In amphibians such as Xenopus laevis, the initial polarity of the oocyte is established during oogenesis to produce animal and vegetal hemispheres with extensive structural and compositional differences. The animal-vegetal polarity ot the egg is reinforced by "Surtace Contraction Waves" (SCWs), occurring immediately prior to each cleavage division (Hara et aI., 1980; Sawai, 1982). These are ins...

During amphibian gastrulation, presumptive endoderm is internalised as part of vegetal rotation, a large-scale movement that encompasses the whole vegetal half of the embryo. It has been considered a gastrulation process unique to amphibians, but we show that at the cell level, endoderm internalisation exhibits characteristics reminiscent of bottle cell formation and ingression, known mechanism...

An animal-vegetal net ionic current identified previously using voltage probe techniques in maturing Xenopus laevis oocytes has now been investigated using noninvasive ion-selective microelectrodes. Three-dimensional fluxes of hydrogen (H(+)), potassium (K(+)), and bicarbonate (HCO(3)(-)) were characterized with respect to the developmental stage and hemisphere of the oocyte and presence of sur...

Prospects of doubling global wheat yields Malcolm J. Hawkesford, Jose-Luis Araus, Robert Park, Daniel Calderini, Daniel Miralles, Tianmin Shen, Jianping Zhang & Martin A. J. Parry Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, United Kingdom Unitat de Fisiologia Vegetal, Facultat de Biologia, Universitat de Barcelona, 08028, Barcelona, Spain Plant Breeding Institute, Faculty of Agricul...

We have measured the expression of 41 maternal mRNAs in individual blastomeres collected from the 8 to 32-cell Xenopus laevis embryos to determine when and how asymmetry in the body plan is introduced. We demonstrate that the asymmetry along the animal-vegetal axis in the oocyte is transferred to the daughter cells during early cell divisions. All studied mRNAs are distributed evenly among the ...

The purpose of this study was to characterize the diet of the fish Brycon opalinus (Characidae) seasonally and locally, allowing for the determination of its food items and trophic relations with the aquatic and terrestrial environments. The study area encompasses three rivers (Paraibuna, Ipiranga and Grande) in the basin of the Paraibuna, southeast Brazil. Twelve monthly collections were made ...

Localization of nuclear beta-catenin initiates specification of vegetal fates in sea urchin embryos. We have identified SpKrl, a gene that is activated upon nuclear entry of beta-catenin. SpKrl is upregulated when nuclear beta-catenin activity is increased with LiCl and downregulated in embryos injected with molecules that inhibit beta-catenin nuclear function. LiCl-mediated SpKrl activation is...

Segregation of the future germ line defines a crucial cell fate decision during animal development. In Xenopus, germ cells are specified by inheritance of vegetally localized maternal determinants, including a group of specific mRNAs. Here, we show that the vegetal localization elements (LE) of Xenopus Dead end (XDE) and of several other germ-line-specific, vegetally localized transcripts media...

Departamento de Biologı́a Molecular de Plantas, Instituto de Biotecnologı́a, Universidad Nacional Autónoma de México, Apartado Postal 510–3, Cuernavaca Morelos 62271, México (L.C., F.S., C.Q.); Biology Department, Morrill Science Center, University of Massachusetts, Box 35810, Amherst, Massachusetts 01003–5810 (T.L.H.-C., J.G.K., P.K.H.); Instituto Gulbenkian de Ciência, P–2780–156 Oeiras, Portug...

Laboratório de Melhoramento Genético Vegetal, Centro de Ciências e Tecnologias Agropecuárias, Universidade Estadual do Norte Fluminense, CEP 28013-600, Campos dos Goytacazes, RJ, Brasil; Departamento de Biologia Aplicada à Agropecuária, Faculdade de Ciências Agrárias e Veterinárias, Universidade Estadual de São Paulo, CEP 14870-000, Jaboticabal, SP, Brasil; Departamento de Fisiologia Vegetal, I...