Analysis of storage compounds and inorganic ions in dimorphic seeds of euhalophyte Suaeda salsa

Plant growth, salt removal capacity, and forage nutritive value of the annual euhalophyte Suaeda salsa irrigated with saline water

Sustainable agricultural development in semiarid and arid regions is severely restricted by soil and water salinization. Cultivation of the representative halophyte Suaeda salsa, which can be irrigated with saline water and cultivated on saline soils, is considered to be a potential solution to the issues of freshwater scarcity, soil salinization, and fodder shortage. However, the salt removal capacity and differences in the forage nutritive value of S. salsa under different saline water treatments remain unknown. Using the methods of field trials and randomized blocks design, we quantified salt accumulation in the aboveground biomass, and the biochemical and nutritive value of field-cultivated S. salsa in arid northwestern China under irrigation with water of different salinities [i.e., freshwater or water containing10, 20, 30, or 40 g/L NaCl). The fresh and dry weights of S. salsa increased, then decreased, with increase in salinity. The salt content of the plant's aboveground biomass increased to a constant range and, thus, the salt extraction of S. salsa was relatively stable under different salinities of irrigation water. Under the experimental conditions, the crude protein content significantly increased to 9.45% dry weight (DW) and then decreased to 6.85% DW, with an increase in salinity (p < 0.05). The neutral detergent fiber (42.93%-50.00% DW) and acid detergent fiber (34.76%-39.70% DW) contents were suitable for forage. The contents of trace elements, such as copper and zinc, were significantly increased after irrigation with saline water (p < 0.05). The forage of S. salsa is of high nutritive value for livestock, and contains low concentrations of anti-nutrients. Therefore, S. salsa can be considered for cultivation in saline soils irrigated with saline water. In addition, it provides a viable additional source of fodder in arid regions, where the availability of freshwater and non-saline arable land is limited.

Evaluation of Salicornia bigelovii Germplasm for Food Use in Egypt and the United Arab Emirates Based on Agronomic Traits and Nutritional Composition

Climate change significantly aggravates the quality of soil and water, especially in desert regions such as the United Arab Emirates (UAE) and Egypt concluding in an alarming increase in salinity in the reservoirs of the natural resources. Saline farming rises as a promising solution, utilizing low-quality water and land resources to grow salt-tolerant varieties of conventional crops and halophytes. Samphire (Salicornia spp.) is among the most popular multi-purpose halophytes that are locally consumed in several countries around the world as a vegetable. Six Salicornia bigelovii genotypes (ICBA-2, ICBA-3, ICBA-4, ICBA-8, ICBA-9, ICBA-10) were evaluated for their agronomic performance and nutritional composition in Dubai in UAE and, for the first time, at the Red Sea Governorate in Egypt in the 2019-2020 season using saline groundwater for irrigation (EC_w = 26 and 6.6 dS/m, respectively). ICBA-10 performed well in both locations with high green biomass and seed yield (10.9 kgm^-2 and 116.3 gm^-2, respectively, in UAE; 7.7 kgm^-2 and 82.9 gm^-2, respectively, in Egypt). ICBA-10 was, overall, also good in ion accumulation, total amino acids and unsaturated fatty acids content in both locations for shoots and seeds. Our results indicated that a lack of a drainage system and leaching fraction, the silt loam texture and the drip irrigation system might have contributed in the gradual accumulation of salts in the soil at Mubarak Valley at the end of the experiment at a higher level than ICBA. Apart from the agronomic parameters, higher salinity levels also affected ion accumulation, the amino acids and the fatty acids content for both shoots and seeds, whereas the proximate composition was affected to a lesser extent. Our findings on the high unsaturated fatty acids content under higher salinity corroborate the nutritional value of S. bigelovii oil. Due to its euhalophyte nature, S. bigelovii is a valuable source of minerals, amino acids and antioxidants that render it the most promising salt-loving plant for food use.

