Anaerobic metabolism in the roots of seedlings of the invasive exotic Lepidium latifolium

Abstract

Lepidium latifolium is an invasive exotic crucifer that is widely distributed in riparian zones and wetlands. In this study, anoxic carbohydrate metabolism and post-anoxic injury in the roots of L. latifolium seedlings were examined. A significant increase in the activity of the fermentative enzymes alcohol dehydrogenase (ADH) and lactate dehydrogenase (LDH) in roots occurred under anoxia and increased with the duration of anaerobic treatment during 7 days. However, pyruvate decarboxylase (PDC) and cytochrome c oxidase (CCO) activity was maintained at relatively stable levels under anaerobic and aerobic conditions. Soluble protein concentration in anoxic roots was two to three times that in aerobic roots throughout 7 days of anoxia. The concentration of the fermentation product ethanol in roots was two times greater under anoxia than under aerobic conditions. The concentration of lactate was much smaller than that of ethanol, but the trend was similar to that of ethanol. There was no significant difference in the concentration of malate between aerobic and anaerobic conditions for 9 days. Superoxide dismutase (SOD) activity in roots was two to three times higher under anoxia than under aerobic conditions throughout 7 days, but this increase in SOD activity decreased slightly with the duration of anoxia. Compared with aerobic conditions, the concentration of malondialdehyde (MDA), an indicator of free radical damage, increased by two to three times under anoxia. Two days after L. latifolium seedlings were returned to aerobic conditions, the concentrations of ethanol and MDA in roots were still significantly higher under the previously anoxic treatment than under continuously aerobic conditions, while no significant difference in enzyme activities or in concentrations of lactate and malate was found between treatments. The metabolism of L. latifolium roots under anoxia is characterized by the concurrent activity of both fermentative pathways and aerobic metabolism. Roots of L. latifolium have metabolically adaptive strategies to anoxia, but there is evidence of oxidative stress under anoxia and of post-anoxic injury from free radicals upon re-exposure to air. Results suggest that L. latifolium exhibit a mixture of characteristics typical of hydrophytic, facultative, and anoxia intolerant species.