The catecholamine compounds in potato (Solanum tuberosum L.) leaves and tubers have been identified by gas chromatography coupled to mass spectrometry (GC-MS) measurements. The finding that the catecholamine level is dramatically increased upon tyrosine decarboxylase (TD) overexpression potentiates the investigation on their physiological significance in plants. It was then evidenced that catecholamines play an important role in regulation of starch-sucrose conversion in plants. In this paper we investigated catecholamine biosynthetic pathway in potato plants exposed to the different stress conditions. The activation of TD (EC 4.1.1.25), tyrosine hydroxylase (TH, EC 1.14.18.1) and l-Dopa decarboxylase (DD, EC 4.1.1.25) was a characteristic feature of the potato leaves treated with abscisic acid (ABA). In high salt condition only TD activity was increased and in drought both TH and DD were activated. UV light activated predominantly DD activity. Leaves of plants grown in the dark and in red light circumstances were characterized by significantly decreased activities of all the three enzymes whereas those grown in cold were characterized by the decreased activity of DD only. In all, stress conditions the normetanephrine level and thus catecholamine catabolism was significantly decreased. Increased catecholamine level in TD-overexpressing potato resulted in enhanced pathogen resistance. Our data suggest that plant catecholamines are involved in plant responses towards biotic and abiotic stresses. It has to be pointed out that this is the first report proposing catecholamine as new stress agent compounds in plants.
Copyright 2004 Elsevier SAS