© 2004 Heron Publishing—Victoria, Canada
Physiological responses of wild type and putrescine-overproducing transgenic cells of poplar to variations in the form and
concentration of nitrogen in the medium
Rakesh Minocha (1, 2), Jae Soon Lee (3), Stephanie Long (1), Pratiksha Bhatnagar (4) and Subhash C. Minocha (4)
1. USDA Forest Service, Northeastern Research Station, P.O. Box 640, Durham, NH 03824, USA / 2. Corresponding author (rminocha@hopper.unh.edu) / 3. Forest Research Institute, Biotechnology Division, Suwon 441-350, Republic of Korea / 4. Department of Plant Biology, University of New Hampshire, Durham, NH 03824, USA / Received December 12, 2002; accepted March 18, 2003; published online March 1, 2004
Summary
We determined: (a) the physiological consequences of overproduction of putrescine in transgenic poplar (Populus nigra × maximoviczii) cells expressing an ornithine decarboxylase transgene; and (b) effects of variation in nitrogen (N) concentration of the
medium on cellular polyamine concentration in transgenic and non-transgenic cells. Cells grown in the presence of supplemental
(to the normal concentrations of N sources in the growth medium) and reduced amounts of NH4NO3 and KNO3 were used to study effects on membrane permeability, mitochondrial respiratory activity, protein accumulation, growth rates
and changes in cellular polyamine concentration. The N concentration of the MS medium was not a limiting factor for continued
overproduction of putrescine in transgenic cells. However, continued supplies of NH4+ and NO3– were required to maintain homeostatic amounts of putrescine in both cell lines. The presence of high amounts of putrescine
in transgenic cells had significant effects on the physiological parameters measured. Compared with non-transgenic cells,
transgenic cells had greater plasma membrane permeability, less tolerance to NH4NO3, more tolerance to KNO3, and accumulated higher amounts of soluble protein.
Keywords:
ammonia, cell viability, mitochondrial activity, nitrate, ornithine decarboxylase, polyamines, spermidine, spermine.
