Comprehensive metabolomic, proteomic and physiological analyses of grain yield reduction in rice under abrupt drought-flood alternation stress.

Abrupt drought-flood alternation (T1) is a meteorological disaster that frequently occurs during summer in southern China and the Yangtze river basin, often causing a significant loss of rice production. In this study, the response mechanism of yield decline under abrupt drought-flood alternation stress at the panicle differentiation stage was analyzed by looking at the metabolome, proteome as well as yield and physiological and biochemical indexes. The results showed that drought and flood stress caused a decrease in the yield of rice at the panicle differentiation stage, and abrupt drought-flood alternation stress created a synergistic effect for the reduction of yield. The main reason for the decrease of yield per plant under abrupt drought-flood alternation was the decrease of seed setting rate. Compared with CK0 (no drought and no flood), the net photosynthetic rate and soluble sugar content of T1 decreased significantly and its hydrogen peroxidase, superoxide dismutase, peroxidase activity increased significantly. The identified differential metabolites and differentially expressed proteins indicated that photosynthesis metabolism, energy metabolism pathway and reactive oxygen species response have changed strongly under abrupt drought-flood alteration stress, which are factors that leads to the rice grain yield reduction.

[Effects of different nitrogen application rates on low temperature resistance of late rice at heading and flowering stage.] / 不同施氮量对晚稻抵御抽穗扬花期低温的影响.

Four levels of nitrogen application (N1, low nitrogen, 90 kg N·hm-2; N2, normal nitrogen, 180 kg N·hm-2; N3, high nitrogen, 250 kg N·hm-2; N4, ultra high nitrogen, 330 kg N·hm-2) were set to examine the effects of nitrogen application on the growth and development, yield formation and related physiological characteristics of late rice under low temperature condition during heading and flowering stage, with super hybrid late rice variety Wufengyou T025 as test material. The results showed that yield of all treatments decreased in different degrees under the low temperature conditions, with the yield of N2 being the highest, and N1 the lowest. The effective panicles per plant and total grains per panicle in N3 and N4 were higher than those of the other treatments, but their seed setting rate and harvest index were significantly decreased. With the increases of nitrogen application rates, pocketed panicle rate, the total dry mass and chlorophyll contents (SPAD value) increased to different extent, while the panicle dry mass of N2 was the highest. After low temperature, chlorophyll content, net photosynthetic rate and transpiration rate of the total treatments decreased to varying degrees, and the declined range of the net photosynthetic rate and trans-piration rate in N3 and N4 were higher than other treatments. The contents of free proline, malondialdehyde and peroxidase activity of all treatments increased to varying extent, while superoxide dismutase, catalyes activities and the soluble protein contents decreased, with the magnitude of variation in N3 and N4 being the greatest. It demonstrated that high amounts of nitrogen application were unfavorable to late rice to resist low temperature at heading and flowering stage and thus misuse of nitrogen fertilizer application should be avoided in production. The suitable amount of nitrogen application in double cropping late rice was not more than 180 kg·hm-2.

QTL mapping and correlation analysis for 1000-grain weight and percentage of grains with chalkiness in rice.

The study of 1000-grain weight (TGW) and percentage of grains with chalkiness (PGWC) is very important in rice. In this study, a set of introgression lines (ILs), derived from Sasanishiki/Habataki with Sasanishiki as the recurrent parent, were used to detect correlations and quantitative trait loci (QTL) on TGW and PGWC in two different environments. Phenotypic correlation analysis showed that there was no significant correlation between TGW and PGWC in both environments, which indicated that the linkage of TGW and PGWC traits could be broken via suitable population. A total of 20 QTL were detected in both environments, nine QTL for 1000-paddy-grain weight (PTGW), five QTL for 1000-brown-grain weight (BTGW) and six QTL for percentage of grains with chalkiness (PGWC). Moreover, five QTL, qPTGW3, qPTGW8.2, qPTGW11.1 for PTGW and qPGWC1.1, qPGWC1.2 for PGWC, were stably expressed in both environments. Phenotypic values were significantly different (P < 0.01) between the introgression lines carrying these five QTL alleles and the genetic background parent, Sasanishiki. The introgression lines carrying these QTL also represent a useful genetic resource in the context of rice yield and quality improvement via a design-breeding approach.

[Low-phosphorus tolerance and related physiological mechanism of Xieqingzao B//Xieqingzao B/Dongxiang wild rice BC1F9 populations].

By the method of water culture, the low-phosphorus tolerance of 221 lines of Xieqingzao B//Xieqingzao B/Dongxiang wild rice BC1 F9 populations was indentified. The morphological indices including plant height, leaf age, yellow leaf number, and shoot dry mass as well as the physiological indices including MDA, soluble sugar, and shoot phosphorus content were measured, also, the phosphorus efficiency was calculated, and the correlations among the indices were analyzed. All the 221 lines had differences in the seven test indices, and the low-phosphorus tolerance lines under low-phosphorus stress had higher values of relative leaf age, relative plant height, relative shoot dry mass, and relative soluble sugar content, but lower values of relative yellow leaf number and relative malondialdehyde content. The relative shoot phosphorus content had less difference. Phosphorus efficiency was positively correlated with phosphorus utilization efficiency and phosphorus uptake efficiency, and the correlation between phosphorus efficiency and phosphorus utilization efficiency was at significant level (P < 0.01), suggesting that the low-phosphorus tolerance capability of the low-phosphorus tolerance lines was mainly attributed to the high phosphorus utilization efficiency of the lines, namely, low-phosphorus tolerance lines had stronger capability in synthesizing dry mass with per unit phosphorus uptake.