The Roles of CCCH Zinc-Finger Proteins in Plant Abiotic Stress Tolerance

Zinc-finger proteins, a superfamily of proteins with a typical structural domain that coordinates a zinc ion and binds nucleic acids, participate in the regulation of growth, development, and stress adaptation in plants. Most zinc fingers are C2H2-type or CCCC-type, named after the configuration of cysteine (C) and histidine (H); the less-common CCCH zinc-finger proteins are important in the regulation of plant stress responses. In this review, we introduce the domain structures, classification, and subcellular localization of CCCH zinc-finger proteins in plants and discuss their functions in transcriptional and post-transcriptional regulation via interactions with DNA, RNA, and other proteins. We describe the functions of CCCH zinc-finger proteins in plant development and tolerance to abiotic stresses such as salt, drought, flooding, cold temperatures and oxidative stress. Finally, we summarize the signal transduction pathways and regulatory networks of CCCH zinc-finger proteins in their responses to abiotic stress. CCCH zinc-finger proteins regulate the adaptation of plants to abiotic stress in various ways, but the specific molecular mechanisms need to be further explored, along with other mechanisms such as cytoplasm-to-nucleus shuttling and post-transcriptional regulation. Unraveling the molecular mechanisms by which CCCH zinc-finger proteins improve stress tolerance will facilitate the breeding and genetic engineering of crops with improved traits.

Insights into the endophytic bacterial community comparison and their potential role in the dimorphic seeds of halophyte Suaeda glauca

BACKGROUND

Seed dimorphism has been thought to be a bet-hedging strategy that helps plants survive in the disturbed environment and has been widely studied for its ecological adaptation mechanism. Many studies showed that seed-associated microorganisms play an important role in enhancing plant fitness, but information regarding endophytic bacteria associated with dimorphic seeds is limited. This study explores the influence of seed coat structure and seed phytochemical properties on the community composition and diversity of endophytic bacteria of dimorphic seeds of Suaeda glauca. In this study, we used 16S rRNA high-throughput gene sequencing method to compare the community composition and bacterial diversity between brown and black seeds of Suaeda glauca.

RESULTS

A significant difference was observed in seed coat structure and phytochemical properties between brown and black seeds of S. glauca. Total 9 phyla, 13 classes, 31 orders, 53 families, 102 genera were identified in the dimorphic seeds. The dominant phyla were Proteobacteria, Firmicutes, and Actinobacteria. The results showed that seed dimorphism had little impact on the diversity and richness of endophytic bacterial communities but significantly differs in the relative abundance of the bacterial community between brown and black seeds. At the phylum level, Actinobacteria tend to be enriched significantly in brown seeds. At the genus level, Rhodococcus, Ralstonia, Pelomonas and Bradyrhizobium tend to be enriched significantly in brown seeds, while Marinilactibacillus was mainly found in black seeds. Besides, brown seeds harbored a large number of bacteria with plant-growth-promoting traits, whereas black seeds presented bacteria with enzyme activities (i.e., pectinase, cellulolytic and xylanolytic activities).

CONCLUSION

The endophytic bacterial community compositions were significantly different between dimorphic seeds of Suaeda glauca, and play an important role in the ecological adaptation of dimorphic seeds by performing different biological function roles. The endophytic bacterial communities of the dimorphic seeds may be influenced mainly by the seed coat structureand partly by the seed phytochemical characteristics. These findings provide valuable information for better understanding of the ecological adaptation strategy of dimorphic seeds in the disturbed environment.

Role of Suaeda salsa SsNRT2.1 in nitrate uptake under low nitrate and high saline conditions

The global annual loss in agricultural production resulting from soil salinization is significant. Although nitrate (NO₃^-) is known to play both nutritional and osmotic roles in the salt tolerance of halophytes, it remains unclear how halophytes such as Suaeda salsa L. take up NO₃^- under saline conditions. In the present study, the gene of nitrate transporter 2.1 (SsNRT2.1) was cloned from S. salsa and its function was identified in both S. salsa and Arabidopsis thaliana under salinity and low NO₃^--N (0.5 mM NO₃^-) conditions. The results revealed that SsNRT2.1 expression and NO₃^- concentration in the roots of S. salsa were higher at 200 mM NaCl, compared with that at 0 and 500 mM NaCl after 24 h treatment. The Arabidopsis overexpression lines showed a higher NO₃^- content compared to the WT lines at 0 and 50 mM NaCl. A similar trend was observed in the root length. In conclusion, salinity promoted the SsNRT2.1 expression in S. salsa, suggesting that this gene may contribute to the efficient NO₃^- uptake in S. salsa under low NO₃^- and high salinity conditions. This trait may explain why S. salsa can tolerate high salinity and produce the highest biomass at about 200 mM NaCl.

