ROOT-GROWTH INHIBITION IN BORON-DEFICIENT OR ALUMINUM-STRESSED SQUASHMAY BE A RESULT OF IMPAIRED ASCORBATE METABOLISM

Although cessation of growth is the most apparent symptom of boron def iciency, the biochemical function of boron in growth processes is not well understood. We propose that the action of boron in root meristems is associated with ascorbate metabolism. Total inhibition of root gro wth in squash (Cucurbita pepo L.) plants transferred to boron-free med ium coincided with a major decrease (up to 98%) in the ascorbate conce ntration of root apices. Under low-boron conditions, in which root gro wth was partially inhibited, ascorbate concentration declined in propo rtion to growth rate. The decline in ascorbate concentration in boron- deficient root tips was not related to ascorbate oxidation. Ascorbate added to the medium improved root growth in plants supplied with insuf ficient boron. Increasing concentrations of aluminum in the nutrient m edium caused progressive inhibition of root growth and a parallel redu ction in ascorbate concentration of root apices. Elevated boron levels improved root growth under toxic aluminum conditions and produced roo t apices with higher ascorbate concentrations. To our knowledge, this is the first report of a correlation between boron nutrition, ascorbat e concentration in root apices, and growth. These findings show that r oot growth inhibition resulting from either boron deficiency or alumin um toxicity may be a consequence of disrupted ascorbate metabolism.