Effect of Shade on Nitrogen Metabolism and Its Mechanism in Cotton Plant at Flowering and Boll-forming Stage

Abstract

Cotton is an important economic crop in China and light is a major limiting factor to yield in cotton. The objective of the experiment was to clarify the effect of low light stress on nitrogen metabolism in cotton (Gossypium hirsutum L.) plant. Cotton cultivars (Sumian 15, Kemian 1) were grew in pots, and treated with three light densities (100%, 80%, 60% of natural light) at the flowering stage in 1st-2nd fruiting node on 6-8th fruiting branches. It was sampled four times with 15-day intervals from onset to bolls open. Cotton root vigor, root absorption and activities of the nitrate reductase, glutamine synthase, glutamate synthase and glutamate dehydrogenase were analyzed. The results showed that with increase of the shading level, root vigor and root absorption decreased seriously. Both in root and function leaf, activities of the nitrogen metabolic enzymes, such as NR, GS, GOGAT were seriously inhibited at the 15th days of shade. The activities of nitrate reductase (NR), glutamine synthase (GS), glutamate synthase (GOGAT) and glutamate dehydrogenase (GDH) decreased by 25.1%, 53.2%, 39.1%, 25.5% in root, while 50.3%, 24.0%, 30.4%, 18.9% in function leaf. The descending of nitrogen absorption in cotton root resulted from the drop of GS/GOGAT activity firstly and the drop of NR activity secondly, but the decreasing of nitrogen metabolic ability in functional leaf induced from the drop of NR activity firstly and the drop of GS/GOGAT activity secondly. Low light could repress root vigor and root absorption. The activities of NR, GS/GOGAT were also suppressed, which resulted decrease of amino acid content, soluble protein content and nitrogen accumulation both in root and function leaf with increase of the shading level. The yield of cotton plant also decreased with the shading and the boll number was the most sensitive to shade.