Browsing by Author "N. Noraho"

Now showing 1 - 5 of 5

Adsorption and uptake of cadmium by Azolla pinnata: kinetics of inhibition by cations.
(1995) J.P. Gaur; N. Noraho
A. pinnata showed a remarkable ability of taking up Cd from the external medium. Of the total Cd taken up by the test plant, surface adsorption was about 90%. Cd adsorption did not occur at a constant rate, however, an equilibrium was reached in 2 h. The uptake of Cd occurred at a constant rate. Test cations, including heavy metals (Ca, Mg, K, Na, Ni, Fe, Cu and Zn), inhibited adsorption as well as uptake of Cd. Cd adsorption was competitively inhibited by Cu, Fe and Zn, whereas Ca, Mg, K, Na and Ni caused non-competitive inhibition. Similarly, Cd uptake was competitively (Ca, Mg, Fe) or non-competitively (Na, K, Ni, Zn) inhibited by cations. Inhibition of Cd uptake by Cu was not wholly competitive.
Cadmium adsorption and intracellular uptake by two macrophytes, Azolla pinnata and Spirodela polyrhiza
(1996) N. Noraho; J.R. Gaur
Azolla pinnata and Spirodela polyrhiza showed profound ability to take up Cd from ambient medium. Cd adsorption by test plants occurred rapidly during the initial stage of incubation, but the process slowed down and reached an equilibrium in 120min. This suggests the presence of two kinds of sites, reacting rapidly or slowly with Cd. S. polyrhiza had more of the former type of sites. Adsorption constituted 71-86% of total Cd uptake by test plants. Intracellular uptake of Cd occurred at a constant rate, following typical Michaelis-Menten kinetics. Dead plants accumulated two times more Cd than living plants, due perhaps to absence of a permeability barrier which resulted in Cd accumulation at intracellular locations as well. Cd adsorbed by dead plants could be effectively displaced with chemicals like NaCl, CaCl2 and EDTA. Cd sorption ability of dead plants did not diminish up to 10 successive cycles of sorption and desorption, as long as plants did not become fragmented.
Effect of cations, including heavy metals, on cadmium uptake by Lemna polyrhiza L.
(Kluwer Academic Publishers, 1995) N. Noraho; J.P. Gaur
Cations, including calcium, magnesium, potassium, sodium, copper, iron, nickel and zinc, inhibited (up to 40%) extracellular binding and intracellular uptake of cadmium by Lemna polyrhiza in solution culture. Test plants showed a high capacity of extracellular cadmium binding which was competitively inhibited by copper, nickel and zinc; however, calcium, magnesium and potassium caused non-competitive inhibition. Iron and sodium increased Km and decreased Vmax, thereby causing mixed inhibition of extracellular binding. Intracellular cadmium uptake displayed Michaelis-Menten kinetics. It was competitively inhibited by calcium, magnesium, iron, nickel and zinc. Monovalent cations (sodium and potassium) caused non-competitive and copper caused mixed inhibition of intracellular cadmium uptake. Thus, high levels of cations and metals in the external environment should be expected to lower the cadmium accumulation efficiency of L. polyrhiza. © 1995 Rapid Communications of Oxford Ltd.
Relationship between heavy metal accumulation and toxicity in Spirodela polyrhiza (L.) Schleid. and Azolla pinnata R. Br.
(1994) J.P. Gaur; N. Noraho; Y.S. Chauhan
The accumulation of Cd, Cr, Co, Cu, Ni, Pb and Zn by Spirodela polyrhiza (L.) Schleid. and Azolla pinnata R. Br. was directly related to the concentration of metals in the medium during a 4 day exposure period. The hierarchy of metal accumulation was Ni>Zn>Co>Cu>Cd>Pb>Cr in S. polyrhiza and Ni>Zn>Co=Cd>Cu>Pb>Cr in A. pinnata. All metals inhibited relative growth rates of test plants in a concentration-dependent manner. Depending on metal concentration in the medium, the hierarchy of metal toxicity was Cd>Cu=Ni>Co>Cr>Zn>Pb for S. polyrhiza and Cd>Cr>Co>Cu>Ni>Pb>Zn for A. pinnata. The present work showed that the sulphur affinity hypothesis cannot be applied to explain variabilities in toxicities of test metals. When toxicity was evaluated in terms of metal concentration in plants the hierarchy of metal toxicity was Cr>Cd>Cu>Co>Ni>MPb>Zn for S. polyrhiza and Cr>Cd>Cu>Co>Pb>Zn>Ni for A. pinnata. © 1994.
Role of certain environmental factors on cadmium uptake and toxicity in Spirodela polyrhiza (L.) Schleid. and Azolla pinnata R. Br.
(1995) J.P. Gaur; N. Noraho
Effects of pH, temperature, EDTA and photosynthetically available radiation on the uptake and toxicity of Cd was investigated in Spirodela polyrhiza (L.) Schleid. and Azolla pinnata R. Br. In general, Cd toxicity was accentuated in conditions which favoured enhanced intracellular Cd uptake. Extracellular binding and intracellular uptake of Cd were lowered at pH values > 7 due to reduced availability of the aquo ion; consequently, toxicity was markedly reduced. At pH value < 7, extracellular binding remained unaffected, although intracellular uptake and toxicity of Cd were enhanced. This perhaps resulted from changes in membrane permeability as extracellular Cd binding was not affected by the decline in pH from 7 to 4. Moreover, speciation of Cd is known to remain unchanged throughout this pH range as most of the Cd (> 99%) remains available as the aquo ion. The presence of EDTA in the medium decreased extracellular binding, intracellular uptake and toxicity of Cd in test plants. This was due to formation of Cd-EDTA complex which was obviously not available to test plants. Elevation of temperature increased intracellular Cd uptake and this resulted in enhanced toxic effects. Similarly, increase in photosynthetically available radiation caused a slight increase in Cd uptake and toxicity in test plants. Obviously, rise in temperature or PAR increased metabolic activities of test plants thereby leading to increased Cd transport and toxicity.