Abstract
Since the essentiality of boron (B) to plant growth was reported nearly one century ago, the implication of B in physiological performance, productivity and quality of agricultural products, and the morphogenesis of apical meristem in plants has widely been studied. B stresses (B deficiency and toxicity), which lead to atrophy of canopy and deterioration of Citrus fruits, have long been discovered in citrus orchards. This paper reviews the research progress of B stresses on Citrus growth, photosynthesis, light use efficiency, nutrient absorption, organic acid metabolism, sugar metabolism and relocation, and antioxidant system. Moreover, the beneficial effects of B on plant stress tolerance and further research in this area were also discussed.
Highlights
Boron (B), an element essential for the growth, differentiation and reproduction of plant, exists in mineral such asborax, borosilicate, albite, brucite, colemanite, cristobalite, datolite and suanite, etc
‘Newhall’ orange (C. sinensis) scion grafted on Carrizo citrange (CC) showed higher tolerance of long-term B deficiency than that grafted on trifoliate orange, which was demonstrated by the fact that low-B decreased leaf CO2 assimilation, stomatal conductance and transpiration rate but increased intercellular CO2 concentration in ‘Newhall’ orange leaves
Sang et al [27,28] investigated the differentially expressed protein profiles of two Citrus species differing in B-toxicity tolerance, and found that B excess increased the abundances of protein species involved in antioxidation, detoxification, proteolysis and cell transport in leaves and roots of C. sinensis more than those of C. grandis
Summary
Boron (B), an element essential for the growth, differentiation and reproduction of plant, exists in mineral such asborax, borosilicate, albite, brucite, colemanite, cristobalite, datolite and suanite, etc. B deficiency decreased the concentrations of chlorophylls (Chls) and carotenoids, CO2 assimilation, impaired photosynthetic electron transport chain, and significantly increased intercellular concentration and the concentrations of photosynthates such as glucose, fructose and starch in Citrus leaves [13,22] Such altered carbohydrate metabolism inevitably affected other biological processes, such as amino acid metabolism, organic acid metabolism, and secondary metabolism. B toxicity decreased the concentrations of proteins and cellulose, and increased carbohydrate concentration and starch grains in P. trifoliata leaves [26] Both B deficiency and B excess could eventually lead to atrophy of canopy and deterioration of Citrus fruits [15]. Up to 74.8% and 22.9% of pummelo (C. grandis) orchards in Pinghe, Zhangzhou, China, are excess in leaf B and soil water-soluble B, respectively [48] This fact highlights the importance of understanding the role of B in Citrus tree growth and fruit production. The beneficial effects of B in Citrus tress tolerance and further research in this area were discussed
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