Spatial patterns of radial oxygen loss and nitrate net flux along adventitious roots of rice raised in aerated or stagnant solution

Abstract

Roots of rice (Oryza sativa L.) grown in stagnant de-oxygenated solution contain a 'tight' barrier to radial oxygen loss (ROL) in basal zones, whereas roots of plants grown in aerated solution do not. It is generally accepted that the barrier to ROL involves anatomical modifications in the apoplast of cell layers exterior to the aerenchyma. A possible drawback of this adaptation is a reduced capacity for nutrient uptake. Whether or not induction of a barrier to ROL influences the capacity of adventitious roots of rice to take up NO₃^– was determined in the present study, using NO₃^–-selective microelectrodes. When transferred into O₂-free root medium, ROL from positions at 30–50 mm behind the tip of adventitious roots of plants raised in stagnant solution was only 4–6% of the rate from roots of plants raised in aerated solution, indicating the barrier to ROL was induced by growth in stagnant solution. For plants transferred into aerobic nutrient solution containing 0.1 mM NO₃^–, net NO₃^– uptake by these root zones, with or without a barrier to ROL, was the same. It is concluded that induction of a barrier to ROL had no effect on the capacity of adventitious roots of rice to take up NO₃^– from aerobic solution.