Stimulation of respiration by Pb²⁺ in detached leaves and mitochondria of C₃ and C₄ plants

Abstract

The exposure of detached leaves of C3 plants (pea, barley) and C4 plant (maize) to 5 mM Pb (NO3)2 for 24 h caused a reduction of their photosynthetic activity by 40-60%, whereas the respiratory rate was stimulated by 20-50%. Mitochondria isolated from Pb2+-treated pea leaves oxidized substrates (glycine, succinate, malate) at higher rates than mitochondria from control leaves. The respiratory control (RCR) and the ADP/O ratio were not affected. Pb2+ caused an increase in ATP content and the ATP/ADP ratio in pea and maize leaves. Rapid fractionation of barley protoplasts incubated at low and high CO2 conditions, indicated that the increased ATP/ADP ratio in Pb2+-treated leaves resulted mainly from the production of mitochondrial ATP. The measurements of membrane potential of mitochondria with a TPP+-sensitive electrode further showed that mitochondria isolated from Pb2+-treated leaves had at least as high membrane potential as mitochondria from control leaves. The activity of NAD-malate dehydrogenase in the protoplasts from barley leaves treated with Pb2+ was 3-fold higher than in protoplasts from control leaves. The activities of photorespiratory enzymes NADH-hydroxypyruvate reductase and glycolate oxidase as well as of NAD-malic enzyme were not affected. The presented data indicate that stimulation of respiration in leaves treated by lead is in a close relationship with activation of malate dehydrogenase and stimulation of the mitochondrial ATP production. Thus, respiration might fulfil a protective role during heavy metal exposure.

Lead (Pb2+) modulation of potassium currents of guinea pig outer hair cells

“…The fact that the effects of Pb 2 + are not completely reversible by washing perhaps is indicative that palliative chelation therapy that prevents or reverses the binding of metallic cations to cellular ligands may not hold excellent promise to prevent or reverse peripheral or central effects of the auditory system due to the effects of Pb 2 + [20]. The association of BLL to a number of neurodevelopmental conditions [12,14,38,46] should not be minimized, however, in spite of the relatively benign effects of Pb 2 + observed in vitro on hair cells in the present investigation, albeit hair cells have an epithelial origin and may therefore react differently than nerve cells. However, based on the present observations, we cannot reconcile differences between acute effects of lead on ion channel function as measured here and potential effects of chronic developmental exposure, which occur in the human population as a cause of hearing loss [5,7,29,31].…”

Chlorophyll a fluorescence as a tool to monitor physiological status of plants under abiotic stress conditions

“…The main sources of Pb in soil and plants are gas emissions from coal-fueled power plants, fuel gases, and industrial technology (Mishra and Dubey 2005). Pb causes modification of respiration and increases ATP and the ATP/ADP ratio, a result of mitochondrial production of this high-energy compound (Romanowska et al 2002). The decrease in the efficiency of photosynthesis in plants under Pb stress is a result of disruption of chloroplast ultrastructure and thylakoid membrane lipid composition, and a reduction of synthesis of chlorophyll and carotenoids (Sharma and Dubey 2005).…”

Lead Uptake, Toxicity, and Detoxification in Plants

“…• inadequate concentration of carbon dioxide via stomatal closure (Romanowska et al 2002(Romanowska et al , 2005(Romanowska et al , 2006), • impaired uptake of essential elements such as Mn and Fe (Chatterjee et al 2004;Gopal and Rizvi 2008) and substitution of divalent cations by lead (Gupta et al 2009;Cenkci et al 2010), • inhibition of Calvin cycle enzymatic catalysis (Mishra et al 2006;Liu et al 2008), and • increased chlorophyllase activity .…”