Sistema reprodutivo do Ipê-Branco: Tabebuia roseo-alba (Ridley) Sandwith (Bignoniaceae)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Cytogenetics and embryology of Eupatorium laevigatum (Compositae)

Embryological studies indicate Eupatorium laevigatum to have Antennaria type diplospory with precocious embryony. The embryo sac is of the Polygonum type and the polar nuclei fuse before anthesis (maturation of the stamens). Endosperm development is autonomous and the central cell divides only after the initial stages of embryo formation. It is estimated that about 10% of the florets in anthesis contain an undivided egg which can be used for sexual reproduction. The study of microsporogenesis revealed abnormalities in chromosome pairing which result in the formation of univalents, bivalents, trivalents and higher polyvalents, with the consequent production of lagging chromosomes, unbalanced nuclei, micronuclei and sterile pollen. We found that, as represented by the material studied, E. laevigatum is an autohexaploid (2n = 6x = 60) in which each chromosome of a basic set of ten chromosomes is repeated six times and that E. laevigatum is an essentialy obligate apomictic.

Partial purification and characterization of lysine-ketoglutarate reductase in normal and opaque-2 maize endosperms

Lysine-ketoglutaratc reductase catalyzes the first step of lysine catabolism in maize (Zea mays L.) endosperm. The enzyme condenses L-lysine and α-ketoglutarate into saccharopine using NADPH as cofactor. It is endosperm-specific and has a temporal pattern of activity, increasing with the onset of kernel development, reaching a peak 20 to 25 days after pollination, and thereafter decreasing as the kernel approaches maturity. The enzyme was extracted from the developing maize endosperm and partially purified by ammonium-sulfate precipitation, anion-exchange chromatography on DEAE-cellulose, and affinity chromatography on Blue-Sepharose CL-6B. The preparation obtained from affinity chromatography was enriched 275-fold and had a specific activity of 411 nanomoles per minute per milligram protein. The native and denaturated enzyme is a 140 kilodalton protein as determined by polyacrylamide gel electrophoresis. The enzyme showed specificity for its substrates and was not inhibited by either aminoethyl-cysteine or glutamate. Steady-state product-inhibition studies revealed that saccharopine was a noncompetitive inhibitor with respect to α-ketoglutarate and a competitive inhibitor with respect to lysine. This is suggestive of a rapid equilibriumordered binding mechanism with a binding order of lysine, α-ketoglutarate, NADPH. The enzyme activity was investigated in two maize inbred lines with homozygous normal and opaque-2 endosperms. The pattern of lysine-ketoglutarate reductase activity is coordinated with the rate of zein accumulation during endosperm development. A coordinated regulation of enzyme activity and zein accumulation was observed in the opaque-2 endosperm as the activity and zein levels were two to three times lower than in the normal endosperm. Enzyme extracted from L1038 normal and opaque-2 20 days after pollination was partially purified by DEAE-cellulose chromatography. Both genotypes showed a similar elution pattern with a single activity peak eluted at approximately 0.2 molar KCL. The molecular weight and physical properties of the normal and opaque-2 enzymes were essentially the same. We suggest that the Opaque-2 gene, which is a transactivator of the 22 kilodalton zein genes, may be involved in the regulation of the lysine-ketoglutarate reductase gene in maize endosperm. In addition, the decreased reductase activity caused by the opaque-2 mutation may explain, at least in part, the elevated concentration of lysine found in the opaque-2 endosperm.

Sporophytic apomixis in polyploid Anemopaegma species (Bignoniaceae) from central Brazil

Apomixis and polyploidy have been important in the evolution of the angiosperms, and sporophytic apomixis has been associated with polyembryony and polyploidy in tropical floras. We studied the occurrence of polyembryony in populations of tetraploid Anemopaegma acutifolium, A.arvense and A.glaucum from the Brazilian cerrados, and histological features of sexual and apomictic processes were investigated in A.acutifolium. All populations and species were polyembryonic (68.9-98.4% of seeds). Normal double fertilization occurred in most ovules, with exceptions being that 3% of ovules were penetrated but not fertilized and in 4% of ovules both synergids were penetrated. The penetration of both synergids suggests a continuous attraction of pollen tubes and polyspermy. Adventitious embryo precursor cells (AEPs) arose from nucellar and integumental cells of the ovule in pollinated and unpollinated A.acutifolium, indicating sporophytic apomixis. However, further embryo and endosperm development required pollination and fertilization. This pseudogamy also allows concurrent sexual embryo development. Similar polyembryony rates and polyploidy indicated that A.arvense and A.glaucum are also apomictic, forming an agamic complex similar to that observed for some species of confamilial, but not closely related Handroanthus. The co-occurrence of apomixis and polyploidy in different groups of Bignoniaceae indicates homoplasious origin of these agamic complexes. © 2013 The Linnean Society of London.

Mating in the pseudogamic apomictic Anemopaegma acutifolium DC: Another case of pseudo-self-compatibility in Bignoniaceae?

