Induced root differentiation in sycamore callus

Abstract

A sycamore callus (S 4) has been isolated and grown on a medium containing salts, vitamins, a casein digest, 2 % sucrose and 1 mg/1. NAA. The callus, which would not grow in the absence of the added auxin, was much firmer in texture than a sycamore callus (S 2) isolated in this laboratory in 1958 which has not been induced to differentiate. When kinetin over the range 0·05–0·5 mg/1. was included in the growth medium of S 4 nodules of xylem and phloem were induced within the tissue and roots frequently grew from the surface of the callus. Some roots developed geotropic sensitivity although the majority grew radially outwards from the callus surface. The roots also varied with respect to the number of root hairs they carried. No roots were produced at sucrose concentrations less than 2%, although histological examination revealed extensive xylem and phloem differentiation relative to the amount of growth which had taken place. When sugars other than sucrose were supplied in the medium at a concentration of 3 % (w/v) roots were also induced in those calluses where the carbon source had supported good growth. Sucrose, glucose and fructose were identified in the ethanol-soluble extracts of all these calluses. Radioactivity was incorporated into sucrose when S 4 was incubated on a medium containing D-[U-¹⁴C]glucose for 24 h. Any sugar which supported growth and differentiation was therefore one which was capable of entering the common metabolic pathway used by the plant for glucose and sucrose. The cells could undergo differentiation so long as the sugar they were supplied with supported active growth and division. The possibility of a physiological role for sucrose is discussed.