Dose-response curves: the next frontier in plant ecology.

A large fraction of experimental work in plant ecology, and thus also on ecosystem functioning and the delivery of ecosystem services, describes experiments that have been carried out under controlled (glasshouse) conditions. Controlled growth settings commonly sacrifice realism through, for example, reducing the densities of plant species in the pots and controlling how environmental settings such as moisture and light vary in favor of a higher mechanistic resolution, which makes these studies particularly suitable for subsequent syntheses. We explore the possibility that further integration of dose-response curves can maximize the impact of existing studies. We suggest that we can expand considerably the scope of the dose and response variables that are considered in plant ecology.

Arbuscular mycorrhizal fungus Rhizophagus irregularis alleviates drought stress in soybean with overexpressing the GmSPL9d gene by promoting photosynthetic apparatus and regulating the antioxidant system.

Drought is the most destructive abiotic stress and negatively affects crop growth and productivity. Modern breeding efforts have produced numerous cultivars with distinct genetic traits that improve crop growth and drought stress tolerance. Arbuscular mycorrhizal fungi (AMF) can enhance drought tolerance in soybean plants by directly providing nutrients to plants, promoting photosynthesis, or influencing interspecific plant interactions in natural communities. However, the interactions between AMF and wild and transgenic soybean genotypes remain unclear. Therefore, in the present study, we evaluated the effect of arbuscular mycorrhizal fungi on the growth performance of drought-stressed transgenic soybean lines (ZXOE-11 and ZXOE-13) overexpressing GmSPL9d gene and their wild soybean Tianlong 1 (TL1) at the seedling stage (45 d after sowing). The results showed that colonization of wild and transgenic soybean with Rhizophagus irregularis significantly decreased the adverse effects of drought on plant growth. AMF inoculation significantly increased plant biomass, root activity, chlorophyll metabolism, photosynthesis, and chlorophyll fluorescence in wild-type and transgenic plants under both control and drought stress conditions. Drought causes the production of ROS, such as hydrogen peroxide, which enhances MDA, thereby decreasing the membrane stability index (MSI). However, AMF-inoculated plants exhibited decreased ROS accumulation and increased MSI. Moreover, AMF treatment significantly improved osmolyte, nitrogen, and nitrate reductase activity under control and drought conditions, which increased the relative water content. Furthermore, AMF treatment enhanced the antioxidant systems of drought-stressed plants by increasing the activities of peroxidase, superoxide dismutase, catalase, and ascorbate peroxidase. AMF improved the growth performance, photosynthesis, and antioxidant activity of transgenic plants under drought stress conditions. The present findings indicate that the AMF contribution to soybean seedling drought tolerance was more significant for the transgenic plants than for the wild plants under drought conditions. The current findings emphasize the possibility of growth and photosynthetic variation in the degree of AMF-associated drought resistance in soybean plants. Our findings suggest that future crop breeding challenges include developing cultivars for sustainable production and maximizing crop cultivar and fungal species (AMF) combinations in drought-stressed regions.

Dysfunction of GmVPS8a causes compact plant architecture in soybean.

Vacuolar Protein Sorting 8 (Vps8) protein is a specific subunit of the class C core vacuole/endosome tethering (CORVET) complex that plays a key role in endosomal trafficking in yeast (Saccharomyces cerevisiae). However, its functions remain largely unclear in plant vegetative growth. Here, we identified a soybean (Glycine max) T4219 mutant characterized with compact plant architecture. Map-based cloning targeted to a candidate gene GmVPS8a (Glyma.07g049700) and further found that two nucleotides deletion in the first exon of GmVPS8a causes a premature termination of the encoded protein in the T4219 mutant. Its functions were validated by CRISPR/Cas9-engineered mutation in the GmVPS8a gene that recapitulated the T4219 mutant phenotypes. Furthermore, NbVPS8a-silenced tobacco (Nicotiana benthamiana) plants exhibited similar phenotypes to the T4219 mutant, suggesting its conserved roles in plant growth. The GmVPS8a is widely expressed in multiple organs and its protein interacts with GmAra6a and GmRab5a. Combined analysis of transcriptomic and proteomic data revealed that dysfunction of GmVPS8a mainly affects pathways on auxin signal transduction, sugar transport and metabolism, and lipid metabolism. Collectively, our work reveals the function of GmVPS8a in plant architecture, which may extend a new way for genetic improvement of ideal plant-architecture breeding in soybean and other crops.

