Regulation of H+ Excretion

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Abstract
Osmotic shock, a 15-min plasmolysis followed by a 15-min rehydration in the cold, is a nondestructive technique which inhibits fusicoccin-stimulated H+ excretion from oat mesophyll cells (Avena sativa L. [cv. Garry]). Osmotic shock causes a loss of intracellular solutes and stimulates H+ uptake, but osmoregulation can still occur and enhanced H+ uptake occurs only at low external pH. Evidently, osmotic shock interferes directly with the excretion of H+ rather than affecting only H+ or counter ion uptake. Plasmolysis alone does not inhibit fusicoccin-enhanced H+ excretion, and the rehydration step must be rapid and in the cold for maximum inhibition. Apparently, the plasma membrane is perturbed, possibly due to release or rearrangement of membrane protein. Compared to corresponding osmolarities of sorbitol or NaCl, polyethylene glycol 4000 is much less effective during the plasmolysis step; the ineffectiveness of polyethylene glycol 4000 may be due to its preservation of plasmodesmata.