Arginine decarboxylase (ADC) is the key enzyme in one of two pathways in the production of putrescine and polyamines. The presence of ADC activity has been widely reported in plants, as well as some bacteria, fungi, protists and animals. ADC activity in plants has been associated with a range of physiological and developmental conditions, such as salt-stress tolerance, flowering and fruit ripening. The ADC enzyme is encoded by a single or low-copy nuclear gene, which appears to lack introns within angiosperms. Based on research within Brassicaceae, ADC is relatively conserved at the amino acid level with a nonsynonymous substitution rate (KA) similar to that of ndhF. The ADC amino acid sequence can be aligned for eudicots, lower dicots, monocots, gymnosperms and even bacteria (e.g. Escherichia coli; speA) using nine regions of high amino acid conservation. A 1230 bp fragment of the approximately 2100 bp ADC gene has been used to compare over thirty taxa representing the major groups of angiosperms, with an emphasis on magnoliid dicots. Amplifications have also been made from a limited number of gymnosperms to provide outgroup taxa sequences. The inferred amino acid sequences were used to generate phylogenetic hypotheses regarding relationships between and among these major groups. Because of molecular features and its physiological importance, ADC is a strong candidate as a useful nuclear gene for assessing phylogenetic relationships within and among families of angiosperms.

Key words: ADC, angiosperms, arginine decarboxylase, nuclear gene systematics, plant polyamines