Abstract
Effects of cyanide and rotenone were examined on respiration (oxygen uptake) in mitochondria isolated from sugar beet (Beta vulgaris L.) taproots at various stages of plant growth and development. In mitochondria from growing and cool-stored taproots, the ability of cyanide-resistant, salicylhydroxamic acid-sensitive alternative oxidase (AO) to oxidize malate, succinate, and other substrates of tricarboxylic acid cycle (TCA) was low and constituted less than 10% compared to predominant activity of the cytochrome oxidase pathway during State 3 respiration. Artificial aging of storage tissue (2-day incubation of tissue sections under high humidity at 20°C) substantially activated AO, but the highest capacity (V alt) of this pathway of mitochondrial oxidation was only observed in the presence of pyruvate and a reducing agent dithiothreitol. At the same time, mitochondria from growing taproots exhibited high rates of rotenone-resistant respiration, and these rates gradually declined during plant growth and development. The slowest rates of this respiration were observed during oxidation of NAD-dependent TCA substrates in mitochondria from dormant storage organ. The results are discussed in relation to significance of alternative electron transport pathways during growth and storage of sugar beet taproots.
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