Seed Development in Araucaria Juss

Abstract

The development of the seed coat, seed wing and food reserve tissue of the female gametophyte was studied in four species of Araucaria: A. cunninghamii, A, heterophylla, A. bidwillii and A. hunsteinii. The means of seed dispersal in each of these species were also recorded. Comparisons were made among these species and others for which published data are available. The species differed with respect to the thickness of the seed coat and anatomical characteristics of the component layers; the thickness and nature of the nucellar layer; the relative degree of enlargement of non-fertilized ovules; the composition of the food reserves; the presence and nature of the seed wing; and the seed dispersal mechanism. The distribution of these features among the species of Araucaria for which data are available is consistent with the generally followed division of the genus into four sections.

Selective forces in the emergence of the seed habit

“…In Podocarpus falcatus (Osborn, 1960) and P. gracilior (Konar & Oberoi, 1969) the ovule increases in size after fertilization. Post-fertilization ovules also enlarge in Agathis robusta (Kaur & Bhatnagar, 1986), Araucaria bidwilli and A. hunsteinii (Haines, 1983). In A. cunninghamia the female gametophyte enlarges after fertilization though the ovule does not increase in size (Haines, 1983).…”

“…Post-fertilization ovules also enlarge in Agathis robusta (Kaur & Bhatnagar, 1986), Araucaria bidwilli and A. hunsteinii (Haines, 1983). In A. cunninghamia the female gametophyte enlarges after fertilization though the ovule does not increase in size (Haines, 1983). I n Taxus (Favre-Duchartre, 1984), Torreyn taxfolia (Coulter & Land, 1905), Ephedra trzfurca (Land, 1907).…”

“…However, female gametophytes of Metaseguoia (Engels & Gianordoli, 1983), Araucaria (Haines, 1983) and Agalhis robusta (Kaur & Bhatnagar, 1986) develop to the archegoniate stage without pollination. Whether or not unpollinated ovules are aborted, seed food reserves only accumulate in fertilized ovules.…”

“…Unfertilized female gametophytes degenerate and their ovules often persist as 'empty seeds' (e.g. Sarvas, 1962Sarvas, , 1968Mikkola, 1969;Sweet, 1973;Haines, 1983;Engels & Gianordoli, 1983;Kaur & Bhatnagar, 1986). It is possible that resources already supplied to gametophytes can be retrieved and allocated elsewhere.…”

Proteômica do desenvolvimento da semente de Araucaria angustifolia

“…O armazenamento de reservas começa nos tecidos mais externos do megagametófito, possibilitando que o eixo embrionário aumente de tamanho. A formação do tecido de reserva, ou seja, do megagametófito e dos cotilédones, é caracterizada pelo aumento do número e tamanho das células, muitas das quais multinucleadas e com o citoplasma espesso, devido à presença de proteínas e um grande número de grãos de amido (HAINES, 1983). Finalmente, quando os cotilédones completam a sua formação, tem início a fase de maturação da semente, a qual é caracterizada pela diminuição nos níveis do AIA e ácido giberélico (GA), e aumento da concentração do ácido abscísico (ABA) (ASTARITA et al, 2003;SILVEIRA et al, 2008).…”