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Background Na + exclusion from leaf blades is one of the key mechanisms for glycophytes to cope with salinity stress. Certain class I transporters of the high-affinity K + transporter (HKT) family have been demonstrated to mediate leaf blade-Na + exclusion upon salinity stress via Na + -selective transport. Multiple HKT1 transporters are known to function in rice ( Oryza sativa ). However, the ion transport function of OsHKT1;4 and its contribution to the Na + exclusion mechanism in rice remain to be elucidated. Results Here, we report results of the functional characterization of the OsHKT1;4 transporter in rice. OsHKT1;4 mediated robust Na + transport in Saccharomyces cerevisiae and Xenopus laevis oocytes. Electrophysiological experiments demonstrated that OsHKT1;4 shows strong Na + selectivity among cations tested, including Li + , Na + , K + , Rb + , Cs + , and NH 4 + , in oocytes. A chimeric protein, EGFP-OsHKT1;4, was found to be functional in oocytes and targeted to the plasma membrane of rice protoplasts. The level of OsHKT1;4 transcripts was prominent in leaf sheaths throughout the growth stages. Unexpectedly however, we demonstrate here accumulation of OsHKT1;4 transcripts in the stem including internode II and peduncle in the reproductive growth stage. Moreover, phenotypic analysis of OsHKT1;4 RNAi plants in the vegetative growth stage revealed no profound influence on the growth and ion accumulation in comparison with WT plants upon salinity stress. However, imposition of salinity stress on the RNAi plants in the reproductive growth stage caused significant Na + overaccumulation in aerial organs, in particular, leaf blades and sheaths. In addition, 22 Na + tracer experiments using peduncles of RNAi and WT plants suggested xylem Na + unloading by OsHKT1;4. Conclusions Taken together, our results indicate a newly recognized function of OsHKT1;4 in Na + exclusion in stems together with leaf sheaths, thus excluding Na + from leaf blades of a japonica rice cultivar in the reproductive growth stage, but the contribution is low when the plants are in the vegetative growth stage.

The link between polyamine oxidases (PAOs), which function in polyamine catabolism, and stress responses remains elusive. Here, we address this issue using Arabidopsis pao mutants in which the expression of the five PAO genes is knocked-out or knocked-down. As the five single pao mutants and wild type (WT) showed similar response to salt stress, we tried to generate the mutants that have either the cytoplasmic PAO pathway (pao1 pao5) or the peroxisomal PAO pathway (pao2 pao3 pao4) silenced. However, the latter triple mutant was not obtained. Thus, in this study, we used two double mutants, pao1 pao5 and pao2 pao4. Of interest, pao1 pao5 mutant was NaCl- and drought-tolerant, whereas pao2 pao4 showed similar sensitivity to those stresses as WT. To reveal the underlying mechanism of salt tolerance, further analyses were performed. Na uptake of the mutant (pao1 pao5) decreased to 75% of WT. PAO activity of the mutant was reduced to 62% of WT. The content of reactive oxygen species (ROS) such as hydrogen peroxide, a reaction product of PAO action, and superoxide anion in the mutant became 81 and 72% of the levels in WT upon salt treatment. The mutant contained 2.8-fold higher thermospermine compared to WT. Moreover, the mutant induced the genes of salt overly sensitive-, abscisic acid (ABA)-dependent- and ABA-independent- pathways more strongly than WT upon salt treatment. The results suggest that the Arabidopsis plant silencing cytoplasmic PAOs shows salinity tolerance by reducing ROS production and strongly inducing subsets of stress-responsive genes under stress conditions.

