Date of Award

Spring 2008

Project Type


Program or Major

Plant Biology

Degree Name

Doctor of Philosophy

First Advisor

Subhash C Minocha


Polyamines are low molecular weight aliphatic amines that are obligatory requirements for cell survival and growth. The commonly occurring polyamines in plants are putrescine, spermidine, and spermine. Suspension cultures of poplar (Populus nigra x maximowiczii), transformed with a mouse ornithine decarboxylase gene (under the control of a 2X 35S CaMV promoter) were used to study the impact of up-regulation of putrescine biosynthesis (and consequent enhanced catabolism) on several aspects of cellular metabolism. The transgenic cells were compared with a control cell line that was transformed with the beta-glucuronidase (GUS) gene.

It was observed that enhanced putrescine metabolism resulted in: (i) increased expression of arginine decarboxylase gene, along with enhanced activity of the corresponding enzyme, (ii) decreased expression of S-adenosylmethionine gene and activity of the enzyme, (iii) changes in the cellular contents of almost all amino acids, (iv) a compromise in cell health due to increased oxidative stress, (v) better tolerance towards Aluminum toxicity, (vi) increased susceptibility to glutamate decarboxylase inhibition, (vii) greater assimilation of carbon from sucrose in the growth medium, and (viii) small changes in the expression of ornithine aminotransferase, proline dehydrogenase and Delta 1-pyrroline-5-carboxylate reductase genes, and an increase in ornithine aminotransferase activity.