- •Despite the importance of the barrier to oxygen losses of the roots of hygrophytes growing in wet environments devoid of oxygen, there are few data available on permeability coefficients for O2 across outer root cell layers (POPR) and how they may change in response to low O2.
- •A gas perfusion technique was used to measure the POPR of rice (Oryza sativa) plants grown in either aerated or deoxygenated solution. The contributions of the apoplast and of living cells to the overall POPR were characterized either by blocking apoplastic pores with precipitates of brown Cu2[Fe(CN)6] or by killing cells with 0.1 N HCl.
- •Compared with that of plants from aerated hydroponics, the POPR of plants grown in deoxygenated medium was smaller by an order of magnitude. Precipitates resulting from CuSO4/K4[Fe(CN)6] treatment only formed in plants grown in aerated solution, where they reduced the POPR by 5–20%. Killing of root segments with HCl increased POPR in plants grown in both conditions by 20–55%.
- •The results indicated that apoplastic barriers effectively restricted radial O2 loss. The relative role of the respiratory O2 consumption of root peripheral layers increased as POPR decreased.