Physiological and Biochemical Parameters of Salinity Resistance of Three Durum Wheat Genotypes

Comparative Performance of Ionic and Agro-Physiological Traits for Detecting Salt Tolerance in Wheat Genotypes Grown in Real Field Conditions

Studying the physiological mechanisms underlying the traits associated with salt tolerance in genotypes could lead to the discovery of new genetic resources for salt tolerance. In this study, the mechanisms of salt tolerance were evaluated, based on ionic, physiological, and agronomic traits in four varieties that differ in their salt tolerance and in 18 F8 recombinant inbred lines (RILs) grown in real field conditions. The salt tolerance of plant materials was assessed under both normal (3.5 mM NaCl) and high salinity stress (150 mM NaCl) conditions for two consecutive years. Different growth and physiological traits were assessed 75 days after sowing, while ion contents in the shoots, grain yield, and its components were determined at the maturity stage. Multivariate analysis was used to conduct a comprehensive evaluation of salt tolerance across various genotypes and traits. The ANOVA results showed significant differences (p ≤ 0.05 and 0.001) among salinity, genotypes, and their interactions for all ionic and agro-physiological traits, with a few exceptions. Salinity stress resulted in a considerable increase in Na+ content and canopy temperature (CT), with a simultaneous decrease of 11.3% to 94.5% in other ionic and agro-physiological traits compared to the control treatment. However, the salt-tolerant genotypes showed minimal increases in Na+ content and CT, as well as decreases in other ionic and agro-physiological traits when compared to salt-sensitive genotypes under salinity stress. All ionic and agro-physiological traits exhibited strong correlations with each other under salinity stress, but these correlations were weak or insignificant under control conditions. The principal component analysis identified Na+ and CT as negative indicators and other ionic and agro-physiological traits as positive indicators for salt tolerance under salinity stress. The negative indicators were strongly linked to salt-sensitive genotypes, while the positive indicators were closely associated with salt-tolerant genotypes. Heatmap clustering, using multiple traits, successfully differentiated the salt-tolerant genotypes from the salt-sensitive ones. The salt-tolerant group showed a significant reduction in Na+ content by 36.9%, in CT by 10.0%, and in HI by 16.7%, along with an increase of 6.3-51.4% in other ionic and agro-physiological traits compared to the salt-sensitive group. In conclusion, the mechanisms associated with Na+ exclusion and high K+/Na+ and Ca2+/Na+ ratios, as well as chlorophyll and relative water content, along with low CT, resulted in significant improvements in growth and yield under salinity stress conditions. Given that the effectiveness of various ionic and agro-physiological traits in evaluating salt tolerance in wheat has been proven in real field conditions, these traits will play a key role in the development of salt-tolerant wheat genotypes.

Salt tolerance in wheat is associated with the maintenance of shoot biomass, stomatal conductance, and sucrose in the phloem

Wheat (Triticum aestivum L.) is a mega-staple for millions of the world's populations and its yield potential is impacted by soil salinization. This study investigated genotypic variation in salt tolerance among six wheat genotypes, Gladius, Drysdale, GD0014, GD0120, GD0180, and GD0185. The study also characterized shoot traits, photosynthetic traits, leaf Na and K concentrations, and phloem sucrose. The plants were grown under controlled growth room conditions at 0 mM NaCl (Control) and 100 mM NaCl. The results showed that the salt tolerance index (STISFW, SFW: shoot fresh weight) varied from 0.52 for GD0120 to 0.69 for GD0180. Based on the STISFW, salt tolerance for the wheat genotypes was in the order, GD0180 > Gladius > GD0185 > Drysdale > GD0014 > GD0120. Projected shoot area (PSA) at all growth stages, 14, 20, 27, 34, and 40 DAS were strongly correlated with SFW at 45 DAS. Salt treatment significantly increased phloem sucrose level in the salt intolerant, Drysdale, while having no effect on this parameter in Gladius. Gladius showed greater maintenance of stomatal conductance than Drysdale. The relative ratio of K/Na between treatment and control was strongly correlated with the relative ratio of SFW (r = .85). The correlation between PSA at 14 DAS and SFW at 45 DAS and the correlation between the relative ratio of K/Na between treatment and control with STISFW identify these parameters to be potential traits for screening salt tolerance in wheat. Higher salt tolerance in Gladius would be associated with higher maintenance of stomatal conductance and enhanced phloem sucrose transport.

