Figure 6.

Oxygen profiles in the rhizosphere and in roots of the investigated species. Vertical axes indicate points of vertical penetration of the microelectrode into and out of the roots. Profiles were taken 10 to 15 mm behind the apex. a, Oxygen profile through a 12-d-old and 5-cm-long adventitious root from T. juruana. The low oxygen concentration indicates hypoxic conditions in the root cortex and stele. No ROL was detectable. b, Measurement of the oxygen distribution revealed the absence of oxygen in the rhizosphere and in roots of L. corymbulosa. c, The oxygen profiles through 10-d-old and 12-cm-long adventitious roots from S. martiana revealed high oxygen concentrations inside the roots and a several-millimeter-thick oxygenated zone around the roots. d, Roots from C. benthami did not exhibit any oxygen inside or outside the roots. Lengths of the roots were 12 cm (S. martiana), 5 cm (T. juruana), or 6 cm (L. corymbulosa and C. benthami). Determinations were performed on 20 different roots from at least six individual plants without major deviations in the overall pattern. Data are from a representative experiment.