Effect of increased polyamine biosynthesis on stress responses in transgenic tobacco by introduction of human S -adenosylmethionine gene Bhavna Waie, Manchikatla Venkat Rajam * Plant Polyamine and Transgenic Research Laboratory, Department of Genetics, University of Delhi */South Campus, Benito Juarez Road, New Delhi 110021, India Received 12 November 2002; received in revised form 8 January 2003; accepted 13 January 2003 Abstract Introduction of a human S -adenosylmethionine decarboxylase (samdc ; EC 4.1.1.50) gene under the control of a constitutive promoter (CaMV35S) in tobacco (Nicotiana tabacum var. xanthi ) led to increased polyamine biosynthesis. Transgenic lines with increasing spermidine and putrescine titres, especially in the conjugated forms, exhibited tolerance to salinity and drought as well as to fungal wilts caused by Verticillium dahliae and Fusarium oxysporum . This is the first report where tolerance to both abiotic and biotic stresses has been observed in transgenic plants following transfer of a polyamine biosynthesis gene. # 2003 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Abiotic stress; Biotic stress; Polyamines; Nicotiana tabacum ; S -adenosylmethionine decarboxylase; Transformation 1. Introduction Polyamines (PAs), putrescine (Put), spermidine (Spd) and spermine (Spm), are polycationic compounds pre- sent in all living organisms. They interact with biologi- cally active molecules such as nucleic acids, proteins as well as cell membranes and thus have been implicated in a number of cellular and molecular processes. PAs play a pivotal role in the regulation of synthesis and function of nucleic acids and proteins, membrane stability, and cell proliferation and differentiation [1  /3]. PAs also accumulate in significant amounts under abiotic and biotic stress conditions and have been shown to play a key role in plant stress adaptation [2,4]. It has been suggested that PA involvement in abiotic stress adapta- tion could be because of their role in osmotic adjust- ment, membrane stability, free-radical scavenging and the regulation of stomatal movements [4  /6]. PAs, especially Put and Spd, also accumulate under biotic stress conditions [2]. The mechanism of action of PAs in biotic stress reactions is not clearly understood, although PA conjugates have been shown to be anti- microbial in nature [2,7]. There have been various attempts to study the role of PAs in cellular and molecular processes through the use of PA biosynthetic inhibitors. This method, however, suffers from major drawbacks such as the non-specific and pleiotropic effects of inhibitors on metabolism and the limitation of this method to only down-regulation of the metabolism [8,9]. The use of transgenics, on the other hand, facilitates modulation of a single step in the pathway and allows the study of the specific role of the transgene. There are a number of reports on transgenics over-expressing PA biosynthesis genes and the role of PAs in in vitro as well as in vivo plant morphogenesis has been demonstrated by using such transgenics [8,10 / 13]. However, the reports on stress responses of these transgenics are scarce and limited to abiotic stresses in adc [14  /16] and odc [13] transgenic plants, but such studies were not done with samdc transgenic plants. Moreover, PA transgenics have not been examined for biotic stress tolerance, although PA conjugates have been shown to have a protective role against various viral and fungal pathogens [2,7]. Therefore, this study * Corresponding author. Tel.:  /91-11-24679866; fax:  /91-11- 26872437. E-mail address: rajam@bol.net.in (M.V. Rajam). Plant Science 164 (2003) 727  /734 www.elsevier.com/locate/plantsci 0168-9452/03/$ - see front matter # 2003 Elsevier Science Ireland Ltd. All rights reserved. doi:10.1016/S0168-9452(03)00030-X