Boron deficiency is correlated with changes in cell wall structure that lead to growth defects in the leaves of navel orange plants

Boron (B) is an essential microelement for vascular plants. Although it has frequently been reported that B deficiency leads to abnormal cell wall structure based on microscopic observation, what exactly occurs in the architecture of cell wall under this condition remains unknown. Navel orange plants that had been treated with different amounts of B were studied through chemical and instrumental (X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR)) analyses. Curling of the leaves and leaf chlorosis were observed only in the upper leaves of B-deficient plants. Boron deficiency significantly increased the relative hemicellulose and cellulose concentrations, and decreased covalently bound pectin in both upper and lower leaves. The results from XPS spectra suggested that the chemical states of carbon and oxygen were changed by B deficiency, and these changes were more serious in the upper leaves. The band at 3417 cm(-1) in the upper leaf walls shifted to 3398 cm(-1) due to B deficiency, suggesting that the mode of hydrogen bonding was changed by B deficiency (only in the upper leaves). The intensity and shape of the vibrations at 1200-900 cm(-1) (the fingerprint region of polysaccharides) varied substantially between B-deficient plant cell walls and the control walls, indicating that B deficiency induced changes in both the amount and assembly of component polymers of cell wall. These results imply that the amount of wall components is not decisive for B deficiency symptoms in orange plants, but that rather structural changes within these fractions are important. (C) 2014 Elsevier B.V. All rights reserved.