Unraveling the Diverse Roles of Neglected Genes Containing Domains of Unknown Function (DUFs): Progress and Perspective.

Domain of unknown function (DUF) is a general term for many uncharacterized domains with two distinct features: relatively conservative amino acid sequence and unknown function of the domain. In the Pfam 35.0 database, 4795 (24%) gene families belong to the DUF type, yet, their functions remain to be explored. This review summarizes the characteristics of the DUF protein families and their functions in regulating plant growth and development, generating responses to biotic and abiotic stress, and other regulatory roles in plant life. Though very limited information is available about these proteins yet, by taking advantage of emerging omics and bioinformatic tools, functional studies of DUF proteins could be utilized in future molecular studies.

Genetic variation in nitrogen-use efficiency and its associated traits in dryland winter wheat (Triticum aestivum L.) cultivars released from the 1940s to the 2010s in Shaanxi Province, China.

BACKGROUND: Improving the nitrogen-use efficiency (NUE) of wheat can help mitigate the problems of poor soil fertility under dryland conditions. We conducted field experiments using three nitrogen (N) fertilization levels (0, 120, and 180 kg ha-1 ) applied to eight dryland wheat cultivars to assess NUE and its associated traits. RESULTS: The grain yield significantly increased with the improvement in variety, mainly as a result of a substantial increase in 1000-grain weight and harvest index. Modern wheat varieties have stabilized at an optimal plant height and exhibited improved performance in terms of NUE, partial N productivity, N harvest index, and grain protein content compared to older varieties. The NUE of wheat gradually increased with variety replacement. The net photosynthesis rate of the flag leaves in the filling stage improved with the year of cultivar release; Increasing soil-plant analysis development (SPAD) values of flag leaves in the flowering and filling stages were observed over time, with the flag leaves of modern varieties showing a high chlorophyll content in the filling stage. Additionally, the principal component analysis showed that the SPAD value, grain number per unit area, transpiration rate, leaf area, and grain protein content positively contributed to the clustering of the N180 and modern cultivars (from the 2000s to 2010s). CONCLUSION: Overall, high levels of N application did not significantly improve the NUE of wheat. However, modern wheat varieties can optimize N distribution, increase flag leaf photosynthetic capacity, and improve photosynthesis ability, thus enhancing NUE to achieve high yields under a suitable level of N supply. © 2022 Society of Chemical Industry.

NAC Transcription Factor GmNAC12 Improved Drought Stress Tolerance in Soybean.

NAC transcription factors (TFs) could regulate drought stresses in plants; however, the function of NAC TFs in soybeans remains unclear. To unravel NAC TF function, we established that GmNAC12, a NAC TF from soybean (Glycine max), was involved in the manipulation of stress tolerance. The expression of GmNAC12 was significantly upregulated more than 10-fold under drought stress and more than threefold under abscisic acid (ABA) and ethylene (ETH) treatment. In order to determine the function of GmNAC12 under drought stress conditions, we generated GmNAC12 overexpression and knockout lines. The present findings showed that under drought stress, the survival rate of GmNAC12 overexpression lines increased by more than 57% compared with wild-type plants, while the survival rate of GmNAC12 knockout lines decreased by at least 46%. Furthermore, a subcellular localisation analysis showed that the GmNAC12 protein is concentrated in the nucleus of the tobacco cell. In addition, we used a yeast two-hybrid assay to identify 185 proteins that interact with GmNAC12. Gene ontology (GO) and KEGG analysis showed that GmNAC12 interaction proteins are related to chitin, chlorophyll, ubiquitin-protein transferase, and peroxidase activity. Hence, we have inferred that GmNAC12, as a key gene, could positively regulate soybean tolerance to drought stress.