Salinity is one of the abiotic stresses that affect crop growth and productivity in arid and semi-arid regions. Unfortunately, there are few known methods to mitigate the deleterious impacts of salt stress on the development and yield of vegetable crops. Blue-green algae (cyanobacteria) are endowed with the potential to curb the negative impacts of salt stress as they are characterized by biostimulant properties. The present work aimed to investigate the effects of Roholtiella sp. as a foliar extract on the growth characteristics, physiological and biochemical responses of bell pepper (Capsicum annuum L.) plants under varying levels of salinity conditions. A soilless water experiment was carried out in a greenhouse where bell pepper seedlings were grown under five salt concentrations (0, 50, 200, 150, and 200 mM of NaCl). Growth characteristics, pigments content, relative water content, and antioxidant activity (CAT) were determined. Our results showed that growth parameters, relative water content (RWC), chlorophyll a & b concentrations under salinity conditions were negatively affected at the highest concentration (200 mM). Interestingly, the application of Roholtiella sp. foliar extract enhanced the plant growth characteristics as shoot length increased by 17.014%, fresh weight by 39.15%, dry and weight by 31.02%, at various salt treatments. Moreover, chlorophyll a and b increased significantly compared with seedlings sprayed with water. Similarly, RWC exhibited a significant increase (92.05%) compared with plants sprayed with water. In addition, antioxidants activities and accumulation of proline were improved in Roholtella sp. extract foliar sprayed seedlings compared to the plants foliar sprayed with water. Conclusively, at the expiration of our study, the Rohotiella sp. extract-treated plants were found to be more efficient in mitigating the deleterious effects caused by the salinity conditions which is an indication of an enhancement potential of tolerating salt-stressed plants when compared to the control group.

Understanding the role of root cell walls in the mechanism of plant tolerance to salinity requires elucidation of the changes caused by salinity in the interactions between the mechanical properties of the cell walls and root growth, and between the chemical composition of the cell walls and root growth. Here, we investigated cell wall composition and extensibility of roots by growing a halophyte (Suaeda salsa) and a glycophyte (Spinacia oleracea) species under an NaCl concentration gradient. Root growth was inhibited by increased salinity in both species. However, root growth was more strongly reduced in S. oleracea than in S. salsa. Salinity reduced cell wall extensibility in S. oleracea significantly, whereas treatment with up to 200 mM NaCl increased it in S. salsa. Meanwhile, S. salsa root cell walls exhibited relatively high cell wall stiffness under 300 mM NaCl treatment, which resist wall deformation under such stress conditions. There was no decrease in pectin content with salinity treatment in the cell walls of the elongation zone of S. salsa roots. Conversely, a decrease in pectin content was noted with increasing salinity in S. oleracea, which might be due to Na+ accumulation. Cellulose content and uronic acid proportions in pectin increased with salinity in both species. Our results suggest that (1) cell wall pectin plays important roles in cell wall extension in both species under salinity, and that the salt tolerance of glycophyte S. oleracea is affected by the pectin; (2) cellulose limits root elongation under saline conditions in both species, but in halophytes, a high cell wall content and the proportion of cellulose in cell walls may be a salt tolerance mechanism that protects the stability of cell structure under salt stress; and (3) the role of the cell wall in root growth under salinity is more prominent in the glycophyte than in the halophyte.

Volatile organic compounds of plant origin can be used to develop biostimulants and plant-growth regulators. While screening volatile compounds from several plant species, safranal (2,6,6-trimethylcyclohexa-1,3-diene-1-carbaldehyde), an apocarotenoid produced by saffron ( Crocus sativus L.), effectively enhanced primary root (PR) elongation in lettuce ( Lactuca sativa L. cv. Legacy) seedlings. Therefore, we aimed to examine the effects of exogenous safranal treatment on the morphological and physiological characteristics of lettuce seedlings. The data showed that, three days after treatment with 19 µmol/L safranal in the dark, lettuce seedlings showed a marked increase in PR length, whereas hypocotyl growth was suppressed. Based on transcriptomic and qRT-PCR analyses, a total of 114 gene expression alterations due to safranal application were detected, including upregulations of ethylene and abscisic acid (ABA) biosynthesis genes. Additionally, safranal promoted ethylene production in both roots and hypocotyls; however, AgNO 3 , an ethylene-signalling inhibitor, did not affect PR or hypocotyl length after safranal treatment. Safranal slightly increased root ABA content. Exogenous treatment with 1 µmol/L fluridone (1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl] pyridin-4(1 H)-one), a carotenoid-biosynthesis inhibitor, did not significantly affect safranal-induced changes in PR or hypocotyl length. Safranal alleviated NaCl (50 mmol/L)-induced inhibition of PR elongation and cell death in lettuce seedlings. Moreover, it mitigated the NaCl-induced increase in root O 2 − and H 2 O 2 content. Altogether, our findings suggest that exogenous safranal regulated PR and hypocotyl lengths. These effects seemingly occur through mechanisms independent of ethylene, ABA, or reactive oxygen species. Safranal apparently alleviated salinity stress by reducing oxidative damage.

