Six day-old seedlings of soybean (Glycines max cv Maple Arrow) were adapted to pH 4.3 without boron (B) supply and then treated with aluminium (Al) Al at different B concentrations. Under these experimental conditions we were able to induce B deficiency and produce roots with different B content in the root apex. B deficiency increased the sensitivity of the roots to Al stress. Al-induced root-growth inhibition was enhanced and Al-induced callose formation could be decreased with higher B supply. In order to explain this effect of B on Al toxicity the cell wall of the 1 cm root apex was characterised. The pectin content was highest in the first 1 mm of the root tip and decreased with increasing distance from the root tip. In the treatment without B the pectin content was strongly increased, especially in the apical three 1-mm segments. The degree of methylation of cell-wall pectin also decreased with increasing distance from the root tip, but did not show a difference between the B treatments. Thus the amount of unmethylated and, therefore, negatively charged pectin increased in B-deficient root apices. This leads to more Al binding sites and might explain the increased Al sensitivity of B-deficient plants.
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机译：在不供应硼（B）的情况下，将六天大的大豆幼苗（Glycines max cv Maple Arrow）调整至pH 4.3，然后用不同B浓度的铝（Al）Al处理。在这些实验条件下，我们能够诱导B缺乏并在根尖产生具有不同B含量的根。 B缺乏会增加根对Al胁迫的敏感性。随着铝供应量的增加，铝诱导的根生长抑制作用增强，铝诱导的ose质形成可能减少。为了解释B对Al毒性的这种作用，对1 cm根尖的细胞壁进行了表征。果胶含量在根尖的前1 mm最高，并且随着距根尖距离的增加而降低。在不使用B的处理中，果胶含量显着增加，尤其是在心尖的三个1毫米节段。细胞壁果胶的甲基化程度也随着距根尖距离的增加而降低，但在B处理之间未显示差异。因此，在缺乏B的根中，未甲基化的果胶带负电荷的数量增加。这导致更多的铝结合位点，并可能解释了缺硼植物对铝的敏感性增加。
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