Boron (B) deficiency and copper (Cu) excess are common problems in citrus orchard soils. Citrus sinensis seedlings were exposed to 25 (B25) or 2.5 (B2.5) mu M H3BO3 and 0.5 (Cu0.5) or 350 (Cu350) mu M CuCl3 for 24 weeks. Cu350 upregulated 2210 (1012) genes and 482 (341) metabolites and downregulated 3201 (695) genes and 175 (43) metabolites in roots at B2.5 (B25). Further analysis showed that the B-mediated mitigation of Cu toxicity in roots involved the coordination of the following aspects: (a) enhancing the ability to maintain cell wall and plasma membrane stability and function; (b) lowering the impairment of Cu350 to primary and secondary metabolisms and enhancing their adaptability to Cu350; and (c) alleviating Cu350-induced oxidative stress via the coordination of reactive oxygen species (ROS) and methylglyoxal detoxification systems. Cu350 upregulated the abundances of some saccharides, amino acids and derivatives, phospholipids, secondary metabolites, and vitamins, and the expression of several ROS detoxification-related genes in roots of B2.5-treated seedlings (RB2.5), but these adaptive responses did not prevent RB2.5 from Cu-toxicity (oxidative damage). The study identified some genes, metabolites, and metabolic processes/pathways possibly involved in root Cu tolerance. Additionally, the responses of gene expression and metabolite profiling to Cu-B treatments differed between leaves and roots. Therefore, this study provided novel information for B to reduce Cu toxicity in roots and might contribute to the development of soil amendments targeting Cu excess in citrus and other crops.

Background Vermicompost contains humic acids, nutrients, earthworm excretions, beneficial microbes, growth hormones, and enzymes, which help plants to tolerate a variety of abiotic stresses. Effective microorganisms (EM) include a wide range of microorganisms' e.g. photosynthetic bacteria, lactic acid bacteria, yeasts, actinomycetes, and fermenting fungi that can stimulate plant growth and improve soil fertility. To our knowledge, no study has yet investigated the possible role of vermicompost and EM dual application in enhancing plant tolerance to water scarcity. Methods Consequently, the current study investigated the effectiveness of vermicompost and EM in mitigating drought-induced changes in wheat. The experiment followed a completely randomized design with twelve treatments. The treatments included control, as well as individual and combined applications of vermicompost and EM at three different irrigation levels (100%, 70%, and 30% of field capacity). Results The findings demonstrated that the application of vermicompost and/or EM significantly improved wheat growth and productivity, as well as alleviated drought-induced oxidative damage with decreased the generation of superoxide anion radical and hydrogen peroxide. This was achieved by upregulating the activities of several antioxidant enzymes, including superoxide dismutase, catalase, peroxidase, ascorbate peroxidase, glutathione peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase. Vermicompost and/or EM treatments also enhanced the antioxidant defense system by increasing the content of antioxidant molecules such as ascorbate, glutathione, phenolic compounds, and flavonoids. Additionally, the overproduction of methylglyoxal in water-stressed treated plants was controlled by the enhanced activity of the glyoxalase system enzymes; glyoxalase I and glyoxalase II. The treated plants maintained higher water content related to the higher content of osmotic regulatory substances like soluble sugars, free amino acids, glycinebetaine, and proline. Conclusions Collectively, we offer the first report that identifies the underlying mechanism by which the dual application of vermicompost and EM confers drought tolerance in wheat by improving osmolyte accumulation and modulating antioxidant defense and glyoxalase systems.

Citrus is mainly cultivated in acid soil with low boron (B) and high copper (Cu). In this study, Citrus sinensis seedlings were submitted to 0.5 (control) or 350 mu M Cu (Cu excess or Cu exposure) and 2.5, 10, or 25 mu M B for 24 weeks. Thereafter, H2O2 production rate (HPR), superoxide production rate (SAPR), malondialdehyde, methylglyoxal, and reactive oxygen species (ROS) and methylglyoxal detoxification systems were measured in leaves and roots in order to test the hypothesis that B addition mitigated Cu excess-induced oxidative damage in leaves and roots by reducing the Cu excess-induced formation and accumulation of ROS and MG and by counteracting the impairments of Cu excess on ROS and methylglyoxal detoxification systems. Cu and B treatments displayed an interactive influence on ROS and methylglyoxal formation and their detoxification systems. Cu excess increased the HPR, SAPR, methylglyoxal level, and malondialdehyde level by 10.9% (54.3%), 38.9% (31.4%), 50.3% (24.9%), and 312.4% (585.4%), respectively, in leaves (roots) of 2.5 mu M B-treated seedlings, while it only increased the malondialdehyde level by 48.5% (97.8%) in leaves (roots) of 25 mu M B-treated seedlings. Additionally, B addition counteracted the impairments of Cu excess on antioxidant enzymes, ascorbate-glutathione cycle, sulfur metabolism-related enzymes, sulfur-containing compounds, and methylglyoxal detoxification system, thereby protecting the leaves and roots of Cu-exposed seedlings against oxidative damage via the coordinated actions of ROS and methylglyoxal removal systems. Our findings corroborated the hypothesis that B addition alleviated Cu excess-induced oxidative damage in leaves and roots by decreasing the Cu excess-induced formation and accumulation of ROS and MG and by lessening the impairments of Cu excess on their detoxification systems. Further analysis indicated that the pathways involved in the B-induced amelioration of oxidative stress caused by Cu excess differed between leaves and roots.

Nitrogen-deficiency (ND) usually occurs in some citrus orchard soils in China. The roles of reactive oxygen species (ROS) and methylglyoxal (MG) generation and their detoxification systems in ND tolerance of horticultural woody plants still need to be revealed. For the first time, we examined the effects of ND on ROS and MG generation and their detoxification systems in leaves and roots of Citrus sinensis seedlings. The objectives are to test the hypotheses that N-deficient leaves and roots can keep high abilities to scavenge ROS and MG, thereby protecting them from oxidative damage, and that ND-induced alterations of ROS and MG formation and their detoxification systems in leaves and roots are different. ND augmented superoxide anion production rate and MG concentrations, but it decreased malondialdehyde (MDA) concentrations and electrolyte leakage in leaves and roots. ND increased the activities of most enzymes involved in ROS (ascorbate-glutathione cycle-related enzymes, antioxidant enzymes, and sulfur metabolism-related enzymes) and MG (glyoxalases) detoxification expressed on a protein basis with a few exceptions, and the concentrations of ascorbate, phytochelatins, and total non-protein thiols in leaves and roots. These results suggested that nitrogen-deficient leaves and roots could keep high abilities to detoxify ROS and MG, and protect them from oxidative damage. Generally viewed, ND affected the production and removal of ROS and MG more in roots than in leaves.