METABOLIC CHANGES ASSOCIATED WITH SHOOT FORMATION IN TOBACCO CALLUS CULTURES

Callus tissue derived from Nicotiana tabacum L. stem pith parenchyma cells was grown either on medium which maintains the callus in an undifferentiated state, or on medium which induces the formation of shoots. Two complementary types of studies were performed with the goal of establishing metabolic markers for the initiation of shoot formation: one designed to characterize the flow of radioactive sucrose into various metabolic pools, and one which allowed measurement of intermediary metabolite concentrations.; Many differences in rates and patterns of sucrose metabolism by non-shoot-forming (NSF) and shoot-forming (SF) calli were apparent within the first week after subculture of undifferentiated callus tissue to NSF and SF media, respectively. Synthesis of hexose monophosphates was the primary rate-limiting reaction in sucrose metabolism of both types of calli. The inceased rates of synthesis of hexose monophosphates by SF calli, relative to NSF calli, was reflected to varying degrees in all other intermediary metabolites. Differences between NSF and SF calli were most pronounced 7 days after subculture, and generally correlate with increased rates of cell division required for "meristemoid" formation in SF calli.; Greater rates of synthesis of many amino acids were observed in SF calli than in NSF calli. These differences are partially explained by increased amino acid concentrations in SF calli, although there is also evidence for stimulation of secondary product formation during the development of shoots. Glutamine, glutamate, phenylalanine, and proline concentrations were greater in SF calli than in NSF calli one week after subculture.; Greater amounts of starch were also observed in SF calli than in NSF calli four days after subculture. This difference was maintained through 21 days, and was reflected in rates of starch synthesis in the two types of calli.; 1-aminocyclopropane-1-carboxylic acid concentrations were greater in NSF calli than in SF calli two days after subculture. This difference was mantained during the first week of growth, and may reflect a mechanism whereby ethylene prevents organized development.