Detoxification of hydrogen peroxide maintains the water transport activity in figleaf gourd (Cucurbita ficifolia) root system exposed to low temperature

The figleaf gourd (Cucurbita ficifolia Bouche) root system has the ability to take up water and nutrients at low soil temperatures, and in the present paper, we attempt to reveal some of the molecular mechanisms behind this low-temperature tolerance. Exposure of figleaf gourd root system to low temperature induced accumulation of H2O2 along the plasma membrane but not in the cytoplasm. H+-ATPase (EC 3.6.1.35) activity of isolated root plasma membranes and root hydraulic conductivity (Lp(r)) were largely insensitive to externally applied H2O2. However, using bromocresol purple, it was shown that the acidification of the medium surrounding the root was strongly inhibited with low temperature- and H2O2-treated roots. Addition of catalase (EC 1.11.1.6) to the root medium during low-temperature exposure led to a recovery of H+-efflux along the root surface and increased Lp(r), demonstrating the importance of an H2O2 detoxification system in the root cells. Additional evidence for an increased Lp(r) was obtained by the Fenton reaction wherein a warming of the solution increased the activity of the detoxification system. All available evidence suggests that the ability of figleaf gourd root system to maintain a low level of H2O2 in the cytoplasm and to detoxify reactive oxygen species is related to the maintenance of water transport activity at low temperatures.