Km. Lukaszewski et Dg. Blevins, ROOT-GROWTH INHIBITION IN BORON-DEFICIENT OR ALUMINUM-STRESSED SQUASHMAY BE A RESULT OF IMPAIRED ASCORBATE METABOLISM, Plant physiology, 112(3), 1996, pp. 1135-1140
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.