NITROGENASE ACTIVITY AND GROWTH OF NITROGEN-FIXING SYMBIOTIC ASSOCIATION OF AZOLLA-CAROLINIANA WITH A SHORTAGE OF CERTAIN ELEMENTS IN THE MEDIUM

Lower growth rates of the nitrogen-fixing symbiotic association of Azo lla caroliniana were observed when there was a shortage of Fe2+, Ca2+, or BO33- in the medium. Nitrate weakened the suppressing effect of Fe 2+ and BO33- deficiency on the growth of Az. caroliniana, but strength ened the effect of Ca2+ deficiency. The nitrogenase activity of the ni trogen-fixing association was lower than when the medium was deficient in Fe2+, MoO42-, Ca2+, or BO33-. The lowering of nitrogenase activity of Az. caroliniana due to shortage of these ions was more pronounced when NO3-was present in the medium. The nitrogenase activity of Az. ca roliniana grown with a deficiency of Mo was restored after transferrin g to a medium containing MoO42- (1.5 muM) or VO3- (1-10 muM). However, the association growing in the presence of vanadium did not form etha ne by reduction of C2H2. The nitrate reductase activity of the associa tion was not changed when grown with a deficiency of Fe2+ or BO33-. Th e addition of Na+ (0.6-6.0 mM) did no affect the growth or nitrogenase activity of Az. caroliniana.