The role of the seed coat in adaptation of dimorphic seeds of the euhalophyte Suaeda salsa to salinity was investigated during germination and early seedling growth. Black and brown seeds were treated with chloroform for 1 min before the extract was used to analyze waxes and the seeds to investigate the protective role of the seed coat under saline conditions. Waxes in black seed coats were more abundant than those in brown seed coats. Salinity (500 mM NaCl) increased the concentration of Na + and decreased the concentration of K + in both black and brown seeds regardless of chloroform treatment. Chloroform treatment alone (in the absence of NaCl) had no effect on the concentration of Na + or K + in black or brown seeds and in the presence of 500 mM NaCl had no effect on the concentration of Na + or K + in brown seeds. However, chloroform treatment increased Na + and decreased K + in black seeds with 500 mM NaCl. A change of MDA (malondialdehyde) concentration in black and brown seeds treated with or without chloroform was similar to the change of Na + concentration. High salinity (1500 mM NaCl) pretreatment for 40 days had a less adverse effect on germination of black seeds compared with brown seeds after they were transferred to fresh water regardless of chloroform treatment. Similar results were found for seedling emergence. In conclusion, a black seed coat may be more protective than a brown seed coat, probably by shielding the embryo from ion toxicity, because of its higher content of waxes. Thus black seeds can better maintain seed viability than brown seeds for extended periods under hypersaline conditions.
Salinity and nitrogen are two important environmental factors that affect the distribution of halophytes in their natural saline habitats. Seeds of the euhalophyte Suaeda salsa L. were harvested from plants that had been treated with 1 or 500 mM NaCl combined with 0.5 or 5 mM NO3 − -N (nitrate) for 115 days in a glasshouse. Germination was evaluated under different concentrations of NaCl and nitrate. Plants exposed to high salinity (500 mM) and low nitrate (0.5 mM) tended to produce heavy seeds. Either high salinity (500 mM) or high nitrate (5 mM) increased the brown/black seed ratio. The concentrations of Na + , K + , and Cl − were higher in brown than in black seeds, and NO3 − concentrations were higher in black than in brown seeds, regardless of NaCl and nitrate treatments during plant culture. Regardless of NaCl and nitrate concentrations during germination, seeds from plants grown with 0.5 mM nitrate generally germinated more rapidly than seeds from plants grown with 5 mM nitrate, and the difference was greater for black than for brown seeds. Exogenous nitrate during germination enhanced the germination of brown seeds less than that of black seeds. Producing more brown seeds and heavy black or brown seeds appears to be an adaptation of S. suaeda to saline environments. Producing more black seeds, which tend to remain dormant, should reduce competition for nitrogen and appears to be an adaptation to nitrogen-limited environments. In conclusion, nitrate provided exogenously or by mother plants to black seeds may act as a signal molecule that enhances the germination of black S. suaeda seeds.
Changes in endogenous hormones and seed-coat phenolics during the storage of the dimorphic seeds of two Suaeda salsa populations were investigated. The results showed that, regardless of salinity, storage did not reduce the germination of brown or black seeds from an inland population, but it significantly decreased the germination of dimorphic seeds from an intertidal population. Abscisic acid (ABA) concentration was significantly higher in old seeds than in fresh seeds (freshly harvested dry seeds), whereas the opposite trend was evident for gibberellic acid (GA, including GA1 and GA3) concentration and GA : ABA ratio in both populations, and especially in the intertidal population. Concentration of seed-coat phenolics extracted from brown seeds was much higher than in black seeds in both populations, regardless of extracting time and storage. Storage increased the concentration of phenolics extracted from brown seeds in the inland population, whereas the opposite trend was evident in the intertidal population. Storage did not significantly change seed-coat phenolics extracted from black seeds relative to brown seeds in either population. The results indicated that changes in seed vigour during storage in dimorphic seeds of the two S. salsa populations are related to changes in endogenous hormones and seed-coat phenolics.
Background Suaeda salsa (S. salsa) is a euhalophyte with high economic value. S. salsa can produce dimorphic seeds. Brown seeds are more salt tolerant, can germinate quickly and maintain the fitness of the species under high saline conditions. Black seeds are less salt tolerant, may become part of the seed bank and germinate when soil salinity is reduced. Previous reports have mainly focused on the ecophysiological traits of seed germination and production under saline conditions in this species. However, there is no information available on the molecular characteristics of S. salsa dimorphic seeds.ResultsIn the present study, a total of 5825 differentially expressed genes were obtained; and 4648 differentially expressed genes were annotated based on a sequence similarity search, utilizing five public databases by transcriptome analysis. The different expression of these genes may be associated with embryo development, fatty acid, osmotic regulation substances and plant hormones in brown and black seeds. Compared to black seeds, most genes may relate to embryo development, and various genes that encode fatty acid desaturase and are involved in osmotic regulation substance synthesis or transport are upregulated in brown seeds. A large number of differentially expressed genes related to plant hormones were found in brown and black seeds, and their possible roles in regulating seed dormancy/germination were discussed.ConclusionsUpregulated genes involved in seed development and osmotic regulation substance accumulation may relate to bigger seed size and rapid seed germination in brown seeds, compared to black seeds. Differentially expressed genes of hormones may relate to seed dormancy/germination and the development of brown and black seeds. The transcriptome dataset will serve as a valuable resource to further understand gene expression and functional genomics in S. salsa dimorphic seeds.Electronic supplementary materialThe online version of this article (10.1186/s12864-017-4104-9) contains supplementary material, which is available to authorized users.
As a precursor of aromatic compounds, fatty acids play important roles in apple fruit quality; however, the genetic and molecular basis underlying fatty acid synthesis and metabolism is largely unknown. In this study, we conducted a genome-wide association study (GWAS) of seven fatty acids using genomic data of 149 Malus accessions and identified 232 significant signals (–log10P>5) associated with 99 genes from GWAS of four fatty acids across 2 years. Among these, a significant GWAS signal associated with linoleic acid was identified in the transcriptional regulator SUPERMAN-like (SUP) MD13G1209600 at chromosome 13 of M. × domestica. Transient overexpression of MdSUP increased the contents of linoleic and linolenic acids and of three aromatic components in the fruit. Our study provides genetic and molecular information for improving the flavor and nutritional value of apple.
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