Abstract
We tested the capability of plants to utilize protein as the exclusive source of nitrogen. The aim of this study was to find out how such a nutrition affected plantlet growth, photosy nthetic performance, and N assimilation metabolism in tobacco ( Nicotiana tabacum L., cv.
Petit Havana SR1) grown in vitro. Plantlets grown in a casein-supplemented (CA) medium were compared to plantlets grown in a complete Murashige-Skoog (MS) medium, plantlets grown in an ammonium-deficient medium (N1), or plantlets grown in a nitrate-reduced medium (N2).
In addition, the plantlets were grown in the presence or absence of 1.5 % (m/v) saccharo se as an additional carbon source. Casein, similarly as inorganic N limitation, reduced generally plantlet growth, whereas no significant effects were observed on photosynthetic parameters evaluated by chlorophyll a fluorescence.
Although addition of saccharose stimulated the plantlet growth particularly in the MS, it showed a ra ther negative influence both on the growth and on the photochemical efficiency of photosystem II in the plantlets grown in the CA and N1. The activities of enzymes involved in N assimilation, such as nitrate reduc tase (NR) and glutamine synthetase (GS), were lower in the plantlets grown in the CA, N1, and N2, both in leaves and in roots.
On the other hand, glutamate synthase and glutamate dehydrogenase were employed by the plantlets grown in the CA. The presence of s accharose in the growth medium stimulated mainly NR and GS activities in the MS grown plantlets, whereas en zyme activities of the plantlets grown on the N1, N2, and CA were not significantly influenced.
We proved that the tobacco plantlets can utilize casein as the sole source of N particularly during their photoautotrophic cultivation.