Seeds of Caesalpinia echinata fill up to physiological maturation phase ~60 days after anthesis (DAA) in the field. These seeds are desiccation tolerant to 0.08 gH2O gDW–1 and can be stored for 2 years under freezing temperatures without losing germinability. Starch (40–50%), soluble carbohydrates (10–15%, mainly sucrose and cyclitols), in addition to traces of raffinose and stachyose detected early at maturation, are supposed to be related to the acquisition of desiccation tolerance. In the present work we demonstrate that desiccation-intolerant immature seeds (45 DAA) of C. echinata can be dried until 0.14 gH2O gDW–1 when previously soaked in polyethylene glycol (PEG) solution, maintaining high germination percentage. In contrast, seeds of 55 DAA tolerated drying until 0.14 gH2O gDW–1 without previous PEG treatment, indicating that they have already reached desiccation tolerance at this developmental stage. High-performance anion exchange chromatography analysis revealed that cyclitols and sucrose increased markedly in the embryonic axes at 45 DAA after PEG treatment, reaching levels found in embryos at 55 DAA. These results suggest that PEG treatment mimics the natural maturation drying of C. echinata seeds, changing carbohydrate metabolism and triggering processes involved in desiccation tolerance.
-The persistence of viable seeds in the soil is an important way to assure plant propagation, especially for species which produce seeds with short lifespan. Poincianella pluviosa is a tree species which seeds have short to medium storability at room temperature. The comprehension of the maturation process is crucial to understand its strategy for propagation and it could provide tools to improve seed viability in ex situ conditions. Flowers were tagged in two consecutive cycles of maturation and pods were periodically harvested until dispersion. Seeds were classified based on their morpho-physiological features, capability to germinate and develop seedlings. The complete maturation process was attained 315-330 days after anthesis, a period longer than reported for seed viability at room temperature. The maximum dry mass and seed vigor were reached at the end of maturation, although elevated seedling production was obtained before physiological maturity. We suggest that the precocious ability to produce seedlings in a long maturation could be a strategy to overcome environmental constraints, as the species is distributed in a wide range of phytogeographic domains in Brazil.Index terms: ex situ conservation, physiological maturity, seed shedding, seed maturation, sibipiruna.
Maturação de sementes de Poincianella pluviosa (Caesalpinoideae)RESUMO -A manutenção de sementes viáveis no solo é uma forma importante para garantir a propagação, especialmente para espécies que produzem sementes de vida útil curta. Poincianella pluviosa é uma espécie arbórea cujas sementes apresentam curto a médio período de armazenamento em condições de laboratório. Assim, a compreensão do processo de maturação é fundamental para entender as estratégias de propagação da espécie, representando uma ferramenta para aprimorar a viabilidade das sementes em condições ex situ. As flores foram marcadas em dois ciclos de maturação consecutivos e os frutos foram colhidos até dispersão. As sementes foram classificadas de acordo com suas características morfofisiológicas e a capacidade de germinar e desenvolver plântulas. Observou-se que o processo completo de maturação (315-330 dias após antese) é maior do que o tempo descrito na literatura para manutenção da viabilidade destas sementes em temperatura ambiente. Valores máximos de massa seca e vigor foram alcançados no final da maturação, embora elevada produção de plântulas tenha sido obtida antes da maturidade fisiológica. Sugere-se que a capacidade precoce de produzir plântulas em um longo período de maturação poderia ser uma estratégia para superar limitações ambientais, já que a espécie está distribuída em diversos domínios fitogeográficos no Brasil.Termos para indexação: conservação ex situ, dispersão de sementes, maturação de sementes, maturidade fisiológica, sibipiruna.
RESUMO O comportamento padrão esperado para as sementes, seja por leigos ou mesmo especialistas no assunto, é o de uma estrutura seca que, colocada em meio com suficiente disponibilidade de água, germina e produz uma nova planta, preservando a espécie. Contudo, há um gigantesco número de espécies que possuem sementes com comportamento totalmente diferente. Sementes que não podem sequer serem secas, denominadas recalcitrantes, são dispersas úmidas no meio e, ao longo da evolução das espécies, desenvolveram sistemas alternativos àqueles padrões esperados. Nesta revisão, procuramos demonstrar um dos mais complexos e interessantes sistemas de preservação de espécies com sementes recalcitrantes, nas espécies do gênero Eugenia, da família Myrtaceae. São abordados tanto a capacidade em regenerar embriões a partir de tecidos cotiledonares, quanto o controle extremamente eficiente em não desperdiçar material de reserva, evitando germinações simultâneas na mesma semente. Neste controle parecem estar envolvidas as espécies reativas de oxigênio (EROs), que também são revistas neste artigo.
During embryogenesis and seed filling, developing seeds are metabolically highly active, while at the desiccation stage of tolerant seeds a decreased metabolism is expected. Seeds of Poincianella pluviosa present an extensive maturation cycle (11 months), longer than seed storability at room temperature (8 months). The metabolic profile of these seeds was characterized during maturation and drying, focusing in their role on seed behavior after shedding. Distinct responses of the embryonic axes and cotyledons to drying were observed depending on the developmental stage. Low proportions of tricarboxylic acids intermediaries until maturity indicated a low respiratory metabolism prior to the desiccation stage. Changes in shikimate, 4-coumarate, and quinate proportions suggest a metabolic shift towards the synthesis of chlorogenate isomers, found in high proportions in dispersed seeds. High proportions of lactate and glycerol were observed in immature seeds after artificial drying, but also in naturally dried axes of dispersed seeds. This suggests an active metabolism prior to drying and an osmotic stress under hypoxia, mechanisms that were never described before in desiccation-tolerant seeds. The results indicated that P. pluviosa seeds are dispersed with an incomplete metabolic switch-off, which can be related to their short lifespan.
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