Acrocomia aculeata is an oil producing tropical palm tree with exceptional potential for producing biofuel.As the propagation of this species is often difficult because of its pronounced seed dormancy, the present work examined the morphology and the anatomy of zygotic embryos and seedlings during in vitro germination. Embryos were put in MS media supplemented with organic compounds and cultivated in the dark at 30°C for 20 days. The dry weights, lengths, and diameters of the cotyledonary petioles, haustoria, roots, ligules, and leaf sheaths of embryos obtained from mature seeds and seedlings removed from culture were measured every 2 days; anatomical and histochemical evaluations were performed on embryos and seedlings removed from culture after 2, 5, 8, 10, 12, and 15 days. Elongation of the embryo axis was observed to initiate after 2 days. Elongation of the cotyledonary petiole was observed starting on the fifth day; this is a morphological indication of germination that is associated with the formation of starch and raphides as well as the differentiation of tracheary elements. The growth of the cotyledon is due to increases in cell volumes as well as the development of a meristematic band peripheral to the haustorium. In spite of the fact that the radicle is less differentiated than the plumule, radicular development is precocious and the root emerges first, indicating the absence of morphological dormancy. Atrophy of the haustorium and the accumulation of phenolic compounds in subepidermal cell layers occur due to culturing conditions.

RESUMO -(Resposta germinativa de duas espécies de Vellozia (Velloziaceae) dos campos rupestres de Minas Gerais, Brasil). Foi avaliado o comportamento germinativo das sementes de Vellozia leptopetala Goeth. et Henr., uma espécie de porte arbustivo que cresce sobre afloramentos rochosos e de V. epidendroides Mart. ex Schult. & Schult., uma herbácea que cresce em campos, na Serra do Cipó. As sementes foram submetidas às temperaturas de 15 a 40 ºC, sob luz ou escuro contínuos, com quatro repetições de 25 sementes por tratamento. Ambas as espécies apresentam sementes pequenas, com 1,31 ± 0,06 mm e 1,15 ± 0,01 mm para V. leptopetala e V. epidendroides, respectivamente. As sementes de V. leptopetala sob luz apresentaram germinabilidade alta (95 a 100%) e semelhante na faixa de 20 a 35 ºC e percentuais inferiores a 15 e 40 ºC (34 e 29%, respectivamente). Na condição de escuro a germinação só ocorreu nas temperaturas mais altas, alcançando 68% a 30 ºC e 3% a 40 o C. Na presença de luz as sementes de V. epidendroides apresentaram altos percentuais de germinação na faixa de 30 a 40 ºC (91 a 84%), com diminuição gradativa da germinabilidade nas temperaturas mais baixas e inibição do processo a 15 ºC. No escuro ocorreu germinação na faixa de 20 a 40 o C (3 a 88%), sendo significativamente superior a 35 e 40 ºC. A produção de sementes capazes de germinar em diferentes condições de temperatura e luminosidade pode ser de grande valor para a espécie, por permitir a colonização de maior diversidade de hábitats, como fendas de rochas sem luz, situação comum para V. leptopetala, ou com densa cobertura por herbáceas, para V. epidendroides. Palavras-chave: fotoblastismo, temperatura, campos rupestres, Vellozia leptopetala, Vellozia epidendroidesABSTRACT -(Germination response of two species of Vellozia (Velloziaceae) from the "campos rupestres" of Minas Gerais, Brazil). The germination behaviour of Vellozia leptopetala Goeth. et Henr., a shrubby species growing on rocky outcrops, and of V. epidendroides Mart. ex Schult. & Schult., an herb growing in grasslands of Serra do Cipó, was evaluated under controlled light and temperature conditions. Seeds were sown at temperatures ranging from 15 to 40 ºC in continuous light or darkness, in four treatments with 25 seeds each. Both species produce small seeds; 1.31 ± 0.06 mm and 1.15 ± 0.01 mm for V. leptopetala and V. epidendroides, respectively. V. leptopetala seeds grown in light had high germinability (95-100%) between 20 and 35 ºC, and lower percentages at 15 and 40 ºC (34 and 29%, respectively). When grown in total darkness, significant germination occurred only at the highest temperatures, reaching 68% at 30 ºC and 3% at 40 ºC. V. epidendroides seeds grown in light had high germinability (91-84%) between 30 and 40 ºC, which gradually decreased at lower temperatures to no germination at 15 ºC. In darkness germination was successful between 20 and 40 ºC (3 to 88%), and was significantly higher at 35 and 40 ºC. The production of seeds capable of germinating in different temperature and li...

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