The ionic sensitivity of secretion-associated organelles in root cap cells of maize.

Ionophores selective for Na+ (monensin, dianemycin), for K+ (valinomycin, nigericin), for Ca2+ (A23 187, X-537A), the calcium deregulatory substances amiprophosmethyl, fluphenazine, caffeine and the chelator EGTA have been applied to intact slime-producing root tips. An accumulation of secretory vesicles within the cells is observed after treatments up to 3 h by all of these agents. Occasionally the vesicles fuse with one another producing an internal "secretion vacuole". Secretory vesicles may or may not remain attached to the dictyosomes but in all cases the cisternae lengthen, ending most often in a cup-shaped form. Application of ionophore plus a 5 mM chloride solution of the corresponding cation had the same effect as treatment with the ionophore alone. These effects are reversible upon withdrawal of the "ion-deregulatory" agents.