Aluminum tolerance in maize is correlated with increased levels of mineral nutrients, carbohydrates and proline, and decreased levels of lipid peroxidation and Al accumulation

Combined application of biochar and peatmoss for mitigation of drought stress in tobacco

Drought poses a significant ecological threat that limits the production of crops worldwide. The objective of this study to examine the impact of soil applied biochar (BC) and peatmoss (PM) on the morpho-biochemical and quality traits of tobacco plants under drought conditions. In the present experiment work, a pot trial was conducted with two levels of drought severity (~ well-watered 75 ± 5% field capacity) and severe drought stress (~ 35 ± 5% field capacity), two levels of peatmoss (PM) @ 5% [PM+ (with peatmoss) and PM- (without peatmoss)] and three levels of rice straw biochar (BC0 = no biochar; BC1 = 150 mg kg- 1; and BC2 = 300 mg kg- 1 of soil) in tobacco plants. The results indicate that drought conditions significantly impacted the performance of tobacco plants. However, the combined approach of BC and PM significantly improved the growth, biomass, and total chlorophyll content (27.94%) and carotenoids (32.00%) of tobacco. This study further revealed that the drought conditions decreased the production of lipid peroxidation and proline accumulation. But the synergistic approach of BC and PM application increased soluble sugars (17.63 and 12.20%), soluble protein (31.16 and 15.88%), decreased the proline accumulation (13.92 and 9.03%), and MDA content (16.40 and 8.62%) under control and drought stressed conditions, respectively. Furthermore, the combined approach of BC and PM also improved the leaf potassium content (19.02%) by limiting the chloride ions (33.33%) under drought stressed conditions. Altogether, the balanced application of PM and BC has significant potential as an effective approach and sustainable method to increase the tolerance of tobacco plants subjected to drought conditions. This research uniquely highlights the combined potential of PM and BC as an eco-friendly strategy to enhance plant resilience under drought conditions, offering new insights into sustainable agricultural practices.

γ-Aminobutyric acid (GABA) priming alleviates acid-aluminum toxicity to roots of creeping bentgrass via enhancements in antioxidant defense and organic metabolites remodeling

MAIN CONCLUSION

γ-Aminobutyric acid alleviates acid-aluminum toxicity to roots associated with enhanced antioxidant metabolism as well as accumulation and transportation of citric and malic acids. Aluminum (Al) toxicity has become the main limiting factor for crop growth and development in acidic soils and is further being aggravated worldwide due to continuous industrial pollution. The current study was designed to examine effects of GABA priming on alleviating acid-Al toxicity in terms of root growth, antioxidant defense, citrate and malate metabolisms, and extensive metabolites remodeling in roots under acidic conditions. Thirty-seven-day-old creeping bentgrass (Agrostis stolonifera) plants were used as test materials. Roots priming with or without 0.5 mM GABA for 3 days were cultivated in standard nutrient solution for 15 days as control or subjected to nutrient solution containing 5 mM AlCl3·6H2O for 15 days as acid-Al stress treatment. Roots were sampled for determinations of root characteristics, physiological and biochemical parameters, and metabolomics. GABA priming significantly alleviated acid-Al-induced root growth inhibition and oxidative damage, despite it promoted the accumulation of Al in roots. Analysis of metabolomics showed that GABA priming significantly increased accumulations of organic acids, amino acids, carbohydrates, and other metabolites in roots under acid-Al stress. In addition, GABA priming also significantly up-regulated key genes related to accumulation and transportation of malic and citric acids in roots under acid-Al stress. GABA-regulated metabolites participated in tricarboxylic acid cycle, GABA shunt, antioxidant defense system, and lipid metabolism, which played positive roles in reactive oxygen species scavenging, energy conversion, osmotic adjustment, and Al ion chelation in roots.

Combined passivators regulate physiological, antioxidant potential and metals accumulation in potato grown in metals contaminated soil

To solve the problem of excessive heavy metals in farmland soil, there is a dire need for research effort to screen for the soil passivator materials. This study aimed to develop a practical novel approach for improving the potato growth and remedial effectiveness of the metals by optimal combination and dosage of various passivators. Experimental treatments were comprised of various levels of passivating agents (sepiolite, quicklime and calcium magnesium phosphate) in individual and combined form. Results showed that application of passivating agents significantly enhanced growth by optimizing photosynthetic attributes, enzymatic antioxidants, and soil health. Balanced application of passivators effectively reduce the bioavailability of metals, curbing their uptake by potato plants. Sole application of all the agents results statistically similar outcomes as compared with combined form. Additionally, passivators indirectly enhance the activity of essential antioxidant enzymes. Synergistic effect of all the agents significantly improved the tuber quality by decreasing the accumulation of proline, malondialdehyde content, and bioaccumulation of Cu, Pb, Cd, and As in potato parts. In crux, combined usage of passivating agents proved to be of better growth, improvement in antioxidative defense system, and better quality of potato. By mitigating heavy metal contamination, passivators not only enhance crop quality and yield but also ensure heavy metal-free potatoes that meet stringent food safety standards.

CcNFYB3-CcMATE35 and LncRNA CcLTCS-CcCS modules jointly regulate the efflux and synthesis of citrate to enhance aluminium tolerance in pigeon pea

Aluminium (Al) toxicity decreases crop production in acid soils in general, but many crops have evolved complex mechanisms to resist it. However, our current understanding of how plants cope with Al stress and perform Al resistance is still at the initial stage. In this study, the citrate transporter CcMATE35 was identified to be involved in Al stress response. The release of citrate was increased substantially in CcMATE35 over-expression (OE) lines under Al stress, indicating enhanced Al resistance. It was demonstrated that transcription factor CcNFYB3 regulated the expression of CcMATE35, promoting the release of citrate from roots to increase Al resistance in pigeon pea. We also found that a Long noncoding RNA Targeting Citrate Synthase (CcLTCS) is involved in Al resistance in pigeon pea. Compared with controls, overexpression of CcLTCS elevated the expression level of the Citrate Synthase gene (CcCS), leading to increases in root citrate level and citrate release, which forms another module to regulate Al resistance in pigeon pea. Simultaneous overexpression of CcNFYB3 and CcLTCS further increased Al resistance. Taken together, these findings suggest that the two modules, CcNFYB3-CcMATE35 and CcLTCS-CcCS, jointly regulate the efflux and synthesis of citrate and may play an important role in enhancing the resistance of pigeon pea under Al stress.

The 5-azacytidine-induced epimutagenesis of sugarcane (Saccharum spp. hybrids) for aluminium tolerance

A protocol for generating aluminium (Al) tolerant sugarcane using 5-azacytidine (5-azaC)-induced epimutagenesis was developed. Eight (8) plantlets per gram of cultivar N51 calli were generated from the 5-azaC (100 μM) and Al (1.5-50 mM) treatment (+Az + Al) when compared with 104 plantlets from non-mutagenised, no Al control treatment. Following in vitro selection on 60 mM Al, ex vitro stress over four rounds of chimera dissolution during vegetative propagation was applied. In the final stress round, 36% of the Mut 2 epilines survived with plants showing higher relative water content (61.2%) when compared with 47.3% from the stressed control (S N51). The Mut 2 line maintained a higher green leaf area (83.4%) and longer roots (32.4 cm) under stress than S N51 (61.4% and 26.3 cm, respectively). Overall, Mut 2 had a high stress tolerance index of 85.4%, compared with 79.0% from the S N51, nearing that of the non-stressed N51 control (NS N51, 100%) when data were analysed using PCA and clustering analyses of morpho-physiological traits. Analysis of molecular variance (AMOVA) revealed high epigenetic differentiation (ɸst = 0.67) and a variation of 66.6% observed among N51 genotypes. The principal coordinate analysis (PCoA) showed that Mut 2 was epigenetically distinct from S N51. These findings support previous studies that 5-azaC can be used for novel trait creation via epimutagenesis and highlights the necessity for chimera dissolution to achieve stable traits in epibreeding of sugarcane.

Variability in morpho-biochemical, photosynthetic pigmentation, enzymatic and quality attributes of potato for salinity stress tolerance

Salt stress has emerged as a growing global concern, exerting a significant impact on agricultural productivity. The challenges of salt stress on potatoes are crucial for ensuring food security and sustainable agriculture. To address this issue a pot trial was executed to evaluate the impacts of NaCl in the soil on the growth, photosynthetic pigments, and quality attributes of potato, plants were grown in soil spiked with various concentrations of NaCl (0, 1, 3, 5, 7 g kg-1 of soil). Results revealed that salt stress have negative impacts on the growth, biomass, photosynthesis and quality attributes of potato. Lower level of salt stress 1 g kg-1 of soil improved the fresh and dry biomass of leaves (78.70 and 47.74%) and tubers (86.04 and 88.92%) as compared to control, respectively. Higher levels of salt stress (7 g kg-1) increased lipid peroxidation in leaves and improved the enzymatic antioxidants. It was observed that enzyme activities i.e., SOD (134.97%), POD (101.02%), and CAT (28.87%) increased in leaves and are inversely related to the NaCl concentration. The combination of reduction in chlorophyll contents and soluble sugars resulted in lower levels of quality attributes i.e., amylose (68.90%) and amylopectin (16.70%) of potato. Linear relationship in growth, biomass and physiological attributes showed the strong association with increased salt stress. Furthermore, the PCA-heatmap synergy offers identifying clusters of co-regulated attributes, which pinpoint the physiological responses that exhibit the strongest correlation with increasing salt stress levels. Findings indicate that potato can be grown successfully with (1 g kg-1 of NaCl in soil) without negative impacts on plant quality. Furthermore, this study contributes valuable insights into the complexities of salt stress on potato plants and provides a foundation for developing strategies to enhance their resilience in salt-affected environments.

