Abstract

Tomato plants were grown at three nitrogen levels: normal supply (control), moderate deficiency (one-eighth the normal supply – 1/8N) and acute deficiency (-N). Plant heights were reduced by 51.4 and 75.7 % respectively at 40 days under the latter two treatments compared with control plants.

The biological activity of growth-promoting and growth-inhibiting substances was determined in the shoot apices of the three sets of plants at three stages: 20, 30 and 40 days after sowing. In general, the endogenous auxin was higher in control than in 1/8N and - N plants. The growth inhibitor level was higher in -N plants than in control and 118N plants. Gibberellin activity was less in nitrogen- starved plants than in controls. - N plants exhibited not only loss of gibberellins but an accumulation of inhibitors at the last stage. A negative correlation between growth promotors (auxins and gibberellins) and growth inhibitors was evident. The interaction between auxins, gibberellins and inhibitors is discussed.