Xiuwen Wu

Boron alleviates the aluminum toxicity in trifoliate orange by regulating antioxidant defense system and reducing root cell injury

Aluminium (Al) toxicity is the most important soil constraint for plant growth and development in acid soils (pHxa0<xa05.5) globally in agricultural regions. Boron (B) is an essential micronutrient for the growth and development of higher plants. The results of previous studies propose that B might ameliorate Al toxicity; however, none of the studies have been conducted on trifoliate orange to study this effect. Thus, a study was carried out in hydroponics comprising of two different Al concentrations, 0 and 400xa0μM. For every concentration, two B treatments (0 and 10xa0μM as H3BO3) were applied to investigate the B-induced alleviation of Al toxicity and exploring the underneath mechanisms. The results revealed that Al toxicity under B deficiency severely hampered the root growth and physiology of plant, caused oxidative stress and membrane damage, leading to severe root injury and damage. However, application of B under Al toxicity improved the root elongation and photosynthesis, while reduced Al uptake and mobilization into plant parts. Moreover, B supply regulated the activities of antioxidant enzymes, proline, secondary metabolites (phenylalanine ammonia lyase and polyphenol oxidase) contents, and stabilized integrity of proteins. Our study results imply that B supply promoted root growth as well as defense system by reducing reactive oxygen species (ROS) and Al concentrations in plant parts thus B induced alleviation of Al toxicity; a fact that might be significant for higher productivity of agricultural plants grown in acidic conditions.

Boron Deficiency in Trifoliate Orange Induces Changes in Pectin Composition and Architecture of Components in Root Cell Walls

Boron (B) is a micronutrient indispensable for citrus and B deficiency causes a considerable loss of productivity and quality in China. However, studies on pectin composition and architecture of cell wall components in trifoliate orange roots under B deficiency condition are not sufficient. In this study, we investigated the alteration in pectin characteristics and the architecture of cell wall components in trifoliate orange [Poncirus trifoliata (L.) Raf.] roots under B starvation. The results showed that B-deficient roots resulted in a significant enlargement of root tips and an obvious decrease in cell wall B and uronic acid content in Na2CO3-soluble pectin compared with B-adequate roots. Meanwhile, they showed a decrease of 2-keto-3-deoxyoctanoic acid in CDTA-soluble and Na2CO3-soluble pectin in cell walls, while the degree of methylation (DM) of CDTA-soluble pectin was significantly increased under B deficiency. Transmission electron microscope (TEM) micrographs of B deficient plants showed a distinct thickening of the cell walls, with the thickness 1.82 times greater than that of control plant roots. The results from Fourier-transform infrared spectroscopy (FTIR) showed that B deficiency changed the mode of hydrogen bonding between protein and carbohydrates (cellulose and hemicellulose). The FTIR spectra exhibited a destroyed protein structure and accumulation of wax and cellulose in the cell walls under B starvation. The 13C nuclear magnetic resonance (13C-NMR) spectra showed that B starvation changed the organic carbon structure of cell walls, and enhanced the contents of amino acid, cellulose, phenols, and lignin in the cell wall. The results reveal that the swelling and weakened structural integrity of cell walls, which induced by alteration on the network of pectin and cell wall components and structure in B-deficient roots, could be a major cause of occurrence of the rapid interruption of growth and significantly enlarged root tips in trifoliate orange roots under B-insufficient condition.

Boron reduces aluminum-induced growth inhibition, oxidative damage and alterations in the cell wall components in the roots of trifoliate orange

Aluminum (Al) toxicity is a major restriction for crops production on acidic soils. The primary symptom of aluminum toxicity is visible in the roots of plants. Recently, several studies reported the alleviation of Al toxicity by the application of Boron (B), however, the information how B alleviates Al toxicity is not well understood. Thus, we investigated the ameliorative response of B on Al-induced growth inhibition, oxidative damages, and variations in the cell wall components in trifoliate orange roots. The results indicated that plants under Al stress experienced a substantial decrement in root length and overall plant growth. The supply of B improved the root elongation by eliminating oxidative stress, membrane peroxidation, membrane leakage, and cell death produced under Al toxicity. Moreover, accumulation of Al on the cell wall and alteration in the cell wall components might be one of the causes resulting in the quick inhibition of root elongation under B-starvation circumstances by providing susceptible negative charges on pectin matrix for binding of Al. The results provide a useful understanding of the insight into mechanisms of B-induced mitigation of Al toxicity especially in the trifoliate orange that might be helpful in the production of crops on acidic soils.

