Autecological studies on Audouinia capitata 5. Seeds

Autecological studies on Audouinia capitata (Bruniaceae). 5. Seed development, abortion and pre-emergent reproductive success
J.H. de Lange, J.J.A. van der Walt and C. Boucher 1993 S.Afr.1.Bot., , 59 156 - 167

Ovule development, megasporogenesis, megagametogenesis, embryogenesis, endosperm development and seed germination of Audouinia capitata are described. In sharp contrast to the relatively high incidence of abortion and non-viability of microspores demonstrated previously, no pre-anthesis aberrations occur in the megagametophyte. In many fertilized ovules the primary endosperm nuclei remain undivided, enlarge considerably for up to five weeks and eventually degenerate, accompanied by abortion of the zygote. A low incidence of abortion is evident after the fifth week. Abortions after 11 weeks of development are identifiable in mature fruits. A substantial number of mature seeds are devoid of, or contain low densities of, protein bodies. After germination, the radicles of these seeds stop growing soon after emergence from the fruits. It is suggested that abortion is regulated by inter-ovular competition for available nutrients, or by a strongly fixed, genetically controlled system. This strategy could have been selected to allow for the economization of reserves in the 6-ovuled, indehiscent ovaries that act as dispersal units. Possible explanations are suggested for abortion rates in excess of those implied by a fixed general system of one seed per indehiscent fruit. When accepting a seed:ovule ratio of 1:6 as full realization of the seed-setting potential, and ignoring all nonsexual factors, the pre-emergent reproductive success is only 9%. This deficiency is a contributing factor in the rarity of the species.

&

"A. capitata seedlings are extremely rare. In an earlier study, Parisi (1985) recorded that no seedlings were found. During the present series of investigations, very low numbers of seedlings were recorded after bums (de Lange &Boucher 1993b). The seedlings have a very prolonged vegetative stage. The exact duration of this non-flowering stage is unknown but is probably more than 15 years (de Lange & Boucher 1993b). A selective strategy with more emphasis on efficient resprouting following fire and longevity than on reproductive capability, seems to be possible. It is likely that large percentages of seedlings may not even have reached the flowering stage at the end of their first inter-fire period. This implies that seedlings would be subjected to selection for resprouting efficiency (and longevity) after the next fire before they even have had the opportunity to produce seeds."

Publicado el junio 16, 2022 07:51 TARDE por tonyrebelo