Oilseed rape (Brassica napus L.), an important oil crop of the world, suffers various abiotic stresses including salinity stress during the growth stage. While most of the previous studies paid attention to the adverse effects of high salinity stress on plant growth and development, as well as their underlying physiological and molecular mechanisms, less attention was paid to the effects of moderate or low salinity stress. In this study, we first tested the effects of different concentrations of NaCl solution on the seedling growth performance of two oilseed rape varieties (CH336, a semi-winter type, and Bruttor, a spring type) in pot cultures. We found that moderate salt concentrations (25 and 50 mmol L−1 NaCl) can stimulate seedling growth by a significant increase (10~20%, compared to controls) in both above- and underground biomasses, as estimated at the early flowering stage. We then performed RNA-seq analyses of shoot apical meristems (SAMs) from six-leaf-aged seedlings under control (CK), low (LS, 25 mmol L−1), and high (HS, 180 mmol L−1) salinity treatments in the two varieties. The GO and KEGG enrichment analyses of differentially expressed genes (DEGs) demonstrated that such a stimulating effect on seedling growth by low salinity stress may be caused by a more efficient capacity for photosynthesis as compensation, accompanied by a reduced energy loss for the biosynthesis of secondary metabolites and redirecting of energy to biomass formation. Our study provides a new perspective on the cultivation of oilseed rape in saline regions and new insights into the molecular mechanisms of salt tolerance in Brassica crops. The candidate genes identified in this study can serve as targets for molecular breeding selection and genetic engineering toward enhancing salt tolerance in B. napus.

Studies on the wheat response under late sowing (LS) and salinity stress (SS) are available, however, in rice-wheat and cotton-wheat cropping systems, wheat planting is often delayed resulting in co-occurrence of LS and SS in salt affected soils. This two-year field study was conducted to evaluate the influence of foliar application of plant growth regulators (PGRs) [thiourea (TU), salicylic acid (SA) and hydrogen peroxide (H 2 O 2 ); water and no application were taken as control] on the productivity, grain quality and economic returns of timely-sown (TS) and LS wheat under normal (NC) and natural saline conditions (SS; EC 11.27 dS m − 1 ). Delay in sowing and planting in naturally saline soils caused a significant decrease in plant growth, grain yield, grain quality and net economic returns during both years of study. Late planting and SS caused a significant reduction in grain yield reduction by 40.58% and 34.72% (LS) and 40.66% and 42.89% (SS) compared with respective controls during 2021 and 2022, respectively. However, the influence of co-occurrence of LS and SS was more devastating than the individual stress causing 62.17% and 60.18% reduction in grain yield than the respective control during 2021 and 2022, respectively. However, the application of all PGRs improved the grain yield, grain quality and economic turnover under SS and LS stress. The order of improvement in grain yield by the application of PGRs treatments was TU > SA > H 2 O 2 . In conclusion, the application of different plant growth regulators improved economic returns, grain yield and quality attributes of late-sown wheat under saline conditions. In this regard, TU application was the most effective.