Magnesium alleviates aluminum-induced growth inhibition by enhancing antioxidant enzyme activity and carbon-nitrogen metabolism in apple seedlings

Previous studies have determined that magnesium (Mg) in appropriate concentrations prevents plants from suffering from abiotic stress. To better understand the mechanism of Mg alleviation of aluminum (Al) stress in apple, we investigated the effect of Mg on plant growth, photosynthetic fluorescence, antioxidant system, and carbon (C) and nitrogen (N) metabolism of apple seedlings under Al toxicity (1.5 mmol/L) via a hydroponic experiment. Al stress induced the production of reactive oxygen in the leaves and roots and reduced the total dry weight (DW) by 52.37 % after 20 days of treatment relative to plants grown without Al, due to hindered photosynthesis and alterations in C and N metabolism. By contrast, total DW decreased by only 11.07 % in the Mg-treated plants under Al stress. Supplementation with 3.0 mmol/L Mg in the Al treatment decreased Al accumulation in the apple plants and reduced Al-induced oxidative damage by enhancing the activity of antioxidant enzymes (superoxide dismutase, catalase, and peroxidase) and reducing the production of H₂O₂ and malondialdehyde (MDA). Under Al stress, the Mg-treated plants showed a 46.17 % higher photosynthetic rate than the non-treated plants. Supplementation with Mg significantly increased the sucrose content by increasing sucrose synthase (SS) and sucrose-phosphate synthase (SPS) activities. Moreover, Mg facilitated the transport of ¹³C-carbohydrates from the leaves to roots. Regarding N metabolism, the nitrate reductase (NR), glutamine synthase (GS), and glutamate synthase (GOGAT) activities in the roots and leaves of the Mg-treated plants were significantly higher than those of the non-treated plants under Al stress. Compared with the non-treated plants under Al stress, the Mg-treated plants exhibited a significantly high level of NO₃^- and soluble protein content in the leaves, roots, and stems, but a low level of free amino acids. Furthermore, Mg significantly improved nitrogen accumulation and enhanced the transport of ¹⁵N from the roots to leaves. Overall, our results revealed that Mg alleviates Al-induced growth inhibition by enhancing antioxidant capacity and C-N metabolism in apple seedlings.

Critical values of soil solution Al3+ activity and pH for canola and maize cultivation in two acidic soils

BACKGROUND

Aluminum (Al) toxicity caused by soil acidification is the main constraint for crop growth in tropical and subtropical areas of southern China. The critical values of soil solution Al³⁺ activity and pH for crops in acidic soils can provide a useful reference for soil acidity amelioration.

RESULTS

A pot experiment in a greenhouse was conducted to investigate the critical values of soil solution Al³⁺ activity and pH for canola and maize in an Ultisol and an Alfisol. The critical values of soil solution Al³⁺ activity in Ultisol and Alfisol for canola were 1.5 and 10.0 μmol L^-1 , and 13.9 and 30.4 μmol L^-1 for maize, respectively. The Al tolerance varied with soil type for the same variety of crop. There was more biomass of roots and shoots and higher plant height under the same Al³⁺ activity, and thus greater critical values of soil solution Al³⁺ activity for both crops in Alfisol than those in Ultisol, owing to higher Ca²⁺ /Al³⁺ , Mg²⁺ /Al³⁺ and K⁺ /Al³⁺ ratios in soil solution caused by higher cation exchange capacity and exchangeable base cations in Alfisol, when compared with those in Ultisol. The critical values of soil solution pH for canola and maize in Ultisol were 5.09 and 4.72, respectively; while those in Alfisol were 4.87 and 4.54, respectively.

CONCLUSION

The critical values of Al³⁺ activity were higher for maize than for canola and the critical values for both crops were higher in Alfisol than in Ultisol. The critical soil pH for both crops showed opposite trends to soil Al³⁺ activity. © 2022 Society of Chemical Industry.

Aluminum phosphate sludge as a phosphorus source for maize production under low soil phosphorus availability

Background

With increasing food demand as a consequence of the growing world population, there is a corresponding demand for additional sources of phosphorus (P). Alum-phosphate (Al-P) sludge is a by-product of wastewater treatment and can be a good source of P. In this study, the response of maize (Zea mays L.) to Al-P sludge was tested. Maize was chosen as the test crop due to its prevalent use as human and animal food and as a source of biofuel. The objective of the study was to investigate Al-P sludge as a source of P compared to a commercial fertilizer (monoammonium phosphate, MAP).

Methods

A growth chamber assay was conducted over four cropping cycles (45 d each). The application rate was 9.7, 19.4, 29.1 and 38.8 mg P kg^-1 dry soil. Amendments were applied once at the start of the first cropping cycle. Plants were harvested after each cycle and pots were re-seeded. Dry matter yield (DMY), total P uptake, Al-P uptake, soil total P and Olsen-P concentrations, pH, and EC were measured.

Results

DMY was significantly greater in pots amended with Al-P sludge than in pots treated with MAP. There was a significant rate × cropping cycle interaction effect on DMY with the differences among rates in cycle 1 different from those in cycle 4. Phosphorus uptake depended on cropping cycle, P source and P application rate. With sludge uptake higher than MAP in all cycles, the highest P uptake was observed at the highest application rate except for cycle 2 where this was observed at the rate of 29.1 mg kg^-1. For MAP, phosphorus recovery efficiency (PRE) at the highest rate was significantly greater than that at the lowest rate whereas PRE in cycle 1 was significantly higher than that in cycle 4. In the first two cycles, aluminum uptake was negligible in both MAP and Al-P sludge treatments; however, in cycles 3 and 4, there was significantly more Al in maize from sludge amended pots. Our results show that Al-P sludge was as effective as MAP in supplying enough P for biomass yield. We, therefore, conclude that Al-P sludge could be an alternative source of P, especially for growing maize as feedstock for bioenergy.

Different antioxidant regulation mechanisms in response to aluminum-induced oxidative stress in Eucalyptus species

Forest ecosystems play an important role in environmental protection and maintaining ecological balance. Understanding the physiological mechanisms of tree species response to aluminum (Al) toxic is crucial to reveal the main causes of plantation decline in acid rain area. As an important afforestation tree species in tropical and subtropical areas, Eucalyptus has high economic value and plays crucial ecological roles. However, continuous fertilization and acid precipitation can exacerbate soil acidification and increase soil active Al, which has a significant negative impact on Eucalyptus growth. Hence, species and genotypes with high Al resistance are required to solve the problem of Al toxicity of acidic soils for sustainable forest production. In this study, E. urophylla was better adapted to Al stress than E. grandis or E. tereticornis; its high Al resistance was attributed to greater antioxidant enzyme activity and non-enzymatic antioxidant content, and a lower degree of membrane lipid peroxidation than E. grandis or E. tereticornis. The differences in adaptability among the three pure species were attributed to their distinct habitats. Eucalyptus urophylla × E. grandis inherited the outstanding adaptability to Al stress from its maternal species (E. urophylla), indicating that Al tolerance is highly heritable and can be selected in Eucalyptus breeding. Our results indicated that the response of Eucalyptus to Al stress may fluctuate according to the time under stress, and might be related to dynamic changes in ROS elimination and accumulation.

Methyl jasmonate increases aluminum tolerance in rice by augmenting the antioxidant defense system, maintaining ion homeostasis, and increasing nonprotein thiol compounds

Aluminum (Al) stress is known as a serious threat to the growth and production of crops in acidic soils. Here, the effects of different concentrations of methyl jasmonate (MJ, 0.5 and 1 µM) on rice plants were investigated hydroponically under different concentrations of Al (0.5 and 1 mM). Aluminum treatments injured membrane lipids and photosynthetic apparatus by reducing the leaf contents of mineral nutrients and increasing the accumulation of free radicals (hydrogen peroxide, methylglyoxal, and superoxide anion), resulting in reduced growth and biomass of rice. In comparison to control plants, 0.5 and 1 μM Al treatments lowered height by 21 and 37% and total dry weight by 24 and 41%, respectively. Exogenously added methyl diminished the inhibitory effects of Al stress on growth and photosynthetic apparatus by restoring ion homeostasis and improving chlorophyll metabolism. The application of MJ, by inducing the activity of antioxidant enzymes and the glyoxalase cycle, lessened the levels of the toxic compounds hydrogen peroxide, methylglyoxal, and superoxide anion and, as a result, dwindled the toxic Al-induced oxidative stress. Methyl jasmonate enhanced the leaf accumulation of nonprotein thiol compounds and improved plant tolerance under Al stress by increasing the activity of enzymes involved in the synthesis of thiol compounds. Methyl jasmonate increased the leaf accumulation of glutathione and phytochelatins in Al-stressed plants by increasing the expression of GSH1, PCS, and ABCC1, which reduced the toxicity of toxic Al accumulated in leaves by sequestering toxic Al in vacuoles. Together, the results revealed that MJ increased the tolerance of rice under Al toxicity by maintaining ion homeostasis, improving the activity of antioxidant enzymes and the glyoxalase system, and increasing the level of non-protein thiol compounds. This research adds to our understanding of how MJ may be used in the future to improve Al stress tolerance in sustainable agriculture.

