Study On The Mechanisms Of Salt Resistance In Dimorphic Seeds Of Suaeda Salsa During Germination

For the purpose of understanding the mechanisms of salt resistance in dimorphic seeds of Suaeda salsa during germination, the effect of storage on seed vigor was investigated in two S. salsa populations. In addition, some differentially expressed genes were found by the transcriptome analysis between dry and 300 mM NaCl treated dimorphic seeds of S. salsa from inland saline soils. The results were as follows:1. The effect of storage on seed germination?seed vigor? in two S. salsa populations under salinityThe germination of fresh seeds?brown and black seeds were dried and stored in a refrigerator at < 4oC for one month? and old seeds?brown and black seeds were dried and stored in a refrigerator at < 4oC for one year? was treated with 0 or 600 mM NaCl. Germination was inhibited by salinity in both fresh and old seeds from the inland population. Salinity had no effect on the germination of fresh brown seeds, but salinity decreased the germination of fresh black seeds and old seeds from the intertidal population. Storage increased seed germination, especially black seeds for the inland population, but the opposite trend was shown for the intertidal population. For the intertidal population, salinity had no adverse effect on the total germination of black and brown seeds, with the exception of old brown seeds. Storage increased the total germination of black seeds for the inland population, while storage had no effect on the total germination of brown seeds regardless of salinity. Storage invariably decreased the total germination in black and brown seeds from the intertidal population irrespective of salinity, especially for brown seeds. A similar trend was shown in the germination index. In conclusion, brown seeds of S. salsa may presently play a more important role than black seeds in the establishment of populations, while black seeds may subsequently play more important role for the survival process for both S. salsa populations in saline environment, especially for the intertidal population.2. The effect of storage on contents of certain substances related to seed vigor in two S. salsa populationsStorage had no significant effect on the contents of H₂O₂ and O2·- with the exception of O2·- content increased in brown seeds from the intertidal population after storage. Activity of SOD decreased in both fresh and old seeds from the two populations during storage. This suggests that the decrease of SOD activity and the increase of O2·- content may be associated with the seed vigor decline in the intertidal population. The content of seed coat phenolics in brown seeds was much higher than black seeds in both populations regardless of extracting time and storage. Storage increased the content of phenolics in brown seeds in the inland population, but the opposite trend was shown in the intertidal population regardless of extracting time. Storage did not significantly change the seed coat phenolics in black seeds compared to brown seeds in both populations. The contents of IAA, ZR, ABA in old seeds was higher than that of fresh seeds, while GA content and the GA/ABA ratio of fresh seeds were higher than old seeds in both populations; these were particularly pronounced in the intertidal population, and the effects were presented in both seed types. The present results indicate that the changes of endogenous hormones such as GA and ABA, and seed coat phenolics may relate to the change of seed vigor during storage in dimorphic seeds of two populations.3. The transcriptome analysis of genes involved in germination of S. salsa dimorphic seeds under salinityBrown and black seeds without any treatment?as control?, and ungerminated seeds treated with 300 mM NaCl for 1h for brown seeds and 24h for black seeds were used in the transcriptome analysis. For black seeds, 4630 genes were differentially expressed between control seeds and those subjected to 300 mM NaCl. Among these DEGs, 2192 genes were up-regulated while 2438 genes were down-regulated in seeds under salinity. For brown seeds, only 18 genes were differentially expressed between control seeds and those subjected to 300 mM NaCl. Among these DEGs, 7 genes were up-regulated and 11 genes were down-regulated in brown seeds under salinity. For black seeds, GO, COG functional classification and KEGG metabolic pathway analysis showed that many unigenes in transcriptome closely correlated with transport, metabolic process and signal transduction. By KEGG analysis, 494 genes were assigned in 108 pathways including some pathways related to seed salt tolerance. But there were few such genes in brown seeds, which may be because that brown seeds has high salt tolerance and can germinate quickly. But black seeds can germinate after long period of storage in saline soils, and a series of complex mechanisms are needed during black seed germination to adapt to saline environments.