increased by increasing sulphur supply. Quercetin and kaempferol were found in leaf mustard by HPLC analysis, and the kaempferol content was 2.46 times as quercetin content in leaf mustard. The quercetin content in cv. Xuelihong was increased by increasing nitrogen application, but the quercetin content in cv. Baobaoqingcai was gra...