osmotic stress

Iran's arid and semi-arid regions span over 1.5 million km², accounting for nearly 92% of the country's total area. Drought is one of the most critical abiotic stresses affecting these areas. Due to challenges faced in breeding improved drought-tolerant genotypes, the domestication and cultivation of drought-resistant plants have emerged as the best solution to prevent the extinction of wild species and restore pastures. Selecting drought-tolerant plants during the germination stage is crucial for successful plant establishment. Seed germination is the first and most important developmental stage, that is influenced by genetic and environmental factors. The hydrotime model describes the relationship between water potential (ψ) and seed germination rate and percentage. This model quantifies the rate of germination progression (hydrotime constant: θH), the uniformity of germination (standard deviation of the base water potential: σψb), and the stress tolerance of germination [base osmotic potential for 50% germination: ψb(50)]. These indicators can be used to determine seed vigor and seed dormancy and the effects of treatments on seed viability. This study aimed to use hydrotime model to predict of germination response of three medicinal species of Nepeta haussknechtii, N. pogonosperma, and N. glomerulosa subsp. staffina to water potential. 

For each species, six water potential levels (0, -0.3, -0.6, -0.9, -1.2, and -1.5 MPa) were applied using a completely randomized design with three replications in 1402 at the Seed Technological Research Laboratory of the Natural Resources Gene Bank, Iran. Seed germination of species was recorded daily at a temperature of 25°C. Since no germination was observed at a potential level of -1.5 MPa, this treatment was excluded from the analysis. The hydrotime model was then fitted to the germination data, and the hydrotime constant (θH), base osmotic potential for 50% germination ψb(50), and standard deviation of the base water potential (σψb) were quantified. 

The analysis of variance revealed significant effects of drought (at five levels of 0, -0.3, -0.6, -0.9, and -1.2 MPa) on all seed germination characteristics of all three Nepeta species (P<0.05). The hydrotime model results showed that the germination rate under drought stress was higher in N. haussknechtii (θH=48.32) than in N. glomerulosa (θH=52.13) and N. pogonosperma (θH=56.57). Furthermore, the germination uniformity of N. haussknechtii (σψb=0.18) was higher than that of N. glomerulosa (σψb=0.39) and N. pogonosperma (σψb=0.24). In terms of drought resistance, N. pogonosperma (ψb(50)=-1.006) exhibited greater resistance compared to N. haussknechtii (ψb(50)=-0.69) and N. glomerulosa (ψb(50)=-0.77).

Osmotic stress significantly impacted the germination pattern, timing, and rate of Nepeta seeds. Since seed quality concerning drought resistance determines the speed and uniformity of germination, the output of the hydrotime model, including parameters θH, σψb, and ψb(50), was effective in predicting germination percentages under drought stress conditions. Drought-tolerant genotypes were identified using the hydrotime model, with N. pogonosperma being the most resistant species, followed by N. haussknechtii and N. glomerulosa. The hydrotime model is a tool in breeding programs for identifying high-efficiency genotypes' resistance to stress conditions.

Drought stress is one of the main obstacles in the of crops  production. A factorial experiment in a completely randomized design with four replications, first factor cultivars include Roshan and Kaver (Drought tolerate), Qods and Mahdavi (drought sensitive), Shole and Tabasi (medium resistance to drought) and the second factor was the osmotic stress applied with polyethylene glycol 8000 at three levels of 0,- 5 and -10 bar, Seeds of germinated cultivars were cultured under hogland conditions for 15 days under osmotic stress. In this study, the importance of the expression of P5CS and P5CR genes in relation to proline and MDA accumulation and their physiological role under osmotic stress conditions in six wheat cultivars was investigated. The effect of cultivars on proline accumulation was significant at 5% level .Proline contents of leaf and root of drought tolerant cultivars was -10 times more resistant than drought sensitive cultivars. In order to compare the mean interactions of osmotic stress × cultivars, the highest mean in the cultivars bright (drought tolerant) at osmotic stress level of -10 bars was showed. No significant accumulation of proline was observed in Roshan and Kaver cultivars, which are known as more resistant cultivars. Increasing osmotic stress and increasing MDA concentration were higher in Shole and Tabasi cultivars than other cultivars. By increasing the level of osmotic stress in the cultivars, the relative expression of genes P5CS and P5CR transcription increased. The genes showed at the level of osmotic stress -10 bar in Qods cultivar (sensitive), the gave highest expression in relative transcripts. While The highest relative expression was observed in the osmotic stress level of -5 bar in the Roshan cultivar (drought resistant).

