EXOGENOUS METHIONINE AS A NUTRIENT SUPPLEMENT FOR INDUCTION OF XYLOGENESIS IN LETTUCE PITH EXPLANTS

The induction of xylogenesis in explants of lettuce pith parenchyma was greatly influenced by the presence of exogenous methionine (0·025 to 0·05 μM) in the culture medium. At the various concentrations of methionine tested, tracheary element differentiation was stimulated in the majority of the explants. Differentiation, however, was markedly depressed in a small number of explants grown under the same cultural conditions in the presence of methionine. Cytodifferentiation in control explants, cultured on a similar medium lacking methionine, gave consistent tracheary cell counts with little variation. These data are consistent with the hypothesis that theenhanced production of ethylene, due to the presence of methionine as a substrate, plays a role in the initiation of xylem differentiation. The concentration of ethylene in the cultured tissue may be a critical factor in determining whether the hormone will stimulate or suppress the initiation of cytodifferentiation. Some thick-walled and pitted cells were observed, and these may represent partially-differentiated xylem elements. © 1978 Annals of Botany Company.