Seasonal Changes in the Levels of Some Cellular Components in the Abscission Zone of Coleus Leaves of Different Ages

The present study with intact petioles of Coleus of varyingages suggests an involvement of the phenomenon of mobilizationwith the abscission process. There was a gradual increase inthe levels of chlorophyll and nucleic acids and also solublenitrogen compounds in the proximal tissues with the approachof abscission with a concomitant decrease of these substancesin the distal tissues. This increase of metabolites in the proximaltissues was clearer in petioles at the first node than at thefourth node suggesting a lesser degree of metabolic activityof the proximal tissues in older petioles. The change of levelsof chlorophyll and nucleic acids and also of soluble nitrogenwas more marked in winter than in summer months. The application of NAA to petioles of the third node; just afterdeblading (i.e. in the auxin-inhibited stage 1), not only stoppedthe decline of nucleic acid levels (particularly RNA) at thedistal tissues but also caused an increase of nucleic acidsover the initial levels. This effect was more pronounced insummer than in winter months. If the initially inhibitory concentration of NAA was appliedin the auxin-promoted stage 2 of abscission, instead of an increase,there followed a quicker rate of decrease in nucleic acids (particularlyRNA). This effect was also more prominent in summer.