Romanowska E, Igamberdiev AU, Parys E, Gardestrom P
Stimulation of respiration by Pb2+ in detached leaves and mitochondria of C-3 and C-4 plants
Physiologia Plantarum: 2002 116:148-154
The exposure of detached leaves of C-3 plants (pea, barley) and C-4 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.
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