Exogenous calcium promotes growth of adzuki bean (Vigna angularis Willd.) seedlings under nitrogen limitation through the regulation of nitrogen metabolism.

Plants exhibit lower nitrogen use efficiency (NUE) under N-limitation conditions. Although the function of calcium (Ca) has been widely studied in plants, it remains to be explored whether regulation of nitrate uptake and reduction is needed. A hydroponics experiment on adzuki beans (Vigna angularis Willd.) was used as a test material to determine the interactions between Ca and three levels of nitrogen supply. The height of the plant, the leaf area per plant, the biomass of the plant, the morphology of the roots, the hydraulic conductivity of the roots, the level of gas exchange, and the level of N metabolism of the adzuki beans were evaluated. Furthermore, RT-qPCR was conducted to explore the expression of genes related to nitrate transporter responses to Ca under N-limitation stress conditions. The rate of accumulation of N in plant tissue increased with the application of Ca. However, plant biomass, photosynthetic parameters, and root activity peaked for Ca2+ supply under N-marginal conditions. Further investigation revealed that the activities of nitrate reductase and glutamine synthetase were relatively high. The transcription of the nitrate transporter (VaNRT1.1; VaNRT2.5) was up-regulated in the roots of the Ca-treated plants. Both N-marginal conditions and N deficiency inhibit N absorption and utilization. The favorable effects of Ca on seedling growth and N metabolism under N-marginal conditions were more significant than those under N-deficiency conditions. The supply of Ca2+ is optimal, as it increases NUE by enhancing photosynthesis, N-metabolizing enzyme activities, and NO3 uptake and transport under N-marginal conditions.

An APETALA2/ethylene responsive factor transcription factor GmCRF4a regulates plant height and auxin biosynthesis in soybean.

Plant height is one of the key agronomic traits affecting soybean yield. The cytokinin response factors (CRFs), as a branch of the APETALA2/ethylene responsive factor (AP2/ERF) super gene family, have been reported to play important roles in regulating plant growth and development. However, their functions in soybean remain unknown. This study characterized a soybean CRF gene named GmCRF4a by comparing the performance of the homozygous Gmcrf4a-1 mutant, GmCRF4a overexpression (OX) and co-silencing (CS) lines. Phenotypic analysis showed that overexpression of GmCRF4a resulted in taller hypocotyls and epicotyls, more main stem nodes, and higher plant height. While down-regulation of GmCRF4a conferred shorter hypocotyls and epicotyls, as well as a reduction in plant height. The histological analysis results demonstrated that GmCRF4a promotes epicotyl elongation primarily by increasing cell length. Furthermore, GmCRF4a is required for the expression of GmYUCs genes to elevate endogenous auxin levels, which may subsequently enhance stem elongation. Taken together, these observations describe a novel regulatory mechanism in soybean, and provide the basis for elucidating the function of GmCRF4a in auxin biosynthesis pathway and plant heigh regulation in plants.

Effects of Different Processing Methods Based on Different Drying Conditions on the Active Ingredients of Salvia miltiorrhiza Bunge.

Compared to the traditional processing method, fresh processing can significantly enhance the preservation of biologically active ingredients and reduce processing time. This study evaluated the influences of fresh and traditional processing based on different drying conditions (sun drying, oven drying and shade drying) on the active ingredients in the roots and rhizomes of S. miltiorrhiza. High-performance liquid chromatography (HPLC) was utilized to determine the contents of six active ingredients in the roots and rhizomes of S. miltiorrhiza. The data were analyzed by fingerprint similarity evaluation, hierarchical cluster analysis (HCA) and principal component analysis (PCA). The results suggest that compared to the traditional processing method, the fresh processing method may significantly increase the preservation of biologically active ingredients. Furthermore, the findings demonstrated that among the three drying methods under fresh processing conditions, the shade-drying (21.02-26.38%) method is most beneficial for retaining the active ingredients in the roots and rhizomes of S. miltiorrhiza. Moreover, the fingerprint analysis identified 17 common peaks, and the similarity of fingerprints among samples processed by different methods ranged from 0.989 to 1.000. Collectively, these results suggest novel processing methods that may improve the yield of active ingredients for S. miltiorrhiza and may be implemented for industrial production.

