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 functionin adventitious roots of wheat (Triticum aestivumL.) whenonly a part of the root system was exposed to O2deficiency.Two experimental systems were used: (1) plants in soilwaterlogged at 200 mm below the surface; or (2) a nutrientsolution system with only the apical region of a single rootexposed to deoxygenated stagnant agar solution with theremainder of the root system in aerated nutrient solution.Porosity increased two- to three-fold along the entire lengthof the adventitious roots that grew into the water-saturatedzone 200 mm below the soil surface, and also increased inroots that grew in the aerobic soil above the water-saturatedzone. Likewise, adventitious roots with only the tipsgrowing into deoxygenated stagnant agar solution developedaerenchyma along the entire main axis. Measurementsof radial O2loss (ROL), taken using root-sleevingO2electrodes, showed this aerenchyma was functional inconducting O2.The ROL measured near tips of intact rootsin deoxygenated stagnant agar solution, while the basal partof the root remained in aerated solution, was sustainedwhen the atmosphere around the shoot was replaced by N2.This illustrates the importance of O2diffusion into the basalregions of roots within an aerobic zone, and the subsequentlongitudinal movement of O2within the aerenchyma, tosupply O2to the tip growing in an O2deficient zone.