Studies on leaflet abscission of blue lupin leaves : I. Interaction of leaf age, kinetin and light.

In blue lupin leaves, each leaflet abscises at an abscission zone situated in the pulvinus at its base. The time to abscission of leaflets of detached leaves is proportional to leaf age. Light accelerates abscission; within certain limits the acceleration is the greater the younger the leaf. At a given concentration, kinetin applied to a single leaflet accelerates leaflet abscission in young leaves kept in darkness, delays it in older ones. There is an interaction between kinetin and light which is dependent also on leaf age and kinetin concentration. The leaf can be considered as consisting of three regions, the petiole, the pulvinar region and the leaflets. The effects of kinetin and of light as well as their interactions depent on the regions of the leaf treated with these agents. Kinetin applied to a leaflet of a young leaf kept in darkness accelerates abscission, but kinetin applied to the pulvinar region of a similar leaf kept in darkness delays abscission. When any part of a leaf is illuminated, abscission is accelerated. The most light-sensitive region of the leaf is the pulvinar region, despite its relatively small area. Acceleration of abscission by light is greatest when illumination of the pulvinar region is combined with illumination of either the leaflets or the petiole. The interaction of light with kinetin is complex. Where the illuminated area includes the pulvinar region, kinetin delays abscission. This effect is most marked in the case where the pulvinar region alone is illuminated and kinetin is applied to a leaflet.Intrafoliar abscission as found in lupin leaves permits study of complex interactions of both distal and proximal stimuli involved in abscission.