Control of the glutathione S-transferase and mas1 ' promoter-driven GUS activity in auxin heterotrophic and autotrophic tobacco calli by exogenous 2,4-d-induced ethylene

Auxin autotrophic and heterotrophic lines of tobacco calli may differ not o nly in their indoleacetic acid (IAA) synthetizing abilities and sensitiviti es to exogenous auxins, but also in their gene expression patterns. Auxin a utotrophic callus tissues from the leaf protoplasts of transgenic Nicotiana tabacum SR1 plants involving mas 1 '::GUS gene fusion were generated and t he growth of cultures was compared with that of the heterotrophic lines of the same transgenic tissues on MS medium containing different concentration s of IAA or 2,4-D. The mas1 '::GUS gene fusion expression was investigated, together with the glutathione S-transferase activities (GST, EC 2.5.1.18) in auxin autotrophic and heterotrophic tobacco calli. Both the mas1 ' promo ter and GST gene promoters contain ocs or ocs-like elements, responsible fo r both auxin and ethylene/wound inducibility. The mas1 ' promoter exhibited a much higher expression activity in the heterotrophic cultures growing on IAA than in the autotrophic ones, but in contrast with the natural auxin, the mas1 '::GUS activity decreased at elevated 2,4-D concentrations in the heterotrophic tissues and increased with increasing 2,4-D concentrations in the autotrophic lines. The induction of GST activity by different exogenou s auxin concentrations was much higher in the autotrophic lines, especially in the case of 2,4-D. Higher concentrations of external 2,4-D resulted in increased ethylene production, which displayed different kinetics in the tw o types of calli. The ethylene-inducing 2,4-D concentrations increased the growth of the heterotrophic, but decreased that of the autotrophic lines. B locking the ethylene receptors and hence the signal perception by 2,5-norbo rnadiene (NBD) in the heterotrophic tissues increased the 2,4-D-induced mas 1 ' promoter and GST activities, suggesting that the gaseous hormone counte racted the auxin response pathway. This was not found in the autotrophic ti ssues, where NBD decreased the mas1 ' -driven GUS activity. The GST activit ies were slightly decreased, or almost independent of the action of ethylen e. It is suggested that the cross-talk between the auxin- and ethylene-indu ced signal transduction pathways may differ in the auxin autotrophic and he terotrophic lines.