| Phosphorus(P)is one of the essential macronutrient elements for plant growth and development.It is also the important component for many metabolites and macromolecular substances in plants,such as nucleic acids,phospholipids,protein,etc.,and participates in the energy transfer,fat metabolism,signal transmission,photosynthesis and respiration,and plays an important role in crop growth and development,resistance,yield and quality formation.Rice(Oryza Sativa L.)is one of the most important staple food in the world.The low absorption and utilization of phosphorus fertilizer is a prominent problem in the rice production.It is a research hotspot at home and abroad to increase phosphate use efficiency of rice.Our earlier work has shown that there were differences in the tolerance to low phosphorus among rice varieties and the varieties with strong tolerance to low phosphorus(the yield and phosphorus use efficiency were higher under low phosphorus stress)were selected.However,the mechanism underlying strong tolerance to low phosphorus remains unclear.It would be of great significance to elucidate the agronomic and physiological characteristics of the varieties with strong tolerance to low phosphorus for breeding and selecting the varieties and the cultivation regulation of high yield and high phosphorus efficiency.In this study,the rice varieties with differences in tolerance to low phosphorus were used as materials to investigate the agronomic and physiological characteristics of shoots,root morphological and physiological traits,phosphorus accumulation and distribution,gene transcriptome analysis and cultivation regulation techniques.The main results are as follows.1.The agronomic and physiological characteristics of shoots of rice varieties with tolerance to low phosphorusTwo varieties with strong tolerance to low phosphorus,Yanjing 2(YJ2)and Yongyou 2640(YY2640),and two varieties with weak tolerance,Zhendao 88(ZD88)and Liming(LM),were grown at normal(NP)and low phosphorus(LP,1/20 P concentration of the NP)concentrations using nutrient solution culture to investigate the agronomic and physiological characteristics of shoots.The results showed that plants grown at LP produced significantly lower grain yield than those grown at NP.The reduction in grain yield was mainly due to that the increase of seed-setting rate and 1000-grain weight could not compensate for the decrease of the number of panicles and spikelets per panicle.The reduction in grian yield was less for the varieties with strong tolerance to low phosphorus than for the varieties with weak tolerance to low phosphorus.Compared to NP,LP reduced the tiller number,shoot biomass,non-structural carbohydrate(NSC)accumulation,leaf area index(LAI),leaf photosynthetic rate,the contents of auxin and cytokinin in leaves,with more reduction for the the varieties with weak tolerance to low phosphorus.Compared to NP,LP increased the number of productive tillers,remobilized NSC reserve,and NSC contribution to grain.The results indicate that rice varieties with strong tolerance to low P have better agronomic and physiological performances in shoots under LP stress.2.The root morphological and physiological traits of rice varieties with tolerance to low phosphorusTwo varieties with strong tolerance to low phosphorus,Yanjing 2(YJ2)and Yongyou 2640(YY2640),and two varieties with weak tolerance,Zhendao 88(ZD88)and Liming(LM),were grown at normal(NP)and low phosphorus(LP)concentrations in nutrient solution to investigate root morphological and physiological traits.The results showed that compared to NP,LP significantly decreased the mean root diameter and cytokinins(trans-zeatin+trans-zeatin riboside)contents in roots of both varieties at the main growth stages,but the reduction was less for the varieties with strong tolerance to low phosphorus than for the varieties with weak tolerance to low phosphorus.LP significantly increased the root biomass,root-shoot ratio,root bleeding rate and root acid phosphatase activity.Total root length,root oxidation activity,root total and active absorbing surface areas,and auxin contents in roots for varieties with strong tolerance to low phosphorus were significantly increased under LP,and the endoroot aerenchyma formation,number of mitochondria and endoplasmic reticulum in root tip cells were increased obviously at tillering stage,whereas the opposite responses were observed for varieties with weak tolerance to low phosphorus.Correlation analysis showed that root morphological and physiological traits were closely associated with aboveground agronomic and physiological characteristics at the main growth stages.These results suggest that large biomass and high root activity are the main root traits of the varieties with strong tolerance to low phosphorus.3.The phosphorus accumulation and distribution of rice varieties with tolerance to low phosphorusThree varieties with strong tolerance to low phosphorus,Yanjing 2(YJ2),Guihuaqiu(GHQ),and Yongyou 2640(YY2640),and two varieties with weak tolerance,Zhendao 88(ZD88)and Liming(LM),were grown at normal(NP)and low phosphorus(LP)concentrations in nutrient solution to investigate phosphorus accumulation and distribution in plants.The results showed that the reduction in grain yield was less for the varieties with strong tolerance to low phosphorus than for varieties with weak tolerance to low phosphorus.Compared to NP,LP increased the phosphorus translocation efficiency(PTE),internal phosphorus efficiency(IPE)and phosphorus harvest index(PHI).Under the LP condition,PTE and IPE were higher for the