Localization of Boron in Cell Walls of Squash and Tobacco and Its Association with Pectin (Evidence for a Structural Role of Boron in the Cell Wall)

Abstract

B deficiency results in a rapid inhibition of plant growth, and yet the form and function of B in plants remains unclear. In this paper we provide evidence that B is chemically localized and strudurally important in the cell wall of plants. The localization and chemical fractionation of B was followed in squash plants (Curcurbifa pepo 1.) and cultured tobacco cells (Nicofiana fabacum) grown in Breplete or B-deficient medium. As squash plants and cultured tobacco cells became deficient, an increasingly large proportion of cellular B was found to be localized in the cell wall. Cytoplasmic B concentrations were reduced to essentially zero as plants became deficient, whereas cell wall B concentration remained ator above 10 pg B/g cell wall dry weight in all experiments. Chemical and enzymic fractionation studies suggest that the majority of cell B is associated with pectins within the cell wall. Physical analysis of Bdeficient tissue indicates that cell wall plastic extensibility is greatly reduced under B deficiency, and anatomical observations indicate that B deficiency impairs normal cell elongation in growing plant tissue. In plants in which B deficiency had inhibited all plant growth, tissues remained green and did not show any additional visible symptoms for at least 1 week with no additional 6. This occurred even though cytoplasmic B had been reduced to extremely low levels (~0 . 2 pg/g). This suggests that B in these species is largely associated with the cell wall and that any cytoplasmic role for B is satisfied by very low concentrations of B. The localization of B in the cell wall, its association with cell wall pectins, and the contingent effects of B on cell wall extensibility suggest that B plays a critical, although poorly defined, role in the cell wall strudure of higher plants.

Distribution of boron and its forms in young “Newhall” navel orange (Citrus sinensisOsb.) plants grafted on two rootstocks in response to deficient and excessive boron

“…Furthermore, previous research in radish (Raphanus sativus) and squash (Curcurbita pepo L.) (Matoh et al 1993;Hu and Brown 1994) indicated that under low B condition, cell wall B represented most of cellular B. However, the results in the present study were not consistent with this (Table 3).…”

“…The symptoms of B deficiency observed in this study could be attributed to the theory that B plays an important role in cell wall structure and plasticity (Hu and Brown 1994). Boron cross-links pectin in cell walls, and the cross-linking appeared to be essential for normal expansion of leaves (O'Neill et al 2001).…”

“…Bound B is B bound on the cell wall probably with pectin polysaccharides, and is a critical B form in plants for the stability of cell walls (Hu and Brown 1994). Hu et al (1996) claimed that cell wall pectin content was correlated to the variability in B requirements between plant species.…”

Boron mobility in eucalyptus clones

“…Deficiency symptoms are noticed in the root apex within hours and within minutes in the pollen tube (Gupta, 1993;Dell & Huang, 1997). Limited retranslocation of B has been attributed to its low mobility in the phloem sap and its fixation in components of mature leaves (Hu & Brown, 1994;Shelp et al, 1995). However, species and genotypes that are less sensitive to B deficiency are able to retranslocate B from the more mature tissues (source) to younger tissues (sink) (Shelp, 1993;Shelp et al, 1995;Brown & Shelp, 1997;Perica et al, 2001) and this capacity of mobilizing and transporting B to tissues with a high demand could explain their lower sensitivity to B deficiency (Brown & Hu, 1998).…”

Distribuição de nutrientes e sintomas visuais de deficiência de boro em raízes de coqueiro-anão verde

“…Das funções atualmente atribuídas ao B, duas são aceitas pela comunidade científica: uma é como constituinte da parede celular -nela, o B, possivelmente, atuaria estabilizando-a (Matoh et al, 1993;Hu & Brown, 1994;Ishii & Matsunaga, 1996;Kobayaski et al, 1996;Fleischer et al, 1998;Pfeffer et al, 2001); a outra função seria a manutenção da integridade da membrana plasmática (Cakmak et al, 1995).…”