Cadmium Stabilization and Redox Transformation Mechanism in Maize Using Nanoscale Zerovalent-Iron-Enriched Biochar in Cadmium-Contaminated Soil

Cadmium (Cd) is a readily available metal in the soil matrix, which obnoxiously affects plants and microbiota; thus, its removal has become a global concern. For this purpose, a multifunctional nanoscale zerovalent-iron enriched biochar (nZVI/BC) was used to alleviate the Cd-toxicity in maize. Results revealed that the nZVI/BC application significantly enhanced the plant growth (57%), chlorophyll contents (65%), intracellular permeability (61%), and biomass production index (76%) by restraining Cd uptake relative to Cd control. A Cd stabilization mechanism was proposed, suggesting that high dispersion of organic functional groups (C-O, C-N, Fe-O) over the surface of nZVI/BC might induce complex formations with cadmium by the ion exchange process. Besides this, the regular distribution and deep insertion of Fe particles in nZVI/BC prevent self-oxidation and over-accumulation of free radicals, which regulate the redox transformation by alleviating Cd/Fe+ translations in the plant. Current findings have exposed the diverse functions of nanoscale zerovalent-iron-enriched biochar on plant health and suggest that nZVI/BC is a competent material, feasible to control Cd hazards and improve crop growth and productivity in Cd-contaminated soil.

Seed priming with brassinosteroids alleviates aluminum toxicity in rice via improving antioxidant defense system and suppressing aluminum uptake

Brassinosteroids (BRs) are growth-promoting hormones that exhibit high biological activities across various plant species. BRs shield plants against various abiotic stresses. In the present study, the effect of BRs against aluminum (Al) toxicity was investigated through seed priming with 24-epibrassinolide (0.01 μM) in two different rice cultivars. BRs application was found effective in confronting plants from Al toxicity (400 μM). The rice seeds primed with BRs showed enhancement in seed germination energy, germination percentage, root and shoot length, as well as fresh and dry weight under Al-absence and Al-stressed conditions as compared to water-priming. Especially under Al stress, BRs priming promoted the growth of rice seedlings more obviously. Al toxicity significantly increased the Al contents in seedling root and shoot, as well as the MDA concentration, H₂O₂ production, and the activities of antioxidative enzymes including ascorbate peroxidase, catalase, and peroxidase. Meanwhile, the photosynthetic pigments of seedling reduced under Al stress. When compared to sensitive cultivar (CY-927), these modifications were more obvious in the tolerant variety (YLY-689). Surprisingly, BRs were able to alleviate the Al injury by lowering MDA and H₂O₂ level and increasing antioxidant activities and photosynthetic pigments under Al stress. The results on antioxidant activities were further validated by gene expression study of SOD-Cu-Zn, SOD-Fe₂, CATa, CATb, APX02, and APX08. It suggested that BRs were responsible for the mitigation of Al stress in rice seedlings by inducing antioxidant activities with an effective response to other seed growth parameters and reduced Al uptake under induced metal stress.

Exogenous application of silicon improves the performance of wheat under terminal heat stress by triggering physio-biochemical mechanisms

Due to climate change, temperature in late February and early March raised up which cause heat stress at reproductive stage (terminal growth phase of wheat crop) which has become the major causative factor towards low wheat production in arid and semiarid regions. Therefore; strategies need to be adopted for improving terminal heat stress tolerance in wheat. In this study, we assessed whether foliar application of silicon (Si) (2 and 4 mM) at terminal growth phase i.e. heading stage of wheat imposed to heat stress (37 ± 2 °C) under polythene tunnel could improve the performance of wheat. Results of the study revealed that heat stress significantly reduced the photosynthetic pigments (chlorophyll a, b and a + b and carotenoids) leading to a lower grain yield. However, a 4 mM Si application (foliar applied) at heading stage prominently increased the chlorophyll a, b and a + b and carotenoids of flag leaf by improving the activities of enzymatic antioxidants (catalase, peroxidase and superoxide dismutase) and osmoprotectants (soluble sugar protein and proline) under terminal heat stress. Improvements in the performance of wheat (chlorophyll contents, carotenoids, soluble sugar and proteins and proline and yield) with foliar application of Si were also observed under control conditions. Correlation analysis revealed strong association (r > 0.90) of chlorophyll contents and carotenoids with grain and biological yield. Negative correlation (-0.81 < r > -0.63) of physio-biochemical components (antioxidants, proline, soluble sugars and proteins) with yield revealed that under heat stress these components produced in more quantities to alleviate the effects of heat, and Si application also improved these physio biochemical components. In crux, foliar application of Si alleviates the losses in the performance of wheat caused by terminal heat stress by improving the antioxidant mechanism and production of osmoprotectants.

Examination of the Productivity and Physiological Responses of Maize (Zea mays L.) to Nitrapyrin and Foliar Fertilizer Treatments

Nutrient stress has been known as the main limiting factor for maize growth and yield. Nitrapyrin, as a nitrification inhibitor-which reduces nitrogen loss-and foliar fertilizer treatments have been successfully used to enhance the efficiency of nutrient utilization, however, the impacts of these two technologies on physiological development, enzymatic responses, and productivity of maize are poorly studied. In this paper, the concentration of each stress indicator, such as contents of proline, malondialdehyde (MDA), relative chlorophyll, photosynthetic pigments, and the activity of superoxide dismutase (SOD) were measured in maize leaf tissues. In addition, biomass growth, as well as quantitative and qualitative parameters of yield production were examined. Results confirm the enhancing impact of nitrapyrin on the nitrogen use of maize. Furthermore, lower activity of proline, MDA, SOD, as well as higher photosynthetic activity were shown in maize with a more favorable nutrient supply due to nitrapyrin and foliar fertilizer treatments. The obtained findings draw attention to the future practical relevance of these technologies that can be implemented to enhance the physiological development and productivity of maize. However, this paper also highlights the importance of irrigation, as nutrient uptake from soil by the crops decreases during periods of drought.

Lipid Peroxide-Derived Short-Chain Aldehydes are Involved in Aluminum Toxicity of Wheat (Triticum aestivum) Roots

Lipid peroxidation is a common event during aluminum (Al) toxicity in plants, and it generates an array of aldehyde fragments. The present study investigated and compared the profile and physiological functions of lipid peroxide-derived aldehydes under Al stress in two wheat genotypes that differed in Al resistance. Under Al stress, the sensitive genotype Yangmai-5 suffered more severe plasma membrane damage and accumulated higher levels of aldehydes in roots than the Al-tolerant genotype Jian-864. The complementary use of high-resolution mass spectrometry and standard compounds allowed the identification and quantification of 13 kinds of short-chain aldehydes sourced from lipids in wheat roots. Among these aldehydes, acetaldehyde, isovaldehyde, valeraldehyde, (E)-2-hexenal (HE), heptaldehyde, and nonyl aldehyde were the predominant species. Moreover, it was found that HE in the sensitive genotype was over 2.63 times higher than that in the tolerant genotype after Al treatment. Elimination of aldehydes using carnosine rescued root growth inhibition by 19.59 and 11.63% in Jian-864 and Yangmai-5, respectively, and alleviated Al-induced membrane damage and protein oxidation. Exogenous aldehyde application further inhibited root elongation and exacerbated oxidative injury. The tolerant genotype Jian-864 showed elevated aldehyde detoxifying enzyme activity and transcript levels. These results suggest that lipid peroxide-derived short-chain aldehydes are involved in Al toxicity, and a higher aldehyde-detoxifying capacity may be responsible for Al tolerance.

Combined passivators regulate the heavy metal accumulation and antioxidant response of Brassica chinensis grown in multi-metal contaminated soils

Passivation of heavy metals is one of the most efficient techniques to remediate soil pollution. However, passivators with single component are usually unsatisfactory in the case of multi-metal contaminated soils. To resolve this problem, a series of combined passivators containing different ratios of Fe-Mn ore, Fe powder, zeolite, bentonite, etc. were designed and used to study their effects on the growth, heavy metal accumulation, and the antioxidant response of Chinese cabbage (Brassica chinensis L.) as well as the soil available forms of heavy metals in a copper refinery's multi-metal (As, Cd, Pb, Cu) contaminated yellow-brown soil and an artificially contaminated (As, Cd, Pb, Cu) calcareous alluvial soil. The results showed that compared with the control, the addition of combined passivators significantly promoted cabbage growth, with the biomass increase up to 1.77 and 3.54 times in yellow-brown soil and calcareous alluvial soil, respectively. The activity of antioxidant enzymes (SOD, CAT, POD) and the content of malondialdehyde (MDA) and glutathione (GSH) decreased, while the chlorophyll content increased significantly, as compared with no passivators. In addition, passivator application decreased As, Cd, Pb, and Cu contents in shoots and roots by 34.8%, 45.6%, 34.9%, and 11.1% and 49.2%, 63.8%, 38.6%, and 46.4% in yellow-brown soil and by 29.8%, 27.3%, 26.8%, and 25.5% and 45.8%, 55.2%, 61.8%, and 5.7% in calcareous alluvial soil, respectively. Besides, the content of soil available heavy metals was reduced by 8.0-17.1% in yellow-brown soil and 3.3-19.1% in calcareous alluvial soil after the application of passivators. The results indicated that the combined passivators formulated in this experiment could efficiently reduce the content of the multi-metals in cabbage and relieve the oxidant stress and could be used as a way to remediate multi-metal polluted soils.

