Uptake and distribution of boron in canola at vegetative and early flowering stages using boron buffered solution culture

In conventional solution culture, differences in boron (B) concentration am ong plant parts and in distribution over time are often confounded with dec lining B supply. Using a B-buffered solution system which maintained soluti ons at values that ranged from deficient to adequate, we examined B uptake and distribution in canola (Brassica napus L.) at 3 growth stages: 10 and 2 2 days after transplanting (DAT) and at early flowering (55 DAT). Boron con centrations in shoots and roots increased strongly with increasing solution B concentrations up to 1-2 mu M B and then more weakly with increases in s olution B above 2 mu M B. At deficient to marginal external B concentration s, stems had higher B concentrations than leaf blades on Days 10 and 22 but not at adequate external B concentrations. In petioles, B concentration re mained unchanged from Day 22 to 55 in most B treatments. With increasing ex ternal B concentrations, relative B content increased in leaf blades, decre ased in roots, and generally remained unchanged in stems and petioles. Alth ough the plants at low external B concentrations (less than or equal to 0.5 5 mu M) maintained vegetative growth they did not produce reproductive part s in contrast to the plants of adequate B. At the flowering stage, maximum B concentration was found in florets and growth of these plant parts was mo re sensitively depressed by low B than vegetative plant parts. At less than or equal to 0.41 mu M external B concentration, reproductive growth was de pressed compared to plants of greater than or equal to 0.86 mu M external B concentration, flowering was delayed for 6-8 days, and flowers aborted soo n after bud burst.