Deficiency and toxicity of boron: Alterations in growth, oxidative damage and uptake by citrange orange plants

Boron (B) deficiency and toxicity are the major factors that affect plant growth and yield. The present study revealed the effect of B deficiency and toxicity on plant growth, morphology, physiology, and cell structure. A hydroponic culture experiment was conducted with five B levels, B deficient (B0), sufficient (B20, B10, B40) and toxic (B100). Our results show that both B deficient as well as excess level inhibit plant growth. In B deficiency, the major visible symptoms were appeared in roots, while B excess burned the leaf margin of older leaves. The antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) decreased at B deficiency and also decreased up to some extent at B excess, while in sufficient treatments, the higher antioxidant enzymes were found at B20. In addition, the MDA concentration decreased at B deficiency and increased with B concentration. Moreover, the photosynthetic rate, transpiration rate, stomatal conductance, leaf gas exchange and intercellular CO2 were reduced at both B deficiency as well as excess and higher at sufficient B20 treatment significantly. The chlorophyll and carotenoid content increased at B20 treatment, while decreased at B deficiency and excess. The middle lamellae of cell wall were found thick at B excess and normal at B20. The current study revealed that B deficiency as well as excess concentration affect plant growth and various morpho-physiological processes.

Interaction of boron and aluminum on the physiological characteristics of rape (Brassica napus L.) seedlings

It has been reported that aluminum (Al) toxicity is a major limiting factor for plant growth and production on acidic soils. Boron (B) is indispensable micronutrient for normal growth of higher plants, and its addition could alleviate Al toxicity. The rape seedlings were grown under three B (0.25, 25 and 500xa0μM) and two Al concentrations [0 (−Al) and 100xa0μM (+Al) as AlCl3·6H2O]. The results indicated that Al stress severely hampered root elongation and root activity at 0.25xa0μM B while the normal (25xa0μM) and excess (500xa0μM) B improved the biomass of rape seedlings under Al exposure. Additionally, normal and excess B treatment reduced accumulation of Al in the roots and leaves under Al toxicity, which was also confirmed by hematoxylin with light staining. This indicates that both normal and excess B could alleviate Al toxicity. Furthermore, it also decreased the contents of malondialdehyde and soluble protein under Al toxicity. Likewise, superoxide dismutase activity (SOD) improved by 97.82 and 131.96% in the roots, and 168 and 119.88% in the leaves at 25 and 500xa0µM B, respectively, while the peroxidase and catalase activities dropped as a result of Al stress. The study results demonstrated that appropriate B application is necessary to avoid the harmful consequences of Al toxicity in rape seedlings.

Different metabolite profile and metabolic pathway with leaves and roots in response to boron deficiency at the initial stage of citrus rootstock growth

Boron (B) is a microelement required for higher plants, and B deficiency has serious negative effect on metabolic processes. We concentrated on the changes in metabolite profiles of trifoliate orange leaves and roots as a consequence of B deficiency at the initial stage of growth by gas chromatography-mass spectrometry (GC-MS)-based metabolomics. Enlargement and browning of root tips were observed in B-deficient plants, while any obvious symptom was not recorded in the leaves after 30 days of B deprivation. The distinct patterns of alterations in metabolites observed in leaves and roots due to B deficiency suggest the presence of specific organ responses to B starvation. The accumulation of soluble sugars was occurred in leaves, which may be attributed to down-regulated pentose phosphate pathway (PPP) and amino acid biosynthesis under B deficiency, while the amount of most amino acids in roots was increased, indicating that the effects of B deficiency on amino acids metabolism in trifoliate orange may be a consequence of disruptions in root tissues and decreased protein biosynthesis. Several important products of shikimate pathway were also significantly affected by B deficiency, which may be related to abnormal growth of roots induced by B deficiency. Conclusively, our results revealed a global perspective of the discriminative metabolism responses appearing between B-deprived leaves and roots and provided new insight into the relationship between B deficiency symptom in roots and the altered amino acids profiling and shikimate pathway induced by B deficiency during seedling establishment.

