Quality Characteristics And Carbon And Nitrogen Metabolism Mechanism Of Good Quality,High Yield And High Nitrogen Efficiency Of Soft Japonica Rice In Yangtze River Delta

The cooked rice of soft japonica rice show smooth and oily appearance,soft and glutinous taste,good eating quality and low retrogradation because of relatively low apparent amylose content,which better meet the local people’s consumption demand for high-quality japonica rice in the Yangtze River Delta region.What are the quality characteristics of soft japonica rice compared with traditional non-soft japonica rice in this region?Compared with high quality japonica rice in the northeast China,is there any difference in the taste of soft rice in Yangtze River Delta region?All above are very worthy of study.In addition,the coordination of carbon and nitrogen metabolism not only affects the growth and development process of rice,but also has a decisive influence on the yield and quality of rice grains.For soft japonica rice in the Yangtze River Delta region,what is the basis of carbon and nitrogen metabolism of yield and quality and what are the dynamics of carbon and nitrogen metabolism of good quality,high yield and high nitrogen efficiency?In view of the above problems,133 conventional japonica rice varieties suitable for planting in the Yangtze River Delta region were extensively collected in this study,including 58 soft japonica rice varieties and 75 non-soft japonica rice varieties.The comparison with traditional non-soft japonica rice varieties revealed the quality characteristics of soft japonica rice,such as processing quality,appearance quality,chemical composition and cooking and eating quality.We compared traits from Daohuaxiang2,the most prominent high-quality japonica rice from the northeast China,Nangeng46 and Nangeng 9108,the most representative soft japonica rice from the Yangtze River Delta region,and Nangeng2728,a cultivar of soft japonica rice from the Yangtze River Delta region with a less desirable taste than that of the other two cultivars.The differences in cooked rice properties,flour/paste properties,chemical compositions,and starch physicochemical properties were compared systematically,in order to clarify the different ways to achieve good food taste of japonica rice in south and north China.In the end,Nangeng9108,a soft japonica rice with good taste was selected as material,different carbon and nitrogen metabolism levels were formed in rice seed stage by setting different application time of panicle fertilizer.Effects of carbon and nitrogen metabolism differences on quality formation of soft japonica rice in Yangtze River Delta region was studied,carbon and nitrogen metabolism pathways and leaf color diagnostic indexes of good quality,high yield and high nitrogen efficiency were explored.This study provided theoretical basis and technical reference for the coordination of good quality,high yield and high nitrogen efficiency of soft japonica rice in Yangtze River Delta region.The main results are as follows:1.Among japonica rice varieties in the Yangtze River Delta region,there were no significant differences in brown rice rate,milled rice rate and milled rice rate between soft japonica rice and non-soft japonica rice.The length-width ratio and length of soft japonica rice were 4.35%and 3.84%lower than those of non-soft rice,respectively.The milled rice of soft japonica rice was slightly short and round.The transparency was one grade higher than that of non-soft japonica rice,and the transparency of soft japonica rice was distribution grade 2 or above.The chalkiness rice rate,chalkiness area ratio and chalkiness degree were 64.75%,68.30%and 67.52%higher than those of non-soft rice japonica rice,respectively.The final viscosity,setback and consistence of soft japonica rice were concentrated below 2000cP,200cP and 700 cP,respectively,while the breakdown was concentrated between 900 cP and 1300cP.The though viscosity,final viscosity,setback and consistence were 17.81%,26.98%,509.09%and 39.46%lower than those of non-soft japonica rice,respectively,and the disintegration value was 24.75%higher than that of non-soft rice.The apparent amylose content of soft japonica rice was concentrated in 8-11%,42.01%lower than that of non-soft japonica rice.There were no significant differences in total protein content,globulin and glutelin content between soft and non-soft rice japonica rice.Albumin content was 76.67%higher and prolamin content was 8.40%lower than that of non-soft rice.The proportion of small grain starch in soft japonica rice rice was more than that of large grain starch.The relative crystallinity was 31-36%,17.30%higher than that of non-soft japonica rice.The iodine blue value of rice soup was concentrated below 0.4A,48.39%lower than that of nonsoft japonica rice.The appearance,viscosity,balance value and taste