Cation and Zn Accumulation in Brown Seeds of the Euhalophyte Suaeda salsa Improves Germination Under Saline Conditions

Salinity inhibits plant growth due to salt ion accumulation in plant cells and reduced absorption of other nutrients such as metal ions; however halophyte plants have evolved mechanisms to survive and thrive in high-salt conditions. The euhalophyte Suaeda salsa generates dimorphic seeds (black and brown), which show marked differences in germination and seedling growth under high-salt conditions. However, it is unclear whether their ionic status differs. Here, to provide insight on the role of ions in salt tolerance, we used inductively coupled plasma mass spectrometry to measure the ion contents in the dimorphic seeds from S. salsa plants treated with or without NaCl. We measured the macroelements Na, K, Mg, and Ca, and the microelements Mn, Fe, Zn, Cu, and Mo. NaCl-treated S. salsa plants produced seeds with significantly reduced metallic element contents and significantly increased Na⁺ contents. The brown seeds of S. salsa plants treated with 0 and 200 mM NaCl had much higher contents of K⁺, Ca²⁺, and Fe²⁺ compared with the black seeds. However, the S. salsa seeds (both black and brown) from NaCl-treated plants were significantly larger, and had higher germination rate and higher seedling salt tolerance compared with seeds from plants not treated with NaCl. Interestingly, we measured significantly higher Zn²⁺ contents in the brown seeds from plants treated with NaCl compared with the black seeds. This suggests that the high contents of Zn²⁺ and other cations affected seed development and salt tolerance during germination under high-salt conditions. These observations provide insight into the mechanisms of salt tolerance in this halophyte and inform efforts to increase salt tolerance in salt-sensitive species.

Salinity relief aniline induced oxidative stress in Suaeda salsa: Activities of antioxidative enzyme and EPR measurements

Wastewater from printing and dyeing processes often contains aniline and high salinity, which are hazardous to aquatic species. Glycophytic plants cannot survive under high-salinity conditions, whereas halophytes grow well in such an environment. In this study, we investigated the influence of NaCl on the antioxidant level in Suaeda salsa affected by aniline stress. The seedlings showed various growth toxicity effects under different concentrations of aniline. The results showed that the effect of the aniline was more severe for the root growth compared to that for the shoot growth. Aniline exposure significantly increased the total free radicals and ·OH radicals in the plants. Suaeda salsa exposure to aniline caused oxidative stress by altering the superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activity, which resulted in the overproduction of H₂O₂ and the inducement of lipid peroxidation. Analysis revealed that the malondialdehyde (MDA) content was enhanced after aniline exposure and that the chlorophyll content was significantly decreased. The results showed that aniline induced the production of free radicals and reactive oxygen species (ROS), and changed the antioxidant defense system. This ultimately resulted in oxidative damage in S. salsa; however, it was found that moderate salinity could mitigate the effects. In conclusion, salinity may alleviate the growth inhibition caused by aniline by regulating the antioxidant capacity of S. salsa.

Heavy metal tolerance and potential for remediation of heavy metal-contaminated saline soils for the euhalophyte Suaeda salsa

Due to irrigation practices and industrial pollution, large areas of the lands in the world are simultaneously affected by salinity and heavy metal contamination. It has been considered that halophytes have adapted to salinity, and can be used to remediate heavy metal-contaminated saline soils. Suaeda salsa L. (S. salsa) is a high salt-resistance plant, which can efficiently absorb and accumulate salt and toxic metals from saline soils, suggesting that this may be potential plant species that can be used for the restoration of saline soils contaminated with heavy metals. The present brief review sheds light on the characteristics of S. salsa in the uptake and accumulation of high levels of heavy metals. Furthermore, the physiological and molecular mechanisms for heavy metal tolerance were highlighted. The potential values of S. salsa in the remediation of saline soils were also summarized.

