Na Sui

Increase in unsaturated fatty acids in membrane lipids of Suaeda salsa L. enhances protection of photosystem II under high salinity

In order to examine the possible role of unsaturated fatty acids in photosynthesis of halophytes under high salinity, the effect of salinity on plant growth, chlorophyll (Chl) content, photochemical efficiency of PSII, membrane lipid content and fatty acids composition of a C3 euhalophyte Suaeda salsa L. was investigated. Salt stress induced a slight increase of the maximal photochemical efficiency of PSII (Fv/Fm), actual PSII efficiency (ΦPSII), Chl a content and Chl a/b ratio. The unsaturated fatty acid content also increased under salt stress. The proportion of MGDG, DGDG, SQDG, and PC decreased, while the proportion of PG increased from 10.9% to 26.9% under salt stress. These results suggest that S. salsa displays high resistance to photoinhibition under salt stress and that increased concentration of unsaturated fatty acids in membrane lipids of S. salsa enhances the tolerance of photosystem II to salt stress.

The CCCH zinc finger protein gene AtZFP1 improves salt resistance in Arabidopsis thaliana.

The CCCH type zinc finger proteins are a super family involved in many aspects of plant growth and development. In this study, we investigated the response of one CCCH type zinc finger protein AtZFP1 (At2g25900) to salt stress in Arabidopsis. The expression of AtZFP1 was upregulated by salt stress. Compared to transgenic strains, the germination rate, emerging rate of cotyledons and root length of wild plants were significantly lower under NaCl treatments, while the inhibitory effect was significantly severe in T-DNA insertion mutant strains. At germination stage, it was mainly osmotic stress when treated with NaCl. Relative to wild plants, overexpression strains maintained a higher K+, K+/Na+, chlorophyll and proline content, and lower Na+ and MDA content. Quantitative real-time PCR analysis revealed that the expression of stress related marker genes KIN1, RD29B and RD22 increased more significantly in transgenic strains by salt stress. Overexpression of AtZFP1 also enhanced oxidative and osmotic stress tolerance which was determined by measuring the expression of a set of antioxidant genes, osmotic stress genes and ion transport protein genes such as SOS1, AtP5CS1 and AtGSTU5. Overall, our results suggest that overexpression of AtZFP1 enhanced salt tolerance by maintaining ionic balance and limiting oxidative and osmotic stress.

The role of salinity in seed maturation of the euhalophyte Suaeda salsa

Controlled conditions were used to investigate how salinity maintains the salt tolerance of seeds and seedlings of the euhalophyte Suaeda salsa. Seeds were harvested from S. salsa plants that had been treated with 1 or 500 mM NaCl for 113 days in a glasshouse. The results showed that high salinity (500 mM NaCl) increased chlorophyll concentration and oxygen production in embryos of maturing seeds. At 500 mM NaCl, the phosphatidylglycerol and sulfoquinovosyldiacylglycerol levels and the digalactosyldiacylglycerol/monogalactosyldiacylglycerol ratio were higher in young seedlings derived from seeds whose source plants were cultured in 500 mM rather than in 1 mM NaCl. When seeds were incubated with 600 mM NaCl, the conductivity and malondialdehyde concentration in the embryos was greater if the source plants had been cultured in 1 mM rather than in 500 mM NaCl. The opposite pattern was evident for seedling survival and shoot weight. In conclusion, salinity during seed maturation may increase the salt tolerance of seeds and seedlings by increasing the oxygen production in the embryos of the maturing seeds and by changing the lipid composition of membranes in the seedlings.

The role of the seed coat in adaptation of dimorphic seeds of the euhalophyte Suaeda salsa to salinity

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.

Overexpression of Glycerol-3-Phosphate Acyltransferase from Suaeda salsa Improves Salt Tolerance in Arabidopsis

Glycerol-3-phosphate acyltransferase is the first acyl esterifying enzyme in phosphatidylglycerol (PG) synthesis process. In this study, we isolated and characterized the glycerol-3-phosphate acyltransferase (GPAT) gene from Suaeda salsa (S. salsa) and obtained the full length of the GPAT gene from S. salsa (SsGPAT) by 5′ and 3′ RACE. The clone contained an open reading frame (ORF) of 1167 bp nucleotides that comprised of 388 amino acid residues. Real-time PCR revealed that the mRNA accumulation of GPAT in S. salsa was induced by salt stress. The highest expression levels were observed when S. salsa leaves were exposed to 300 mM NaCl treatment. At the germination stage, the germination rate and root length of overexpressed Arabidopsis strains were significantly higher than WT under different concentrations of NaCl treatments, while the inhibitory effect was significantly severe in T-DNA insertion mutant strains. In the seedling stage, chlorophyll content, the photochemical efficiency of PSII, PSI oxidoreductive activity (ΔI/Io), and the unsaturated fatty acid content of PG decreased less in overexpressed strains and more in mutant strains than that in WT under salt stress. These results suggest that the overexpression of SsGPAT in Arabidopsis enhances salt tolerance and alleviates the photoinhibition of PSII and PSI under salt stress by improving the unsaturated fatty acid content of PG.

