Ferricyanide-Mediated Transport of Chloride by Anaerobic Corn Roots.

Active transport of salts by higher plant tissues has been shown to depend on aerobic respiration (13). Although active transport under anaerobic condlitions has been reported for a number of animal tissues (19, 32) and for yeast (5, 6), transport in higher plants has been taken to be 02 (lependent. During aerobic respiration, electrons are transferred fronm respiratory intermediates to 02 via organized assemblies of carriers, the mlost important of which includes the cytochrome systenm. The mechanism linking electron transfer to active salt transport is the subject of various hypotheses. Mitchell (29) has suggested that metabolic energy participates in salt uptake by the formation and opening of covalent bonds between certain memiibrane constituents an(l the carried nmolecules. The hypotheses of Go,ldacre (9) and Bennet-Clark (2) propose the participation of high-energy phosphate compounds in ion transport. In these cases the connection with electron transfer is indirect. On the other hand Lundegardh (24, 25) has contende(d that ion transport, specifically anion transport, is effected directly by the cytochronme chain, the members of which in the oxidized state are positively charged an(l are heldl to bind anions electrostatically. In this view, electrons nmove from substrate to O. while avowedly causing anions to move in the opposite (lirection. Anion uptake by this mechanismii is a property only of the comlplete cytochromiie chain and begins with the oxidase (24); accumulation is explainedl by interposing a (liffusion barrier sonmewhere along the chain. The foregoing scheme (loes not specifically explain how ions enter the vacuole, which Lunclegarclh (24) and mlany others regar(d as the final (lestinationi of the bulk of transported ions in plant cells. The evidence for the mitochondrial location of the cytochromes appears overwhelnming, hence the electron ladder hypothesis at best refers to ion transport into the mitochondria. Moreover, even in this context the value of Lundegardh's hypothesis is unclear, since the spatial arrangemiient of the cytochromes with respect to the mitoclhon(drial surface nmembranes remains un(lefine(l. The consi(lerable evidlence linkiiig salt transport