Storage organ development in radish (Raphanus sativus L.). 2. Effects of growth promoters on cambial activity in cultured roots, decapitated seedlings and intact plants

Abstract

The radish varieties Cherry Belle and Long White Icicle were used to investigate the role of the shoot and the effects of synthetic growth promoters in controlling cambial activity in the seedling axis.Development was compared in excised roots, roots with hypocotyls attached and intact seedlings cultured aseptically on a nutrient medium. No cambial divisions were seen in isolated radicles which had been cultured for ten days following excision but retention of hypocotyl tissue or the entire shoot resulted in cambial activity and the production of secondary vascular tissues. Enriching the culture medium by raising the sucrose conantration to 8% and including 10-5 M indol-3yl acetic acid (IAA) 5 × 10-6 M 6-benzylaminopurine (BA) and 5 × 10-4M inositol enhanced root thickening, increasing stele and xylem diameters in roots cultured both with and without attached shoot tissues. The effects of shoot tissues and enrichment of the medium were additive.The effects of auxin, cytokinin and gibberellin (gibberellic acid, GA2) were also studied on daxpitated seedlings. BA was much more effective in inducing cell divisions in the hypocotyl than either IAA or GA supplied separately but a mixture of IAA+GA also produced clearly defined arcs of cambial tissue. Little secondary tissue had been produced after seven days' treatment, and stelar enlargement was due to the development of a cambial zone and cell expansion in the primary tissues. Only minor differences in response were observed between the two varieties.No stimulation of storage organ development occurred when auxin, cytokinin or inositol was inwrporated into the inorganic culture solution in which plants of Cherry Belle were grown. © 1980 Annals of Botany Company.