Molecular analysis and expression of glutathione S-transferase-coding genes in tobacco

Glutathione S-transferases (GSTs: EC 2.5.1.18) are enzymes that detoxify xenobiotic compounds by covalently linking glutathione to a substrate, forming a glutathione conjugate. Two auxin-responsive cDNAs (Nt 107 and parB) that code for GSTs were Isolated from 2,4-D (2,4-dichlorophenoxyacetic acid)-treated tobacco (Nicotiana tabacum cv. Xanthi) suspension culture cells using reverse transcription polymerase chain reaction. Expression of Nt 107 in Escherischia coli resulted in >300-fold increase in GST specific activity, demonstrating that Nt 107 encodes an active GST. E. coli cultures that express Nt 707 also exhibited glutathione peroxidase (GPX: EC 1.11.1.9) activity against the substrates cumene hydroperoxide, hydrogen peroxide and tert-butyl hydroperoxide. These findings indicate that Nt 107 is likely to be actively involved in the protection against cell stress.

To determine the factors that affect the expression of Nt 107, we have analyzed its response to a wide variety of factors in the wild type tobacco. Stress-signaling compounds that include abscisic acid, hydrogen peroxide, methyl jasmonate and salicylic acid; heavy metals CuSO^ and FeS04; and salt were found to induce Nt 707 expression in a concentration-dependent manner, indicating that Nt 107 participates in the responses of plants to stress conditions.