Arbuscular Mycorrhizae Mitigate Aluminum Toxicity and Regulate Proline Metabolism in Plants Grown in Acidic Soil

Arbuscular mycorrhizal fungi (AMF) can promote plant growth and induce stress tolerance. Proline is reported to accumulate in mycorrhizal plants under stressful conditions, such as aluminum (Al) stress. However, the detailed changes induced in proline metabolism under AMF–plant symbiosis has not been studied. Accordingly, this work aimed to study how Al-stressed grass (barley) and legume (lotus) species respond to AMF inoculation at growth and biochemical levels. The associated changes in Al uptake and accumulation, the rate of photosynthesis, and the key enzymes and metabolites involved in proline biosynthesis and degradation pathways were studied. Soil contamination with Al induced Al accumulation in tissues of both species and, consequently, reduced plant growth and the rate of photosynthesis, while more tolerance was noticed in lotus. Inoculation with AMF significantly reduced Al accumulation and mitigated the negative impacts of Al on growth and photosynthesis in both species; however, these positive effects were more pronounced in barley plants. The mitigating action of AMF was associated with upregulation of proline biosynthesis through glutamate and ornithine pathways, more in lotus than in barley, and repression of its catabolism. The increased proline level in lotus was consistent with improved N metabolism (N level and nitrate reductase). Overall, this study suggests the role of AMF in mitigating Al stress, where regulation of proline metabolism is a worthy mechanism underlying this mitigating action.

New sources of lentil germplasm for aluminium toxicity tolerance identified by high throughput hydroponic screening

Aluminium (Al) toxicity in acid soils inhibits root elongation and development causing reduced water and nutrient uptake by the root system, which ultimately reduces the crop yield. This study established a high throughput hydroponics screening method and identified Al toxicity tolerant accessions from a set of putative acid tolerant lentil accessions. Four-day old lentil seedlings were screened at 5 µM Al (pH 4.5) for three days in hydroponics. Measured pre and post treatment root length was used to calculate the change in root length (ΔRL) and relative root growth (RRG%). A subset of 15 selected accessions were used for acid soil Al screening, and histochemical and biochemical analyses. Al treatment significantly reduced the ΔRL with an average of 32.3% reduction observed compared to the control. Approximately 1/4 of the focused identification of germplasm strategy accessions showed higher RRG% than the known tolerant line ILL6002 which has the RRG% of 37.9. Very tolerant accessions with RRG% of > 52% were observed in 5.4% of the total accessions. A selection index calculated based on all root traits in acid soil screening was highest in AGG70137 (636.7) whereas it was lowest in Precoz (76.3). All histochemical and biochemical analyses supported the hydroponic results as Northfield, AGG70137, AGG70561 and AGG70281 showed consistent good performance. The identified new sources of Al tolerant lentil germplasm can be used to breed new Al toxicity tolerant lentil varieties. The established high throughput hydroponic method can be routinely used for screening lentil breeding populations for Al toxicity tolerance. Future recommendations could include evaluation of the yield potential of the selected subset of accessions under acid soil field conditions, and the screening of a wider range of landrace accessions originating from areas with Al toxic acid soils.

Improvement of the Cu and Cd phytostabilization efficiency of perennial ryegrass through the inoculation of three metal-resistant PGPR strains

To explore a novel strategy for the remediation of soils polluted with Cu and Cd, three strains of plant-growth-promoting rhizobacteria (PGPRs) isolated from contaminated mines and two grass species (perennial ryegrass and tall fescue) were selected in this study. The performance of PGPR strains in metal adsorption, maintaining promotion traits under stress, and ameliorating phytostabilization potential was evaluated. Cd²⁺ exerted a stronger deleterious effect on microbial growth than Cu²⁺, but the opposite occurred for grass seedlings. Adsorption experiment showed that the growing PGPR strains were able to immobilize maximum 79.49% Cu and 81.35% Cd owing to biosorption or bioaccumulation. The strains exhibited the ability to secrete indole-3-acetic acid (IAA) and dissolve phosphorus in the absence and presence of metals, and IAA production was even enhanced in the presence of low Cu²⁺ (5 mg L^-1). However, the siderophore-producing ability of the isolates was strongly suppressed under Cu and Cd exposure. Ryegrass was further selected for pot experiments owing to its higher germination rate and tolerance under Cu and Cd stress than fescue. Pot-experiment results revealed that PGPR addition significantly increased the shoot and root biomasses of ryegrass by 11.49%-44.50% and 43.53%-90.29% in soil co-contaminated with 800 mg Cu kg^-1 and 30 mg Cd kg^-1, respectively. Metal uptake and translocation in inoculated ryegrass significantly decreased owing to the reduced diethylenetriamine pentaacetic acid-extractable metal content and increased residual metal-fraction percentage mediated by PGPR. Interestingly, stress mitigation was observed in these inoculated plants; in particular, their malondialdehyde content and superoxide dismutase activity were even significantly lower than those of ryegrass under normal conditions. Therefore, PGPR could be a promising option to enhance the phytostabilization efficiency of Cu and Cd in heavily polluted soils.

Identification and Characterization of Wheat Germplasm for Salt Tolerance

Salinity is one of the limiting factors of wheat production worldwide. A total of 334 internationally derived wheat genotypes were employed to identify new germplasm resources for salt tolerance breeding. Salt stress caused 39, 49, 58, 55, 21 and 39% reductions in shoot dry weight (SDW), root dry weight (RDW), shoot fresh weight (SFW), root fresh weight (RFW), shoot height (SH) and root length (RL) of wheat, respectively, compared with the control condition at the seedling stage. The wheat genotypes showed a wide genetic and tissue diversity for the determined characteristics in response to salt stress. Finally, 12 wheat genotypes were identified as salt-tolerant through a combination of one-factor (more emphasis on the biomass yield) and multifactor analysis. In general, greater accumulation of osmotic substances, efficient use of soluble sugars, lower Na+/K+ and a higher-efficiency antioxidative system contribute to better growth in the tolerant genotypes under salt stress. In other words, the tolerant genotypes are capable of maintaining stable osmotic potential and ion and redox homeostasis and providing more energy and materials for root growth. The identified genotypes with higher salt tolerance could be useful for developing new salt-tolerant wheat cultivars as well as in further studies to underline the genetic mechanisms of salt tolerance in wheat.

Physiological, Biochemical, and Transcriptomic Responses of Neolamarckia cadamba to Aluminum Stress

Aluminum is the most abundant metal of the Earth's crust accounting for 7% of its mass, and release of toxic Al3+ in acid soils restricts plant growth. Neolamarckia cadamba, a fast-growing tree, only grows in tropical regions with acidic soils. In this study, N. cadamba was treated with high concentrations of aluminum under acidic condition (pH 4.5) to study its physiological, biochemical, and molecular response mechanisms against high aluminum stress. High aluminum concentration resulted in significant inhibition of root growth with time in N. cadamba. The concentration of Al3+ ions in the root tip increased significantly and the distribution of absorbed Al3+ was observed in the root tip after Al stress. Meanwhile, the concentration of Ca, Mg, Mn, and Fe was significantly decreased, but P concentration increased. Aluminum stress increased activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase from micrococcus lysodeiktic (CAT), and peroxidase (POD) in the root tip, while the content of MDA was decreased. Transcriptome analysis showed 37,478 differential expression genes (DEGs) and 4096 GOs terms significantly associated with treatments. The expression of genes regulating aluminum transport and abscisic acid synthesis was significantly upregulated; however, the genes involved in auxin synthesis were downregulated. Of note, the transcripts of several key enzymes affecting lignin monomer synthesis in phenylalanine pathway were upregulated. Our results shed light on the physiological and molecular mechanisms of aluminum stress tolerance in N. cadamba.

Genotypic variation among chickpea and wild Cicer spp. in nutrient uptake with increasing concentration of solution Al at low pH

In many acidic soils, high concentrations of toxic Al³⁺ hamper plant growth by restricting root growth which in turn restricts water and nutrient absorption. Previous research showed variation among chickpea (Cicer arietinum L.) and wild Cicer species in root elongation at 15 μM Al or more, but effects on nutrient absorption have not been examined. The variation in nutrient uptake of two chickpea varieties (PBA HatTrick and PBA Striker) and two wild Cicer species (C. echinospermum (C. echi) and C. reticulatum (C. reti)) was determined in low pH (4.2) nutrient solution with increasing Al concentrations (0, 7.5, 15, 30 μM Al). While C. echi, PBA HatTrick and PBA Striker had thicker roots and more lateral roots compared to C. reti, C. reti had greater aluminium tolerance index (AlTI) at 15 and 30 μM Al. The C. echi had higher uptake of root and shoot Al (7.5, 15 and 30 μM Al), P and S (15 and 30 μM Al) while its uptake was marginally lower for Mg, Ca (all Al treatments) and K (15 and 30 μM Al). By contrast, C. reti contained higher shoot Ca concentration at 15 and 30 μM Al and it had lower root Al uptake. Manganese uptake by C. reti roots and shoots were high enough to induce moderate Mn toxicity at 0 and 7.5 μM Al. Therefore, in response to Al toxicity, C. reti maintained greater AlTI and restricted Al uptake while increasing Ca uptake.

