Aloni, B., Institute of Field and Garden Crops, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel

The reduction of 2,3,5-triphenyl tetrazolium chloride (TTC) in slices, prepared from petioles of celery leaves (Apium graveolens L.) and potato tubers (Solanum tuberosum), was found to be highly sensitive to dehydration. Incubation of the slices in mannitol or sucrose solutions with an osmotic potential slightly higher than isotonicity, inhibited the TTC reduction by about 70%. The inhibition was instantaneous and reached a maximal value as the tissue reached equilibrium with the dehydrating solution. The inhibition of TTC reduction was reversed if the slices were rehydrated in distilled water and regained the initial water content. However, under conditions at which the dehydrated state could not be fully reversed, the inhibition of the TTC reduction was not reversed. Incubation of tissue slices in non-dehydrating concentrations of KCl, NaCl, CaCl2 and MgCl2 for 60 min caused marked inhibition of TTC staining, with the divalent salts being inhibitory at much lower concentrations than the monovalent salts. Soluble MDH from celery petiole slices was affected similarly by the monovalent and the divalent salts. The results suggest that the changes in TTC reduction under mild dehydration conditions are caused by in vivo reversible inactivation of dehydrogenases activity and that these enzymatic changes are related to alteration of the ionic concentration in the cytoplasm. © 1982.