The Metabolism of Oat Leaves During Senescence: II. Senescence in Leaves Attached to the Plant

The course of senescence in the first leaves of light-grown Avena seedlings when attached to the plant has been compared with that previously studied in detached leaves and leaf segments. Proteolysis in the leaf, whether attached or detached, is accompanied by markedly polar basipetal transport of amino acids. This polar transport can be superimposed on the known transport of amino acids towards a locally applied cytokinin. In the intact plant, it results in a strong movement into the roots. The reducing sugars, which are set free in senescence, do not participate appreciably in this polar transport phenomenon.If cytokinin is applied directly to the roots, then, if the plants are 7 days old, it becomes transported upward into the basal parts of the leaf and there delays the senescence process. However, if the plants are 10 days old, a "reverse Mothes effect" occurs, in which senescence of the leaf is actually promoted and part of the amino acids transported into the roots is synthesized into root protein.