Evaluation of the genetic diversity of wild Salvadora persica 'Arak' from Saudi Arabia.

Assessment of genetic diversity is crucial for efficient selection genotypes in plant breeding and improvement programs. Studies of genetic diversity of S. persica are rare relative to the large species diversity in Saudi Arabia, despite its valuable importance as one of the most popular medicinal plants. We investigate the genetic variability and genetic differentiation among and within wild Salvadora persica populations distributed in four regions of Saudi Arabia. Twelve sequence-related amplified polymorphism (SRAP) primers combination generated 326 alleles, with an average of 27.2 alleles per primer. All primers showed 100 polymorphism percentage, and higher PIC values exceeded 0.90. Jaccard similarity values varied between 0.04 to 0.43, with an average of 0.31, which showed a weak relationship among the accessions and their origin. Based on UGPMA and principal coordinate analysis, accessions collected from the same region showed less aggregation. Genetic diversity parameters showed that both Aflaj and Joodah populations recorded the highest mean values for the effective number of alleles (1.26 and 1.24). Shannon index and genetic heterozygosity (0.23 and 0.15 for both populations), and percent of polymorphism 45.45% for Aflaj and 43.87 for Joodah population. Most of the genetic variation was because of differences within populations (77%) and 23% among populations. SRAP markers explored the genetic diversity among and within S. persica populations. In this work, genetic diversity within populations was high, and the population structure was weak. We detected no specific geographic structure, which may reveal an active movement of plants among populations.

Exogenous melatonin mitigates boron toxicity in wheat.

Boron (B) toxicity is an important abiotic constraint that limits crop productivity mainly in arid and semi-arid areas of the world. High levels of B in soil disturbs several physiological and biochemical processes in plant. The aim of this study was to investigate the function of melatonin (Mel) in the regulation of carbohydrate and proline (Pro) metabolism, photosynthesis process and antioxidant system of wheat seedlings under B toxicity conditions. High levels of B inhibited net photosynthetic rate (PN), stomatal conductance (gs), content of chlorophyll (Chl) a, b, δ-aminolevulinic acid (δ-ALA), nitrogen (N) and phosphorus (P), and increased accumulation of B, Chl degradation and activity of chlorophyllase (Chlase; a Chl degrading enzyme), and downregulated the activity of enzymes (δ-ALAD; δ-aminolevulinic acid dehydratase) involved in the biosynthesis of photosynthesis pigments, photosynthesis (carbonic anhydrase and ribulose-1,5-bisphosphate carboxylase/oxygenase) and carbohydrate metabolism (cell wall invertase, CWI) in wheat seedlings. Also, high levels of B caused oxidative damage by increasing the content of malondialdehyde, superoxide anion and H2O2, and activity of glycolate oxidase (an H2O2-producing enzyme) in leaves of seedlings. However, foliar application of Mel significantly improved photosynthetic pigments concentration by increasing δ-ALA, δ-ALAD and decreasing Chl degradation and Chlase activity and led to an increase of plant growth attributes under both B toxicity and non-toxicity conditions. Under normal and B toxicity conditions, exogenous Mel also improved content of N, P, total soluble carbohydrates (TSCs) and Pro, and upregulated activity of CWI and Δ1-pyrroline-5-carboxylate synthetase. Mel significantly suppressed the adverse effects of excess B by alleviating cellular oxidative damage through enhanced reactive oxygen species scavenging by superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase and lipoxygenase, and content of total phenolic compounds (TPC), ascorbate and reduced glutathione. These results postulate that Mel induced plant defense mechanisms by enhancing Pro, TSCs, TPC, nutrients (N and P) uptake and enzymatic and non-enzymatic antioxidants.

Hydrogen Sulfide-Mediated Activation of O-Acetylserine (Thiol) Lyase and l/d-Cysteine Desulfhydrase Enhance Dehydration Tolerance in Eruca sativa Mill.

Hydrogen sulfide (H2S) has emerged as an important signaling molecule and plays a significant role during different environmental stresses in plants. The present work was carried out to explore the potential role of H2S in reversal of dehydration stress-inhibited O-acetylserine (thiol) lyase (OAS-TL), l-cysteine desulfhydrase (LCD), and d-cysteine desulfhydrase (DCD) response in arugula (Eruca sativa Mill.) plants. Dehydration-stressed plants exhibited reduced water status and increased levels of hydrogen peroxide (H2O2) and superoxide (O2•-) content that increased membrane permeability and lipid peroxidation, and caused a reduction in chlorophyll content. However, H2S donor sodium hydrosulfide (NaHS), at the rate of 2 mM, substantially reduced oxidative stress (lower H2O2 and O2•-) by upregulating activities of antioxidant enzymes (superoxide dismutase, peroxidase, and catalase) and increasing accumulation of osmolytes viz. proline and glycine betaine (GB). All these, together, resulted in reduced membrane permeability, lipid peroxidation, water loss, and improved hydration level of plants. The beneficial role of H2S in the tolerance of plants to dehydration stress was traced with H2S-mediated activation of carbonic anhydrase activity and enzyme involved in the biosynthesis of cysteine (Cys), such as OAS-TL. H2S-treated plants showed maximum Cys content. The exogenous application of H2S also induced the activity of LCD and DCD enzymes that assisted the plants to synthesize more H2S from accumulated Cys. Therefore, an adequate concentration of H2S was maintained, that improved the efficiency of plants to mitigate dehydration stress-induced alterations. The central role of H2S in the reversal of dehydration stress-induced damage was evident with the use of the H2S scavenger, hypotaurine.