Anoxia tolerance in the aquatic monocot Potamogeton pectinatus: Absence of oxygen stimulates elongation in association with an unusually large Pasteur effect

Abstract

Elongation by stems of overwintered tubers of Potamogeton pectinatus (L.) is strongly promoted over several days by oxygen-free conditions. Characteristics of the respiration underpinning this unusual response were examined. Anaerobic plants produced ethanol and CO2 in approximately equimolar amounts, indicating that glycolysis coupled to alcoholic fermentation was the principal CO2-producing respiratory pathway. Rates of CO2 evolution by aerobic and anaerobic whole plants (shoot and tuber) were similar, suggesting a rate of glycolysis three times that of aerobic plants, i.e. a strong Pasteur effect. In the shoot alone, anaerobic CO2 production was twice the aerobic rate indicating a 6-fold increase in the rate of glycolysis in this tissue. Anoxic stems contained more sucrose at a stronger concentration than slower-growing aerobic stems or anaerobic leaves, demonstrating that sugar supply to the site of most rapid growth exceeded demand in the absence of oxygen. Concentrations of potentially toxic acetaldehyde in the external medium were small (approximately 0.2 mol m-3) during anoxia and on return to aerated conditions. Lactic acid was undetectable under anaerobic conditions and in vivo 31p-NMR analysis of shoots revealed a cytoplasmic acidification of only ≤0.2 pH units. In contrast, shoots of Pisum sativum, an anoxiaintolerant species, showed much stronger cytoplasmic acidification when transferred to oxygen-free conditions.