Effect of osmotic stress on the respiratory properties of shoots and roots of Arnica alpina

Abstract

Arnica alpina plants were exposed to 0.3 or 0.6 M sorbitol for 5 days to investigate the effect of long-term osmotic stress on the cytochrome and alternative respiratory pathways in both shoots and roots. Exposure to 0.3 M (−0.72 MPa) sorbitol significantly reduced growth in both shoots and roots. Increased alternative pathway activity was observed in shoots, exposed to 0.3 M sorbitol whereas increased cytochrome pathway activity, with a concomitant increase in the theoretical rate of ATP production, was found in the roots. Despite a reduction in shoot and root ethanol-soluble sugars, respiration was never substrate limited. These results suggest that the reduced demand for shoot growth energy was offset by an equally increased demand for maintenance energy. In roots, however, additional ATP production was required to meet the metabolic demands of exposure to 0.3 M sorbitol. Exposure to 0.6 M (−1.44 MPa) sorbitol completely stopped shoot and root growth and decreased respiration after only 1 day. In shoots, cytochrome pathway activity was inhibited, whereas in roots both pathways were transiently stimulated. By day 5, respiration along both pathways was significantly inhibited. The possible role of the alternative pathway as an energy overflow and an energy overcharge during osmotic stress is discussed. Key words: alternative pathway respiration, Arnica alpina, ATP, cytochrome pathway respiration, osmotic stress, respiration.