Effects of NaCl stress on the growth and photosynthetic characteristics of Ulmus pumila L. seedlings in sand culture

The effects of NaCl stress on the growth and photosynthetic characters of Ulmus pumila L. seedlings were investigated under sand culture condition. With increasing NaCl concentration, main stem height, branch number, leaf number, and leaf area declined, while Na+ content and the Na+/K+ ratio in both expanded and expanding leaves increased. Na+ content was significantly higher in expanded leaves than in those just expanding. Chlorophyll (Chl) a and Chl b contents declined as NaCl concentration increased. The net photosynthetic rate, intercellular CO2 concentration, stomatal conductance, and transpiration rate also declined, but stomatal limitation value increased as NaCl concentration increased. Both the maximal quantum yield of PSII photochemistry and the effective quantum yield of PSII photochemistry declined as NaCl concentration rose. These results suggest that the accumulation of Na+ in already expanded leaves might reduce damage to the expanding leaves and help U. pumila endure high salinity. The reduced photosynthesis in response to salt stress was mainly caused by stomatal limitation.

Photoinhibition of Suaeda salsa to chilling stress is related to energy dissipation and water-water cycle

To investigate the photoprotection of energy dissipation and water-water cycle, a C3 euhalophytic herb, Suaeda salsa L., was exposed either to chilling temperature (4°C) accompanied by moderate irradiance (600 μmol m−2 s−1) (CM) and/or to chilling temperature (4°C) accompanied by low irradiance (100 μmol m−2 s−1) (CL). During chilling stress, both the maximal photochemical efficiency of PSII (Fv/Fm) and the oxidizable P700 decreased in S. salsa leaves either under CM or CL, which indicated the severe photoinhibition. Relative to Fv/Fm, the oxidizable P700 decreased markedly under CL, which indicated that PSI was more sensitive to CL treatment than PSII. Initial fluorescence, number of closed PSII centers, and nonphotochemical quenching increased under CM, but more markedly under CL in S. salsa leaves. Activity of superoxide dismutase and ascorbate peroxidase was higher under CM than that under CL. The production of reactive oxygen species (ROS) decreased first and then increased under both treatments, but the content of O2·− and H2O2 was higher under CL than that under CM after 12 h of chilling stress. These results suggested that photoinhibition in S. salsa might be related to the accumulation of reactive oxygen species (ROS) induced by excess energy. The water-water cycle could not dissipate energy efficiently under CL, which caused the great accumulation of ROS.

Transcriptomic and Physiological Evidence for the Relationship between Unsaturated Fatty Acid and Salt Stress in Peanut

Peanut (Arachis hypogaea L.) is one of the five major oilseed crops cultivated worldwide. Salt stress is a common adverse condition for the growth of this crop in many countries and regions. In this study, physiological parameters and transcriptome profiles of peanut seedlings exposed to salt stress (250 mM NaCl for 4 days, S4) and recovery for 3 days (when transferred to standard conditions for 3 days, R3) were analyzed to detect genes associated with salt stress and recovery in peanut. We observed that the quantum yield of PSII electron transport (ΦPSII) and the maximal photochemical efficiency of PSII (Fv/Fm) decreased in S4 compared with the control, and increased in R3 compared with those in S4. Seedling fresh weight, dry weight and PSI oxidoreductive activity (ΔI/Io) were inhibited in S4 and did not recover in R3. Superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities decreased in S4 and increased in R3, whereas superoxide anion (O2-•) and hydrogen peroxide (H2O2) contents increased in S4 and decreased in R3. Transcriptome analysis revealed 1,742 differentially expressed genes (DEGs) under salt stress and 390 DEGs under recovery. Among these DEGs, two DEGs encoding ω-3 fatty acid desaturase that synthesized linolenic acid (18:3) from linoleic acid (18:2) were down-regulated in S4 and up-regulated in R3. Furthermore, ω-3 fatty acid desaturase activity decreased under salt stress and increased under recovery. Consistent with this result, 18:3 content decreased under salt stress and increased under recovery compared with that under salt treatment. In conclusion, salt stress markedly changed the activity of ω-3 fatty acid desaturase and fatty acid composition. The findings provide novel insights for the improvement of salt tolerance in peanut.

Energy dissipation and antioxidant enzyme system protect photosystem II of sweet sorghum under drought stress

The effect of drought stress on energy dissipation and antioxidant enzyme system in two sweet sorghum inbred lines (M-81E and Roma) was investigated. Results showed that the germination indicator increased more in M-81E than that in Roma under rehydration. Under drought stress, both the maximal photochemical efficiency of PSII (Fv/Fm) and oxidoreductive activity (ΔI/I0) of Roma decreased more than those in M-81E. Relative to Fv/Fm, the ΔI/I0 decreased markedly, which indicated that PSI was more sensitive to drought stress than PSII. Increases in the reduction state of QA (1–qp), nonphotochemical quenching (NPQ) and minimal fluorescence yield of the dark-adapted state (F0) were greater in Roma than those in M-81E; meanwhile, the H2O2 content was lower in M-81E than that in Roma. Our results suggested that the photoinhibition might be related to the accumulation of reactive oxygen species (ROS). The antioxidant enzyme system and energy dissipation of M-81E could respectively increase drought tolerance by eliminating ROS and excess energy more efficiently than that of Roma.

Transcriptomic profiling of genes in matured dimorphic seeds of euhalophyte Suaeda salsa

BackgroundSuaeda 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.