Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2017-01-03T20:39:14Z No. of bitstreams: 1 AnaPaulaAvelinoDosSantos_DISSERT.pdf: 2080451 bytes, checksum: 9737052d213c1f0b3b98f544f229f3a2 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2017-01-09T13:34:57Z (GMT) No. of bitstreams: 1 AnaPaulaAvelinoDosSantos_DISSERT.pdf: 2080451 bytes, checksum: 9737052d213c1f0b3b98f544f229f3a2 (MD5) / Made available in DSpace on 2017-01-09T13:34:57Z (GMT). No. of bitstreams: 1 AnaPaulaAvelinoDosSantos_DISSERT.pdf: 2080451 bytes, checksum: 9737052d213c1f0b3b98f544f229f3a2 (MD5) Previous issue date: 2016-06-23 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / A degrada??o das reservas, a parti??o de metab?litos e a atividade de enzimas degradadoras foram estudadas em pl?ntulas de girassol cultivadas in vitro sob fotoper?odo de 12/12 h (claro/escuro) ou na aus?ncia de luz (escuro) para investigar o envolvimento da rela??o fonte-dreno e da insufici?ncia de carbono nos mecanismos que regulam a mobiliza??o das reservas durante a exposi??o ao escuro cont?nuo. Nas primeiras 24 h de tratamento (fase de aclimata??o), a aus?ncia de luz n?o afetou o crescimento, mas restringiu a utiliza??o de carbono e nitrog?nio, indicada pela acumula??o de a??cares e amino?cidos nos diferentes ?rg?os da pl?ntula. Ap?s 5 dias de tratamento (fase de sobreviv?ncia), a exposi??o prolongada ao escuro limitou o crescimento e retardou a mobiliza??o dos lip?deos e das prote?nas de reserva devido ? insufici?ncia de carbono, evidenciada pela deple??o de carboidratos nos cotil?dones e no hipoc?tilo e de amino?cidos no hipoc?tilo e nas ra?zes. As altera??es verificadas na rela??o fonte-dreno devem ter sido uma resposta ? escurid?o prolongada, ao inv?s de um mecanismo utilizado para regular a mobiliza??o das reservas, considerando que estas altera??es n?o puderam ser associadas ? retroinibi??o mediada pela acumula??o de metab?litos. A degrada??o dos lip?deos de reserva depende, pelo menos em parte, de mecanismos que regulam coordenadamente as atividades de lipases e ICL, mas as atividades de proteases ?cidas e amilases n?o puderam ser diretamente relacionadas ? regula??o da hidr?lise das prote?nas de reserva e do amido. Os resultados obtidos permitem sugerir que a mobiliza??o das reservas em pl?ntulas de girassol cultivadas no escuro deve ser regulada por mecanismos que percebem a aus?ncia de luz e preveem a insufici?ncia de carbono, ajustando a utiliza??o das reservas de acordo com as demandas energ?ticas futuras para garantir, pelo menos a curto prazo, a sobreviv?ncia da pl?ntula. / Reserve mobilization, metabolite partitioning, and reserve-degrading enzyme activities were studied in sunflower seedlings cultivated in vitro under 12-h photoperiod or in the absence of light to investigate the involvement of source-sink relation and carbon starvation in the mechanisms that regulate reserve mobilization during the exposure to continuous darkness. At the first 24 h of treatment (acclimation phase), the absence of light did not affect growth, but restricted carbon and nitrogen utilization, indicated by sugar and amino acid accumulation in the different seedling parts. After 5 days of treatment (survival phase), extended exposure to darkness limited growth and retarded storage lipid mobilization due to carbon starvation, evidenced by the depletion of carbohydrates in cotyledons and hypocotyl, as well as the consume of amino acids in hypocotyl and roots. Alterations in the source-sink relation may have been a response to extended darkness, instead of a mechanism utilized to regulate reserve mobilization, as these alterations cannot be associated with negative feedback mediated by metabolite accumulation. Storage lipid degradation depended, at least in part, on mechanisms that co-ordinately regulate the activities of lipases and isocitrate lyase, but the activities of acid proteases and amylases could not be directly related to the regulation of storage protein and starch hydrolysis, respectively. Taking these results together, it is possible to suggest that reserve mobilization in sunflower seedlings cultivated in the dark may be regulated by mechanisms that perceive the absence of light and predict carbon starvation, adjusting reserve utilization according to future energy demands to allow, at least in short term, seedling survival.