Characterisation of the oxygen fluxes in the division, elongation and mature zones of Vitis roots: influence of oxygen availability

Oxygen fluxes into and from root cells of Vitis rupestris (flooding sensitive), V. riparia (flooding tolerant) and V. vinifera (medium tolerance to flooding) were measured under different levels of O-2 availability using a recently developed polarographic O-2-selective, vibrating-microelectrode system. The system enables fluxes to be measured with a spatial resolution of 2-3 mum and a temporal resolution of 10 s. No difference in root porosity was found among the genotypes when grown for 30 days in an aerated solution. Under normoxic conditions, O-2 influx was characterised by two distinct peaks, one in the division zone and the other in the elongation zone of the roots. This pattern was found in all three species studied, although the fluxes showed a different magnitude. The peak in the elongation zone coincided with maximum relative elemental growth rates. When the energetics of the cell was disturbed by cyanide, both growth and oxygen O-2 influxes ceased at the same time. Under hypoxic conditions, V. riparia plants showed a precise strategy directed toward the maintenance of enough O-2 for the respiratory needs of mitosis in the apical meristem of the roots. Thus, whereas in the division zone of V. rupestris and V. vinifera, at bulk O-2 concentrations of 0.094 mol m(-3), the O-2 influx was reduced by 70.5 and 38.5%, respectively, for V. riparia no variation in the O-2 influx was detected down to bulk O-2 concentrations of 0.078 mol m(-3). Moreover, in accordance with the different tolerances of the plants, the Vitis genotypes were found to differ in their radial O-2 loss from the adventitious roots when in an O-2-free environment. The results are discussed in terms of possible mechanisms of response to anoxia in Vitis species with different tolerances to flooding.