Fluctuations in environmental water potential caused by drought and salinity are the most important abiotic stress factors in many natural habitats of organisms. Compatible solutes stabilize biomolecules and whole cells and play as stress-protective agents. Ectoine and its derivative 5-hydroxyectoine as compatible solutes are synthesized widely by the members of the bacteria, a few archaea, and eukarya in response to high salinity and osmolarity. Previously reported that the genetically engineered ectoine synthesis using ectA, ectB or ectC has resulted in increased hyperosmotic tolerance of model plants. In this review, the importance of current and potential applications of ectoines as protecting agents for macromolecules, cells, and tissues, are discussed. Besides, the leading theory for the protection mechanism of ectoines including the exclusion of ectoines molecules from the protein surface, slows the diffusion of water molecules and preserve the native state of the protein were explained. The experimental data of the past decades concerning alleviating drought and salinity stresses by ectoines and the prospects for their use in different fields of modern biotechnology, including genetic engineering techniques, have been summarized in this review article.

Osmotic stress (such as drought stress) is a serious limiting factor to rice production and yield stability in worldwide. In order to locate the QTL associated with tolerance to osmotic stresses in germination stage and determine the contribution of each QTL on the phenotypic variation caused 96 lines of F8 Anbarboo × Sepeedrud (tolerant and sensitive to drought stress in germination stage, respectively) an experiment was conducted at Gonbad Kavous university in 2011-2013. For construction of genetic linkage map, 365 SSR marker and 32 primer combination were evaluated. 136 polymorphic SSR markers and 21 primer combination were used for providing of linkage map. Germination components including root length, shoot, coleoptile and the percentage of seed germination was recorded for 100 seed of each line in the osmotic stress resulting from sucrose, sorbitol and mannitol. For root length in all three stress conditions was found a QTL on chromosome 4 that had positive effect in all cases. Among the identified QTL, qSUC-5 (QTL for coleoptile length under sucrose stress) on chromosome 5, qSUR-2 (QTL for radicle length under sucrose stress) on chromosome 2 and qSUR-4 (QTL for radicle length under sucrose stress) on chromosome 4, respectively, 23, 23 and 26% of phenotypic variation for coleoptile and root length were justified in terms of osmotic stress. This QTL explained that due to the high percentage of candidates for marker-assisted selection programs recombinant line population of Iranian rice.

DREB transcription factors are one of the four independent regulation systems in plants which involves in abiotic stress signaling pathway and activation of stress responsive genes. For identification and isolation of DREB genes, one-year-old own-rooted grapevine’ were used. Potted plants were subjected to150mM NaCl during the experiment and total RNA was extracted. Specific primers were designed based on predicted DREB and SbDREB2A gene homologue in halophilic plant Salicornia brachiata. VvDREB and VvsDREB (DREB like 2C) genes were isolated from grapevine (Vitis vinifera L.’ Askari’). Bioinformatics results indicated that VvDREB gene has 85% similarity with DREB2 genes from soybean family and VvsDREB gene has 80% similarity with SbDRE 2A gene. SbDREB2A and VvsDREB proteins motif studies in ELM database showed that there are no five motifs (BRCT, MAPK, PKB, NES, NLS) in VvsDREB protein.