Prevention of aluminium toxicity with supplemental boron. I. Maintenance of root elongation and cellular structure

Aluminium toxicity is an important factor limiting plant growth mi acid soils. Symptoms of B deficiency and Al toxicity are very similar and generally associated with impaired membrane Function and root growth. Thus the objective of this study was to determine whether supplemental B prevents Al inhibition of root growth and development. Squash (Cucurbita pepo L. cv. Sunbar) was grown in hydroponic nutrient media with 44 mmol m^?3 free Al and B concentrations extending from 5 to 100 mmol m^?3. Our results establish that B protects against Al inhibition of root growth. Protection was apparent at all levels of organization examined: primary root and lateral root lengths; primary root cell elongation, cell production rate, tissue organization and cell structure; primary root morphology and maturation. Protection against Al inhibition was also apparent for shoot growth. These studies were undertaken in solution culture to limit the variables examined; however, the underlying motivation for this study is the problem of worldwide Al toxicity in soils. Therefore, the effect of adding additional B to a high-Al soil was also investigated and is the subject of the companion paper (Le Noble. Blevins & Miles 1996, Plant, Cell and Environment 19, 1143–1148).