Effects Of Salt Stress On Rice Young Panicle Development

Rice(Oryza sativa),as an important food crop,is the main source of food for two-thirds of the world’s population,especially for the residents of Asia and Africa.The panicle primordium differentiation and development stage is a key period for rice yield formation,and it is also a period particularly sensitive to salt stress.At present,little has been known about the effect of salt stress on rice panicle development.It is necessary to study the sensitive period and tolerance level of salt during panicle development stage.Also,the morphological and physiological changes of rice plants under salt stress conditions,and differential expression and isolation of salt-tolerance-related genes are both necessary to study.They have extremely important theoretical and practical significance for further revealing the mechanism of rice salt tolerance,cultivating salt-tolerant rice varieties,and guiding the production of rice in saline-alkali regions.In this study,two varieties,58M(higher salt tolerance)and 58L(lower salt tolerance)with different salt tolerances,were used as test materials with potted method.The young panicles of rice irrigated with running water were used as control group.The 58 M and 58 L were treated with 0.2%,0.4%,and 0.6% Na Cl as treatment group.The development morphology of young panicles,primary branch,secondary branch and spikelet degradation status,pollen activity were observed.Meanwhile,the content of malondialdehyde(MDA),soluble sugar(SS)soluble protein(SP)content,proline(Pro)content and superoxide dismutase(SOD)activity were measured in young panicles.The 58 M and 58 L were treated with 0.6% Na Cl for 0 h,6 h,and 24 h to select young panicles to transcriptome sequencing analysis and analyze the differential expression of genes after salt stress.The main research results were as follows:1.After the salt stress treatment,the development of the panicles of two test materials at the heading stage was investigated,and it was found that the effects of salt stress on the differentiation and development of the young panicles of the two test materials were different.Under the treatment of relatively low salt concentrations(0.2% Na Cl),the morphology of the young panicles of 58 M changed little.When the salt concentration continued to increase,the influence of salt stress on young panicles began to appear.While the 58 L showed obvious inhibitory effect ubder all the stress under all treatment of salt concentration.The statistics of the primary and secondary branch degeneration rate,spikelet degradation rate and pollen abortion rate of the two varieties showed that low salt stress mainly affected the differentiation of secondary branch differentiation,and high salt stress mainly caused spikelet degeneration.When58 M was treated with 0.6% Na Cl,the degradation rates of primary branches,secondary branches,and spikelets were 12.92%,42.15%,and 19.56%,respectively.While under the same salt stress,58 L primary and secondary branches and spikelets degeneration rates were 9.14%,41.53% and 67.5%,which were significantly higher than 58 M.2.Throughout the process of salt stress,the MDA content of 58 L young panicles showed a continuous upward trend,while the MDA content of 58 M young panicles showed a "rising-falling-rising" change.The SOD content of young panicles increased gradually with the growth process under salt stress.Among them,the SOD content of58 M increased more and was always significantly higher than 58 L.Under salt treatment,the soluble sugar content,the soluble sugar content,and the content of proline in the young panicles of the two rice varieties showed a continuous increasing trend,while the content of soluble protein showed different trends.Throughout the process of salt stress,the changes of soluble sugar content and proline content showed that salt stress promoted the accumulation of soluble sugar and proline in rice.Under high salt(0.6% Na Cl)stress,the 58 M strain could produce more soluble sugars and free proline to alleviate the inhibition of salt stress than the 58 L strain,showing stronger salt tolerance.The soluble proteins in the young panicles of the two varieties at different periods showed different trends,reflecting the complexity of protein dynamic changes in plants under salt stress.3.Transcriptome analysis was performed on the young ears of the 58 M and 58 L lines after 0,6,and 24 h of salt stress.Taking the young ears of 0 h as a control,there were 1483 up-regulated and 1085 down-regulated 58 M differential genes after 6 h ofsalt stress;The 58 L had 931 up-regulated differential genes,2614 down-regulated differential genes.937 differential genes were up-regulated and 459 were down-regulated of 58 M after 24 h of salt stress treatment.58 L had 930 up-regulated differential genes and 1299 down-regulated differential genes.Compared with the difference genes of 6h and 24 h under salt stress,there were 1189 up-regulated and1164 down-regulated genes of 58 M under salt stress.There were 2439 differentially expressed genes up-regulated and 808 down-regulated in 58 L.At 0 h,6 h,24 h of salt stress,the differential genes of 58 M and 58 L were analyzed at the same time.Compared with 58 M,58L had 2472 up-regulated genes and 3669 down-regulated genes at 0 h,had 2409 up-regulated genes and 5292 down-regulated genes at 6 h;had1930 up-regulated genes and 4061 down-regulated genes at 24 h.Through the enrichment analysis of these differential genes with GO and KEGG,we can determine the pathways and molecular functions.After GO function annotation and KEGG Pathway analysis,it was found that these differentially expressed genes were mainly involved in phenylpropane biosynthesis,photosynthesis-antenna protein,photosynthesis,metabolic pathway,terpene biosynthesis,flavonoid biosynthesis,phenylalanine metabolism,protein processing in endoplasmic reticulum,and other pathways closely related to salt tolerance.