value were 39.53%,28.00%,36.36%and 21.82%higher than those of non-soft rice,respectively,while hardness and elasticity were 13.92%and 7.55%lower than those of non-soft rice.The taste quality was better than that of non-soft rice.2.The apparent amylose content of good quality soft rice Nangeng46 and Nangeng9108 in Yangtze River Delta was 36.03%and 34.77%lower than that of Daohuaxiang2,respectively.The total protein content was 33.77%and 40.83%higher than that of Daohuaxiang2,respectively.There was no significant difference in taste value between Nangeng46,Nangeng9108 and Daohuaxiang2.Because of low protein content,Daohuaxiang2 exhibited harder but more elastic cooked rice.The soft rice Nangeng46 and Nangeng9108 exhibited a softer texture of cooked rice because of its lower AC.All of them are favored by consumers.Therefore,as long as a balance of hardness,softness,adhesiveness and elasticity is achieved in cultivars of rice,the cooked grains are expected to have excellent taste irrespective of the amylose and protein contents and other physicochemical properties.Nangeng2728,both soft rice,was not as tasty as Nangeng46 and Nangeng9108,and they also had great differences in rice characteristics:The rice taste value,appearance,elasticity and viscosity of Nangeng46 and 9108 were 32.26%.25.81%;41.38%,29.31%;3.81%,1.90%and 2.76%,1.73%higher than those of Nangeng2728,respectively,and their hardness were 13.25%and 10.84%lower than those of Nangeng2728,respectively.Water absorption rate,expansion volume,iodine blue value and dry matter weight of rice soup were 19.19%,8.08%;19.20%,5.07%;11.81%,24.41%and 44.16%,23.38%higher than those of Nangeng2728,respectively.Compared with Nangeng2728,Nangeng46 and Nangeng9108 showed relatively higher peak viscosity,though viscosity and final viscosity during gelatinization.The pasted rice paste showed higher storage modulus G ’and loss modulus G’.The total protein content and glutelin content were relatively lower.The average chain length of amylopectin was higher in Fa and Fbl,lower in Fb3.The average volume,average surface area,relative crystallinity,gelation enthalpy and regeneration value of starch particles were smaller,and the lamellar thickness was larger.3.Different application time of panicle fertilizer will cause different carbon and nitrogen metabolism levels in rice filling stage.The average non-structural carbohydrates（NSC）stored in stem before anthesis and the transport amount of NSC after heading of panicle fertilizer applied at top sixth（L11 Treatment）and fifth（L12 Treatment）leaf were 5.11%,8.29%,13.46%,17.86 and 4.09%,5.15%,6.43%,10.08%higher than those panicle fertilizer applied at top fourth（L13 Treatment）,third（L14 Treatment）,twice（L15 Treatment）and first（L16 Treatment）leaf,respectively.The activities of related starch synthase were higher in the whole grain filling stage（except the activities of AGPase and SSS in late filling stage）,which resulted in the more accumulation of starch in grains.The average nitrogen accumulation in the whole growth period of L11 and L12 Treatment was 7.39%,6.51%,4.50%and 2.94%lower than those in L13,L14,L15 and L16 Treatment,respectively,and the activities of NR,GS and GOGAT were lower,resulting in less accumulation of protein and protein components.As a result,L11 and L12 Treatment formed a high carbon and low nitrogen metabolism level.Although the NSC stored in stem in L13 and L14 Treatment was not as high as that in L11 and L12 Treatment before heading,the functional leaves of L13 and L14 Treatment were larger and stronger,and the photosynthetic efficiency was higher after flowering,which was conducive to the formation of more photosynthetic product.The average leaf nitrogen transport of L13 and L14 Treatment from heading to maturity was 5.34%,3.98%,9.18%and 14.25%higher than that of L11,L12,L15 and L16 Treatment,and the appropriate nitrogen metabolism in the middle and late filling stage kept the protein content at the moderate level.As a result,L13 and L14 Treatment formed a balanced carbon-nitrogen metabolism level.L15 and L16 Treatment had less NSC stored in stem before anthesis and less transport amount of NSC after heading,and lower activities of related starch synthases during the whole grain filling stage（except the activities of AGPase and SSS in late filling stage）,which resulting in less starch accumulation in grains.Higher activities of key enzymes of nitrogen assimilation in the process from 14 days after anthesis to maturity increased the accumulation of total protein and other protein components except albumin content.As a result,L15 and L16 Treatment formed a low carbon and high nitrogen metabolism level.4.The average number of panicles per mu in high carbon and low nitrogen metabolism level formed by early application of panicle fertilizer was 6.84%and 11.00%higher than that in balanced carbon-nitrogen