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Floral initiation is an important process for temperate woody perennials that affects the subsequent development of the flower. Although this process is well known in annual plants such as Arabidopsis thaliana, not much research has been done in woody plants. This review summarizes the knowledge about mechanisms of flowering induction in woody perennials, compared to the findings in model plants, especially A. thaliana, including factors involved in the regulation of the flowering process. In particular, FT-like genes and TFL1-like genes, which play an important role in the regulation of flowering induction, are discussed in detail. In temperate woody plants the dormancy period follows the floral induction before the floral development. Periodic regulation of this stage is controlled endogenously and, in addition to other factors, it is affected by expression of DAM genes. The genetic mechanisms regulating endodormancy release in woody perennials are similar to vernalization in herbs. Better understanding of processes such as the floral induction and endodormancy release can help us to develop cultivars with a modified flowering time.

Small RNAs (sRNA) are broadly defined as regulatory molecules of 21-24 nucleotides in length which belong to the class of noncoding RNAs. They usually originate in response to the presence of double-stranded RNA in the cells and facilitate transcriptional and posttranscriptional gene silencing of complementary sequences. Their role lies not only in defence against exogenous nucleic acids, but primarily in the regulation of endogenous genes. Typical target molecules of plant sRNA are transposable elements and genes encoding the transcription factors involved in the control of key developmental transitions like the initiation of the reproductive phase and the regulation of its progress. The aim of this thesis is a summary of functional roles of individual small RNA in plant reproductive development, with focus to the female and male gametophytes and in the protection against the transition of transposable elements to following generations. Both endogenous and exogenous sRNA are amply utilized in plants, because they provide an immediate and direct response of the organism to rapidly changing conditions, and thus undoubtedly belong to the key factors which contribute to their phenotypic plasticity.

A population of an endangered orchid species Spiranthes spiralis was discovered in 1980 in the National natural monument Pastviště u Fínů in village Albrechtice, near Sušice. Since 1985 the number of flowering individuals of this population has been regularly monitored. Since autumn 1998 all the specimen found there have been marked and biometrically measured. Since the beginning of monitoring, big fluctuations in the number of flowering specimens or in survival of the individual plant rosettes have been observed among the years. The aim of this thesis was to design the so called index of shading and to verify the possibility of its use to explain some phenomena of plant population dynamics. The index was designed with image analysis and biometric data. The hypothesis has been tested, that the basic variable determining the plant{\crq}s fitness (survival, flowering, vegetative propagation etc.) is the rate of shading by neighboring vegetation (expressed with the index of shading). It has been found that the effect of shading on flowering is not significant or hidden by other factors (such as the course of the weather in the season etc.). The size of the leaf area affects the probability of flowering, number of blooms and height of the inflorescence stem. My thesis also focused on costs of flowering, survival probability (since 1998) and flowering dynamics (since 1986).