Research On The Changes Of Seed Vigor And Protection Mechanism Of Mature Dehydration During Wheat Seeds Development

Seed vigor is formed in the process of seed development which as a key index to reflect the seed quality.The seeds were dehydrated in the process of maturation in wheat,and the seed vigor was changed at the same time.Moreover,the environmental temperature also had an effect on the formation of seed vigor.Wheat seeds were not able to germinate in the early developmental stages,while the more mature seeds could be with germination ability,and the fresh seeds that with no germination ability maybe germinate through the desiccation,indicating that the dehydration plays a crucial role in the formation of seed vigor.However,little research has been focused on the physiological and biochemical basis of the mature dehydration of wheat seeds,and the complicated interaction between the various mechanisms were still unclear.Our experiment was carried out to study the changes of seed vigor at different development stages and its response to environmental temperature,and the protection mechanism of mature dehydration in wheat seeds was explored from the physiological and molecular level at the same time,which will has a certain meaning and reference value to deep the understanding of development process and the protection mechanism of mature dehydration in wheat seeds.Two wheat cultivars(Jimai 22 and Shannong 23)were selected as experimental materials in this research.The main stem that with the same growth trends and flowered on the same day were chosen and tagged.The basal kernels from the middle part of ears were collected from 5 day after anthesis(daa)to full ripe stage every 2~3 day to study the changes of seed physical morphology and seed vigor,as well as the response of the mature dehydration mechanism during wheat seeds development.The main results were as follows:1.The changes of seed vigor at different developmental stages in wheatThe germination ability of fresh seeds was appeared around 26 daa in Jimai 22 and Shannong 23,and then the germination rate of fresh seeds displayed an overall upward trend during the wheat seeds development.The germination energy,germination rate and germination index of dry seeds were rapidly increased from 5 to 8 daa,and then remained stable relatively,while the vigor index of two cultivars increased continually and reached the peak in 32 or 34 daa respectively in 2015 and 38 or 42 daa in 2016,which effected by the increase of seedling dry weight.The dry seeds of different developmental stages were also studied by field-planting and the seed vigor of their progenies was also determined.For Jimai 22,the results indicated that on the one hand,the field emergence of dry seeds at 17 daa were higher and the plant could be formed grains,on the other hand,there were no significant differences on germination rate and vigor index among different progeny seeds.2.The response of seed vigor at different developmental stages to environmental temperature in wheatThe changes of seed vigor at different development stages were significant effected by the environmental temperature,when the year with the high mean daily average temperature,high mean daily maximum temperature,high mean daily minimum temperature after anthesis,and big mean daily temperature difference after anthesis,the seed development time was shorter,but 100-grain weight and seed vigor reached the peak earlier,otherwise,the seed development time was longer,but the 100-grain weight and seed vigor reached the peak later.There was a significant positive correlation between the accumulated temperature after anthesis and seed vigor index or 100-grain weight during wheat seeds development,the seed vigor and 100-grain weight were higher in the year of high accumulated temperature after anthesis at full ripe stage.3.The changes of related physiological indexes during the process of mature dehydration in wheat seedsIn the process of seed mature dehydration(32~38 daa),the MDA content of fresh seeds showed a slight increase,while the SOD,POD activity,soluble protein and soluble sugar content were all increased to protect the seeds from dehydration damage,these protective substances played an important role in mature dehydration mechanism of wheat seeds,but it was difficult to establish a relationship between the CAT activity and seeds mature dehydration.4.Comparative proteome analysis during the process of mature dehydration in wheat seedsA total of 128 proteins showed that at least 1.5-fold differences in abundance were found during seeds development in this research,and most of which were related to stress/defense,storage proteins and oleosin,photosynthesis,energy metabolism,starch and sucrose metabolism,protein synthesis/assembly/degrade,lipid metabolism,signal transduction,transcription/translation,cell division,and unknown.DAPs that involved in the stress/defense were closely related to the mature dehydration of wheat seeds,in which five late embryogenesis abundant proteins(LEAs),five Sperins,a heat shock cognate 70 kDa protein and 17.7 kDa class I Heat shock proteins were all up-regulated and reached their highest expression at 38 daa.Moreover,starch and sucrose metabolism was also associated with the mature dehydration of wheat seeds with the Trehalose-6-phosphate synthase 7 increasing in abundance during middle and late stages of wheat seed development.