metabolism level and low carbon and high nitrogen metabolism level.However,the lack of nitrogen metabolism in the late filling stage had a great influence on grain number and grain weight per panicle,which was not beneficial to yield formation and nitrogen absorption and utilization.The grain protein content of rice at mature stage was 4.50%and 9.43%lower than that of balanced carbon-nitrogen metabolism level and low carbon and high nitrogen metabolism level,respectively,and the taste value of cooked rice was 2.49%and 6.71%higher than that of other two metabolism levels,respectively.The cooker rice showed better appearance,higher viscosity and balance value,and lower hardness.Grain number per panicle,actual yield and apparent nitrogen use efficiency of high nitrogen metabolism level formed by timely application of panicle fertilizer were 12.15%,8.07%;9.94%,11.85%and 8.97%,6.64%higher than those of other two metabolism levels,respectively.Starch content and protein content in grains were at medium level at mature stage.The taste value of cooked rice balanced carbon-nitrogen metabolism level was slightly lower than that of high carbon and low nitrogen metabolism level but better than that of low carbon and high nitrogen metabolism level.The number of panicles per mu and grain number per panicle of low carbon and high nitrogen metabolism level formed by delayed application of panicle fertilizer decreased caused by nitrogen deficiency at the early stage of spike differentiation,which affected the population spikelets and was detrimental to the formation of yield.At the same time,the higher nitrogen metabolism level in the late filling stage resulted in higher protein content in rice grains at the mature period,which affected the taste quality.5.In order to achieve the balance of carbon and nitrogen metabolism during rice filling stage and the coordination of good quality,high yield and high nitrogen use efficiency,the diagnostic approach of rice leaf color was as follows.Applying panicle fertilizer when the color difference between top third and top fourth leaves is about 0.2 before heading,the leaf color could change from black to yellow before joining.At this time of nitrogen fertilizer not only increased the function leaf area and the grain number per panicle,but also maintain a higher photosynthetic rate in late filling stage,which increased the photosynthetic product after anthesis,the nitrogen accumulation from heading to mature period,and formed appropriate protein content of rice grains,resulted in high yield and nitrogen use efficiency,and improved the taste quality.If the color difference between the top third and top fourth leaves was lower than 0 during the application of panicle fertilizer,the nitrogen in the population was surplus.At this time of nitrogen fertilizer,the leaf color was too black in early stage.The color difference between the top third and top fourth leaves was over 0.5 at booting stage with population lacked nitrogen,the leaf color was too yellow not black in filling stage,was not conducive to the formation of yield and the absorption and utilization of nitrogen.If the color difference between the top third and top fourth leaves was higher than 0.4 during the application of panicle fertilize,the population was short of nitrogen,the leaf color was too yellow in the early and middle stages,the color difference between top third and top fourth leaves was lower than 0 in booting stage,and the leaf color was too black in filling stage,which was not conducive to the formation of yield and the improvement of taste quality.In conclusion,the taste quality of soft japonica rice in the Yangtze River Delta region was significantly better than that of non-soft japonica rice,but not all soft japonica rice had higher taste value,and there were still great differences in taste quality among soft japonica rice varieties.Reducing protein content（especially glutelin）and increasing short amylopectin chains ratio could make soft rice have better appearance,higher viscosity,lower hardness and higher taste,thus further improving the taste quality of soft rice in Yangtze River Delta region.Applying panicle fertilizer when the color difference between top third and top fourth leaves is about 0.2 before heading,the leaf color could change from black to yellow before joining,guaranteeing the balanced carbon and nitrogen metabolism of soft rice.It increased grain number per panicle,made functional leaves larger and stronger,maintained high photosynthetic efficiency after anthesis,increased the photosynthetic product after anthesis,kept appropriate nitrogen metabolism enzyme activities in middle and late filling stage and appropriate protein content,increased total nitrogen uptake and nitrogen accumulation from heading to maturity stage,in addition to improve the eating quality,yield and nitrogen efficiency.