ABSTRACT
A reliable plant regeneration system is described for the production of adventitious shoots from root explants of spinach. Explants from roots of axenic shoots and roots induced on cultured hypocotyl explants were used for adventitious shoot induction. Explants from apical, middle and basal root regions were incubated on Nitsch and Nitsch medium supplemented with α-naphthaleneacetic acid, gibberellic acid and kinetin. Optimum shoot regeneration was from explants of apical and middle root regions on medium with 20 µM α-naphthaleneacetic acid and 5.0 µM gibberellic acid. Shoots originated directly from root tissues without an intervening callus phase. Adventitious shoots were rooted and were grown to maturity in the glasshouse. This plant regeneration procedure has been exploited in preliminary studies of Agrobacterium-mediated transformation.
Subject(s)
Biology , Education, Graduate , Research , Universities , Training Support , United KingdomABSTRACT
The natural occurrence of cytokinins existing both in a free form and as a constituent of transfer RNA was examined in serial segments of young seedling roots of pea. Purified ethanol extracts of root apices were resolved into four factors capable of inducing soybean callus tissue proliferation. The most active factor was identified as zeatin or some closely related compound; it produced polyploid divisions and tracheary element differentiation when tested on cultured pea root segments. The terminal 0- to 1-millimeter root tip contained 43 to 44 times more free cytokinin on a fresh weight or a per cell basis than the next 1- to 5-millimeter root segment. Extracts of more proximal segments behind the tip contained no measurable free cytokinin. Acid hydrolysates of transfer RNA exhibited reproducible cytokinin activity. Bioassays revealed that the predominant amounts of free cytokinin and that present in transfer RNA were restricted to the extreme root tip. There was approximately 27 times more free cytokinin than the amount detected in transfer RNA in root apices.
