Effect Of Salinity On Seed Germinationof Mulberry Seeds From Different Regions And Alleviating Function Of Exogenous GA₃ And Calcium

Soil salinization is a worldwide problem of resources and ecology,which seriously affects the growth and yield of crops.The soil salinization and secondary salinization are becoming more and more serious.Therefore,breeding of salt tolerant varieties has become a problem to be solved.Gibberellin is a kind of plant hormone,which is involved in the regulation of seed germination,leaf expansion,stem elongation and flowering,and plays an important role in the process of plant adaptation to salt stress.Calcium plays an important physiological role in plants and is involved in the whole process of plant life,and it can also improve the salt tolerance of plants.Mature seeds of mulberry（Morus L.）were collected from the open field in three different regions including Hetian,Harbin and Haian,which belong to the region or provinces of Sinkiang,Heilongjiang and Jiangsu,respectively in China.These seeds were exposed to different salt stress and the relative germination rate,osmotic adjustment substances and antioxidant enzyme activity were analyzed to study the physiological responses to NaCl inthe germinated seedlings.Furthermore,real-time PCR was also performed to analyze the transcriptional expression patterns of POD1（Cationic peroxidase 1）and sodC（sodC protein）in the Harbin seeds.Then the seeds from the field of Hetian were used as experimental materials to study the effect of exogenous GA₃ and CaCl₂ on the fresh weight,root length,germ length,contents of soluble protein,soluble sugar and proline and POD activity under salt stress,and evaluate the optimal concentrations of exogenous GA₃ and CaCl₂ for enhanced salt tolerance.The main results and conclusion were as follows:1.The relative germination rates of three different types of seeds decreased with the increase of NaCl concentration;In contrast,both proline content and soluble protein content always declined continuously under the same condition of NaCl stresses;The soluble sugar contents and SOD activities in the seedlings above showed a wave-like pattern,i.e.,increased initially and then declined with the increase of NaCl concentration.The results confirmed that the mulberry tree has the potential to develop and apply in saline alkali land,and the salt tolerance of mulberry seeds from the region of Hetian is the best.2.The changes of POD1 gene and sodC gene transcription level and corresponding enzyme activities in germinated seedlings were studied by using mulberry seeds from Harbin as experimental materials.Real-time PCR result showed that the expression patterns of POD1 and sodC did not coincide with its enzyme activity,respectively.The results also suggested that the transcription level of POD1 gene and sodC gene could not be the only one to evaluatethe salt tolerance of the mulberry tree.3.The GA₃ solution with different concentrations was added to the seeds from Hetian under the salt stress of 5g/L NaCl solution.The fresh weight,root length,germ length,soluble protein content,soluble sugar content and proline content of the seed germination of mulberry seed increased initiallyand then decreased with the increase of GA₃ concentration,and the increase was the highest in the G2 treatment group,while the change of POD activity showed a tendency to decrease first and then increase.The results showed that the addition of 10 ug/mL GA₃ solution had the best effect,and the results also showed that exogenous GA₃ could alleviate salt damage by promoting the growth of germ.4.The CaCl₂ solution with different concentration gradient was added to the seeds from Hetian under the salt stress of 5g/L NaCl solution.The fresh weight,root length,germ length,soluble protein content,soluble sugar content and proline content of the seed germination of mulberry seed increased first and then decreased with the increase of CaCl₂ concentration,and the increase was the highestin the C3 treatment group,While the change of POD activity showed a tendency to decrease first and then increase.The results showed that the addition of 10 mmol/L CaCl₂ solution had the best effect,and the results also showed that exogenous CaCl₂ could alleviate salt damage by promoting the growth of radicle.