• Acid growth;
  • anaerobiosis;
  • aquatic plants;
  • carbon dioxide;
  • extension growth;
  • plant hormones;
  • Potamogeton pectinatus

Dark-grown shoots of tubers of the aquatic monocot Potamogön pectinatus L. elongated more strongly in anaerobic than aerobic solutions over 5 days. The response was located in the stem rather than the leaf. Anaerobic carbon dioxide (CO2) production was similar to that in aerobic conditions. Approximately half the anaerobic stem extension was attributed to acidification of the submerging medium by respiratory CO2. Sparging with an anaerobic gas mixture of nitrogen and hydrogen to remove dissolved CO2 inhibited stem elongation and prevented acidification of the medium. Similarly, supplying CO2 anaerobically promoted stem elongation while acidifying the medium. Carbon dioxide was also active on aerobic shoots. The effect of CO2 on anaerobic stem extension could be mimicked with an acidic buffer. Anaerobic stem extension was inhibited by exogenous abscisic acid (ABA), while gibberellic acid and the gibberellin-biosynthesis inhibitor paclobutrazol proved inactive. Exogenous indole-3-acetic acid promoted stem extension in the absence of oxygen. A strong gravitropic response by anaerobic stems of P. pectinatus was inhibited by the auxin-efflux inhibitor naphthylphthalamic acid.