Alternative or cytochrome? Respiratory pathways in traps of aquatic carnivorous bladderwort <i>Utricularia reflexa</i>.

Carnivorous plants of the genus <i>Utricularia</i> (bladderwort) form modified leaves into suction bladder traps. The bladders are metabolically active plant tissue with high rates of mitochondrial respiration (R_D). In general, plants possess two mitochondrial electron transport pathways to reduce oxygen to water: cytochrome and an alternative. Due to the high metabolic rate in the bladders, it is tempting to assume that the bladders prefer the cytochrome <i>c</i> oxidative pathway. Surprisingly, we revealed that alternative oxidase (AOX), which yields only a little ATP, is much more abundant in the bladders of <i>Utricularia reflexa</i> in comparison with the shoots. This pattern is similar to the carnivorous plants with passive pitcher traps (e.g. <i>Sarracenia, Nepenthes</i>) and seems to be widespread across many carnivorous taxa. The exact role of AOX in the traps of carnivorous plants remains to be investigated.