Seed Germination Behavior, Growth, Physiology and Antioxidant Metabolism of Four Contrasting Cultivars under Combined Drought and Salinity in Soybean.

Drought and salinity stresses are persistent threat to field crops and are frequently mentioned as major constraints on worldwide agricultural productivity. Moreover, their severity and frequency are predicted to rise in the near future. Therefore, in the present study we investigated the mechanisms underlying plant responses to drought (5, 10 and 15% polyethylene glycol, PEG-6000), salinity (50, 100, and 150 mM NaCl), and their combination, particularly at the seed germination stage, in terms of photosynthesis and antioxidant activity, in four soybean cultivars, viz., PI408105A (PI5A), PI567731 (PI31), PI567690 (PI90), and PI416937 (PI37). Results showed that seed germination was enhanced by 10% PEG and decreased by 15% PEG treatments compared to the control, while seed germination was drastically decreased under all levels of NaCl treatment. Furthermore, combined drought and salinity treatment reduced plant height and root length, shoot and root total weights, and relative water content compared with that of control. However, the reductions were not similar among the varieties, and definite growth retardations were observed in cultivar PI5A under drought and in PI37 under salinity. In addition, all treatments resulted in substantially reduced contents of chlorophyll pigment, anthocyanin, and chlorophyll fluorescence; and increased lipid peroxidation, electrolyte leakage, and non-photochemical quenching in all varieties of soybean as compared to the control plants. However, proline, amino acids, sugars, and secondary metabolites were increased with the drought and salinity stresses alone. Moreover, the reactive oxygen species accumulation was accompanied by improved enzymatic antioxidant activity, such as that of superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase. However, the enhancement was most noticeable in PI31 and PI90 under both treatments. In conclusion, the cultivar PI31 has efficient drought and salinity stress tolerance mechanisms, as illustrated by its superior photosynthesis, osmolyte accumulation, antioxidative enzyme activity, and secondary metabolite regulation, compared to the other cultivars, when stressed.

Co-inoculation of Arbuscular Mycorrhizal Fungi and the Plant Growth-Promoting Rhizobacteria Improve Growth and Photosynthesis in Tobacco Under Drought Stress by Up-Regulating Antioxidant and Mineral Nutrition Metabolism.

Drought stress is a major environmental concern that limits crop growth on a large scale around the world. Significant efforts are required to overcome this issue in order to improve crop production. Therefore, the exciting role of beneficial microorganisms under stress conditions needs to be deeply explored. In this study, the role of two biotic entities, i.e., Arbuscular mycorrhizal fungi (AMF, Glomus versiforme) and plant growth-promoting rhizobacteria (PGPR, Bacillus methylotrophicus) inoculation in drought tolerance of tobacco (Nicotiana tabacum L.), was investigated. The present results showed that drought stress considerably reduced tobacco plant's growth and their physiological attributes. However, the plants co-inoculated with AMF and PGPR showed higher drought tolerance by bringing up significant improvement in the growth and biomass of tobacco plants. Moreover, the co-inoculation of AMF and PGPR considerably increased chlorophyll a, b, total chlorophylls, carotenoids, photosynthesis, and PSII efficiency by 96.99%, 76.90%, and 67.96% and 56.88%, 53.22%, and 33.43% under drought stress conditions, respectively. Furthermore, it was observed that drought stress enhanced lipid peroxidation and electrolyte leakage. However, the co-inoculation of AMF and PGPR reduced the electrolyte leakage and lipid peroxidation and significantly enhanced the accumulation of phenols and flavonoids by 57.85% and 71.74%. Similarly, the antioxidant enzymatic activity and the plant nutrition status were also considerably improved in co-inoculated plants under drought stress. Additionally, the AMF and PGPR inoculation also enhanced abscisic acid (ABA) and indole-3-acetic acid (IAA) concentrations by 67.71% and 54.41% in the shoots of tobacco plants. The current findings depicted that inoculation of AMF and PGPR (alone or in combination) enhanced the growth and mitigated the photosynthetic alteration with the consequent up-regulation of secondary metabolism, osmolyte accumulation, and antioxidant system.

