Root aeration in rice (Oryza sativa): Evaluation of oxygen, carbon dioxide, and ethylene as possible regulators of root acclimatizations

Abstract

• Adventitious roots of rice (Oryza sativa) acclimatize to root-zone O2 deficiency by increasing porosity, and induction of a barrier to radial O2 loss (ROL) in basal zones, to enhance longitudinal O 2 diffusion towards the root tip. • Changes in root-zone gas composition that might induce these acclimatizations, namely low O2, elevated ethylene, ethylene - low O2 interactions, and high CO 2, were evaluated in hydroponic experiments. • Neither low O2 (0 or 0.028 mol m-3 O2), ethylene (0.2 or 2.0 μl l-1), or combinations of these treatments, induced the barrier to ROL. This lack of induction of the barrier to ROL was despite a positive response of aerenchyma formation to low O2 and elevated ethylene. Carbon dioxide at 10 kPa had no effect on root porosity, the barrier to ROL, or on growth. • Our findings that ethylene does not induce the barrier to ROL in roots of rice, even though it can enhance aerenchyma formation, shows that these two acclimatizations for improved root aeration are differentially regulated. © New Phytologist (2006).