Uptake of Lead and Cadmium by Maize Seedlings and the Effect of Heavy Metals on the Activity of Phosphoenolpyruvate Carboxylase Isolated from Maize

Abstract

Maize seeds and five-day-old maize seedlings were incubated in media containing Pb 2+ at concentrations of 50, 100, and 200 mg 1 -l and Cd 2+ at concentrations of 1, 5, 10 and 50 mg 1 -l. After five days of incubation, both heavy metals were determined by means of AAS following wet mineralisation of roots and shoots. The results obtained indicate that Pb 2 § were transported to shoots from roots at a lower rate than Cd 2+.Phosphoenolpyruvate carboxylase (PEPC) isolated from germinating maize seeds was inhibited to a comparable degree by solutions containing 0.001 mmol 1-1 Pb 2+, 0.01 mmol 1 -I Cd 2+, and 0.005 mmol 1-1 Cu 2 § The enzyme was protected against this inhibition by the addition of mercaptoethanol, the substrate (PEP), or the cofactor (Mg 2 § The inhibition increased during a 20 min incubation of the enzyme with salts of the metals. Mn 2+, Ni 2+, and Co 2 § ions could partially substitute for the metal cofactor Mg 2 § Km values for these metal ions were as follows: for Mg 2 § 0.07 mmol 1 -l in the range from 0 to 0.30 mmol 1-1 Mg2+; 0.71 mmol 1 -I for 0.30 to 2.50 mmol 1 -~ MgZ+; for Mn ~ § 0.36 mmol l-l; for Ni 2 § 0.34 mmol l-l; and for Co 2+ 0.20 mmol 1 -l. The activity of the enzyme reached with Mn 2+ 85 %, with Ni 2+ 65 %, and with Co 2 § 55 % of the activity recorded with Mg 2+.

Effects of Some Heavy Metals on Seed Germination Characteristics of Canola (Barassica napus), Wheat (Triticum aestivum) and Safflower (Carthamus tinctorious) to Evaluate Phytoremediation Potential of These Crops

“…There is some reports that excess concentrations or hyper accumulation of some heavy metals in soils such as Cd(II), Cr(VI), CuII), Ni(II), and Zn(II) have caused the disturbanceof both natural aquatic and terrestrial ecosystems (GardeaTorresdey et al, 1996;Meagher, 2000).tolerate high concentration of heavy metals and other toxic substances (Banuelos et al, 1997;Blaylock & Huang, 2000;Raskin & Ensley, 2000;Dahmani Muller et al, 2000). More over different studies have been conducted in order to evaluate the effects of different heavy metal concentrations on herbal organisms (Thompson et al, 1997;Raskin & Ensley, 2000) but in contrast there are small number of studies on seeds which have been exposed to the pollutants (Claire et al, 1991;Vojtechova & Leblova, 1991;Xiong, 1998). Judia and Fulekar (2008) reported that inhibitory effect of heavy metal on seed gerniantion sis concentration depedent process in alfalfa.…”

Effect of aluminum and chromium on the growth and germination of mesquite (Prosopis juliflora swartz.) DC.

“…Heavy metals persist indefinitely in soil thereby posing an ever-increasing threat to human health and agriculture (Leyval et al 1995). Metal toxicity primarily depends on plant species as they exhibit considerable genetic variation in their ability in tolerating amounts and the concentration of specific heavy metals (Vojtechova and Leblova 1991). Some heavy metals are essential micronutrients for plants but their excess may result in metabolic disorders and growth inhibition in most of the plant species (Claire et al, 1991).…”

Determination of the Content of Hazardous Heavy Metals on Lycopersicon Esculentum Mill. Grown around a Contaminated Area

“…Plants are known to have at least two defense mechanisms whereby they are able to incorporate metals into their tissues and continue to survive. In response to the toxic elements, plants can synthesize metalchelating proteins called metallothioneins [15]- [17]. Another mechanism which may account for the accumulation of heavy metals in plants is the synthesis of phytochelatins, as suggested by Rauser [18].…”