Inhibition of Nitrogen Fixation in Alfalfa by Arsenate, Heavy Metals, Fluoride, and Simulated Acid Rain

Abstract

The acute effects of aqueous solutions of As, Cd, Cu, Pb, F, and Zn ions at concentrations from 0.01 to 100 micrograms per milliliter and solutions adjusted to pH 2 to 6 with nitric or sulfuric acid were studied with respect to acetylene reduction, net photosynthesis, respiration rate, and chlorophyll content in Vernal alfalfa (Medicago sativa L. cv. Vernal). The effects of the various treatments on acetylene reduction varied from no demonstrable effect by any concentration of F-and 42% inhibition by 100 micrograms Pb2+ per milliliter, to 100% inhibition by 10 micrograms Cd2" per milliliter and 100 micrograms per milliliter As, Cu21, and Zn2+ ions. Zn2+ showed statistically significant inhibition of activity at 0.1 micrograms per milliliter. Acid treatments were not inhibitory above pH 2, at which pH nitric acid inhibited acetylene reduction activity more than did sulfuric acid. The inhibition of acetylene reduction by these ions was Zn2+ > Cd2" > Cu2+ > AsOs-> Pb2+ > F-. The sensitivity of acetylene reduction to the ions was roughly equal to the sensitivity of photosynthesis, respiration, and chlorophyll content when Pb2+ was applied, but was 1,000 times more sensitive to Zn2+. The relationship of the data to field conditions and industrial pollution is discussed.by treatment with 18 ltM Cd2+. The latter of these two reports includes preliminary data from the study reported here and includes the effects of a variety of pollutants on a cyanobacterium (Anabaena sp), soybeans (Glycine max L. cv. Kent), yellow sweetclover (Melilotus officinalis L.), and two "species" of lichen (Col-

Cadmium induced inhibition of ammonium and phosphate uptake in anacystis nidulans: Interaction with other divalent cations.

“…Therefore, the non-competitive inhibition of NH4+ uptake in the present organism, is attributable to Cd2+ induced depletion of ATP and reluctant pools as suggested for inhibition of N2 fixation and photosynthesis in Anabaena inaequalis by Cd2+ ions (5). The present observations on Cd2+ induced inhibition of NH4+ uptake, are in agreement with the earlier reports that the heavy metal results in exhaustion of energy yielding substrates (18) and binding of the metal with sulfhydryl groups of enzymes (19). The P043-uptake by A. nidulans in graded concentrations (0.2-2 mM), also conformed to the Michaelis-Menten kinetics with a linear pattern of uptake up to 4 hr with a saturation level at 2 mM.…”

Heavy metals, occurrence and toxicity for plants: a review

“…Lead administrated to potted sugar beet plants at rates of 100-200 ppm caused chlorosis and growth reduction (Hewilt 1953). In contrast, there was no visual symptoms of lead toxicity in alfa alfa plants exposed to 100 mg/mL (Porter and Cheridan 1981). Low amounts of lead (0.005 ppm) caused significant reduction in growth of lettuce and carrot roots (Baker 1972).…”

Crescimento e nodulação de Acacia mangium, Enterolobium contortisiliquum e Sesbania virgata em solo contaminado com metais pesados

“…Trabalhos com sais de metais adicionados ao solo têm mostrado maior toxidez de Cd, comparado ao Cu ou Zn, para a formação do nódulo e FBN, com ordem de toxidez: Cd > Co > Cu > Zn (Mcllveen & Cole, 1974) e Cd > Ni > Cu > Zn (Porter & Sheridan, 1981;Päivöke, 1983a,b), respectivamente. Chaudri et al (1992b mostraram que a ordem de toxidez de metais ao rizóbio e, indiretamente à FBN, foi Cd > Zn > Cu, quando adicionados ao solo em soluções de sulfato.…”