Structural aspects of the zygotic embryogenesis of Acca sellowiana (O. Berg) Burret (Myrtaceae)

Abstract

RESUMO -(Aspectos estruturais da embriogênese zigótica em Acca sellowiana (O. Berg) Burret (Myrtaceae)). Acca sellowiana apresenta óvulos anátropos, bitegumentados e crassinucelados. Os tegumentos externo e interno são constituídos por duas camadas de células, exceto na região da micrópila em que têm maior número de camadas; a micrópila apresenta-se em ziguezague. O aparelho oosférico ocupa a região micropilar com sinérgides apresentando aparato fibrilar conspícuo. Na região calazal, as três antípodas estão presentes antes da ocorrência da dupla fecundação. O zigoto é formado 21 dias após a polinização controlada, e o endosperma do tipo nuclear já está presente. O zigoto sofre a primeira divisão mitótica no 24 o dia. Embriões nas fases globular, cordiforme e torpedo foram observados no 30 o , 45 o e 60 o dia após a polinização, respectivamente. O embrião maduro, caracterizado pela presença de um eixo hipocótilo-radicular bem desenvolvido e com dois cotilédones carnosos e dobrados, foi observado após 120 dias da polinização. As sementes são exospérmicas e com um único embrião do tipo espiral, característico de Myrtinae. Os estudos da embriogênese zigótica de A. sellowiana mostram que esta espécie apresenta características embriológicas que se adéquam ao conhecido para Myrtaceae (Myrteae, Myrtinae), e ampliam o conhecimento sobre a reprodução sexual dessa espécie nativa, cujo cultivo comercial tem sido incrementado.Palavras-chave: embrião zigótico, feijoa, goiaba-serrana, megagametófito, óvulo ABSTRACT -(Structural aspects of the zygotic embryogenesis of Acca sellowiana (O. Berg) Burret (Myrtaceae)). Acca sellowiana has anatropous, bitegmic and crassinucellate ovules. The outer and inner integuments are double-layered except in the micropyle, where they are composed of more layers; the micropyle is zig-zag shaped. The egg apparatus lies at the micropylar pole, and the zynergids present a conspicuous filiform apparatus. The antipodal cells are present in the chalazal region, persisting before the occurrence of double fertilization. The zygote is visible 21 days after pollination; nuclear endosperm is already present. The first mitotic division of the zygote occurs at 24 th day. The globular, cordiform and torpedo embryo stages can be seen at 30, 45 and 60 days after pollination, respectively. The mature embryo characterized by the presence of a well-developed hypocotyl-radicular axis with two fleshy and folded cotyledons was observed 120 days after pollination. Endosperm is absent in the seeds, and the embryo has spiral form, characteristic of Myrtinae. The zygotic embryology studies of A. sellowiana indicate that this species has embryological characteristics which are in agreement with those reported for Myrtaceae (Myrteae, Myrtinae), and also broaden the knowledge about the sexual reproduction of this native species, whose commercial cultivation has been growing.

The anatomy of the seed-coat includes diagnostic characters in the subtribe Eugeniinae (Myrteae, Myrtaceae)

“…The non-linear micropyle is a highly variable character between species of different sections and within the same section, as seen in the present study, which makes its use in phylogenetic discussions difficult. This character was also reported for other species of Myrteae that belong to subtribes Pimentinae and Myrciinae ( Moreira-Coneglian, 2007 ; Pescador et al, 2009 ; Machado, 2014 ). Endress (2011) reported that in campylotropous ovules, the anti-raphe develops strongly, so that the outer integument becomes long and overlaps the inner integument, which gives rise to a “zig-zag” appearance.…”

“…Two to three layers arose on more than one linage independently within Eugenia. The presence of two layers in the inner integument found in most species of subtribe Eugeniinae in this study showed 93.11% probability to be the ancestral state in Eugeniinae, and it was described for Myrteae by Van Wyk and Botha (1984), Moreira-Coneglian (2007, Pescador et al (2009), andMachado (2014), for Myrtaceae by Corner (1976), and for Myrtales by Tobe and Raven (1983) and Endress (2010). The proliferative inner integument in E. pyriformis, discernable until the mature seed, is a new record for the family.…”

Microsporogenesis, Megasporogensis and Male and Female Gametophyte Development in Feijoa sellowiana (Myrtaceae)

“…The ovules in F. sellowiana 'Mammoth' were anatropous (Fig. 3B), and their structure resembled that described for other Feijoa species (Pescador et al, 2009).…”

“…Scale bars: D = 100 μm; A-C and E-H = 50 μm the formation patterns of the anther walls in taxa other than Feijoa are unknown. Pescador et al (2009) reported that the main cellular events occur synchronously in the zygotic embryogenesis structures in F. sellowiana, but details for the male gametophyte developmental process are lacking.…”

“…Therefore, it is important to study the reproductive biology of Feijoa. However, only a few published accounts of Feijoa sexual reproduction are available (Pescador et al, 2009;Finatto et al, 2011). This lack of basic knowledge is more evident for Feijoa trees.…”