Reposo invernal y desarrollo de flor en cerezo (Prunus avium)

Many woody perennials adapt to cold winters entering a dormant stage. While the mechanisms behind dormancy are unknown, empirical evidence shows that proper flowering requires cold accumulation during the winter and that failure to accumulate cold is a main restriction for the colonization of particular species to warmer latitudes. In temperate fruit trees each cultivar has its own cold requirements that shape the geographical distribution of that cultivar. In cherry trees there is a growing demand for early cropping cultivars. However, plant breeding efforts are hampered by the lack of knowledge on the biological basis for the parameters to be selected. Cold requirements are calculated in an empirical way through temperature records in relation to plant response, and information is surprisingly thin, in spite of the biological importance and the economic reflection of this matter. The objective of this work is to characterise what is happening during winter dormancy in cherry flower buds. This main objective is developed along three objectives that progressively shape developmental changes in the flower bud, framing these changes in a dormancy context. The first objective (1) characterise flower development from the end of the summer to the next spring. The second objective (2) explores under the microscope changes in both the stamens and the pistil. Finally, the third objective (3) quantifies starch content in these structures. Flower bud development was similar for three cultivars examined, and for one cultivar over two years. But differences were apparent between cultivars and years after dormancy. However, all flower buds entered dormancy and remained dormant at a very same stage of development, with all flower whorls differentiated. Microscopic observations, following a series of histochemical staining, showed that at dormancy the stamens had a differentiated sporogenous tissue; and the ovule primordia were present in the ovary. In all cultivars and years, meiosis took place once the chilling requirements were fulfilled, but preceding flower bud growth at bud burst. During dormancy, no anatomical or morphological changes were apparent. However, starch gradually accumulated in the ovary, following a pattern that paralleled chilling hour accumulation. Chilling fulfilment coincided with maximum starch content, and thereafter starch decreased from the ovary. These results provide a biological basis for the understanding of cold requirements and open a way to search for biological indicators of this process.