Effect of boron supply on nitrate concentration and its reduction in roots and leaves of tobacco plants

Shoot and root mass of tobacco plants treated with only 0.05 A mu M boron was decreased by 25 and 50 %, respectively, when compared to plants sufficiently supplied with B (2 and 5 A mu M). Leaf B content of 0.05 A mu M B-treated plants decreased (about 80-90 %) when compared to 2 A mu M B treated plants; this drop of B content were not as marked (about 25-45 %) in roots. Leaf and root nitrate contents in B-deficient plants were 45-60 % and 35-45 % lower, respectively, than those from 2 and 5 A mu M B treated plants. It is suggested that B deficiency might decrease nitrate uptake rather than nitrate reductase activity in tobacco plants.