The effect of auxin treatment on the formation of apomictic – endospermless grains in Poa pratensis was investigated in the study. Four polish cultivars: Skiz, Eska 46, Alicja, Ani as well as six breeding lines: POB 13, SK-W-33, SKW-15, SKW-35A, SK-W-35A and SK-W-35B were tested by embryological methods to reveal the reproduction pathway in greenhouse and field conditions. The obtained results showed that four genotypes, i.e. Alicja, Ani, Eska 46 and SK-W-35B are facultative apomictic and the other have formed seeds only on the apomictic way. In facultative apomicts it was found that in many cases both endospermless ovules containing embryo sacs with embryos or embryo sacs with well developed endosperm were formed. In the case of apomictic genotypes only endospermless seeds were observed.
Origin of embryo sacs was examined in further two Alchemilla species: A. acutiloba and A. montícola. The central region of multicellular archesporium shows meiotic tendencies but as a rule, the meiotic division did not advance further than up to I ptophase. Apomeiotic embryo sacs arise from unreduced cells, either from megaspore mother cells (diplospory) or from cells of somatic character (apospory). In the same ovule a few embryo sacs of both types may be formed. Usually only one of them reaches a distinct prevalence and the full maturity.
Haploid wheat plants have been produced by a new method of zygote rescue carried out after distant pollination. Wheat stigmas were pollinated with maize pollen and subsequently the activated egg cells from the elongated ovaries were rescued for in vitro plant development in single cell culture. As the control, 2-week-old embryos were also dissected and then cultured. The efficiency of both techniques was comparable. Wheat was also pollinated with rice, and the further development of rescued zygotes into multicellular structures is reported here for the first time. Because the lack of a normal endosperm hampers embryo development even in the early stages, early zygote rescue (two days after distant pollination) may represent a more efficient way of producing double haploid (DH) plants in cultivars that are recalcitrant in androgenic cultures, after further optimization of in vitro culture of isolated single cells.
Of the 30 extant orders of insects, scale insects (Hemiptera: Coccoidea) have one of the best fossil records among insects that probably extends to the early Mesozoic. Most fossil Coccoidea records are of adult males which have been trapped in amber, whereas adult females are less common, probably because of their sedentary occurrence on plants. Descriptions, photos, and SEM micrographs are presented of over 250 well−preserved scale covers of adult females and nymphal stages of armoured scale insects (Hemiptera: Coccoidea: Diaspididae) which were found on dicotyledonous and monocotyledonous fossil leaves in Middle Eocene deposits from Germany. The structure of these fossil scale covers closely agrees with that of extant Diaspididae. These armoured scale insects belong to the subfamily Aspidiotinae. The age of this insect−plant association—47 to 44 million−year−old—indicates that the Diaspididae have a long history in the Palaearctic region.
The paper reviews female gametophyte development in vitro, the pathways of gynogenetic embryogeny, and autonomous endosperm development in vitro, and presents some implications for future investigation of apomictic processes. In most species studied so far, the pattern of embryo sac development was not altered by in vitro conditions, and some rare deviations could be additional sources of gynogenetic embryos. Meiosis in vitro resulted in megaspore formation followed by embryo sac development or direct embryogenesis. Gynogenesis in vitro occurs via various embryological processes. Embryos developed parthenogenetically from egg cells in twelve species. Apogamic development from the synergid or from antipodal cells was found in six species. Early development of gynogenetic embryos showed some similarities to zygotic embryogenesis, but then the embryos often remained undifferentiated or formed microcalli and protocorm-like structures. In nine species the central cell in ovary/ovule cultures was sporadically stimulated to divide into free-nuclear endosperm. Generally only one gynogenetic structure developed per embryo sac, and no embryos appeared in ovules containing autonomous endosperm. Cellular programs for the autonomous development of endosperm and embryo seem quite different or even competitive in vitro. Various approaches should be taken in future research on apomixis. Classical and novel cytological methods, and in vitro organ and cell cultures should be combined with molecular techniques and genetic studies.
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