Ameliorative effects of boron on aluminum induced variations of cell wall cellulose and pectin components in trifoliate orange (Poncirus trifoliate (L.) Raf.) rootstock

Aluminum (Al) phytotoxicity is a major limitation in the production of crops in the soils with pHu202f≤u202f5. Boron (B) is indispensable nutrient for the development of higher plants and B role has been reported in the alleviation Al toxicity. Trifoliate orange rootstock was grown in two B and two Al concentrations. The results of the present study showed that Al toxicity adversely inhibited root elongation and exhibited higher oxidative stress in terms of H2O2 and O2- under B-deficiency. Additionally, the X-ray diffraction (XRD) analysis confirmed the increase of the cellulose crystallinity in the cell wall (CW). Al-induced remarkable variations in the CW components were prominent in terms of alkali-soluble pectin, 2-keto-3-deoxyoctonic acid (KDO) and the degree of methyl-esterification (DME) of pectin. Interesting, B supply reduced the pectin (alkali-soluble) under Al toxicity. Moreover, the results of FTIR (Fourier transform infrared spectroscopy) and 13C-NMR (13C nuclear magnetic resonance) spectra revealed the decrease of carboxyl groups and cellulose by B application during Al exposure. Furthermore, B supply tended to decrease the Al uptake, CW thickness and callose formation. The study concluded that B could mitigate Al phytotoxicity by shielding potential Al binding sites and by reducing Al induced alterations in the CW cellulose and pectin components.

Boron supply alleviates Al-induced inhibition of root elongation and physiological characteristics in rapeseed (Brassica napus L.)

ABSTRACT Aluminum (Al) toxicity is one of the major problems affecting crop production. Boron (B) is an essential micronutrient for higher plants. In the present study, we investigated the alleviation of Al-induced inhibition of root growth and physiological characteristics by B in rapeseed. The rapeseeds were grown in different Al concentrations (0 and 300u2005μM), and for every concentration, two B treatments (2.5 and 25u2005µM as H3BO3) were applied. The results showed that Al toxicity under low B drastically inhibited root growth. The supply of B improved root length, photosynthesis, root activity, total chlorophyll by 60.15%, 104.7%, 102%, and 106.3%, respectively under Al toxicity. This further resulted in improvement of peroxidase, catalase, and ascorbate peroxidase activities while decreasing malondialdehyde, H2O2, and Al contents in roots and leaves. It might be supposed that B alleviates Al toxicity by less mobilization of Al in plant parts and through improving antioxidant enzyme activities.

Changes in chemical composition and structure of root cell wall of citrus rootstock seedlings in response to boron deficiency by FTIR spectroscopy

ABSTRACT Boron (B) is an essential microelement for higher plants, and plays a role in cell wall formation. Citrange seedlings with different amounts of B were studied through Fourier-transform infrared spectroscopy (FTIR) analyses. The results showed that the growth and development of new roots were evidently inhibited by B deficiency. Boron-deficiency significantly increased cell wall biomass (CWB) as a percentage of root fresh weight and the ratio of B concentration in cell wall to the total B in roots. The findings from CWB FTIR spectra showed the band at 3429 cm−1 under control condition was shifted to 3442 cm−1 after being B deprived, suggesting that the mode of hydrogen bonding was changed by B deficiency. Boron deficiency clearly decreased the peak height of carboxylic ester band around 1741 cm−1, but increased that of COO− stretching band around 1400 cm−1, suggesting that the relative amount and degree of esterification of carboxylic groups was decreased and pectin content and structure was altered. These results demonstrate that changes in amount, structure, and assembly of root cell wall polymers may be either specific or adaptive responses of citrange seedlings to B deficiency and FTIR can be an appropriate method to study changes in cell wall under B deficiency.

Photosynthate transport rather than photosynthesis rate is critical for low potassium adaptation of two cotton genotypes

Potassium (K) is an essential macronutrient for plant growth and development. Plant growth and development can be seriously affected by K deficiency. However, plants with different K efficiencies behave differently. It is still not fully understood how plants with higher K efficiency could maintain better growth in a low K environment and what is the relationship between K recycling and photosynthesis metabolism. The aim of this study was to investigate whether the difference in K re-translocation and photosynthesis transportation can explain genotype differences in K efficiency between K-efficient genotype 103 and K-inefficient genotype 122. Results of this study showed that the dry matter accumulation of genotype 122 decreased much more than that of genotype 103 affected by K deficiency environment. Root growth of the two genotypes was inhibited by K deficiency, but genotype 122 was affected more than genotype 103. Using the K utilization index as an evaluation factor for K efficiency, it was found that genotype 103 was significantly higher than genotype 122. Potassium affected the K distribution in plants for both the genotypes. Potassium was distributed more to the stem and leafstalk in a normal K environment whereas it was more to the leaf and root in a low K environment, especially for genotype 103. Potassium also affected photosynthetic products’ distribution. The leaf of genotype 122 accumulated most of its photosynthetic product while genotype 103 had better ability to transport it into the root to maintain better growth under a K-deficient environment. Results of this study indicated that more K recycling into the root and more efficient transport of the photosynthetic product into the root contribute to better root growth and therefore increased tolerance to K deficiency.