Exogenous melatonin reduces water deficit-induced oxidative stress and improves growth performance of Althaea rosea grown on coal mine spoils.

Coal mining activities are responsible for significant land degradation and often long-term irreversible effects on ecosystem functioning. To better understand how coal mined sites could be re-vegetated and ecosystem functioning restored, we address the role of the signalling hormone melatonin, which controls plant growth and development under adverse environmental conditions. We assessed the effects of exogenous melatonin on the plant species Althaea rosea by measuring morphological growth attributes, photosynthetic efficiency, reactive oxygen species (ROS)-induced oxidative damage and antioxidant defence developed by the seedlings when grown on coal-mined spoils under various water regimes. Water deficit and negative effects of coal mine spoils significantly decreased morphological growth attributes (i.e. plant height, root length and dry biomass), gas-exchange traits (i.e. net photosynthesis rate, inter intercellular concentration of CO2, transpiration rate, stomatal conductance and water use efficiency) and photosynthetic pigments (chlorophyll and carotenoid contents) by increasing the ROS-induce oxidative damage and decreasing antioxidant enzyme activities of A. rosea seedlings. However, melatonin applications increased photosynthetic performance and antioxidant enzyme activities and decreased hydrogen peroxide and malondialdehyde contents and ultimately improved growth performance of A. rosea in coal-mined spoils. Overall, our findings show how the application of optimum water (63.0 %field capacity equivalent to 1.67 mm day-1) and melatonin (153.0 µM dose) significantly improves the re-vegetation of coal-mined spoils with A. rosea. Our study provides new insight into melatonin-mediated water stress tolerance in A. rosea grown on coal-mined spoils, and this strategy could be implemented in re-vegetation programmes of coal mine-degraded areas under arid and semiarid conditions of the north-western part of China and perhaps across other arid areas worldwide.

Characterization of Root System Architecture Traits in Diverse Soybean Genotypes Using a Semi-Hydroponic System.

Phenotypic variation and correlations among root traits form the basis for selecting and breeding soybean varieties with efficient access to water and nutrients and better adaptation to abiotic stresses. Therefore, it is important to develop a simple and consistent system to study root traits in soybean. In this study, we adopted the semi-hydroponic system to investigate the variability in root morphological traits of 171 soybean genotypes popularized in the Yangtze and Huaihe River regions, eastern China. Highly diverse phenotypes were observed: shoot height (18.7-86.7 cm per plant with a median of 52.3 cm); total root length (208-1663 cm per plant with a median of 885 cm); and root mass (dry weight) (19.4-251 mg per plant with a median of 124 mg). Both total root length and root mass exhibited significant positive correlation with shoot mass (p ≤ 0.05), indicating their relationship with plant growth and adaptation strategies. The nine selected traits contributed to one of the two principal components (eigenvalues > 1), accounting for 78.9% of the total genotypic variation. Agglomerative hierarchical clustering analysis separated the 171 genotypes into five major groups based on these root traits. Three selected genotypes with contrasting root systems were validated in soil-filled rhizoboxes (1.5 m deep) until maturity. Consistent ranking of the genotypes in some important root traits at various growth stages between the two experiments indicates the reliability of the semi-hydroponic system in phenotyping root trait variability at the early growth stage in soybean germplasms.

Genome-wide association study uncovers major genetic loci associated with seed flooding tolerance in soybean.

