Abstract

Pea seedlings grown in divided gas-tight containers were arranged so that O₂ concentration of soil air around the radicles could be varied independently of that around the cotyledons and plumules. When the soil around the radicle tip contained 0.21 atm O₂, no significant reduction in radicle elongation rate was observed until the gas mixture surrounding the cotyledons was reduced below 0.10 atm partial pressure. Even with O₂ partial pressure at 0 around the cotyledons radicle elongation rate was 50% as high as that of the controls.

When O₂ concentration around the radicle was varied, while that around the cotyledons remained at 0.21 atm, the radicle elongation rate at a given O₂ level was markedly reduced. At zero O₂ around the radicle elongation rate was only 20% of normal. It is suggested that a high diffusion impedance between internal gas channels and the relatively undifferentiated tissues near the root tip limits O₂ supply to respiring tissue.

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