Comparative adaptability assessment of bread wheat and synthetic hexaploid genotypes under saline conditions using physiological, biochemical, and genetic indices

The tolerance to salinity stress is an intricate phenomenon at cellular and whole plant level that requires the knowledge of contributing physiological and biochemical processes and the genetic control of participating traits. In this context, present study was conducted with objective to evaluate the physiological, biochemical, and genetic responses of different wheat genotypes including bread wheat (BW) and synthetic hexaploids (SHs) under saline and control environment. The experiment was conducted in two factorial arrangement in randomized complete block design (RCBD), with genotypes as one factor and treatments as another factor. A significant decline in physiological traits (chlorophyll, photosynthesis, stomatal conductance, transpiration, and cell membrane stability) was observed in all genotypes due to salt stress; however, this decline was higher in BW genotypes as compared to four SH genotypes. In addition, the biochemical traits including enzymes [superoxide dismutase, catalase, and peroxidase (POD)] activity, proline, and glycine betaine (GB) illustrated significant increase along with increase in the expression of corresponding genes (TaCAT1, TaSOD, TaPRX2A, TaP5CS, and TaBADH-A1) due to salt stress in SHs as compared to BW. Correspondingly, highly overexpressed genes, TaHKT1;4, TaNHX1, and TaAKT1 caused a significant decline in Na+/K+ in SH as compared to BW genotypes under salt stress. Moreover, correlation analysis, principal component analysis (PCA), and heatmap analysis have further confirmed that the association and expression of physiological and biochemical traits varied significantly with salinity stress and type of genotype. Overall, the physiological, biochemical, and genetic evaluation proved SHs as the most useful stock for transferring salinity tolerance to other superior BW cultivars via the right breeding program.

Halotolerant Endophytic Bacteria Regulate Growth and Field Performance of Two Durum Wheat Genotypes with Contrasting Salinity Tolerance Potential

Soil salinity hampers durum wheat plant growth and development at various stages. The detrimental effects of salinity on plant cellular and physiological processes necessitate strategies to alleviate its negative impact and improve overall crop yield. This study investigates the efficacy of plant growth-promoting rhizobacteria (PGPR) bacteria inoculation in mitigating salinity stress on two durum wheat genotypes with contrasting degrees of salinity tolerance (Tamaroi, salt-sensitive and Line 5004, salt-tolerant) under greenhouse and field conditions. For this purpose, two halotolerant-PGPR strains, Pseudomonas jordanii strain G34 and Oceanobacillus jordanicus strain GSFE11, were utilized for the inoculation. For the greenhouse experiment, the two selected genotypes were subjected to salinity at the flag leaf stage with continuous irrigation with a Hoagland solution supplemented with 50 mM NaCl. Field experiments were conducted across two locations with contrasting salinity levels over two growing seasons. At the end of both experiments, various parameters including total weight, spike weight, grain weight, spike number, spikelet number, grains per spike and thousand kernel weight were measured. The halotolerant PGPRs, P. jordanii strain G34 and O. jordanicus strain GSFE11, proved effective in alleviating salinity-induced adverse effects and enhancing growth under greenhouse and field conditions. However, bacterial inoculation significantly improved growth in the salt-sensitive genotype and such effects were not observed in the tolerant genotype, emphasizing genotype-specific responses. Notably, inoculation with O. jordanicus increased Na+ and Ca2+ uptake in the salt-tolerant "Line 5004" without hindering growth, suggesting one of its potential mechanisms for salt tolerance. This research demonstrates the potential of halotolerant-PGPR inoculation in enhancing durum wheat production in saline environments, but also underscores the importance of understanding genotype-specific responses for tailored interventions.

Codium fragile (Suringar) Hariot as Biostimulant Agent to Alleviate Salt Stress in Durum Wheat: Preliminary Results from Germination Trials

Soil salinization is a critical environmental problem in arid and semiarid regions of the world. The aim of the present study was to evaluate the effect of an algae-based biostimulant on germination and seedling vigour of durum wheat (Triticum turgidum L. subsp. durum (Desf.) Husn.), under different saline conditions (0, 100, and 200 mM NaCl). The experiment was carried out under controlled-environment conditions. Seeds were sprayed with a solution containing a combination of fungicide and different concentrations of Codium fragile (Suringar) Hariot algae (0%w/v, 10%w/v, 20%w/v, and 30%w/v). All experimental units were placed in a germination cabinet. The effect of the seaweed extract (SWE) on seed germination and seedling performance under salinity stress was evaluated over a period of 8 days. Coleoptile length and biomass were found to be significantly and positively affected by the application of different SWE doses as compared to the control treatment (0% algae). As for germination traits, seeds treated with SWE showed a final germination (from 82% to 88%), under severe saline conditions, significantly higher than that observed in the control treatment (61%). Our findings indicate that the appropriate dose of biostimulant can markedly improve the germination and the seedlings vigour of durum wheat seeds under saline conditions. Additional studies will be needed to understand the mechanism of action of this biostimulant and its effectiveness in longer studies under field conditions.

