REGULATION OF OXYGEN DIFFUSION IN LEGUME NODULES

A review is presented of advances recently made in studies on the stru cture and mechanisms of the variable O-2 diffusion barrier of legume n odules. These suggest that the barrier is a complex of structures invo lving intercellular space occlusions in the mid-cortex and osmocontrac tile responses in the inner cortex. There are also several metabolic o r structural changes which could occur within the infected region. An attempt is made to integrate these various layers within a temporal fr amework. It is also hypothesised that this framework is integrated thr ough the use of enhanced production of activated oxygen species, parti cularly H2O2, which act as sensors and signals for the diffusion barri er. Finally, the potential for exploiting the regulation of O-2 diffus ion is considered in terms of the requirements for low O-2 conditions for gene expression, the control of O-2 supply under stress conditions and the use of the O-2 barrier by the host plant to regulate N-2 fixa tion activity. (C) 1997 Elsevier Science Ltd.