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Abstract. During the vase life of a rose flower, changes in the levels of abscisic acid (ABA) were observed: a decrease during the first 3 days, followed by a steady state at a low level, and finally a sharp increase in late senescence. Feeding [2-t4C]ABA to isolated petals showed that metabolism was very active despite the age of the flower, oxidation processes increased with age, whereas conjugation decreased but the level of nonmetabolized ABA remained stable. When the isolated petal was subjected to water stress, whatever its age, the ABA level increased. Hydrolysis of ABA-GE was not involved in this phenomenon. Thus, ABA synthesis occurred in the isolated petal; it could be directly correlated to the decrease in water potential. However, the ABA increase in isolated petals was limited. Moreover, on the rose tree, increases in ABA levels were not correlated to water potential changes. ABA levels seemed, therefore, mainly regulated by changes in import from leaves and other parts of the flower.As early as 1972, Mayak and Halevy showed that endogenous levels of abscisic acid (ABA) increased in rose petals as the flower senesced. Moreover, higher ABA levels were found in short-lived cultivars compared to long-lived cultivars Mayak 1975, Mayak et al. 1972). In a stomataless" system (leafless flower shoots) or in leafy shoots held in darkness when all stomates are closed, ABA enhanced aging of the flowers and some biochemical processes associated with it (Halevy et al. 1974). These results indicate that ABA participates in the endogenous regulation of senescence processes in rose flowers (Halevy and Mayak 1981).However, little is known about the regulatory mechanisms which control ABA levels in relation to senescence. Synthesis, transport, and breakdown may be involved. In order to define the respective contribution of each of these processes, we compared endogenous ABA levels, during natural senescence or during senescence induced by a water stress, of isolated petals, or of petals maintained on the cut flower in the presence or absence of leaves, or on the whole plant. At the same time isolated petals were fed with [2-taC]ABA in order to determine changes in uptake and breakdown of ABA during senescence. Materials and Methods Plant MaterialRoses (Rosa hyb.) cv. Royalty were cut in a greenhouse of Srlection Meilland (Antibes) and were brought to the laboratory after 24 h at 4~ Flowers were kept in water at 20~ for 2, 6, 9, and 13 days. After preliminary experiments showed heterogeneity between petals according to their position, the three external petals were discarded and measurements were performed only on the five remaining petals (4--8).All experiments were repeated two or three times and the results obtained for the various experiments were similar. Therefore, the results presented here are taken from one experiment of each series. Dehydration Treatment in Controlled ConditionsFor the drying treatment, isolated petals were placed in a desiccator over activated Actigel at 20~ for various periods of time (2,...

SUMMARYDormant as well as completely after-ripened embryos of Pyrus malus L. var. Golden Delicious were cultured aseptically on media of different compositions. Distilled water was used as the simplest medium. The influence of the addition of agar (8 g T^), of mineral substances (macroand micro-elements of the Heller's medium) and of sucrose (10 or 20 g T^) was studied. On the agar-solidified media, three different modes of culture were used, depending upon the nature of the contact between the embryo and the medium. The criteria used to evaluate the depth of dormancy were the germination percentages and the progression in the greening of the cotyledons.Completely after-ripened embryos behaved similarly on all the media used whatever the mode of culture. Dormant embryos behaved differently depending upon the composition of the medium and of the mode of culture. Dormancy was always deeper on agar-solidified media than on liquid media and in the presence of sucrose than in its absence.In order to determine whether these differences in behaviour were due to quantitative differences in the leaching of free abscisic acid (ABA) into the medium, a two-step culture method was introduced, using [i*C]ABA. Dormant embryos were cultured first on water-agar containing lO'^ M (±) [2-"C]ABA (355 KBq fimol'^), then on one of the following media deprived of ABA: water-sucrose-agar, water-agar, water.Observations during the first cukure indicated that the amount of [i*C]ABA absorbed was partially metabolized after only 2 days of uptake. During the course of the second culture, part of the original radioactivity of the embryos (4 days ["C]ABA uptake) was released into the medium. Leaching was much greater and lasted longer on water than on media solidified with agar: it^does not depend upon the volume of the liquid used (3 or 15 ml). The presence of sucrose (20 g ri) in the agar medium does not modify the amounts of ^^C-radioactivity released. The mam part of the radioactivity released in water and in water-agar was shown to be ABA.

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