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Limited data are available on boron (B)-toxicity-responsive proteins in plants. We first applied 2-dimensional electrophoresis (2-DE) to compare the effects of B-toxicity on leaf protein profiles in B-tolerant Citrus sinensis and B-intolerant Citrus grandis seedlings, and identified 27 (20) protein species with increased abundances and 23 (25) protein species with decreased abundances from the former (latter). Generally speaking, B-toxicity increased the abundances of protein species involved in antioxidation and detoxification, proteolysis, cell transport, and decreased the abundances of protein species involved in protein biosynthesis in the two citrus species. The higher B-tolerance of C. sinensis might include following several aspects: (a) protein species related to photosynthesis and energy metabolism in C. sinensis leaves were more adaptive to B-toxicity than in C. grandis ones, which was responsible for the higher photosynthesis and for the better maintenance of energy homeostasis in the former; and (b) the increased requirement for detoxification of reactive oxygen species and cytotoxic compounds due to decreased photosynthesis was less in B-toxic C. sinensis leaves than in B-toxic C. grandis ones. B-toxicity-responsive protein species involved in coenzyme biosynthesis differed between the two species, which might also contribute to the higher B-tolerance of C. sinensis., Biological Significance: B-toxicity occurs in many regions all over the world, especially in arid and semiarid regions due to the raising of B-rich water tables with high B accumulated in topsoil. In China, B-toxicity often occurs in some citrus orchards. However, the mechanisms of citrus B-tolerance are still not fully understood. Here, we first used 2-DE to identify some new B-toxicity-responsive-proteins involved in carbohydrate and energy metabolism, antioxidation and detoxification, signal transduction and nucleotide metabolism. Our results showed that proteins involved in photosynthesis and energy metabolism displayed more adaptive to B-toxicity in B-tolerant C. sinensis than in B-intolerant C. grandis, which might play a key role in citrus B-tolerance. Therefore, our results reveal some new mechanisms on plant B-response and tolerance., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Background: In China, nitrogen (N)-deficiency often occurs in Citrus orchards, which is one of the main causes of yield loss and fruit quality decline. Little information is known about the adaptive responses of Citrus carbon (C) and N metabolisms to N-deficiency. Seedlings of 'Xuegan' (Citrus sinensis (L.) Osbeck) were supplied with nutrient solution at an N concentration of 0 (N-deficiency), 5, 10, 15 or 20 mM for 10 weeks. Thereafter, we examined the effects of N supply on the levels of C and N in roots, stems and leaves, and the levels of organic acids, nonstructural carbohydrates, NH4+-N, NO3−-N, total soluble proteins, free amino acids (FAAs) and derivatives (FAADs), and the activities of key enzymes related to N assimilation and organic acid metabolism in roots and leaves. Results: N-deficiency elevated sucrose export from leaves to roots, C and N distributions in roots and C/N ratio in roots, stems and leaves, thus enhancing root dry weight/shoot dry weight ratio and N use efficiency. N-deficient leaves displayed decreased accumulation of starch and total nonstructural carbohydrates (TNC) and increased sucrose/starch ratio as well as a partitioning trend of assimilated C toward to sucrose, but N-deficient roots displayed elevated accumulation of starch and TNC and reduced sucrose/starch ratio as well as a partitioning trend of assimilated C toward to starch. N-deficiency reduced the concentrations of most FAADs and the ratios of total FAADs (TFAADs)/N in leaves and roots. N-deficiency reduced the demand for C skeleton precursors for amino acid biosynthesis, thus lowering TFAADs/C ratio in leaves and roots. N-deficiency increased (decreased) the relative amounts of C-rich (N-rich) FAADs, thus increasing the molar ratio of C/N in TFAADs in leaves and roots. Conclusions: Our findings corroborated our hypothesis that C and N metabolisms displayed adaptive responses to N-deficiency in C. sinensis seedlings, and that some differences existed between roots and leaves in N-deficiency-induced alterations of and C and N metabolisms. [ABSTRACT FROM AUTHOR]

• N-deficient citrus leaves and roots kept high abilities to detoxify ROS and MG. • N-deficiency (ND) affected ROS and MG metabolism more in roots than in leaves. • ND enhanced n distribution in roots and R/S, and delayed root senescence. • ND reduced MDA levels and electrolyte leakage in citrus 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. [ABSTRACT FROM AUTHOR]

• Magnesium deficiency induces leaf chlorosis, leaf curling and impaired growth of C.sinensis seedlings. • Magnesium deficiency upregulates the relative abundances of most monosaccharides and amino acids in C.sinensis leaves. • Magnesium deficiency decreases the relative abundances of most pigment compounds and organic acids in C.sinensis leaves. In south China, Magnesium (Mg) deficiency is commonly found in Citrus orchard due to soil acidification. However, less information is available discussing the global metabolic profile of Mg-deficient leaves in Citrus species. In the study, seedlings of 'Xuegan' [ Citrus sinensis (L.) Osbeck] were treated with Mg-plus (2 mM, as Control) or Mg-deficiency (0 mM) for 16 weeks by sandy culture, respectively. The untargeted metabolomics based on UHPLC-Q-TOF/MS were investigated to reveal the metabolic responses to Mg-deficiency in leaves of C. sinensis. The results indicated severe growth inhibition and obvious leaf chlorosis in Mg-deficient seedlings of C. sinensis compared to control. The principal component analysis (PCA) and orthogonal partial least squares-discriminate analysis (OPLS-DA) on the LC/GC data demonstrated a clear discrimination between the profiles of metabolites in control leaves and Mg-deficient leaves of C.sinensis. Besides, the identification and classification of those differential expressed metabolites (DEMs) revealed Mg-deficiency upregulated relative abundances of 78.42 % lipids and lipid-like molecules. In contrast, Mg-deficiency downregulated 89.42 % phenylpropanoids and polyketides in leaves of C.sinensis. Remarkably, relative abundances of most monosaccharides and amino acids increased while relative abundances of most leaf pigment compounds and organic acids decreased in response to Mg-deficiency in C. sinensis leaves. Those results support both primary and secondary metabolic modifications in C. sinensis leaves exposed to Mg-deficiency. Overall, the findings of present study contribute to a better understanding on the metabolic changes of Mg-deficient Citrus species, which will provide references for nutrient management and quality control in Citrus production. [ABSTRACT FROM AUTHOR]