Beschreibung:
<jats:title>Abstract</jats:title><jats:p>Sunflower plants (7 weeks old) were transferred from a modified Hoagland solution to a N‐free nutrient medium and kept there for 7 days. Abscisic acid (ABA) was determined in several parts of the plants and in exudates collected from the roots of some of these plants.</jats:p><jats:p>N‐deficiency considerably increased the ABA content of the leaves, especially the older ones, and also considerably increased the ABA content of the upper parts of the stem when compared to the control plants. In the roots and the exudates of these plants no ABA could be detected.</jats:p><jats:p>After dissecting the stems the ABA content in the roots of the control plants with normal N supply dropped quickly, probably due to rapid metabolization. Judging by results obtained, it seems unlikely that the roots are responsible for the remarkable increase of the ABA content in the shoots caused by N‐deficiency.</jats:p>