PREVENTION OF ALUMINUM TOXICITY WITH SUPPLEMENTAL BORON .1. MAINTENANCE OF ROOT ELONGATION AND CELLULAR STRUCTURE

Aluminium toxicity is an important factor limiting plant growth on aci d 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 supplementa l B prevents Al inhibition of root growth and development. Squash (Cuc urbita pepo L. cv. Sunbar) was grown in hydroponic nutrient media with 43 mmol m(-3) free Al and B concentrations extending from 5 to 100 mm ol 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 elo ngation, cell production rate, tissue organization and cell structure; primary root morphology and maturation. Protection against Al inhibit ion was also apparent for shoot growth. These studies were undertaken in solution culture to limit the variables examined; however, the unde rlying motivation for this study is the problem of worldwide Al toxici ty 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).