Transplasma membrane electron transport in relation to cell growth and iron uptake

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Abstract
Cells have a transplasmalemma electron transport system which can transfer electrons across the plasma membrane from cytosolic reductants, NADH or NADPH, to external oxidants, such as iron compounds or impermeable dyes. This electron transport has been shown to control cell growth, ion and iron transport, and membrane potential. Natural electron acceptors can be oxygen, semidehydroascorbate or iron chelates. For carrot cells, growth control is limited to external oxidants with a redox potential over 0 millivolts. Ferric pyrophosphate with a redox potential below 0 mV cannot be reduced and has no effect on growth. The reduction of semidehydroascorbate and high potential artificial acceptors is controlled by hormones and is accompanied by proton release. The high potential external redox site may be part of a growth control system and also act as an iron reduction site, whereas low potential iron chelates are not reduced except in the presence of high affinity ferrous chelators.