Self-compatibility in apomictic pseudogamic species is considered fundamental to assure reproduction by seeds in extreme situations, making apomictic species more advantageous than sexual ones in these scenarios. Anemopaegma acutifolium is a polyploidy, apomictic sporophytic species with no endosperm development in ovules of unpollinated pistils, which indicates obligate pseudogamy. Thus, the aim of the present work is to study the breeding system and post-pollination events to test if there is similar pseudogamous development irrespective of pollination treatment. We analysed fruit and seed set obtained in controlled experimental pollinations, as well as embryo number per seed, and the progress of ovule penetration, fertilisation and early endosperm development between self- and cross-pollinated pistils. We found that the species is self-fertile and that spontaneous selfing fruit set is also possible, although emasculated flowers never form fruits. Selfed pistils were as efficient as crossed ones for all parameters analysed, except for a delay in endosperm development observed in the former that may be an effect of the late-acting self-incompatibility. Therefore, the avoidance of selfed pistil abortion seems to be promoted by the presence of adventitious embryos and a normal endosperm. We conclude that A. acutifolium shows apomixis-related pseudo-self-compatibility, as in other self-fertile apomictic species of Bignoniaceae, which confer reproductive assurance and increases fruit-set and persistence ability in fast-changing tropical habitats. © 2012 German Botanical Society and The Royal Botanical Society of the Netherlands.

Embriologia de Nymphaea L. (Nymphaeales - Nymphaeaceae): implicações para a evolução inicial das angiospermas

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Seed priming improves endosperm weakening, germination, and subsequent seedling development of Solanum lycocarpum St. Hil.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Embryology and seed development of Blastocaulon scirpeum and Paepalanthus scleranthus (Eriocaulaceae)

The embryology and seed structure of Blastocaulon scirpeum (Mart.) Giul. and Paepalanthus scleranthus Ruhland were studied in order to contribute to the embryology of Eriocaulaceae and supply data for future taxonomic studies. Both species present: anther with 4-layered wall; conspicuous endothecium with fibrous thickenings; secretory tapetum with uninucleate cells; successive microsporogenesis forming isobilateral microspore tetrads; bicellular pollen grains; orthotropous, bitegmic and tenuinucellate ovule; micropyle formed by the inner integument alone; megagametophyte of the Polygonum type, with a conspicuous antipodal cyst; nuclear and starchy endosperm; reduced, undifferentiated, and bell-shaped embryo; operculate and endotestal seed; seed coat derived from the two ovule integuments; and tanniniferous endotegmen. In addition, Blastocaulon scirpeum shows a bisporangiate anther and a 3-layered ovary wall, while P. scleranthus presents a tetrasporangiate anther that becomes bisporangiate at maturity, and a 2-layered ovary wall. This investigation shows that the bisporangiate condition does not suffice to separate Blastocaulon from Paepalanthus, since it is common to both. It also indicates, based on several embryological aspects, the proximity of Eriocaulaceae and Xyridaceae, which comply mainly with the features presented by the other commelinid families. These results may be used in future cladistic analysis of the family, and contribute to a better understanding of its phylogeny.

Embryology and seed development of Syngonanthus caulescens (Poir.) Ruhland (Eriocaulaceae-Poales)

The embryology and the seed development of Syngonanthus caulescens are presented. This species possesses: a bithecous and tetrasporangiate anther, with a four-layered wall, a conspicuous endothecium of the baseplate type, a secretory tapetum formed by uninucleate cells, successive microsporogenesis resulting in isobilateral microspore tetrads, spiraperturate and binucleate pollen grains, an orthotropous, pendulous, bitegmic and terminucellate ovule, with a micropyle formed only by the inner integument, a megagametophyte of the Polygonum type, with formation of an antipodal cyst, free-nuclear and starchy endosperm, a broad and bell-shaped embryo, operculate and endotestal seeds, a seed coat derived from the inner layers of both integuments, and tanniniferous endotegmen. These embryological aspects are characteristic not only for Syngonanthus, but for the whole family, with few differences between genera. Furthermore, the pollen grain of the spiraperturate type and the cystic arrangement of the antipodals in the megagametophyte are peculiar and very distinctive features of Eriocaulaceae within the other Poales (commelinids). (c) 2006 Elsevier B.V. All rights reserved.

Comparative study of ovule and fruit development in species of Hypolytrum and Rhynchospora (Cyperaceae, Poales)

The development of the ovule and of the fruit of Hypolytrum bullatum and H. schraderianum (Mapanioideae) and of Rhynchospora consanguinea and R. rugosa (Cyperoideae) are described. All species share anatropous, bitegmic and crassinucellate ovules, funicular obturator, megagametophyte of the Polygonum type, presence of starch grains in the mature megagametophyte, free-nuclear endosperm, Onagrad-type embryogeny, testal-tegmic seed, and a simple fruit of the achene type. Rhynchospora species have characters typical of the family: micropyle formed by the inner integument alone; 3-4-layered parietal tissue; and hard achene. Hypolytrum species differ in those characters by presenting a slightly zigzag micropyle formed by both integuments connected with the funicular obturator, 5-8-layered parietal tissue, and fibrous-spongy achene. The peculiar formation of the micropyle in Hypolytrum is a feature reported here for the first time in the family. The ontogeny provides evidence for a better understanding of the dispersal unit in Hypolytrum supporting the classification as a true achene, like that of Rhynchospora, which is characteristic of the family.

Seed development in Malpighiaceae species with an emphasis on the relationships between nutritive tissues

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Ovule, fruit and seed development in Abolboda (Xyridaceae, Poales): implications for taxonomy and phylogeny

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Development of ovule, fruit and seed of Xyris (Xyridaceae, Poales) and taxonomic considerations

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)