Effect of exogenously-applied abscisic acid, putrescine and hydrogen peroxide on drought tolerance of barley

The objective of this study was to identify the effect of abscisic acid (ABA), putrescine (Put) and hydrogen peroxide (H2O2) foliar pre-treatment on drought tolerance of barley. Despite water limitation, ABA-sprayed plants preserved increased water content, photosynthetic efficiency of PSII (ΦPSII) and CO2 assimilation rate (Pn) compared to untreated stressed plants. The ABA-treated plants presented also the lowest rate of lipid peroxidation (MDA), lowered the rate of PSII primary acceptor reduction (1 – qP) and increased the yield of regulated energy dissipation (NPQ) with higher accumulation of PGRL1 (PROTON GRADIENT REGULATION LIKE1) protein. These plants preserved a similar level of photochemical efficiency and the rate of electron transport of PSII (ETRII) to the well-watered samples. The significantly less pronounced response was observed in Put-sprayed samples under drought. Additionally, the combined effects of drought and H2O2 application increased the 1 – qP and quantum yield of non-regulated energy dissipation in PSII (ΦNO) and reduced the accumulation of Rubisco activase (RCA). In conclusion, ABA foliar application allowed to balance water retention and preserve antioxidant capacity resulting in efficient photosynthesis and the restricted risk of oxidative damage under drought. Neither hydrogen peroxide nor putrescine has been able to ameliorate drought stress as effectively as ABA.

Melatonin mitigates cadmium and aluminium toxicity through modulation of antioxidant potential in Brassica napus L

Melatonin has emerged as an essential molecule in plants, due to its role in defence against metal toxicity. Aluminium (Al) and cadmium (Cd) toxicity inhibit rapeseed seedling growth. In this study, we applied different doses of melatonin (50 and 100 µm) to alleviate Al (25 µm) and Cd (25 µm) stress in rapeseed seedlings. Results show that Al and Cd caused toxicity in rapeseed seedling, as evidenced by a decrease in height, biomass and antioxidant enzyme activity. Melatonin increased the expression of melatonin biosynthesis-related Brassica napus genes for caffeic acid O-methyl transferase (BnCOMT) under Al and Cd stress. The genes BnCOMT-1, BnCOMT-5 and BnCOMT-8 showed up-regulated expression, while BnCOMT-4 and BnCOMT-6 were down-regulated during incubation in water. Melatonin application increased the germination rate, shoot length, root length, fresh and dry weight of seedlings. Melatonin supplementation under Al and Cd stress increased superoxide dismutase, catalase, peroxidase, ascorbate peroxidase, proline, chlorophyll and anthocyanin content, as well as photosynthesis rate. Both Cd and Al treatments significantly increased hydrogen peroxide and malondialdehyde levels in rapeseed seedlings, which were strictly counterbalanced by melatonin. Analysis of Cd and Al in different subcellular compartments showed that melatonin enhanced cell wall and soluble fractions, but reduced the vacuolar and organelle fractions in Al- and Cd-treated seedlings. These results suggest that melatonin-induced improvements in antioxidant potential, biomass, photosynthesis rate and successive Cd and Al sequestration play a pivotal role in plant tolerance to Al and Cd stress. This mechanism may have potential implications in safe food production.

Terminal drought and heat stress alter physiological and biochemical attributes in flag leaf of bread wheat

Heat stress along with low water availability at reproductive stage (terminal growth phase of wheat crop) is major contributing factor towards less wheat production in tropics and sub-tropics. Flag leaf plays a pivotal role in assimilate partitioning and stress tolerance of wheat during terminal growth phase. However, limited is known about biochemical response of flag leaf to combined and individual heat and drought stress during terminal growth phase. Therefore, current study investigated combined and individual effect of terminal drought and heat stress on water relations, photosynthetic pigments, osmolytes accumulation and antioxidants defense mechanism in flag leaf of bread wheat. Experimental treatments comprised of control, terminal drought stress alone (50% field capacity during reproductive phase), terminal heat stress alone (wheat grown inside plastic tunnel during reproductive phase) and terminal drought stress + terminal heat stress. Individual and combined imposition of drought and heat stresses significantly (p≤0.05) altered water relations, osmolyte contents, soluble proteins and sugars along with activated antioxidant defensive system in terms of superoxide dismutase (SOD), peroxidase (POD) and ascorbate peroxidase (APX). Turgor potential, POD and APX activities were lowest under individual heat stress; however, these were improved when drought stress was combined with heat stress. It is concluded that combined effect of drought and heat stress was more detrimental than individual stresses. The interactive effect of both stresses was hypo-additive in nature, but for some traits (like turgor potential and APX) effect of one stress neutralized the other. To best of our knowledge, this is the first report on physiological and biochemical response of flag leaf of wheat to combine heat and drought stress. These results will help future studies dealing with improved stress tolerance in wheat. However, detailed studies are needed to fully understand the genetic mechanisms behind these physiological and biochemical changes in flag leaf in response to combined heat and drought stress.

GsMAS1 Encoding a MADS-box Transcription Factor Enhances the Tolerance to Aluminum Stress in Arabidopsis thaliana

The MADS-box transcription factors (TFs) are essential in regulating plant growth and development, and conferring abiotic and metal stress resistance. This study aims to investigate GsMAS1 function in conferring tolerance to aluminum stress in Arabidopsis. The GsMAS1 from the wild soybean BW69 line encodes a MADS-box transcription factor in Glycine soja by bioinformatics analysis. The putative GsMAS1 protein was localized in the nucleus. The GsMAS1 gene was rich in soybean roots presenting a constitutive expression pattern and induced by aluminum stress with a concentration-time specific pattern. The analysis of phenotypic observation demonstrated that overexpression of GsMAS1 enhanced the tolerance of Arabidopsis plants to aluminum (Al) stress with larger values of relative root length and higher proline accumulation compared to those of wild type at the AlCl3 treatments. The genes and/or pathways regulated by GsMAS1 were further investigated under Al stress by qRT-PCR. The results indicated that six genes resistant to Al stress were upregulated, whereas AtALMT1 and STOP2 were significantly activated by Al stress and GsMAS1 overexpression. After treatment of 50 μM AlCl3, the RNA abundance of AtALMT1 and STOP2 went up to 17-fold and 37-fold than those in wild type, respectively. Whereas the RNA transcripts of AtALMT1 and STOP2 were much higher than those in wild type with over 82% and 67% of relative expression in GsMAS1 transgenic plants, respectively. In short, the results suggest that GsMAS1 may increase resistance to Al toxicity through certain pathways related to Al stress in Arabidopsis.

Response of Common Bean Cultivars and Lines to Aluminum Toxicity

The soils in the common bean-producing regions (Phaseolus vulgaris L.) of Brazil are usually acid and conta\y66\yin toxic levels of aluminum (Al) for plants. This ion causes yield losses by inhibiting root cell expansion, thus reducing water and nutrient uptake. This study investigates the optimal Al concentration for the screening of genotypes in hydroponics cultivation and tries to identify cultivars and lines for cultivation in Al-toxic soils. The study consisted of two series of experiments. In the first one, four cultivars were evaluated at five Al concentrations (0, 2.5, 5, 7.5 and 10 ppm) and in the second, four independent tests were carried out (1-carioca, 2-black, 3-red, and 4-white), each with seven genotypes and two Al concentrations (0 and 4 ppm). The optimized concentration of Al in the first stage was 4 ppm, which allowed the early identification of genotypes with less affected development under Al toxicity in the second stage. The common bean cultivars IPR Quero-Quero (carioca group), BRS Esplendor (black group), KID 44 (red group), and WLine 5 (white group) may be indicated for cultivation under Al toxicity.

A Maize ZmAT6 Gene Confers Aluminum Tolerance via Reactive Oxygen Species Scavenging

Aluminum (Al) toxicity is the primary limiting factor that affects crop yields in acid soil. However, the genes that contribute to the Al tolerance process in maize are still poorly understood. Previous studies have predicted that ZmAT6 is a novel protein which could be upregulated under Al stress condition. Here, we found that ZmAT6 is expressed in many tissues and organs and can be dramatically induced by Al in both the roots and shoots but particularly in the shoots. The overexpression of ZmAT6 in maize and Arabidopsis plants increased their root growth and reduced the accumulation of Al, suggesting the contribution of ZmAT6 to Al tolerance. Moreover, the ZmAT6 transgenic maize plants had lower contents of malondialdehyde and reactive oxygen species (ROS), but much higher proline content and even lower Evans blue absorption in the roots compared with the wild type. Furthermore, the activity of several enzymes of the antioxidant system, such as peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX), increased in ZmAT6 transgenic maize plants, particularly SOD. Consistently, the expression of ZmSOD in transgenic maize was predominant upregulated by Al stress. Taken together, these findings revealed that ZmAT6 could at least partially confer enhanced tolerance to Al toxicity by scavenging ROS in maize.

Silicon dioxide nanoparticles ameliorate the phytotoxic hazards of aluminum in maize grown on acidic soil

Aluminum (Al) toxicity is a major constraint for crop production in acid soils. Therefore, looking for sustainable solutions to increase plant tolerance to Al toxicity is needed. Although several studies addressed the potential utilization of silica or silicon dioxide nanoparticles (SNPs) to ameliorate heavy metal phytotoxicity, the exact mechanisms underlying SNPs-induced stress tolerance are still unknown. The current study investigated how SNPs could mitigate Al toxicity in maize plants grown on acidic soil. The impact of Al alone or in combination with SNPs on Al accumulation and detoxification, plant growth, photosynthetic C assimilation and redox homeostasis has been investigated. Al accumulation in stressed-maize organs reduced their growth, decreased photosynthesis related parameters and increased production of reactive oxygen species, through induced NADPH oxidase and photorespiration activities, and cell damage. These effects were more pronounced in roots than in leaves. SNPs ameliorated Al toxicity at growth, physiological and oxidative damage levels. Co-application of SNPs significantly reduced the activities of the photorespiratory enzymes and NADPH oxidase. It stimulated the antioxidant defense systems at enzymatic (superoxide dismutase, catalase, ascorbate and glutathione peroxidases) and non-enzymatic (ascorbate, glutathione, polyphenols, flavonoids, tocopherols, and FRAP) levels. Moreover, SNPs increased organic acids accumulation and metal detoxification (i.e. glutathione-S-transferase activity) in roots, as a protective mechanism against Al toxicity. The SNPs induced-protective mechanisms was dependent on the applied Al concentration and acted in organ-specific manner. Overall, the current study suggests the promising application of SNPs as an innovative approach to mitigate Al phytotoxicity in acidic soils and provides a comprehensive view of the cellular and biochemical mechanisms underlying this mitigation capacity.