Measurements of Leaf Gas-Exchange Parameters Using Portable CIRAS-3 Infrared Gas Analyzer, with a Parkinson Leaf Chamber (PLC6)

Ranges of portable systems to measure leaf gas-exchange parameters are available. They allow real-time measurements of the photosynthesis rate (A), transpiration rate (E), stomatal conductance (gs), and intercellular CO2 concentration (Ci). Photosynthetic CO2 uptake is one of the most frequently studied plant physiological processes. The measurement is precise, simple, and noninvasive to perform in vivo. We describe the use of this method in environmental-controlled plant production systems at different temperatures on the growth and development of common buckwheat.

Ameliorating the adverse effects of salinity on wheat plants using the bio-wastes (pomegranate peel extract and /or compost)

Climate changes and the related rise in the frequency of excessive weather proceedings have a strong influence on the physical, chemical, and hydrological processes in soils. Recently the investigators confirmed that the use of biological treatments and resources to overcome abiotic stress is fruitful. Thus, pomegranate peel extract (PPE) because of its high efficacy and/or compost application could improve soil characteristics, soil organic matter and nutrient status. This effect may be referred back to the enhancement in the plant antioxidative defense system against stress conditions. This experiment was done to study the influence of spraying wheat plants with pomegranate peel extract (PPE) with and/or without soil compost added under salt stress on some growth parameters and physiological aspects. Wheat plants were grown in the presence or absence of compost in the soil and foliar sprayed with PPE (600 and 1200 mg L-1) under salt irrigation (3000 and 6000 mg L-1). Growth and yield traits were decreased with salinity stress. High levels of PPE (1200 mg L-1) induced the highest values of osmoprotectants (Total soluble sugars, total soluble protein, proline and free amino acids) in both unstressed or salinity-stressed plants presence or absence compost. Using compost in soil for cultivating wheat plants and PPE spraying treatments increased growth traits photosynthetic pigments and yield components. Moreover, these treatments increased the accumulation of minerals content (N, P, K and Ca) in plants. In general, the results of correlation coefficients showed a significant strong positive relationship among measured yield traits and other tested parameters. The correlation between 1000-grain Wt. and grain Wt./spike (r = 0.94**) was the highest. Meanwhile, a strong negative correlation coefficient between Na% and all yield parameters was recorded. Compost adding to soil and spraying pomegranate peel extract is a successful method for increasing wheat growth, yield and improving the nutritional value of the produced grains under salt stress.

Polyphosphate fertilizer impacts the enzymatic and non-enzymatic antioxidant capacity of wheat plants grown under salinity

By 2050, the predicted global population is set to reach 9.6 billion highlighting the urgent need to increase crop productivity to meet the growing demand for food. This is becoming increasingly challenging when soils are saline and/or deficient in phosphorus (P). The synergic effect of P deficiency and salinity causes a series of secondary stresses including oxidative stress. Reactive Oxygen Species (ROS) production and oxidative damage in plants caused either by P limitation or by salt stress may restrict the overall plant performances leading to a decline in crop yield. However, the P application in adequate forms and doses could positively impact the growth of plants and enhances their tolerance to salinity. In our investigation, we evaluated the effect of different P fertilizers forms (Ortho-A, Ortho-B and Poly-B) and increasing P rates (0, 30 and 45 ppm) on the plant's antioxidant system and P uptake of durum wheat (Karim cultivar) grown under salinity (EC = 3.003 dS/m). Our results demonstrated that salinity caused a series of variations in the antioxidant capacity of wheat plants, at both, enzymatic and non-enzymatic levels. Remarkably, a strong correlation was observed between P uptake, biomass, various antioxidant system parameters and P rates and sources. Soluble P fertilizers considerably enhanced the total plant performances under salt stress compared with control plants grown under salinity and P deficiency (C+). Indeed, salt-stressed and fertilized plants exhibited a robust antioxidant system revealed by the increase in enzymatic activities of Catalase (CAT) and Ascorbate peroxidase (APX) and a significant accumulation of Proline, total polyphenols content (TPC) and soluble sugars (SS) as well as increased biomass, Chlorophyll content (CCI), leaf protein content and P uptake compared to unfertilized plants. Compared to OrthoP fertilizers at 45 ppm P, Poly-B fertilizer showed significant positive responses at 30 ppm P where the increase reached + 18.2% in protein content, + 156.8% in shoot biomass, + 93% in CCI, + 84% in shoot P content, + 51% in CAT activity, + 79% in APX activity, + 93% in TPC and + 40% in SS compared to C+. This implies that PolyP fertilizers might be an alternative for the suitable management of phosphorus fertilization under salinity.

