Cadmium induced inhibition of nitrate Uptake in Anacystis nidulans: Interaction with other divalent cations.

Abstract

The effect of Cd2+ (4 ppm) and a combination of Cd2+ with the noninhibitory levels of metals like Ca2+ (150 ppm), Zn2+ (2 ppm), and Hg2+ (0.04 ppm) on the uptake of nitrate by Anacystis nidulans IU 625 (ATCC 27144) was investigated. The N03-uptake kinetics was studied by monitoring short-term uptake rates at different N03-levels (1-20 mM). The values for Vmag (0.8 ,umol/, tg protein/hr) and half saturation constant for uptake (Km 3.03 mM) were obtained employing the double reciprocal plot. A 4 ppm level of Cd2+ inhibited 50 % of the N03 uptake rate (at saturating N03-level) compared to Cd2+-less control. Cd2+ inhibition of N03-uptake (Km 5.88 mM) was alleviated as a result of competitive interaction by either Ca2+ (Km 4.34 mM) or Zn2+ (Km 4.08 mM). Hg2+ ions, however, interacted synergistically with Cd2+ (Km 12.5 mM). There was no change in the uptake capacity (Vmax 0.8 umol/pg protein/hr) for N03-under various treatments.Heavy metal toxicity to algae has been reviewed quite extensively (1-3). Cyanobacteria, however, appear to have been little explored in this respect (4-10) and overall observations suggest that heavy metals induce formative changes and inhibition of algal metabolism through depletion of ATP and reductant pools; the site of inhibition/interaction still remains obscure. Recently, we demonstrated that the acquisition of Cd2+ tolerance in Nostoc calcicola resulted in cross-resistance to other metals and antibiotics (11).While the toxicity of Cd2+ per se is well established, it is imperative to recognize that its interactions with other elements in the environment, both in aquatic and terrestrial systems, can modulate the resultant metal-toxicity to cyanobacteria or biota in general. Such metal interactions have been studied in eucaryotic algae 297

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

“…A similar observation exists for the filamentous cyanobacterium Anabaena inaequalis (6). Also, the noninhibitory levels of Hg2+ were too low (0.01 ppm) for NH4+ and P043-uptake by A, nidulans in the present study compared to the relative resistance of N03-uptake reported earlier (11). We have also observed synergism between Cd2+ and Hg2+ ions in long-term growth experiments on Nostoc calcicola (32).…”

“…4b). We observed similar behaviour of Zn2+ in antagonizing the Cd2+-inhibited uptake of N03~ by A. nidulans (11). Zn2+ as a micronutrient for algae, is also Alnmonium and Phosphate Uptake under Cd-stress 85 the metal component of dehydrogenases (28).…”

“…The subsequent addition of Cd2+ (0-10 ppm) to the ammonia medium, resulted in the inhibition of ammonia uptake by the test organism with a 50% inhibition at 2 ppm. This indicates that the NH4+ uptake may be more sensitive to Cd2+ than the N03 uptake, since a 50 % inhibition of the N03-uptake process required 4 ppm of Cd2+ (11). The uptake was approximately at the zero level at 10 ppm of Cd2+ (Fig.…”

“…2b). The pattern of NH4+ uptake thus was found to be noncompetitive as against a competitive inhibition of N03-uptake by Cd2+ (11). Ammonia assimilation in cyanobacteria is mediated by the ATP-dependent glutamine synthetase (15)(16)(17).…”

“…The morphometric analyses of Plectonema boryanum cells exposed to Cd2+ revealed the coalescence of cellular lipids and an increase in the volume of the polyphosphate bodies and surface area of thylakoids (12). Cd2+ is known to inhibit vital metabolic processes of cyanobacteria, such as nitrogen fixation (12,13), CO2 fixation (5) and uptake of nitrate (11). Since the environment contains a combination of heavy metals, investigations have been directed to unravel their interactive behaviour.…”