| Salt stress seriously affects the yield of crops around the world,and is one of the important environmental stresses that has caused grain yield decrease.Therefore,it is very important for the world food security to screen and identify good salt tolerant crop germplasm resources.In this study,33 traditional landraces collected from Lei-Qiong area of south China were analyzed,by employing Nona bokra(salt tolerant control)and IR29(salt sensitive control)from International Rice Research Institute as control materials.The salt tolerant local landraces were selected first.Then,phenotypic traits,physiological performances and biochemical regulations of the salt tolerant materials and the control samples were observed and analyzed in germination,seedling and mature stages respectively.The mechanism of salt tolerance of rice landraces in LeiQiong area was discussed.The results are as follows:(1)The 33 rice landraces collected from Lei-Qiong area were incubated in aqueous solution with 0.5% Na Cl(during three leaves and one heart period).By combination of the indoor and outdoor screening results,salt-tolerant rice landraces C24,C34,and C6 were selected.(2)Two of the salt-tolerant landraces C34,C24 and one less salt-tolerant rice HG1 combined with two control samples were used as experimental materials for further study,Na Cl concentrations in used for germination rate analysis were 0 m M,50 m M,100 m M,150 m M,200 m M,250 m M and 300 m M,respectively.The relative damage rate,and shoot/root inhibition rate of these materials were observed after salt treatments.The results showed that increase of salt concentration,caused more salt damage on rice.The germination rate was gradually reduced,whereas the salt damage rate and inhibition rate were gradually increased when salt concentration increased.C24 and C34 were less affected by salt damage when compared with other samples,showing good salt resistance at germination stage.(3)These five materials were tested for phenotypic traits at the seedling stage with salt concentrations of 0m M,80 m M,100 m M,120 m M,and 150 m M.The results showed that C24 and C34 performed better than other rice samples.These two salt-tolerant rice landraces showed less chlorosis symptoms under salt stress,which indicated that they had better water-holding ability.In addition,the content of MDA,soluble sugar and proline,and activities of ROS,CAT and POD were measured at seedlings stage after treated with 100 m M Na Cl for 5 days and 10 days,respectively.Less cellular membrane damage and a stronger antioxidant enzyme system were found in two Lei-Qiong rice samples.Studies have shown that traditional rice landraces grown along the coast of Lei-Qiong in China have good salt tolerance at seedling stage.(4)The above materials were tested for salt tolerance at maturity after treated during three leaves and one heart period.Under 0 m M,80 m M,100 m M,120 m M,and 150 m M salt treatments.It was found that Lei-Qiong landraces had better performances in plant heights,highest panicle length,and thousand grain weight.(5)Two salt tolerant related genes,Os HAL3 and Osi SAP8,were cloned from rice C34,C24 and HG1,which were treated in Na Cl solution for 10 days.The sequences of these two genes were sequenced and analyzed.It was found that there was no difference in the sequence of Os HAL3 gene among the three local landraces of Lei-Qiong area.Interestingly,there was difference of a base pair within the sequence of Osi SAP8 between C34,C24 and HG1.Followingly,the protein sequences of this gene between different samples were compared.The result showed that there was a difference in the translated amino acid within this protein,in which the target site of amino acid sequence was cysteine in C34 and C24,whereas arginine in HG1 and Nippon bare,suggesting the change of salt tolerance gene sequences may,to certain extent,be ralated to differences in salt tolerance of the holders,however,futher comfirm needed.(6)The transcriptome of Nona Bokra,C34 and IR29 were measured after six hours of 100 m M salt treatment.The results of RNA-sequencing showed that there were a large number of differentially expressed genes in different samples,which fully showed that salt stress induced a large number of gene expression fluctuations.It can be seen from the annotation analysis of GO and KEGG that a large number of genes have been annotated into plant hormone signal transduction,carbon metabolism,amino acid biosynthesis,porphyrin and chlorophyll metabolism,photosynthesis antenna protein,biological carbon fixation in photosynthesis,fatty acid degradation,glycolysis and other pathways,indicating that salt stress has a significant impact on plant photosynthesis function,pigment synthesis and so on,in C34,Nona Bokra and IR29.In addition,it can also be seen that DEGs annotated by amino sugar and nucleotide sugar metabolism,valine,leucine and isoleucine degradation,starch and sucrose metabolism,arginine and proline metabolism,endoplasmic reticulum protein processing and other pathways are more up-regulated in C34,while DEGs annotated by ribosome and pyrimidine metabolism are more down-regulated in IR29.Therefore,it is speculated that the large differences in the salt tolerance regulatory networks of different rice landraces may lead to the different salt tolerance between the three rice samples.Based on the above results,we preliminarily discussed the molecular mechanism of salt tolerance of different rice samples,and concluded that some of Lei-Qiong landraces,such as C34 and C24,had better salt tolerance.Under salt stress,they permormed better in germination rate,growth inhibition,water-holding capacity,chlorophyll content,osmoregulation substance accumulation,cell membrane damage,antioxidant enzyme system,etc.Next,the difference in the sequence of a salt tolerence related gene(protein)was also found between the salt tolerant and salt sensitive samples.At last,the results of transcriptome analysis showed that amino sugar and nucleotide sugar metabolism,valine,leucine and isoleucine degradation,starch and sucrose metabolism,arginine and proline metabolism,endoplasmic reticulum protein processing and other related genes were up-regulated in local salt tolerant landrace,while ribosome,pyrimidine metabolism and other pathways annotated related genes were less down-regulated in comparison with IR29.These differences,together with the potential sequence varieties in salt tolerant genes,may be the main reasons of that some Lei-Qiong rice landraces are more salt-tolerantt. |
PDF Full Text Request