T HAS recently been found that chromosome aberrations of the types I induced by various kinds of radiations occur spontaneously during the development of the pollen grains in diploid species and especially in species hybrids of Tradescantia (GILES 1940). The present studies have shown that the frequency of these aberrations is even higher in triploid Tradescantia hybrids. Furthermore, it has be...

Male germ line development in flowering plants is initiated with the formation of the generative cell that is the progenitor of the two sperm cells. While structural features of the generative cell are well documented, genetic programs required for generative cell cycle progression are unknown. We describe two novel Arabidopsis (Arabidopsis thaliana) mutants, duo pollen1 (duo1) and duo pollen2 ...

Introduction: In amphibians, blood may act as a hematopoietic tissue. However, the knowledge concerning hematological features is scarce, there not much information that allows an analysis about possible explanations of this physiological feature. Objective: This study aimed to evaluate relationship between immature red cells (RBCs) mitosis and presence parasites in amphibians. Methods: We samp...

Although it is well known that Tyr phosphatases play a critical role in signal transduction in animal cells, little is understood of the functional significance of Tyr phosphatases in higher plants. Here, we describe the functional analysis of an Arabidopsis gene (AtPTEN1) that encodes a Tyr phosphatase closely related to PTEN, a tumor suppressor in animals. The recombinant AtPTEN1 protein, lik...

To investigate the regulation of gene expression during male gametophyte development, we analyzed the promoter activity of two different genes (LAT52 and LAT59) from tomato, isolated on the basis of their anther-specific expression. In transgenic tomato, tobacco and Arabidopsis plants containing the LAT52 promoter region fused to the beta-glucuronidase (GUS) gene, GUS activity was restricted to...

Pollen embryogenesis provides exciting opportunities in the areas of breeding and biotechnology as well as representing a convenient model for studying the process of plant cell proliferation in general and embryogenesis in particular. A cell culture system was devised in which immature barley pollen could be cultured as a monolayer trapped between the bottom glass-cover slip of a live-cell cha...

Immature Xenopus laevis were unilaterally nephrectomized and implanted subcutaneously with stage 38 (prefeeding) larvae. Rat kidney extract was injected 8 and 16 days after the operation and the mitotic incidence (MI) in the host and implant tissues was measured by the colcemid metaphase arrest technique. The MI in the kidney of nephrectomized hosts was higher than normal at 8 days but had retu...

Centromeres are responsible for the correct segregation of chromosomes during mitosis and meiosis. Holocentric chromosomes, characterized by multiple centromere units along each chromatid, have particular adaptations to ensure regular disjunction during meiosis. Here we show by detecting CENH3, CENP-C, tubulin, and centromeric repeats that holocentromeres may be organized differently in mitosis...