Exposure to High Salinity During Seed Development Markedly Enhances Seedling Emergence and Fitness of the Progeny of the Extreme Halophyte Suaeda salsa

Irrigation with 200 mM NaCl significantly increases vegetative and reproductive growth of the extreme halophyte Suaeda salsa. However, little is known about how the progeny of S. salsa plants grown under a continuous NaCl supply behave in terms of growth and seed set parameters. We investigated various plant growth and reproductive parameters of the progeny that germinated from seeds harvested from mother plants grown under 0 or 200 mM NaCl over three generations. Seedling emergence, plant height, stem diameter, total branch length, flowering branch length, flowering branch ratio, and seed production were all significantly enhanced in the progeny produced by mother plants grown with 200 mM NaCl compared to progeny of mother plants grown on low salinity conditions. Therefore, irrigation with 200 mM of NaCl is beneficial to seed development in the halophyte S. salsa and possibly contributes to population establishment in high salinity environments. Likewise, the prolonged absence of NaCl in the growth environment inhibits seed development, results in lower seed quality, and thus limits seedling growth of the progeny, thereby restricting S. salsa to a high salinity ecological niche.

Progress in the Study and Use of Seawater Vegetables

As global soil salinization increases, halophytes that can grow in saline soils are the primary choice for improving soil quality. Some halophytes can even be irrigated with seawater and used as vegetables. These so-called seawater vegetables include those that can be planted on saline and alkali soils and some edible halophytes and ordinary vegetables that are salt-tolerant. The cultivation of seawater vegetables on saline soil has become a matter of increasing interest. In this review, we focus on the salt-tolerance mechanisms and potential applications of some seawater vegetables. We also summarize their value to health, medicine, industry, and the economy as a whole. Further improvement and development to support the use of seawater vegetables will require in-depth research at the cellular and molecular levels.

Transcriptomic analysis identifies novel genes and pathways for salt stress responses in Suaeda salsa leaves

Salinity is a critical abiotic stress, which significantly impacts the agricultural yield worldwide. Identification of the molecular mechanisms underlying the salt tolerance in euhalophyte Suaeda salsa is conducive to the development of salt-resistant crops. In the present study, high-throughput RNA sequencing was performed after S. salsa leaves were exposed to 300 mM NaCl for 7 days, and 7,753 unigenes were identified as differently expressed genes (DEGs) in S. salsa, including 3,638 increased and 4,115 decreased unigenes. Moreover, hundreds of pathways were predicted to participate in salt stress response in S. salsa by Gene Ontology (GO), MapMan and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses, including ion transport and sequestration as well as photoprotection of photosystem (PS) II. The GO enrichment analysis indicated that genes related to ion transport, reactive oxygen species (ROS) scavenging and transcriptional factors were highly expressed upon NaCl treatment. The excessive Na+ and Cl- ions were supposed to be absorbed into the vacuole for ion sequestration and balance adjustment by potassium transporters (such as KEA3) with high expressions. Moreover, we predicted that mutiple candidate genes associated with photosynthesis (such as PSB33 and ABA4), ROS (such as TAU9 and PHI8) and transcriptional regulation (HB-7 and MYB78) pathways could mitigate salt stress-caused damage in S. salsa.

Adaptation of euhalophyte Suaeda salsa to nitrogen starvation under salinity

Suaeda salsa L. (S. salsa) is an annual euhalophyte with high salt tolerance. The NO₃^- content in soils where S. salsa populations occur are very low, especially in intertidal habitat. However, it remains unclear how S. salsa populations adapt to low nitrogen environments. Plants of two S. salsa populations were pre-cultured with nitrate nitrogen (1 mM of NO₃^--N) for 30 days. Then, the seedlings were cultured with 1 mM of NO₃^--N and N-free solution (N starvation) at 200 mM of NaCl for an additional 14 days. The expression of two genes in S. salsa, nitrate transporter 1.7 (SsNRT1.7) and nitrate transporter 2.5 (SsNRT2.5) in old and mature leaves, was markedly upregulated during N starvation in the intertidal population, when compared to the inland population, but this was not the case in young leaves. After N starvation, the decrease in NO₃^- and chlorophyll content, net photosynthetic rate in young leaves, and shoot dry weight in the intertidal population were lower than those in the inland population. In conclusion, SsNRT1.7 and SsNRT2.5 may play a role in NO₃^- remobilization, especially in the intertidal population, during N starvation. This trait may benefit the intertidal population for adapting to low nitrogen environments.