BACKGROUND: Seed flooding stress is one of the threatening environmental stressors that adversely limits soybean at the germination stage across the globe. The knowledge on the genetic basis underlying seed-flooding tolerance is limited. Therefore, we performed a genome-wide association study (GWAS) using 34,718 single nucleotide polymorphism (SNPs) in a panel of 243 worldwide soybean collections to identify genetic loci linked to soybean seed flooding tolerance at the germination stage. RESULTS: In the present study, GWAS was performed with two contrasting models, Mixed Linear Model (MLM) and Multi-Locus Random-SNP-Effect Mixed Linear Model (mrMLM) to identify significant SNPs associated with electrical conductivity (EC), germination rate (GR), shoot length (ShL), and root length (RL) traits at germination stage in soybean. With MLM, a total of 20, 40, 4, and 9 SNPs associated with EC, GR, ShL and RL, respectively, whereas in the same order mrMLM detected 27, 17, 13, and 18 SNPs. Among these SNPs, two major SNPs, Gm_08_11971416, and Gm_08_46239716 were found to be consistently connected with seed-flooding tolerance related traits, namely EC and GR across two environments. We also detected two SNPs, Gm_05_1000479 and Gm_01_53535790 linked to ShL and RL, respectively. Based on Gene Ontology enrichment analysis, gene functional annotations, and protein-protein interaction network analysis, we predicted eight candidate genes and three hub genes within the regions of the four SNPs with Cis-elements in promoter regions which may be involved in seed-flooding tolerance in soybeans and these warrant further screening and functional validation. CONCLUSIONS: Our findings demonstrate that GWAS based on high-density SNP markers is an efficient approach to dissect the genetic basis of complex traits and identify candidate genes in soybean. The trait associated SNPs could be used for genetic improvement in soybean breeding programs. The candidate genes could help researchers better understand the molecular mechanisms underlying seed-flooding stress tolerance in soybean.

Arbuscular mycorrhizal fungi improve growth, essential oil, secondary metabolism, and yield of tobacco (Nicotiana tabacum L.) under drought stress conditions.

Drought is a major environmental threat limiting worldwide crop production. Drought stress affects the tobacco quality and yield; therefore, the current research studies were undertaken to investigate the effectiveness of arbuscular mycorrhizal fungi (AMF) under drought stress on morphological and biochemical attributes of tobacco (Nicotiana tabacum L. variety Yunyan 87). AMF-inoculated and AMF-non-inoculated plants were maintained in a greenhouse and irrigated with a half-strength Hoagland solution (100 mL pot-1) once a week. At harvesting, the plant height, number of leaves, fresh and dry weights, mycorrhizal colonization, and concentration of leaf photosynthetic pigments and photosynthetic rate were measured. Data were statistically analyzed by ANOVA and the principal component (PCA) analyses. The effect of root colonization significantly increased biomass production and essential oil accumulation. Results showed that drought at mild and severe stressed levels significantly affected tobacco growth by decreasing plant height, biomass, and a number of leaves. However, inoculation of AMF considerably increased plant height, fresh and dry weights, chlorophyll (a, b), total chlorophyll, and carotenoid content by 43.84, 40.87 and 49.76, 185.29, 325.60, 173.12, and 211.49%, respectively. Compared with non-inoculated plants, AMF inoculation significantly enhanced the essential oil yield and the uptake of nitrogen, phosphorus, and potassium with the increase of 257.36, 102.71, and 90.76, 62.32, and 84.51%, respectively, in mild drought + AMF-treated plants. Similarly, the antioxidant enzymatic activity, glomalin-related soil protein (GRSP), and accumulation of phenols and flavonoids and osmolytes content were also significantly improved in inoculated plants under drought stress. Additionally, AMF inoculation significantly upregulated the lipoxygenase (LOX) and phenylalanine ammonia-lyase (PAL) enzymes by 197 and 298.44% under drought conditions. These findings depicted that the symbiotic association of AMF improved the overall growth pattern and secondary metabolism in tobacco plants under severe drought stress conditions and may be used as an approaching source of important drugs in the field of pharmacology.