Mining candidate gene for rice aluminum tolerance through genome wide association study and transcriptomic analysis

BACKGROUND

The genetic mechanism of aluminum (Al) tolerance in rice is great complicated. Uncovering genetic mechanism of Al tolerance in rice is the premise for Al tolerance improvement. Mining elite genes within rice landrace is of importance for improvement of Al tolerance in rice.

RESULTS

Genome-wide association study (GWAS) performed in EMMAX for rice Al tolerance was carried out using 150 varieties of Ting's core collection constructed from 2262 Ting's collections with more than 3.8 million SNPs. Within Ting's core collection of clear population structure and kinship relatedness as well as high rate of linkage disequilibrium (LD) decay, 17 genes relating to rice Al tolerance including cloned genes like NRAT1, ART1 and STAR1 were identified in this study. Moreover, 13 new candidate regions with high LD and 69 new candidate genes were detected. Furthermore, 20 of 69 new candidate genes were detected with significant difference between Al treatment and without Al toxicity by transcriptome sequencing. Interestingly, both qRT-PCR and sequence analysis in CDS region demonstrated that the candidate genes in present study might play important roles in rice Al tolerance.

CONCLUSIONS

The present study provided important information for further using these elite genes existing in Ting's core collection for improvement of rice Al tolerance.

Potential of plant beneficial bacteria and arbuscular mycorrhizal fungi in phytoremediation of metal-contaminated saline soils

Phytoremediation has been considered as a promising technique to decontaminate polluted soils. However, climatic stress particularly salinity, is a potential threat to soil properties and plant growth, thus restricting the employment of this technology. The aim of this study was to access the impact of microbial inoculation on phytoremediation of nickel (Ni) contaminated saline soils using Helianthus annuus. Salt resistant plant beneficial bacterium (PBB) Pseudomonas libanensis TR1 and arbuscular mycorrhizal fungus (AMF) Claroideoglomus claroideum BEG210 were used. Inoculation of P. libanensis alone or in combination with C. claroideum significantly enhanced plant growth, changed physiological status (e.g. electrolyte leakage, chlorophyll, proline and malondialdehyde contents) as well as Ni and sodium (Na⁺) accumulation potential (e.g. uptake and translocation factor of Ni and Na⁺) of H. annuus under Ni and salinity stress either alone or in combination. These results revealed that bioaugmentation of microbial strains may serve as a preferred strategy for improving phytoremediation of metal-polluted saline soils.

Aluminum stress differentially affects physiological performance and metabolic compounds in cultivars of highbush blueberry

Aluminum (Al) toxicity is one of the major factors that limit the growth and production of crops in acid soils. Highbush blueberry (Vaccinium corymbosum L.) cultivars differing in resistance to Al toxicity regarding root growth and photosynthetic performance were used. In this study, we compared the physiological and metabolic strategies to cope with Al toxicity among the highbush blueberry cultivars [two new ones (Camellia and Cargo) and three established ones (Brigitta (Al-resistant), Star and Duke)]. Aluminum concentration in roots and leaves increased in all cultivars after 24 and 48 h of exposure to Al, but less so in roots of cultivar Camellia and leaves of cultivar Cargo. These two cultivars displayed minor effects of Al exposure in terms of photosynthetic activity in comparison with the established cultivars. Furthermore, Cargo did not vary fluorescence parameters, whereas Camellia exhibited a decrease in effective quantum yield (ΦPSII) and electron transport rate (ETR) and a change in non-photochemical quenching (NPQ) and maximum quantum yield (Fv/Fm) under Al after 48 h. The Al treatment increased total phenols in leaves of Brigitta, Cargo, and Camellia, whereas antioxidant activity increased in Star and Cargo after 48 h. Aluminum exposure decreased malate concentration in roots of all cultivars, but no change was noted in fumarate concentration. The antioxidant activity correlated with photosynthetic performance and the total phenol concentration in the leaves of new cultivars exposed to Al, suggesting enhanced resistance in the short-term experiment. The principal component analysis separated the new from the established cultivars. In conclusion, the new cultivars appear to be more Al-resistant than the established ones, with Star being most Al-sensitive. Regarding the Al-resistance mechanisms of the new cultivars, it is suggested that Camellia could have a root Al-exclusion mechanism under Al toxicity. This mechanism could be explained by low Al concentration in roots, suggesting that this cultivar could exude organic acid, allowing to chelate Al in the rhizosphere. Nonetheless, further researches are needed to confirm this assumption.

Redox balance, metabolic fingerprint and physiological characterization in contrasting North East Indian rice for Aluminum stress tolerance

Aluminum (Al) toxicity is a serious problem for rice crop productivity in acidic soils worldwide. The present work was conducted to look out for the alteration in ROS homeostasis; metabolic fingerprint; and morphology in two contrasting Indica rice cultivars of North East India (NE India) to Al toxicity. Al stress led to excess accumulation of ROS (H₂O₂ and O₂⁻), and this in turn induced ROS mediated cellular damage, as indicated by lipid peroxidation both qualitatively as well as quantitatively. This excessive ROS production also led to significant reduction in chlorophyll content and stomatal conductance. This was followed by the loss of photosynthetic efficiency as detected by chlorophyll fluorescence. This excessive damage due to ROS prompted us to check the anti-oxidative machinery. Antioxidants, especially enzymes (SOD, APX, POX, GR, CAT, DHAR, MDHAR) are very important players in maintenance of ROS homeostasis. In tolerant variety Disang, higher activity of these enzymes and vice versa in sensitive variety, was observed in response to Al treatment. The non-enzymatic antioxidants (proline, ascorbate and glutathione) also showed similar trend. Though the tolerant variety showed strong anti-oxidative machinery, it was unable to completely nullify the stress experienced by the seedlings. Organic acids are also important players in detoxification of Al stress through efflux in the rhizosphere. In tolerant genotype, citrate exudate was found to be more when compared to sensitive genotypes on exposure to high dose of Al. This is supported by higher abundance of FRDL4, a citrate transporter. Not only FRDL4, other stakeholders for Al stress response like ART1 and ALS1 depicted prominent transcript abundance in the tolerant variety. In conclusion, through this study detailed physiological and metabolic characterisation of two contrasting Indica rice varieties Disang and Joymati, native to NE India for Al tolerance was performed for the very first time.

Nitric oxide precursors prevent Al-triggered auxin flow inhibition in Triticum aestivum roots

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Endogenous NO levels are higher in roots of Al-tolerant wheat.

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NO precursors decrease Al accumulation in wheat root cells.

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NO precursors stimulate auxin flow towards roots in Al-treated wheat.

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Al-induced oxidative stress is attenuated in wheat roots by NO precursors.

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Increased endogenous NO content contribute, in part, to wheat Al tolerance.

Aluminum (Al) is an element widely distributed in soils, even though Al³⁺ is one of the most detrimental cations to plant growth. The effect of nitric oxide (NO) precursors on indole-3-acetic acid (IAA) flow towards roots upon Al treatment is herein reported using two Triticum aestivum (wheat) cultivars with recognized differential Al tolerance. Roots of Al-tolerant seedlings with no treatment (control) accumulated higher amounts of NO than Al-sensitive ones. The treatment with Al further stimulated NO production in root cells while root exposure to NO₃⁻, L-arginine (Arg) or the NO donor S-nitrosoglutathione (GSNO) decreased both Al and lipid peroxide accumulation in both cultivars. Regardless of the cultivar, NO₃⁻, Arg or GSNO prevented the blockage of IAA flow towards roots. Overall, the treatment of wheat roots with NO precursors prior to Al treatment effectively guarantees normal IAA flow towards roots, a condition that favors the organ’s growth and development.

Photosystem II Is More Sensitive than Photosystem I to Al3+ Induced Phytotoxicity

Aluminium (Al) the most abundant metal in the earth's crust is toxic in acid soils (pH < 5.5) mainly in the ionic form of Al3+ species. The ability of crops to overcome Al toxicity varies among crop species and cultivars. Here, we report for a first time the simultaneous responses of photosystem II (PSII) and photosystem I (PSI) to Al3+ phytotoxicity. The responses of PSII and PSI in the durum wheat (Triticum turgidum L. cv. 'Appulo E') and the triticale (X Triticosecale Witmark cv. 'Dada') were evaluated by chlorophyll fluorescence quenching analysis and reflection spectroscopy respectively, under control (-Al, pH 6.5) and 148 μM Al (+Al, pH 4.5) conditions. During control growth conditions the high activity of PSII in 'Appulo E' led to a rather higher electron flow to PSI, which induced a higher PSI excitation pressure in 'Appulo E' than in 'Dada' that presented a lower PSII activity. However, under 148 μM Al the triticale 'Dada' presented a lower PSII and PSI excitation pressure than 'Appulo E'. In conclusion, both photosystems of 'Dada' displayed a superior performance than 'Appulo E' under Al exposure, while in both cultivars PSII was more affected than PSI from Al3+ phytotoxicity.

