Response of shoot and root growth to supply of different nitrogen forms is not related to carbohydrate and nitrogen status of tobacco plants

In the present study, we investigated effects of homogeneous or localized supply of different nitrogen (N) forms on shoot and root growth of tobacco. While homogeneous supply of NH4+ and N deprivation inhibited shoot growth compared with application of NO3—, the N form had no significant effect on root growth. In contrast, in a split-root experiment, application of NH4+ or N deprivation in one half of the root system repressed root growth compared with the other part of the root, which was supplied with NO3—. However, shoot growth was not affected by localized NH4+ application or local N deprivation. Inhibitory effects on shoot and root growth by variations of N supply could not be related to limitations in N or C status of the plants or to NH4+ toxicity. A possible involvement of NO3— as a signal compound including of phytohormones is discussed.