Changes in the activity of the enzymes involved in nitrogen metabolism in Catharanthus roseus depending on different nitrogen sources

Abstract

The activities of the enzymes nitrate reductase (EC 1.6.6.1) and nitrite reductase (EC 1.7.99.3) were measured in the leaves and roots of whole plants of Catharanthus roseus grown in different nitrogen sources: water (control), 20 mM KNO 3 , 2 mM NH 4 Cl, and a mixture of nitrate and ammonium. The activities of these enzymes were also measured in leaf explants incubated in the same nitrogen sources. The results indicate that nitrate reductase and nitrite reductase in leaves behaved very differently from those in roots. Activity of leaf nitrate reductase measured in vitro decreased with nitrate and increased with ammonium, while in the root, it only decreased when the mixture of both nitrogen sources was employed. In contrast, nitrite reductase from roots was modified by the nitrogen source while the enzyme from the leaves was not. The amino acid pool was increased by all of the nitrogen sources in both whole plants and explants.

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