Yield Losses in Transgenic Cry1Ab and Non-Bt Corn as Assessed Using a Crop-Life-Table Approach

In this study, we constructed crop life tables for Bacillus thuringiensis Berliner (Bt) Cry1Ab and non-Bt corn hybrids, in which yield-loss factors and abundance of predaceous arthropods were recorded during 2 yr at two locations. Corn kernel/grain was the yield component that had the heaviest losses and that determined the overall yield loss in the corn hybrids across years and locations. Yield losses in both corn hybrids were primarily caused by kernel-destroying insects. Helicoverpa zea (Boddie) and Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) were the key loss factors at one location, while at the other, the key loss factor was the silk fly larvae, Euxesta spp. (Diptera: Ulidiidae). Although the realized yield of corn grains was not different (P > 0.05) between Cry1Ab and non-Bt corn hybrids, the Bt corn hybrid reduced (P < 0.05) the damage by H. zea and S. frugiperda in three of the four field trials, particularly at the location where Lepidoptera were the key loss factors. As expected, no reduction in the abundance of predaceous arthropods was observed in Cry1Ab corn fields. Various species of natural enemies were recorded, particularly the earwig Doru luteipes (Scudder) (Dermaptera: Forficulidae), which was the most abundant and frequent predaceous insect. These results indicate that integration of pest management practices should be pursued to effectively minimize losses by kernel-destroying insects during corn reproductive stages when growing non-Bt or certain low-dose Bt corn cultivars for fall armyworm and corn earworm, such as those producing Cry1Ab or other Cry toxins.

Modeling of Cd adsorption to goethite-bacteria composites

The accurate modeling of heavy metal adsorption in complex systems is fundamental for risk assessments in soils and associated environments. Bacteria-iron (hydr)oxide associations in soils and sediments play a critical role in heavy metal immobilization. The reduced adsorption of heavy metals on these composites have been widely reported using the component additivity (CA) method. However, there is a lack of a mechanism model to account for these deviations. In this study, we established models for Cd adsorption on goethite-Pseudomonas putida composites at 1:1 and 5:1 mass ratios. Cadmium adsorption on the 5:1 composite was consistent with the additivity method. However, the CA method over predicted Cd adsorption by approximately 8% on the 1:1 composite at high Cd concentration. The deviation was corrected by adding the site blockage reactions between P. putida and goethite. Both CA and "CA-site masking" models for Cd adsorption onto the composites were in line with the ITC data. These results indicate that CA method in simulating Cd adsorption on bacteria-iron oxides composites is limited to low bacterial and Cd concentrations. Therefore the interfacial complexation reactions that occur between iron (hydr)oxides and bacteria should be taken into account when high concentrations of bacteria and heavy metals are present.

Phosphorus application reduces aluminum toxicity in two Eucalyptus clones by increasing its accumulation in roots and decreasing its content in leaves

Under acidic conditions, aluminum (Al) toxicity is an important factor limiting plant productivity; however, the application of phosphorus (P) might alleviate the toxic effects of Al. In this study, seedlings of two vegetatively propagated Eucalyptus clones, E. grandis × E. urophylla 'G9' and E. grandis × E. urophylla 'DH32-29'were subjected to six treatments (two levels of Al stress and three levels of P). Under excessive Al stress, root Al content was higher, whereas shoot and leaf Al contents were lower with P application than those without P application. Further, Al accumulation was higher in the roots, but lower in the shoots and leaves of G9 than in those of DH32-29. The secretion of organic acids was higher under Al stress than under no Al stress. Further, under Al stress, the roots of G9 secreted more organic acids than those of DH32-29. With an increase in P supply, Al-induced secretion of organic acids from roots decreased. Under Al stress, some enzymes, including PEPC, CS, and IDH, played important roles in organic acid biosynthesis and degradation. Thus, our results indicate that P can reduce Al toxicity via the fixation of elemental Al in roots and restriction of its transport to stems and leaves, although P application cannot promote the secretion of organic acid anions. Further, the higher Al-resistance of G9 might be attributed to the higher Al accumulation in and organic acid anion secretion from roots and the lower levels of Al in leaves.

The Role of the Plasma Membrane H+-ATPase in Plant Responses to Aluminum Toxicity

Aluminum (Al) toxicity is a key factor limiting plant growth and crop production on acid soils. Increasing the plant Al-detoxification capacity and/or breeding Al-resistant cultivars are a cost-effective strategy to support crop growth on acidic soils. The plasma membrane H+-ATPase plays a central role in all plant physiological processes. Changes in the activity of the plasma membrane H+-ATPase through regulating the expression and phosphorylation of this enzyme are also involved in many plant responses to Al toxicity. The plasma membrane H+-ATPase mediated H+ influx may be associated with the maintenance of cytosolic pH and the plasma membrane gradients as well as Al-induced citrate efflux mediated by a H+-ATPase-coupled MATE co-transport system. In particular, modulating the activity of plasma membrane H+-ATPase through application of its activators (e.g., magnesium or IAA) or using transgenics has effectively enhanced plant resistance to Al stress in several species. In this review, we critically assess the available knowledge on the role of the plasma membrane H+-ATPase in plant responses to Al stress, incorporating physiological and molecular aspects.

Inoculation of Brassica oxyrrhina with plant growth promoting bacteria for the improvement of heavy metal phytoremediation under drought conditions

The aim of this study was to investigate the effects of drought resistant serpentine rhizobacteria on plant growth and metal uptake by Brassica oxyrrhina under drought stress (DS) condition. Two drought resistant serpentine rhizobacterial strains namely Pseudomonas libanensis TR1 and Pseudomonas reactans Ph3R3 were selected based on their ability to stimulate seedling growth in roll towel assay. Further assessment on plant growth promoting (PGP) parameters revealed their ability to produce indole-3-acetic acid, siderophore and 1-aminocyclopropane-1-carboxylate deaminase. Moreover, both strains exhibited high resistance to various heavy metals, antibiotics, salinity and extreme temperature. Inoculation of TR1 and Ph3R3 significantly increased plant growth, leaf relative water and pigment content of B. oxyrrhina, whereas decreased concentrations of proline and malondialdehyde in leaves under metal stress in the absence and presence of DS. Regardless of soil water conditions, TR1 and Ph3R3 greatly improved organ metal concentrations, translocation and bioconcentration factors of Cu and Zn. The successful colonization and metabolic activities of P. libanensis TR1 and P. reactans Ph3R3 represented positive effects on plant development and metal phytoremediation under DS. These results indicate that these strains could be used as bio-inoculants for the improvement of phytoremediation of metal polluted soils under semiarid conditions.

Cadmium accumulation and tolerance of Lagerstroemia indica and Lagerstroemia fauriei (Lythraceae) seedlings for phytoremediation applications

Contamination by heavy metals is one of the most serious environmental problems generated from human activities. Because phytoremediation utilizes plants to uptake contaminants, it could potentially be used to remediate metal-contaminated areas. A pot culture experiment with four levels of cadmium (Cd) (0, 20, 40, and 80 mg of Cd/kg dry soil) was conducted to investigate Cd accumulation and tolerance of roots, shoots, and leaves of Lagerstroemia indica and Lagerstroemia fauriei as well as their potential for phytoremediation. Experimental results indicated that Cd inhibited seedling growth only at the higher Cd exposure concentration (40 and 80 mg/kg). The tolerance index revealed that on average L. indica is more tolerant of Cd than L. fauriei. Moreover, plants in the experiment accumulated Cd differentially. In comparisons between L. indica and L. fauriei, the leaves of the former had higher concentrations of Cd, while the roots of latter had higher concentrations of Cd. Furthermore, the roots, shoots, and leaves had very high bioaccumulation factors that markedly exceeded 1.0 (exceptional only in shoots of 80 mg/kg for L. fauriei), indicating that the seedlings extracted Cd from the soil. The leaves' translocation factor of L. indica was greater than 1.0, being significantly higher than that of L. fauriei. Chlorophyll a, Chlorophyll b and total declined in both species significantly as Cd concentrations exceeded 40 mg/kg in the soil. In contrast, lipid peroxidation and proline content was found to increase with increasing Cd concentration. From the assessments of biomass production, Cd tolerance and uptake L. indica and L. fauriei could stand as excellent species for remediating Cd-contaminated soils.

Application of Plant-Growth-Promoting Fungi Trichoderma longibrachiatum T6 Enhances Tolerance of Wheat to Salt Stress through Improvement of Antioxidative Defense System and Gene Expression

Soil salinity is a serious problem worldwide that reduces agricultural productivity. Trichoderma longibrachiatum T6 (T6) has been shown to promote wheat growth and induce plant resistance to parasitic nematodes, but whether the plant-growth-promoting fungi T6 can enhance plant tolerance to salt stress is unknown. Here, we determined the effect of plant-growth-promoting fungi T6 on wheat seedlings' growth and development under salt stress, and investigated the role of T6 in inducing the resistance to NaCl stress at physiological, biochemical, and molecular levels. Wheat seedlings were inoculated with the strain of T6 and then compared with non-inoculated controls. Shoot height, root length, and shoot and root weights were measured on 15 days old wheat seedlings grown either under 150 mM NaCl or in a controlled setting without any NaCl. A number of colonies were re-isolated from the roots of wheat seedlings under salt stress. The relative water content in the leaves and roots, chlorophyll content, and root activity were significantly increased, and the accumulation of proline content in leaves was markedly accelerated with the plant growth parameters, but the content of leaf malondialdehyde under saline condition was significantly decreased. The antioxidant enzymes-superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) in wheat seedlings were increased by 29, 39, and 19%, respectively, with the application of the strain of T6 under salt stress; the relative expression of SOD, POD, and CAT genes in these wheat seedlings were significantly up-regulated. Our results indicated that the strain of T6 ameliorated the adverse effects significantly, protecting the seedlings from salt stress during their growth period. The possible mechanisms by which T6 suppresses the negative effect of NaCl stress on wheat seedling growth may be due to the improvement of the antioxidative defense system and gene expression in the stressed wheat plants.