The study of effect of elevated temperature on the mechanisms of salt tolerance in plants are of great interest and perspective under global climate change. This study investigated the individual and combined effects of prolonged heat and four days moderate salinity on morphophysiological and biochemical parameters (biomass, photosystems I and II ( F v / F m ) efficiencies, apparent photosynthesis intensity, transpiration, dark respiration, water-use efficiency, contents of water, free proline, Na + and K + in aboveground parts of plants) in the С 4 xero-halophyte Кochia prostrata. The physiological processes and biochemical parameters actively involved during acclimation to stress under different treatments (control, heat, salinity, heat + salinity) were identified. A decrease in biomass and change in the K + /Na + ratio was observed under all treatments. Acclimation to heat resulted in increased dark respiration intensity (Rd) and K + content. Under salinity conditions, an increase in Na + content, a decrease in PSI efficiency and transpiration intensity were observed. Combined stress (heat + salinity) resulted in increased proline and Na + contents in addition to high values of Rd and K + . Principal component analysis showed that under combined stress, dark respiration, K + and proline are actively involved in acclimation. It was found that acclimation to elevated temperature affects the salt tolerance mechanisms in K. prostrata, since under combined stress, sodium ions accumulated 3-fold less than in plants under normal temperature and salinity. It is assumed that in K. prostrata plants grown at elevated temperature, K + and proline are more involved in the acclimation to salinity than Na + . Dark respiration is likely the source of additional energy costs. We conclude that acclimation of С 4 halophytes to elevated temperature changes the importance of sodium and potassium ions, as well as proline, in the mechanisms of salt tolerance.

Glycoside Hydrolase 3 (GH3), a member of the Auxin-responsive gene family, is involved in plant growth, the plant developmental process, and various stress responses. The GH3 gene family has been well-studied in Arabidopsis thaliana and Zea mays. However, the evolution of the GH3 gene family in Oryza species remains unknown and the function of the GH3 gene family in Oryza sativa is not well-documented. Here, a systematic analysis was performed in six Oryza species/subspecies, including four wild rice species and two cultivated rice subspecies. A total of 13, 13, 13, 13, 12, and 12 members were identified in O. sativa ssp. japonica, O. sativa ssp. indica, Oryza rufipogon, Oryza nivara, Oryza punctata, and Oryza glumaepatula, respectively. Gene duplication events, structural features, conserved motifs, a phylogenetic analysis, chromosome locations, and Ka/Ks ratios of this important family were found to be strictly conservative across these six Oryza species/subspecies, suggesting that the expansion of the GH3 gene family in Oryza species might be attributed to duplication events, and this expansion could occur in the common ancestor of Oryza species, even in common ancestor of rice tribe (Oryzeae) (23.07~31.01 Mya). The RNA-seq results of different tissues displayed that OsGH3 genes had significantly different expression profiles. Remarkably, the qRT-PCR result after NaCl treatment indicated that the majority of OsGH3 genes play important roles in salinity stress, especially OsGH3-2 and OsGH3-8. This study provides important insights into the evolution of the GH3 gene family in Oryza species and will assist with further investigation of OsGH3 genes’ functions under salinity stress.

γ-Aminobutyric acid (GABA) accumulates in plants in response to environmental stresses. The activity levels of glutamate decarboxylase (GAD), an enzyme involved in GABA biosynthesis, are reported to increase during germination under salinity stress. However, it is not clear which tissues of the plant seeds are affected by GAD activity in response to salinity stress. In this study, the effects of salinity stress on the distribution of barley seeds GAD activity during germination were investigated. The mass spectrometry imaging (MSI) method was optimized, and the distribution of GAD activity in germinated seeds exposed to salinity stress at different germination stages from 12 to 48 h after imbibition was investigated. In this study, MSI was successfully applied to enzyme histochemistry to visualize the relative GAD activity in germinating barley seeds for the first time. The salinity stress increased the GAD activity, mostly due to the increase in relative GAD activity in the embryo. Higher GAD activity was detected in seeds exposed to salinity stress in the scutellum or aleurone layer, which are difficult to separate for extraction. This method can be used to clarify the role of GABA shunts, including GAD enzyme responses, in barley seeds under stress.