RESUMO
There is evidence that the ABA signaling pathway has greatly contributed to increase the complexity of land plants, thereby sustaining their ability to adapt in an ever-changing environment. The regulatory functions of the ABA signaling pathway go well beyond the movements of stomata and the dormancy of seeds. For instance, the ABA signaling regulates the flavonoid biosynthesis, consistent with the high integration of ABA and light signaling pathways, which occurs at the level of key signaling components, such as the bZIP transcription factors HY5 and ABI5. Here we focus on the regulation of 'colorless' (UV-absorbing) flavonol biosynthesis by the ABA signaling and, about how flavonols may regulate, in turn, the ABA signaling network. We discuss very recent findings that quercetin regulates the ABA signaling pathway, and hypothesize this might occur at the level of second messenger and perhaps of primary signaling components as well. We critically review old and recent suggestions of the primary roles played by flavonols, the ancient class of flavonoids already present in bryophytes, in the evolution of terrestrial plants. Our reasoning strongly supports the view that the ABA-flavonol relationship may represent a robust trait of land plants, and might have contributed to their adaptation on land.
Assuntos
Ácido Abscísico/metabolismo , Embriófitas/fisiologia , Flavonóis/metabolismo , Reguladores de Crescimento de Plantas/metabolismo , Transdução de Sinais , Adaptação Fisiológica , Evolução Biológica , Embriófitas/genética , Embriófitas/efeitos da radiação , Fenótipo , Quercetina/metabolismoRESUMO
Ultraviolet-A radiation (UV-A: 315-400nm) is a component of solar radiation that exerts a wide range of physiological responses in plants. Currently, field attenuation experiments are the most reliable source of information on the effects of UV-A. Common plant responses to UV-A include both inhibitory and stimulatory effects on biomass accumulation and morphology. UV-A effects on biomass accumulation can differ from those on root: shoot ratio, and distinct responses are described for different leaf tissues. Inhibitory and enhancing effects of UV-A on photosynthesis are also analysed, as well as activation of photoprotective responses, including UV-absorbing pigments. UV-A-induced leaf flavonoids are highly compound-specific and species-dependent. Many of the effects on growth and development exerted by UV-A are distinct to those triggered by UV-B and vary considerably in terms of the direction the response takes. Such differences may reflect diverse UV-perception mechanisms with multiple photoreceptors operating in the UV-A range and/or variations in the experimental approaches used. This review highlights a role that various photoreceptors (UVR8, phototropins, phytochromes and cryptochromes) may play in plant responses to UV-A when dose, wavelength and other conditions are taken into account.
Assuntos
Embriófitas/efeitos da radiação , Fotorreceptores de Plantas/efeitos da radiação , Fotossíntese , Estruturas Vegetais/efeitos da radiação , Raios Ultravioleta , Biomassa , Embriófitas/crescimento & desenvolvimento , Embriófitas/metabolismo , Flavonoides/metabolismo , Fotorreceptores de Plantas/metabolismo , Pigmentos Biológicos/metabolismo , Estruturas Vegetais/crescimento & desenvolvimento , Estruturas Vegetais/metabolismoRESUMO
Plant growth depends solely on light energy, which drives photosynthesis. Thus, linking growth control to light signals during certain developmental events, such as seed or spore germination and organ formation, is a crucial feature that plants evolved to use energy efficiently. How light controls the cell cycle depends on growth habitats, body plans (unicellular vs. multicellular), and photosensors. For example, the photosensors mediating light signaling to promote cell division appear to differ between green algae and land plants. In this review, we focus on cell-cycle regulation by light and discuss the transition of its molecular mechanisms during evolution. Recent advances show that light-dependent cell-cycle control involves global changes in transcription of cell-cycle genes, and is mediated by auxin and cytokinin.
Assuntos
Regulação da Expressão Gênica de Plantas , Desenvolvimento Vegetal , Plantas/efeitos da radiação , Transdução de Sinais , Evolução Biológica , Ciclo Celular/efeitos da radiação , Clorófitas/genética , Clorófitas/crescimento & desenvolvimento , Clorófitas/efeitos da radiação , Citocininas/metabolismo , Embriófitas/genética , Embriófitas/crescimento & desenvolvimento , Embriófitas/efeitos da radiação , Ácidos Indolacéticos/metabolismo , Luz , Fotorreceptores de Plantas/genética , Fotorreceptores de Plantas/metabolismo , Reguladores de Crescimento de Plantas/metabolismo , Plantas/genéticaRESUMO
The colonization and radiation of multicellular plants on land that started over 470 Ma was one of the defining events in the history of this planet. For the first time, large amounts of primary productivity occurred on the continental surface, paving the way for the evolution of complex terrestrial ecosystems and altering global biogeochemical cycles; increased weathering of continental silicates and organic carbon burial resulted in a 90 per cent reduction in atmospheric carbon dioxide levels. The evolution of plants on land was itself characterized by a series of radical transformations of their body plans that included the formation of three-dimensional tissues, de novo evolution of a multicellular diploid sporophyte generation, evolution of multicellular meristems, and the development of specialized tissues and organ systems such as vasculature, roots, leaves, seeds and flowers. In this review, we discuss the evolution of the genes and developmental mechanisms that drove the explosion of plant morphologies on land. Recent studies indicate that many of the gene families which control development in extant plants were already present in the earliest land plants. This suggests that the evolution of novel morphologies was to a large degree driven by the reassembly and reuse of pre-existing genetic mechanisms.