title: Regulation of reserve mobilisation in sunflower during late seedling establishment in continuous darkness.
abstract: Reserve mobilisation, metabolite partitioning and reserve-degrading enzyme activity were studied in sunflower seedlings cultivated in vitro under a 12-h photoperiod or in the dark to investigate the involvement of source-sink relation and carbon starvation in the regulation of reserve mobilisation under continuous darkness. Reserves, metabolites and enzyme activity were determined with standard spectrophotometric methods. At the first 24 h of treatment (acclimation phase), darkness did not affect growth, but restricted carbon and nitrogen use, as indicated by sugar and amino acid accumulation in the different seedling parts. After 5 days of treatment (survival phase), extended darkness limited growth and retarded storage lipid mobilisation due to carbon starvation, as evidenced by the depletion of carbohydrates in cotyledons and hypocotyl, as well as the consumption of amino acids in hypocotyls and roots. Alterations in the source-sink relationship might have been a response to prolonged darkness, instead of a mechanism used to regulate reserve mobilisation, as these alterations cannot be associated with negative feedback mediated by metabolite accumulation. Storage lipid degradation depends, at least in part, on mechanisms that co-ordinately regulate the activities of lipases and isocitrate lyase. Taking these results together, it is possible that reserve mobilisation in sunflower seedlings cultivated in the dark might be regulated by mechanisms that perceive the absence of light and predict carbon starvation, adjusting reserve use according to future energy demands to allow, at least in the short term, seedling survival.
authors.affiliation: Departamento de Biologia Celular e Genética, Centro de Biociências, Universidade Federal do Rio Grande do Norte, Natal, Rio Grande do Norte, Brazil.
authors.forename: A P
authors.initials: AP
authors.lastname: Avelino
authors.affiliation: Departamento de Biologia Celular e Genética, Centro de Biociências, Universidade Federal do Rio Grande do Norte, Natal, Rio Grande do Norte, Brazil.
authors.forename: D F A
authors.initials: DF
authors.lastname: de Oliveira
authors.affiliation: Departamento de Biologia Celular e Genética, Centro de Biociências, Universidade Federal do Rio Grande do Norte, Natal, Rio Grande do Norte, Brazil.
authors.forename: H A
authors.initials: HA
authors.lastname: da Silva
authors.affiliation: Departamento de Biologia Celular e Genética, Centro de Biociências, Universidade Federal do Rio Grande do Norte, Natal, Rio Grande do Norte, Brazil.
authors.forename: C E C
authors.initials: CE
authors.lastname: de Macêdo
authors.affiliation: Departamento de Biologia Celular e Genética, Centro de Biociências, Universidade Federal do Rio Grande do Norte, Natal, Rio Grande do Norte, Brazil.
authors.forename: E L
authors.initials: EL
authors.lastname: Voigt
mesh_terms: D002244:Carbon / Q000378:metabolism; D002338:Carotenoids / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D018548:Cotyledon / Q000254:growth & development; D003624:Darkness; D004798:Enzymes / Q000378:metabolism*; D006368:Helianthus / Q000502:physiology*; D050356:Lipid Metabolism; D017440:Photoperiod; D010940:Plant Proteins / Q000378:metabolism; D018517:Plant Roots / Q000254:growth & development; D036226:Seedlings / Q000254:growth & development* / Q000378:metabolism* / Q000502:physiology
chemical_list: D004798:Enzymes; D010940:Plant Proteins; D002734:Chlorophyll; D002338:Carotenoids; D002244:Carbon
keywords: Carbon starvation; Helianthus annuus L.; reserve-degrading enzymes; source-sink relations; storage lipid degradation