Improving growth and photosynthetic performance of drought stressed tomato by application of nano-organic fertilizer involves up-regulation of nitrogen, antioxidant and osmolyte metabolism.

Organic fertilizer usage is been introduced into agricultural practices for preventing the damaging effects of chemical fertilizers. Present study investigated the beneficial role of organic fertilizer (nano-vermicompost) on the growth, oxidative stress parameters, antioxidant and nitrogen metabolism, osmolyte accumulation and mineral elements in tomato under drought stress. Drought stress resulted in reduced growth and biomass accumulation by triggering oxidative stress due to excess accumulation of reactive oxygen species (ROS) and reduced mineral uptake. Application of nano-vermicompost proved significantly beneficial in improving growth and mitigating the drought induced growth decline. Nano-vermicompost increased growth and dry matter content and ameliorated the decline in chlorophyll contents, photosynthesis and PSII activity more significantly at higher concentration (100 mg kg-1 soil). ROS accumulation was significantly reduced by nano-vermicompost application thereby enhancing the membrane stability under normal as well as drought conditions. Furthermore, lipid peroxidation and activities of protease and lypoxygenase were significantly reduced. Drought up-regulated antioxidant system and application of nano-vermicompost further enhanced the activities of antioxidant enzymes and the contents of non-enzymatic antioxidant components. Accumulation of osmolytes including proline, glycine betaine and sugars increased significantly due to nano-vermicompost application. Besides, decline in the activity of nitrate reductase and content of essential mineral elements like nitrogen, potassium and phosphorous was also ameliorated by nano-vermicompost application.

Acetylcholine ameliorates the adverse effects of cadmium stress through mediating growth, photosynthetic activity and subcellular distribution of cadmium in tobacco (Nicotiana benthamiana).

Acetylcholine (ACh), a well-known major neurotransmitter, plays a potential role in response to abiotic stresses. However, the mechanism of ACh-mediated cadmium (Cd) toxicity in tobacco seedlings is largely uncharacterized. In this study, a hydroponics experiment was conducted under 100 µM Cd stress in the presence or absence of ACh (50 µM) to investigate the potential effects of ACh on Cd toxicity. The results revealed that ACh application effectively alleviated Cd-induced reductions in plant growth, photosynthetic pigments and gas exchange attributes and improved the photosystem II activity. Ultrastructural observation indicated that Cd exposure ruptured the internal structure of chloroplasts, and even caused the accumulation of osmiophilic granules in chloroplasts, whereas these phenomena were alleviated by the addition of ACh. Cd stress also caused a marked increase in oxidative stress, as evidenced by the accumulation of O2- and H2O2, which were efficiently minimized after ACh application by up-regulating antioxidant enzyme activities (superoxide dismutase, SOD; catalase, CAT; ascorbate peroxidase, APX; glutathione reductase, GR). Besides, Cd stress considerably increased the levels of glutathione (GSH), Non-protein thiols (NPTs) and phytochelatins (PCs), whereas ACh application to Cd-stressed seedlings further increased those contents, thereby enhancing the tolerance of Cd-stressed plants. Moreover, exogenously applied ACh declined the accumulation of Cd and minimized the damage from Cd toxicity by modulating the distribution of Cd in the vacuole and cell wall. Therefore, these results provide insights into the ameliorative effects of ACh on Cd-induced a series of physiological reactions.

Improved Drought Tolerance by AMF Inoculation in Maize (Zea mays) Involves Physiological and Biochemical Implications.

