Salt Tolerance Evaluation Of Salix Linearistipularis And Its Salt Tolerance Differences Between Female And Male

Soil salinity is one of the major environmental factors affecting the productivity of agriculture and forestry.To survive under adverse conditions,plants have evolved intricate salt tolerance mechanisms,especially halophytes growing in high saline soils.Investigation of salt tolerance mechanisms may help identify plants that better cope with salinity.Moreover,the salt tolerant plants are important resources for the utilization and improvement of saline soils.Salix(Franch.)K.S.Hao,a member of the Salicaceae family,is a woody plant naturally distributed on the Songnen Plain saline-alkali land in the northeast of China.S.shows strong adaptability to salinity,so it can be used as an important tree species for greening and afforestation of saline-alkali land,and has great ecological and economic value.S.linearistipularis is a dioecious plant.In many dioecious plant species,there are differences in morphology,physiology,and heredity,as well as environmental adaptability between female and male plants.The species Salix linearistipularis and Salix matsudana Koidz.are willow species naturally distributed in northeast China.The Chinese willow(S.matsudana)is one of the most widely distributed and commonly cultivated willow species in China.In this present study,firstly,we analyzed and compared the morphological and physiological responses of two willow species(S.linearistipularis and S.matsudana)from different habitats to salt stress,and we evaluated the salt tolerance of S.linearistipularis.Secondly,to study the sexual differences of S.linearistipularis in salinity tolerance,the physiological and transcriptional responses to salinity of female and male cuttings were compared.Based on these studies,the following results are mainly obtained:(1)S.linearistipularis exhibited higher seed germination rates than S.matsudana under 100～200 mM NaCl,especially under 200 mM NaCl treatment,S.linearistipularis seeds still had a 25%germination rate,whereas S.matsudana seeds were completely unable to germinate.(2)S.linearistipularis exhibited higher seedling root Na+ efflux than S.matsudana under salt stress.Salt treatment in seedling stage showed that the Na+content in S.linearistipularis leaf was lower than that in S.matsudana leaf.(3)Under salt stress,S.linearistipularis leaves exhibited less damage to leaf cell structure than S.matsudana leaves.After 300 mM NaCl 48h treatment,S.linearistipularis leaf cell structure remained unchanged,whereas S.matsudana leaf cell structure was almost completely damaged.(4)S.leaves exhibited less chlorophyll loss and reduction in photosynthetic capacity than leaves of S.matsudana under salt treatment.(5)Scanning electron microscopy combined with gas chromatography mass spectrometry showed that S.linearistipularis leaves had higher cuticular wax loads than S.matsudana leaves.Moreover,the water loss rate of S.linearistipularis leaves under salt stress was significantly lower than that of S.matsudana leaves.(6)Under salinity stress,the female leaves showed higher superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT)activities and photosynthetic abilities,and lower H2O2 content than the male leaves.(7)Gene expression analysis showed that the expression level of three antioxidant enzyme genes in female leaves was higher than that in male leaves under salt stress.(8)Under salinity stress,sodium(Na+)accumulation in female leaves was lower than that in the male leaves.The non-invasive micro-test showed that the net Na+ efflux in the salt-treated female roots was higher than that in male roots.(9)Physiological responses revealed that female cuttings are better salinity tolerant than males,which may be mainly due to females having less leaf Na+accumulation and stronger root Na+ efflux ability than males.Transcriptional analysis showed that 108 differentially expressed salt-responsive genes were identified in both female and male roots;most of these showed sexual differences in expression patterns under salinity stress.(10)RNA-seq combined with qPCR analysis showed that the salt-induced expression of four Na+/H+ antiporter(NHX)genes in female roots was higher than that in male roots.Furthermore,three NHX gene sequences in male and female are identical,and they may be mainly localized in the cell inner membrance system.In a word,we identified differences in salinity tolerance between S.linearistipularis and S.matsudana,and female and male plants of S.linearistipularis by the comparison of salt-tolerant morphology,physiological traits and transcriptional profiling.Two major conclusions are summarized:First,our results showed that S.linearistipularis had higher salt tolerance than S.matsudana,which was associated with different morphological and physiological responses to salt stress.Second,in female roots,the differential expression of salt-response genes,especially NHXs,may cause stronger Na+efflux,which further leads to less Na+accumulation in leaves than in male roots.Lower Na+accumulation in female leaves may be associated with higher antioxidant enzyme activity and lower H2O2 levels.Therefore,our study suggested that S.linearistipularis could be a promising tree species for saline-alkali land greening and improvement.And in the afforestation process of S.linearistipularis for greening and ecological restoration of saline-alkali soil in the future,different salinity tolerance characteristics of females and males should be considered.