OXYGEN DIFFUSION IN LUPIN NODULES .1. VISUALIZATION OF DIFFUSION BARRIER OPERATION

Root nodules of Lupinus albus (L.) cv. Multolupa were subjected to sho rt- and medium-term stresses by lowering rhizosphere temperature from 25 to 16-degrees-C (2 h), detopping plants (3 h), darkening plants (21 h) or exposing roots to 20 mol m-3 KNO3 for 4 d. All experimental tre atments produced increases in oxygen diffusion resistance, compared wi th control plants. These correlated with structural changes in the nod ule cortex, which is described in detail for the first time. The most noticeable change is the occlusion of intercellular spaces by a glycop rotein which was identified using the monoclonal antibody MAC236. This glycoprotein was also found surrounding bacteria in intercellular spa ces of the cortex of control nodules.