Citrus Physiological and Molecular Response to Boron Stresses

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.

Keywords: B deficiency; B excess; Citrus; boron stress; tolerance.

Figure 1

Symptoms of B deficiency in the leaves of C. sinensis (A) and C. grandis (B), and the fruits of “Ponkan” (C. reticulata) (C). Seedlings of C. sinensis (A) and C. grandis (B) were treated with 0 μM H₃BO₃ for 15 weeks, respectively. Fruits of “Ponkan” were collected from Citrus orchard in Yongchun county, Quanzhou, Fujian province, China (C).

Figure 2

Leaf symptoms of B toxicity on pummelo (C. grandis) in field.

Figure 3

Effects of B deficiency and B excess on leaf CO₂ assimilation (A) and intercellular CO₂ concentration (B) in C. sinensis. Seedlings of C. sinensis were treated with 10 (Control), 0 (B-deficiency) and 400 μM (B-excess) H₃BO₃ for 15 weeks, respectively. Bars represent means ± SD (n = 4). Differences among the treatments were analyzed by ANOVA. Different letters above the bars indicate a significant difference at p < 0.05.