varieties with strong tolerance to low phosphorus than for the varieties with weak tolerance to low phosphorus.Under LP,the phosphorus accumulation of stems and sheaths,leaves,roots and grains,and phosphorus dry matter production efficiency of stems and sheaths and leaf at main growth stages were significantly higher for the varieties with strong tolerance to low phosphorus than for the varieties with weak tolerance to low phosphorus.The leaf and root acid phosphatase activity were higher for the varieties with strong tolerance to low phosphorus than for varieties with weak tolerance to low phosphorus.The results indicate that more phosphorus could be absorbed and transported to shoots and grains for the varieties with strong tolerance to low phosphorus,leading to higher phosphorus use efficiency of dry matter production and IPE under low phosphorus stress.4.The RNA-seq analysis for rice varieties with tolerance to low phosphorusTwo varieties,one with strong tolerance to low phosphorus,Yanjing 2(YJ2)and the other with weak tolerance,Zhendao 88(ZD88),were grown at normal(NP)and low phosphorus(LP)concentrations in nutrient solution to investigate the RNA-seq analysis.The results showed that 2183 differential expressed genes(646 up-regulated genes,1537 down-regulated genes of YJ2 and 1168 differential expressed genes(805 up-regulated genes,363 down-regulated genes of ZD88)were identified in roots.In leves,1243 differential expressed genes(623 up-regulated genes,620 down-regulated genes of YJ2 and 610 differential expressed genes(266 up-regulated genes,344 down-regulated genes of ZD88 were identified.Kyoto encyclopedia of genes and genomes(KEGG)and gene ontology(GO)enrichment analysis indicated that these differential expressed genes in roots were mainly reflected in biological processes such as secondary metabolic biosynthesis,plant-pathogen interaction,RNA degradation,carbon metabolism,plant hormone signal transduction and phosphate ion transport under LP.These differential expressed genes in leaves were mainly reflected in the biological processes of secondary metabolites biosynthesis,photosynthesis,metabolism of starch and sucrose,plant hormone signal transduction and antioxidant enzyme system.These results suggest that these important biological processes play an important role in the adaptation of rice to low phosphorus stress.Meanwhile,compared with the variety with week tolerance to low phosphorus,the variety with strong tolerance to low phosphorus showed stronger abilities of auxin regulation,starch synthesis,photosynthesis,and scavenging reactive oxygen species under low phosphorus stress.5.Effects of alternate wetting and drying irrigation on grain yield and phosphorus use efficiency of riceTwo varieties,one with strong tolerance to low phosphorus,Yanjing 2(YJ2)and the other with weak tolerance,Zhendao 88(ZD88),were grown in pots.Two phosphorus levels of low phosphorus treatment(LP)and normal phosphorus treatment(NP)and two irrigation regimes,continuous flooding(CF)and alternate wetting and moderate soil drying(AWD)were conducted duing the whole rice growing season.The effects of alternate wetting and drying irrigation on grain yield and phosphorus use efficiency of rice were investigated.The results showed that compared to NP,LP decreased the grain yield,the decrease in yield varied with varieties.YJ2 exhibited stronger tolerance to LP than ZD88.Compared to CF,the plants grown with AWD produced higher grain yield,water use efficiency,and partial factor productivity and agronomic efficiency of phosphorus fertilizer,and the performance of YJ2 was better than that of ZD88.Under LP,YJ2 had higher ratio of productive tillers,root dry weight,root-shoot ratio,the remobilization of NSC from stems to the grain,activities of root acid phosphatase in roots and peroxidases in grains.Adoption of alternate wetting and drying irrigation could synergistically improve grain yield and phosphorus use efficiency of rice,especially under low phosphorus stress.6.Effects of phosphorus application rates on grain yield and phosphorus use efficiency of riceTwo varieties,one with strong tolerance to low phosphorus,Yanjing 2(YJ2)and the other with weak tolerance,Zhendao 88(ZD88),were grown in pots.Five phosphorus rates were applied,i.e.,T1,6.8 mg kg-1;T2,20.1 mg kg-1;T3,33.4 mg kg-1;T4,46.9 mg kg-1;and T5,60.2 mg kg-1.The effects of phosphorus application rates on grain yield and phosphorus use efficiency of rice were investigated.The results showed that with the increase of phosphorus application rates,grain yield of the two varieties was increased gradually.The grain yield was the highest under T4.With the increase of phosphorus application rates,both partial factor productivity and agronomic efficiency of phosphorus fertilizer were decreased significantly.Regression analysis showed that when the maximum grain yield was the similar for both varieties,the optimum soil phosphorus level was lower for YJ2 than for ZD88.Under lower phosphorus application rates,YJ2 had higher tiller number,ratio of productive tillers,shoot dry matter weight,root dry weight,leaf chlorophyll value(SPAD)and root oxidation activity.The results suggest that for the varieties with strong tolerance to low phosphorus,the phosphorus application rate could be appropriately reduced,and high yield and phosphorus use efficiency could be obtained.The better aboveground and root traits account for the improvement in high yield and phosphorus use efficiency of the varieties with strong tolerance to low phosphorus. |
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