The role of arbuscular mycorrhizal fungus (AMF, Glomus versiforme) in amelioration of drought-induced effects on growth and physio-biochemical attributes in maize (Zea mays L.) was studied. Maize plants were exposed to two drought regimes, i.e., moderate drought (MD) and severe drought (SD), with and without AMF inoculation. Drought at both levels reduced plant height, and chlorophyll and carotenoid content, thereby impeding photosynthesis. In addition, drought stress enhanced the generation of toxic reactive oxygen species (ROS), including H2O2, resulting in membrane damage reflected as increased electrolyte leakage and lipid peroxidation. Such negative effects were much more apparent under SD conditions that those of MD and the control, however, AMF inoculation significantly ameliorated the deleterious effects of drought-induced oxidative damage. Under control conditions, inoculation of AMF increased growth and photosynthesis by significantly improving chlorophyll content, mineral uptake and assimilation. AMF inoculation increased the content of compatible solutes, such as proline, sugars and free amino acids, assisting in maintaining the relative water content. Up-regulation of the antioxidant system was obvious in AMF-inoculated plants, thereby mediating quick alleviation of oxidative effects of drought through elimination of ROS. In addition, AMF mediated up-regulation of the antioxidant system contributed to maintenance of redox homeostasis, leading to protection of major metabolic pathways, including photosynthesis, as observed in the present study. Total phenols increased due to AMF inoculation under both MD and SD conditions. The present study advocates the beneficial role of G. versiforme inoculation in maize against drought stress.

Nitrogen availability prevents oxidative effects of salinity on wheat growth and photosynthesis by up-regulating the antioxidants and osmolytes metabolism, and secondary metabolite accumulation.

BACKGROUND: Salinity is one of the damaging abiotic stress factor. Proper management techniques have been proposed to considerably lower the intensity of salinity on crop growth and productivity. Therefore experiments were conducted to assess the role of improved nitrogen (N) supplementation on the growth and salinity stress tolerance in wheat by analyzing the antioxidants, osmolytes and secondary metabolites. RESULTS: Salinity (100 mM NaCl) stress imparted deleterious effects on the chlorophyll and carotenoid synthesis as well as the photosynthetic efficiency. N supplementation resulted in increased photosynthetic rate, stomatal conductance and internal CO2 concentration with effects being much obvious in seedlings treated with higher N dose. Under non-saline conditions at both N levels, protease and lipoxygenase activity reduced significantly reflecting in reduced oxidative damage. Such effects were accompanied by reduced generation of toxic radicals like hydrogen peroxide and superoxide, and lipid peroxidation in N supplemented seedlings. Antioxidant defence system was up-regulated under saline and non-saline growth conditions due to N supplementation leading to protection of major cellular processes like photosynthesis, membrane structure and function, and mineral assimilation. Increased osmolyte and secondary metabolite accumulation, and redox components in N supplemented plants regulated the ROS metabolism and NaCl tolerance by further strengthening the antioxidant mechanisms. CONCLUSIONS: Findings of present study suggest that N availability regulated the salinity tolerance by reducing Na uptake and strengthening the key tolerance mechanisms.

Role of Arbuscular Mycorrhizal Fungi in Plant Growth Regulation: Implications in Abiotic Stress Tolerance.

Abiotic stresses hamper plant growth and productivity. Climate change and agricultural malpractices like excessive use of fertilizers and pesticides have aggravated the effects of abiotic stresses on crop productivity and degraded the ecosystem. There is an urgent need for environment-friendly management techniques such as the use of arbuscular mycorrhizal fungi (AMF) for enhancing crop productivity. AMF are commonly known as bio-fertilizers. Moreover, it is widely believed that the inoculation of AMF provides tolerance to host plants against various stressful situations like heat, salinity, drought, metals, and extreme temperatures. AMF may both assist host plants in the up-regulation of tolerance mechanisms and prevent the down-regulation of key metabolic pathways. AMF, being natural root symbionts, provide essential plant inorganic nutrients to host plants, thereby improving growth and yield under unstressed and stressed regimes. The role of AMF as a bio-fertilizer can potentially strengthen plants' adaptability to changing environment. Thus, further research focusing on the AMF-mediated promotion of crop quality and productivity is needed. The present review provides a comprehensive up-to-date knowledge on AMF and their influence on host plants at various growth stages, their advantages and applications, and consequently the importance of the relationships of different plant nutrients with AMF.