Molecular Mechanisms of Plant Defense against Abiotic Stress

The climatic changes and anthropogenic factors in recent decades (global warming, drought, salinity, extreme temperature, environmental pollution) have led to an increase in the negative impact of environmental factors on plants. Abiotic stress strongly influences the important processes of plants and thus affects their growth and development. The effects of stressors on the plants depend on the intensity, frequency, and duration of stress, plant species as well as a combination of various stressors. Plants have developed different mechanisms to limit adverse environmental conditions. In the publications in this Special Issue, Molecular Mechanisms of Plant Defense against Abiotic Stress, new information on plant defense mechanisms against abiotic and biotic stress is presented. The studies help us better understand plants' protection mechanisms again global climate change.

AtCIPK16, a CBL-interacting protein kinase gene, confers salinity tolerance in transgenic wheat

Globally, wheat is the major source of staple food, protein, and basic calories for most of the human population. Strategies must be adopted for sustainable wheat crop production to fill the ever-increasing food demand. Salinity is one of the major abiotic stresses involved in plant growth retardation and grain yield reduction. In plants, calcineurin-B-like proteins form a complicated network with the target kinase CBL-interacting protein kinases (CIPKs) in response to intracellular calcium signaling as a consequence of abiotic stresses. The AtCIPK16 gene has been identified in Arabidopsis thaliana and found to be significantly upregulated under salinity stress. In this study, the AtCIPK16 gene was cloned in two different plant expression vectors, i.e., pTOOL37 having a UBI1 promoter and pMDC32 having a 2XCaMV35S constitutive promoter transformed through the Agrobacterium-mediated transformation protocol, in the local wheat cultivar Faisalabad-2008. Based on their ability to tolerate different levels of salt stress (0, 50, 100, and 200 mM), the transgenic wheat lines OE1, OE2, and OE3 expressing AtCIPK16 under the UBI1 promoter and OE5, OE6, and OE7 expressing the same gene under the 2XCaMV35S promoter performed better at 100 mM of salinity stress as compared with the wild type. The AtCIPK16 overexpressing transgenic wheat lines were further investigated for their K⁺ retention ability in root tissues by utilizing the microelectrode ion flux estimation technique. It has been demonstrated that after 10 min of 100 mM NaCl application, more K⁺ ions were retained in the AtCIPK16 overexpressing transgenic wheat lines than in the wild type. Moreover, it could be concluded that AtCIPK16 functions as a positive elicitor in sequestering Na⁺ ions into the cell vacuole and retaining more cellular K⁺ under salt stress to maintain ionic homeostasis.

Photosynthetic machinery under salinity stress: Trepidations and adaptive mechanisms

Chloroplasts and photosynthesis are the physiologically fateful arenas of salinity stress. Morphological and anatomical alterations in the leaf tissue, ultrastructural changes in the chloroplast, compromise in the integrity of the three-layered chloroplast membrane system, and defects in the light and dark reactions during the osmotic, ionic, and oxidative phases of salt stress are conversed in detail to bring the salinity-mediated physiological alterations in the chloroplast on to a single platform. Chloroplasts of salt-tolerant plants have evolved highly regulated salt-responsive pathways. Thylakoid membrane remodeling, ion homeostasis, osmoprotection, upregulation of chloroplast membrane and stromal proteins, chloroplast ROS scavenging, efficient retrograde signalling, and differential gene and metabolite abundance are the key attributes of optimal photosynthesis in tolerant species. This review throws light into the comparative mechanism of chloroplast and photosynthetic response to salinity in sensitive and tolerant plant species.