Relations of endogenous and applied gibberellins to growth and accumulation of essential elements in oregano plants grown in copper rich soils

Oregano plants were grown in soils containing various levels of copper [0.3 (control), 13.0, 17.0, 19.0, 22.0 and 24.5 µM Cu/g of soil]. Treated plants showed a reduction in height which was concentration dependent. In spite of this effect, the levels of gibberellin-like substances in the stem apices and leaves of the treated plants were higher than those of the control. Application of 30 µM, gibberellic acid (GA₃) (drops put on the stem apical meristem) resulted in a significant increase of the height of the controls. GA₃-treated plants grown in copper rich soil also exhibited a not statistically significant increase in height. The uptake and distribution of essential elements in the organs of the orégano plants were also studied. Differences among the elements concerning their accumulation in the plant organs were observed. Their levels became modified when gibberellic acid was added on the stem apex. With some exceptions, application of GA 3 decreased the levels of Cu and other metals in the plant organs compared to non-treated plants. The negative effect of copper on the growth of orégano plants is considered not to be due to the level of GAs, but probably to other parameters (toxicity, etc.).