Differential Effects of Sucrose, Abscisic Acid, and Benzyladenine on Shoot Growth and Callus Formation in the Abscission Zone of Excised Citrus Buds

Abstract

The omission of sucrose from basal medium stimulated callus formation in bud explants of Citrus sinensis (L.) Osbeck. It increased abscisic acid-induced callus proliferation reported earlier in the presence of 5% sucrose. Inhibition of callus formation by addition of sucrose was not due to high osmotic potential of the medium. Benzyladenine induced callus formation slightly in all sucrose concentrations up to 5%. The high level of sucrose was required for growth of shoots from buds cultured on basal and benzyladenine-containing media. Uptake of 14C-sucrose by bud explants was linear for at least 98 h and was enhanced significantly by abscisic acid and benzyladenine during the initial 24-h period. Abscisic acid enhanced the absorption of 14C-sucrose and accumulation of sugars in buds cultured at high levels of sucrose. More than 50% of the total label accumulated in the callus of abscisic acid-treated explants, whereas only 16 and 23% were observed in growing shoots of control and cytokinin-treated explants, respectively. Sucrose starvation apparently induced initial callus formation, and high levels retarded further proliferation of the callus.