ROLE OF OTHER PLANT ORGANS IN GIBBERELLIC ACID-INDUCED DELAY OF LEAF SENESCENCE IN ALSTROEMERIA CUT FLOWERS

Chlorophyll loss in leaves of cut flowers of alstroemeria (Alstroemeri a pelegrina L. cv. Westland) was rapid in darkness and counteracted by irradiation and treatment of the flowers with gibberellic acid (GA3). The mechanism of the effect of GA3 under dark conditions was investig ated. The content of various carbohydrates in the leaves under dark co nditions rapidly decreased; this was not influenced by treatment with GA3, indicating that the loss of carbohydrates in the leaves did not i nduce the loss of chlorophyll. Placing the cut flowers in various solu tions of organic and inorganic nutrients exhibited no significant effe ct on the retention of chlorophyll in leaves of dark-senescing flowers . The total nitrogen content in leaves of dark-senescing cut flowers d ecreased with time. Leaves of GA3-treated flowers retained more nitrog en. In contrast, the buds of GA3-treated flowers retained less nitroge n during senescence in the dark than control buds. To investigate whet her GA3 affects export of assimilates from the leaf to various parts o f control and GA3-treated flowers, we labelled one leaf with radioacti ve carbon dioxide. C-14-assimilates accumulated preferentially in the flowers, in which the relative specific activity of the youngest flora l buds was highest. No significant differences were observed in the di stribution of C-13-labelled compounds between the buds of control and GA3-treated flowers. To establish the importance of source-sink relati ons for the loss of leaf chlorophyll we removed the flower buds (i.e. the strongest sink) from the cut flowers. This removal only slightly d elayed chlorophyll loss as compared to the large delay caused by GA3-t reatment. In addition, detached leaf tips exhibited chlorophyll loss i n the dark, which was delayed by GA3-treatment in a fashion comparable with that in flowers. Together these data demonstrate that interactio ns of the leaves with other plant organs are not essential for chlorop hyll loss during senescence in the dark. Additionally, we have found n o evidence that GA3 delays the loss of chlorophyll by affecting the tr ansport of nutrients within the cut flowers.