Aerenchyma formation and radial O2 loss along adventitious roots of wheat with only the apical root portion exposed to O2 deficiency

This study investigated aerenchyma formation and function in adventitious roots of wheat (Triticum aestivum L.) when only a part of the root system was exposed to O-2 deficiency. Two experimental systems were used: (1) plants in soil waterlogged at 200 mm below the surface; or (2) a nutrient solution system with only the apical region of a single root exposed to deoxygenated stagnant agar solution with the remainder of the root system in aerated nutrient solution. Porosity increased two- to three-fold along the entire length of the adventitious roots that grew into the water-saturated zone 200 mm below the soil surface, and also increased in roots that grew in the aerobic soil above the water-saturated zone. Likewise, adventitious roots with only the tips growing into deoxygenated stagnant agar solution developed aerenchyma along the entire main axis. Measurements of radial O-2 loss (ROL), taken using root-sleeving O-2 electrodes, showed this aerenchyma was functional in conducting O-2. The ROL measured near tips of intact roots in deoxygenated stagnant agar solution, while the basal part of the root remained in aerated solution, was sustained when the atmosphere around the shoot was replaced by N-2. This illustrates the importance of O-2 diffusion into the basal regions of roots within an aerobic zone, and the subsequent longitudinal movement of O-2 within the aerenchyma, to supply O-2 to the tip growing in an O-2 deficient zone.