Effect Of Nitrogen Fertilizer On Rice Appearance Quality And Its Carbon And Nitrogen Metabolism Foundation

Appearance quality is one of the main quality indexes of rice. Chalkiness, which is highly related to the price of rice, is the most important indicator of appearance quality. In China, the chalkiness of new varieties compliance rate is raised, but problems such as high chalkiness percentage and chalkiness degree in main cultivars are still exist in main japonica rice production areas of South China. Nitrogen (N), one of the most important management practices, has significant effect on both rice yields and quality. To determine the effects of N and genotype on rice appearance quality and endosperm structure of chalkiness rice, field and pot experiments involving six japonica rice cultivars of Jiangsu province and seven N fertilizer treatments was conducted at Danyang experimental station. Changes of major carbon and nitrogen metabolites and activity of synthase were analyzed to reveal the effect of N on rice appearance quality and its metabolism foundation. The results were shown as follows:1 Effect of N fertilization rates on rice yield and appearance quality were studied under different N treatments. As N rate increased, rice yield increased. Increase of the percentage of panicle fertilizer, the yield was increased obviously. In addition, perfect rice kernel (PRK) rate decreased as N rate increased, whereas the percentage of green rice and others increased, which led to deterioration of appearance quality. Meanwhile, both white-core rice kernel rate (WCRK) and white-belly rice kernel rate (WBRK) decreased with N rate increased. It suggested that N application can reduce the rate of chalkiness. 2 White-belly rice cultivars (Wuyujing3 and 武运粳7号) and white-core rice cultivars (Ningjingl and Zaofeng9) were used to observe the endosperm structure. The result showed that differences of endosperm structure were found between WBRK and WCRK. In belly of WBRK, compound starch granule was large ellipsoid and single starch granule was regular polyhedron, which were arranged densely by each other, but the interspaces of them couldn’t be filled because of proteosome inadequate accumulation. In core of WCRK, the starch granule was hypoplastic and easy to disintegrate to rubbly single starch granules by external force. The interspaces between starch granules and protein body (less than WBRK’S) was large because of loose combine by each other. In addition, the formation of physiological mechanism had obviously difference between WBRJC and WCRK. One of the major reason may be that the protein bodies were not sufficient to fill interspace of the starch granules. Increasing N application can promote the accumulation of protein and consequently reduce the chalk rice kernel.3 Changes of content of protein component, amylopectin, amylose and total starch of rice were studied under different N treatments and analyzed composition of amino acids of chalk rice materials from(2). The results showed that with the increase of nitrogen fertilizer rate, especially for top dressing, the content of protein components raised obviously. Amylose content increased while amylopectin and total starch content decreased with increasing nitrogen fertilizer rate. Compared to PRK, relative content of amino acid, especially aromatic amino acid decreased in WBRK under higher N application, while reverse tendency in WCRK. This indicated that the difference of amino acid components was found in different types of chalk rice.4 Changes of biochemical component and key enzymes in the process of carbon and nitrogen metabolism under different N treatments were analyzed using pot experiment. The result indicated that sucrose and starch content in leaves and grains was restricted by panicle fertilizer during full heading stage, and was improved by granular fertilizer 17 days after anthesis. Especially in the late growth stage, granular fertilizer alleviated the decrease of sucrose content. Synthetase activity of sucrose and starch in leaves and grains was improved by panicle and granular fertilizer, especially in the late growth stage, Synthetase activity increased evidently compared to control. Genotypic differences were found in different synthetase activities, e.g. Wuyujing3 had relatively lower enzymatic activity during the whole growth stage and was insensitive to granular fertilizer, while 武运粳7号 had higher enzymatic activity and was sensitive to granular fertilizer.5 A pot experiment was conducted to study content of chlorophyll in leaves and transaminase activity and various amino acid components in leaves and grains under different N treatments. The result indicated that content of chlorophyll and activity of GOT and GPT in leaves were improved by panicle and granular fertilizer. The effect of N on amino acid was different during different growth stages, the maximum effect of free amino acid and non-free amino acid in leaves was at 27 days after anthesis but in grains was at 17 days after anthesis. For free amino acids, methionine, tyrosine and histidine were sensitive to N, but glutamic acid, phenylalanine and lysine were not. For non-free amino acids, histidine and isoleucine were sensitive to N, while arginine, lysine and phenylalanine were not.Increasing application of nitrogen fertilizer leads to the appearance quality of rice becoming inferior, which mainly dues to the increasing of green rice and others. Increasing application of nitrogen fertilizer reduced the rate of WBRK and WBCK, both of which were different in the endosperm morphology and mechanism of metabolic physiology. The relationship of competition and shifting were existed in the end products of carbon and nitrogen metabolism. The reason of the decrease of chalk rice rate mainly dues to the enhancement of protein accumulation and decrease of starch content. The competition and shifting of the biochemical components between the carbon and nitrogen metabolism of the plant were showed as the synthesize of sucrose and amino acids.