Efeito da secagem, do armazenamento e da germinação sobre a micromorfologia de sementes de Eugenia pyriformis Camb

Abstract

Recebido em 9/06/2006. Aceito em 21/11/2006 RESUMO -(Efeito da secagem, do armazenamento e da germinação sobre a micromorfologia de sementes de Eugenia pyriformis Camb.). Eugenia pyriformis Camb. é uma espécie arbórea frutífera de porte mediano, cujos frutos saborosos apresentam sementes grandes de tegumento delgado (cartáceo), as quais perdem rapidamente a viabilidade quando submetidas à dessecação. O objetivo foi investigar a estrutura do embrião das sementes, bem como as alterações ultra-estruturais resultantes de secagem, germinação e armazenamento. O eixo embrionário tem menos de 1,0 mm de comprimento, enquanto os cotilédones carnosos podem variar de 1,0 a 2,0 cm. O embrião é maciço, globoso, de cor esbranquiçada e preenche todo o espaço delimitado pelo tegumento. A dessecação das sementes provocou gradativa desestruturação celular, a qual também ocorreu com o envelhecimento das sementes. Durante a germinação, o meristema apical do caule altera-se da forma côncava para a cônica e ocorre alongamento do eixo hipocótilo radicular, com protrusão da raiz. Nessa fase, as células apresentam conteúdo íntegro e hidrólise de reservas. Foi avaliada a variação no conteúdo de água das sementes e discutem-se as conseqüências fisiológicas dessa variação.Palavras-chave: Myrtaceae, uvaia, morfoanatomia de sementes, embrião eugenóide, microscopia eletrônica de varredura, conteúdo de água da semente ABSTRACT -(The effect of drying, storage and germination on the ultra-structure of Eugenia pyriformis Camb. seeds). Eugenia pyriformis Camb. is a tree species of medium height that produces savory fruits with large thin-coated seeds. These seeds quickly lose viability when submitted to desiccation. Our aim was to investigate embryo structure in E. pyriformis seeds and the ultra-structural changes that result from drying, germination and storage. The axis was less than 1.0 mm long, while the fleshy cotyledons varied from 1.0 to 2.0 cm. The apical and radicular meristem lie in opposing positions. There is a procambium and a medulla of parenchymatous nature, rich in starch grains. Leafy primordia were identified around the stem meristem and there were unicellular trichomes and stomata on the adaxial epidermis of the cotyledons. The gradual desiccation of the seeds provoked cellular structure disarrangement, which also occurred as the seeds aged. Apical meristem form changed from concave to conical during germination and the radicular hypocotyl axis became elongated, with root protrusion. In this phase, the cells have structured content and hydrolysis of reserves. Seed water content variation was evaluated and the physiological consequences of this change are discussed.

Physiological performance of cagaita seeds (Eugenia dysenterica DC.) Subjected to drying

“…These results corroborate the slow water loss in the seeds from this species during the drying process as they require approximately 28 days for attaining 20% water content. This behavior was also observed in seeds from other species of the genus Eugenia, as reported by Justo et al (2007) such as the uvaia seeds (Eugenia pyriformis Camb.). The water content of these seeds was slightly reduced in milder drying treatments (16 and 72 h at 20 °C and 16 h at 35 °C) in comparison to that of the initial water content.…”

Germination inhibits the growth of new roots and seedlings in Eugenia uniflora and Eugenia brasiliensis

“…This feature can be used technologically to increase the potential of plantlet production. Also, there is obvious interest in understanding the factors involved in this regenerative capacity that allows the formation of new seedlings when fractionated; Eugenia embryo anatomy, for example, has been studied (Justo et al, 2007;Delgado et al, 2010). Interestingly, however, the formation of new roots and seedlings rarely occurs spontaneously: some kind of injury apparently is necessary for them to be formed (Silva et al, 2005;Amador and Barbedo, 2011).…”

“…Despite the existence of polyembryony in species of the Myrtaceae family (Landrum and Kawasaki, 1997), the Eugenia embryos have been described as monoembryonic, which appear as globular structures, wherein the difference between the cotyledon and the radicle hypocotyl axis is visible only microscopically (Gurgel and Soubihe Sobrinho, 1951;Salomão and Allem, 2001;Justo et al, 2007;Delgado et al, 2010). However, since the development of new tissues depend on the fractionation, it is possible that injuries in seeds can start a process of inducing the formation of new roots and seedlings, or can block self-inhibition of these formations in germinating seeds.…”

Physiological, morphological and biochemical characteristics of the sexual propagation of Piper aduncum (Piperaceae)

“…We analyzed 50 diaspores, which were fixed and prepared by usual proceedings in scanning electron microscopy, described by Justo et al (2007). For observation of internal structures, the seeds were frozen in liquid nitrogen, sectioned longitudinally, according to Alves (2004), and observed under a Scanning Electron Microscope.…”