Genetic mechanisms of salt stress responses in halophytes

Abiotic stress is a major threat to plant growth and development, resulting in extensive crop loss worldwide. Plants react to abiotic stresses through physiological, biochemical, molecular, and genetic adaptations that promote survival. Exploring the molecular mechanisms involved in abiotic stress responses across various plant species is essential for improving crop yields in unfavorable environments. Halophytes are characterized as plants that survive to reproduce in soils containing high salt concentrations, and thus act as an ideal model to comprehend complicated genetic and physiological mechanisms of salinity stress tolerance. Plant ecologists classify halophytes into three main groups: euhalophytes, recretohalophytes, and pseudo-halophytes. Recent genetic and molecular research has showed complicated regulatory networks by which halophytes coordinate stress adaptation and tolerance. Furthermore, investigation of natural variations in these stress responses has supplied new perspectives on the evolution of mechanisms that regulate tolerance and adaptation. This review discusses the current understanding of the genetic mechanisms that contribute to salt-stress tolerance among different classes of halophytes.

Analysis of widely targeted metabolites of the euhalophyte Suaeda salsa under saline conditions provides new insights into salt tolerance and nutritional value in halophytic species

BACKGROUND

Suaeda salsa L. (S. salsa) is an annual euhalophyte with high salt tolerance and high value as an oil crop, traditional Chinese medicine and vegetable. However, there are few comprehensive studies on the metabolomics of S. salsa under saline conditions.

RESULTS

Seedlings of S. salsa were cultured with 0, 200 and 500 mM NaCl for two days. Then, widely targeted metabolites were detected with ultra performance liquid chromatography and tandem mass spectrometry. A total of 639 metabolites were annotated. Among these, 253 metabolites were differential metabolites. Salt treatment increased the content of certain metabolites, such as nucleotide and its derivates, organic acids, the content of amino acids, lipids such as α-linolenic acid, and certain antioxidants such as quercetin. These substances may be correlated to osmotic tolerance, increased antioxidant activity, and medical and nutritional value in the species.

CONCLUSION

This study comprehensively analyzed the metabolic response of S. salsa under salinity from the perspective of omics, and provides an important theoretical basis for understanding salt tolerance and evaluating nutritional value in the species.

Exogenous salicylic acid improves the germination of Limonium bicolor seeds under salt stress

Salicylic acid (SA) may improve plant tolerance to abiotic stresses; however, little is known about the underlying mechanisms by which this is achieved. Here, we investigated the effects of exogenous SA application on seed germination in the halophyte Limonium bicolor (Kuntze) under salt stress. Specifically, we examined the effect of salt stress on seed germination, sugar and protein contents, amylase activity, and the contents of various hormones, both in the presence and absence of exogenous SA treatments. Germination was significantly suppressed by a 200 mM NaCl treatment but was significantly improved when 0.08 mM SA was concurrently applied. During germination, the seeds treated with SA had high levels of gibberellic acid (GA) and high levels of amylase and α-amylase activity, but low abscisic acid (ABA) contents. The SA treatment upregulated the expression of key genes involved in GA biosynthesis while downregulating those involved in ABA biosynthesis, thereby triggering a favorable hormonal balance between GA and ABA that enhanced seed germination under salt stress.

Seed Heteromorphism: An Important Adaptation of Halophytes for Habitat Heterogeneity

Seed germination is a very critical and important step for seedling establishment under saline environments, as high level of salinity in the soil can prevent seed germination. However halophytes exhibit an interesting mechanism to cope with salt stress. Many halophytes produce heteromorphic seeds, which have different dormancy and germination behavior under saline conditions. This characteristic is related to the structural and physiological differences among heteromorphic seeds. It was unclear that how heteromorphic seeds differently accumulate organic and inorganic substances under saline conditions, and what are the physiological and molecular mechanisms involved in the production of heteromorphic seeds, and in the development of transgenerational plasticity in heteromorphic seeds. In the current brief review, dormancy and germination and the possible role of seed coat and storage compounds in this process of heteromorphic seeds development have been discussed. Moreover, the role of maternal effects on heteromorphic seeds production under saline environments and growth and reproduction capability of the descendants from them have been highlighted.