Assessment of the impact of Aluminum on germination, early growth and free proline content in Lactuca sativa L

Aluminum (Al) toxicity is a major problem in crop production on acid soils. The use of industrial or municipal wastewaters, which may be contaminated with metals, for irrigation in agriculture is common over the world. This action can increase the concentration of these agents in the soil and decrease crops yields. In order to evaluate the toxicological effects of recommended Al levels in irrigation water, under acidic conditions, on lettuce, seeds of two cultivars ("cv Reine de Mai" and "cv White Boston") were exposed to five different Al concentrations (0, 0.05, 0.5, 5 and 20mg/L) and germination percentage, root and shoot lengths were measured. Also, the germination rate and the vigor index were calculated, and the proline content was estimated for all concentrations. Results showed that seed germination was not negatively affected by Al, but the germination rate decreased in both cultivars. For the other factors analyzed, with the exception of 20mg/L concentration for "cv White Boston", Al induced, in general, negative effects including the content of proline that increased in the seeds that were exposed to this metal. The "cv Reine de Mai" was more sensitive for the analyzed concentrations than the other cultivar.. The results indicated that even recommended Al concentrations for irrigation, under acidic conditions, can interfere negatively in seed germination and seedling establishment and possibly with crop production.

Physiological Mechanisms behind Differences in Pod Shattering Resistance in Rapeseed (Brassica napus L.) Varieties

Pod shattering resistance index (SRI) is a key factor affecting the mechanical harvesting of rapeseed. Research on the differences in pod shattering resistance levels of various rapeseed varieties can provide a theoretical basis for varietal breeding and application in mechanical harvesting. The indicators on pod shattering resistance including pod morphology and wall components were evaluated on eight hybrids and open pollinators, respectively, during 2012–2014. The results showed the following: (1) From the current study, SRI varied greatly with variety, and conventional varieties had stronger resistance than hybrid according to the physiological indexes. and (2) Under the experimental conditions, the SRI was linearly related to pod wall weight and the water content in pod walls, and the goodness-of-fit measurements for the regression model of the SRI based on pod wall weight and water content were 0.584** and 0.377*, respectively, reaching the significant level. This illustrated that pod wall weight and the water content in pod walls determined the SRI. (3) Compared with the relative contents of biochemical components in pod walls, the contents of particular biochemical components in pod walls had closer correlations with SRI. Among the biochemical components, the hemicellulose content was the decisive factor for the SRI.

Oxidative Metabolism of Rye (Secale cereale L.) after Short Term Exposure to Aluminum: Uncovering the Glutathione-Ascorbate Redox Network

One of the major limitations to plant growth and yield in acidic soils is the prevalence of soluble aluminum ions (Al(3+)) in the soil solution, which can irreversible damage the root apex cells. Nonetheless, many Al-tolerant species overcome Al toxicity and are well-adapted to acidic soils, being able to complete their life cycle under such stressful conditions. At this point, the complex physiological and biochemical processes inherent to Al tolerance remain unclear, especially in what concerns the behavior of antioxidant enzymes and stress indicators at early plant development. Since rye (Secale cereale L.), is considered the most Al-tolerant cereal, in this study we resort to seedlings of two genotypes with different Al sensitivities in order to evaluate their oxidative metabolism after short term Al exposure. Al-induced toxicity and antioxidant responses were dependent on rye genotype, organ and exposure period. Al affected biomass production and membrane integrity in roots and leaves of the sensitive (RioDeva) genotype. Catalase was the primary enzyme involved in H2O2 detoxification in the tolerant (Beira) genotype, while in RioDeva this task was mainly performed by GPX and POX. Evaluation of the enzymatic and non-enzymatic components of the ascorbate-glutathione cycle, as well the oxalate content, revealed that Beira genotype coped with Al stress by converting DHA into oxalate and tartarate, which posteriorly may bind to Al forming non-toxic chelates. In contrast, RioDeva genotype used a much more ineffective strategy which passed through ascorbate regeneration. So, remarkable differences between MDHAR and DHAR activities appear to be the key for a higher Al tolerance.

Aluminum resistance in wheat involves maintenance of leaf Ca(2+) and Mg(2+) content, decreased lipid peroxidation and Al accumulation, and low photosystem II excitation pressure

The phytotoxic aluminum species (Al(3+)) is considered as the primary factor limiting crop productivity in over 40 % of world's arable land that is acidic. We evaluated the responses of two wheat cultivars (Triticum aestivum L.) with differential Al resistance, cv. Yecora E (Al-resistant) and cv. Dio (Al-sensitive), exposed to 0, 37, 74 and 148 μM Al for 14 days in hydroponic culture at pH 4.5. With increasing Al concentration, leaf Ca(2+) and Mg(2+) content decreased, as well as the effective quantum yield of photosystem II (PSII) photochemistry (Φ PSII ), while a gradual increase in leaf membrane lipid peroxidation, Al accumulation, photoinhibition (estimated as F v /F m ), and PSII excitation pressure (1 - q p ) occurred. However, the Al-resistant cultivar with lower Al accumulation, retained larger concentrations of Ca(2+) and Mg(2+) in the leaves and kept a larger fraction of the PSII reaction centres (RCs) in an open configuration, i.e. a higher ratio of oxidized to reduced quinone A (QA), than plants of the Al-sensitive cultivar. Four times higher Al concentration in the nutrient solution was required for Al-resistant plants (148 μM Al) than for Al-sensitive (37 μM Al), in order to establish the same closed RCs. Yet, the decline in photosynthetic efficiency in the cultivar Dio was not only due to closure of PSII RCs but also to a decrease in the quantum yield of the open RCs. We suggest that Al(3+) toxicity may be mediated by nutrient deficiency and oxidative stress, and that Al-resistance of the wheat cultivar Yecora E, may be due at least partially, from the decreased Al accumulation that resulted to decreased reactive oxygen species (ROS) formation. However, under equal internal Al accumulation (exposure Al concentration: Dio 74 μM, Yecora E 148 μM) that resulted to the same oxidative stress, the reduced PSII excitation pressure and the better PSII functioning of the Al-resistant cultivar was probably due to the larger concentrations of Ca(2+) and Mg(2+) in the leaves. We propose that the different sensitivities of wheat cultivars to Al(3+) toxicity can be correlated to differences in the redox state of QA. Thus, chlorophyll fluorescence measurements can be a promising tool for rapid screening of Al resistance in wheat cultivars.

Salt effects on proline and glycine betaine levels and photosynthetic performance in Melilotus siculus, Tecticornia pergranulata and Thinopyrum ponticum measured in simulated saline conditions

We measured proline and glycine betaine levels and photosynthetic performance (net-photosynthetic rate (Pn), stomatal conductance (gs), maximum quantum yield of PSII (Fv/Fm) and non-photochemical quenching (NPQ)) in relation to Na+ and Cl- accumulation in Melilotus siculus (Turra) B.D.Jacks. (Fabaceae), Tecticornia pergranulata (J.M.Black) K.A.Sheph. & Paul G.Wilson (Amaranthaceae: Salicornioideae) and Thinopyrum ponticum (Podp.) Z.-W.Liu & R.-C.Wang (Poaceae) grown under saline conditions in the greenhouse. These plants were selected in this study because of their known salt-tolerance capacity and value as forage plants. Moreover, the pasture legume M. siculus is considered to have particular potential for saline land remediation because of its salinity and waterlogging tolerance. Maximum Na+ and Cl- accumulation occurred in Te. pergranulata shoots. Minimum was in Th. ponticum shoots. Maximum Na+ accumulation occurred in the roots of Te. pergranulata, whereas that of Cl- occurred in the roots of Th. ponticum. Accumulation of both Na+ and Cl- was the least in M. siculus roots. Te. pergranulata metabolized high levels of glycine betaine (110µmolg-1 DW). M. siculus metabolized high levels of proline (6µmolg-1 DW). Th. ponticum accumulated intermediate levels of these organic osmolytes. No significant change occurred in Fv/Fm values. Pn value increased and NPQ value decreased in Te. pergranulata with increasing salinity and the reverse occurred in both M. siculus and Th. ponticum. A negative significant correlation occurred between Pn and glycine betaine in M. siculus and Th. ponticum. A positive significant correlation occurred between NPQ and glycine betaine in M. siculus. No correlation occurred between proline and Pn, proline and NPQ in the tested three plants. Te. pergranulata could maintain cell-osmotic balance by synthesising high levels of organic osmolytes especially glycine betaine and concurrently showing the most efficient photosynthetic performance. Compared with the levels of osmolytes in Te. pergranulata, the levels of osmolytes that occur in M. siculus and Th. ponticum were insufficient to maintain cell-osmotic balance and also that M. siculus and Th. ponticum showed a lower level of photosynthetic performance. We conclude that glycine betaine is potentially the vital organic osmolyte for Te. pergranulata and Th. ponticum enabling salinity stress tolerance. However, in M. siculus, proline appears to be the potential organic osmolyte in salinity stress tolerance. In terms of the potential of these species for stabilising saline soils in central-western New South Wales, Te. pergranulata would be the candidate of choice; however, for greater pasture value Th. ponticum would be the next.