Calcium Transport in Sealed Vesicles from Red Beet (Beta vulgaris L.) Storage Tissue 1: II. Characterization of

• Published in: Plant physiology (Bethesda) 1987-12, Vol.85 (4), p.1137-1142
• Main Authors: Giannini, John L., Ruiz-Cristin, Jose, Briskin, Donald P.
• Format: Article
• Language: English
• Subjects: Membranes and Bioenergetics
• ISSN: 0032-0889; 1532-2548

Calcium uptake was examined in sealed plasma membrane vesicles isolated from red beet ( Beta vulgaris L.) storage tissue using 45 Ca 2+ . Uptake of 45 Ca 2+ by the vesicles was ATP-dependent and radiotracer accumulated by the vesicles could be released by the addition of the calcium ionophore A23187. The uptake was stimulated by gramicidin D but slightly inhibited by carbonylcyanide m -chlorophenylhydrazone. Although the latter result might suggest some degree of indirect coupling of 45 Ca 2+ uptake to ATP utilization via δμH + , no evidence for a secondary H + /Ca 2+ antiport in this vesicle system could be found. Following the imposition of an acid-interior pH gradient, proton efflux from the vesicle was not enhanced by the addition of Ca 2+ and an imposed pH gradient could not drive 45 Ca 2+ uptake. Optimal uptake of 45 Ca 2+ occurred broadly between pH 7.0 and 7.5 and the transport was inhibited by orthovanadate, N ,N′-dicyclohexylcarbodiimide, and diethylstilbestrol but insensitive to nitrate and azide. The dependence of 45 Ca 2+ uptake on both calcium and Mg:ATP concentration demonstrated saturation kinetics with K m values of 6 micromolar and 0.37 millimolar, respectively. While ATP was the preferred substrate for driving 45 Ca 2+ uptake, GTP could drive transport at about 50% of the level observed for ATP. The results of this study demonstrate the presence of a unique primary calcium transport system associated with the plasma membrane which could drive calcium efflux from the plant cell.