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

Xiuwen Wu,Muhammad Riaz,Chenqing Du,Yalin Liu,Cuncang Jiang,Lei Yan

doi:10.3389/fpls.2017.01882

Xiuwen Wu, Muhammad Riaz + Show 4 more

Open Access

https://doi.org/10.3389/fpls.2017.01882

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Abstract

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.

Highlights

Boron (B) is an essential micronutrient for higher plants
In B-deficient trifoliate orange seedlings, the proportion of cell wall B in root B was much greater than that of the control. These results suggested that B in roots was assigned preferentially to cell walls under B starvation
The results suggested that the reduction of pectin and B binding sites induced by B deficiency hindered the binding of B to cell wall, and the toughness of cell wall was destroyed because of the increase of degree of methylation (DM) of CDTA-soluble pectin

Summary

Introduction

Boron (B) is an essential micronutrient for higher plants. The deficiency of boron causes various growth defects mainly in the young and growing parts of plants (Loomis and Durst, 1992). Boron Deficiency Induce Pectin Change in allocation of B in cell walls, pectin composition, cell wall components and structure (Hu and Brown, 1994; Pan et al, 2012; Liu et al, 2013, 2014). The primary function of B is involved in the formation of cell walls through diester bridges between two rhamnogalacturonan II (RG-II) molecules to cross-link cell wall pectin (Ishii and Matsunaga, 1996; Kobayashi et al, 1996; O’Neill et al, 2001). The variation in the degree of methylation (DM) of pectin after releasing carboxyl groups leads to an alteration in the binding capacity of B (OH) in the synthesis of the cell wall structure (Kobayashi et al, 1996; O’Neill et al, 1996).

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