Influence Of Methyl Jasmonate On The Morphological And Physiological Properties Of Oryza Sativa L.under Salinity Stress

Rice(Oryza sativa L.)is a major contributor to food security as it provides more than half of the world’s population with calorific input and is cultivated in more than 100 countries.Climate change and environmental problems,such as drought,fluctuation in temperatures,and soil salinity,impact rice yield in arid and semiarid regions around the world,especially in the costal saline regions.Many factors curtailing affect rice production.This study insight changes in some influential factors such as biochemical,physiological traits(florescence and photosynthesis),Na+/K+homeostasis,and OsHKT genes expressions,and further studied the alleviative effect of methyl jasmonate on morphological and physiological characteristics of rice under salt stress,which would provide a theoretical basis for the cultivation of highquality and high-yield rice in the saline area.The main results are as below:1.In this experiment,we studied ten rice cultivars at germination and early seedlings stage under different concentrations of salinity stresses "0,6.4,12.8,19.2,and 25.6 dS/m(NaCl)".We investigated the impact on final germination percentage,speed of germination,germination capacity,shoot length,root length,seedling vigor index,and total plant dry weight to evaluate cultivars at germinating and seedling stage.Salinity stress significantly decreased the final germination percentage,speed of germination,germination capacity shoot and root length,and seedling dry weight in all cultivars,and it was severely affected by 19.2 and 25.6 dS/m NaCl.The most limiting factor at high NaCl concentration was the dry matter;therefore,based on reduction in it,rice cultivars were classified as tolerant,moderately tolerant,moderately susceptible,and susceptible.Rice cultivars NJ9108,3Y9H,6Y9H,XD22,5W01,and HLYH3,showed greater efficiency in salt tolerance during germination at 19.2 dS/m salinity.However,20H025,6Y9H,and XD22 performed better based on their dry weight reduction in the seedlings stage.The findings suggested that NJ9108 and XD22 might be used to investigate the effects of salinity on development processes and physiological consequences at the advanced stage of growth,as salt tolerance during germination and the early seedling stage may be varied from the developed stages.2.This experiment aims to elucidate the influence of methyl jasmonate,which plays a crucial role in regulating growth and development under salt stress.Salinity stress increased the MDA and H2O2 activities while decreasing the antioxidant activities of rice seedlings.However,we observed that MeJA at 125 μM and slightly at 250 μM could delay the leaves from drying and increase the length of the first and second leaf in both cultivars at both salinity treatments.Plants treated with MeJA promoted the plant height,leaves length,root length and root numbers per plant.Under higher salt stress,seedlings also responded to MeJA by enhancing fresh weight,dry weight and water contents compared to non-treated MeJA.At higher saline conditions(100 μM),foliar application significantly promoted the chlorophyll a,b and total chlorophyll contents and preserved the RWC in the seedling.Salinity stress(100 mM NaCl)significantly reduced the leaf MSI in both cultivars;however,it slightly enhanced by 4.6%and 5.4%in NJ9108 and XD22,respectively,when treated with MeJA.The total soluble sugar increased by 19.72 and 22.66%,and proline contents by 6.67,and 7.81%in the NJ9108 and XD22,respectively,by spraying MeJA(S2C2),under salinity stresses.These findings provides evidence that the exogenous MeJA has an encouraging influence on rice seedlings when exposed to salinity.3.In this pot experiment,we investigated the influence of MeJA on two rice cultivars(NJ9108 and XD22)under different salinity stresses.Salinity stress reduced the water use efficiency,relative water contents,and membrane stability index in both cultivars,whereas MeJA treatment partially alleviated the negative effects.MeJA treatment significantly increased the maximum photochemical efficiency(Fv/Fm)and electron transfer to photosystem Ⅱ(Fv/Fo).Under salinity stress,only MeJA treatment significantly triggered the H2O2,and APX accumulation,while POD and SOD remained unchanged in both cultivars.Salt stress increased Na+concentration in the roots and leaves but decreased K+concentration and the K+/Na+ratio in both cultivars.However,MeJA-treated plants had the maximum K+accumulation in both leaves and roots under saline conditions.The differential expression pattern of OsHKT and OsHAK genes implied that ion homeostasis is crucial to growth under salt stress.These findings suggest that MeJA can be an alternative source of reducing salinity stress and improving rice growth in field conditions.4.The high-affinity potassium transporter(HKT)genes are key ion transporters,regulating the plant response to salt stress via sodium(Na+)and potassium(K+)homeostasis.The main goal of this research was to find and understand the HKT genes in rice and their potential biological activities in response to brassinosteroids(BRs),jasmonic acid(JA),seawater,and NaCl stress.The in silico analyses of seven OsHKT genes involved their evolutionary tree,gene structures,conserved motifs,and chemical properties,highlighting the key aspects of OsHKT genes.The Gene Ontology(GO)analysis of HKT genes revealed their roles in growth and stress responses.Promoter analysis showed that the majority of the HKT genes participate in abiotic stress responses.Tissue-specific expression analysis showed higher transcriptional activity of OsKT genes in roots and leaves.Under NaCl,BR,and JA applications,OsHKT1 was expressed differentially in roots and shoots.Additionally,the Na+to K+ratio under different concentrations of NaCl stress has been evaluated.Our data highlighted the important role of the OsHKT gene family in regulating the JA and BR mediated rice salinity tolerance and could be useful for future rice breeding programs.