The mature embryo sac of the sugar beet, Beta vulgaris: A structural investigation

The mature embryo sac of Beta vulgaris consists of one egg cell, one persistent and one degenerated synergid, one cental cell with two fused polar nuclei, and five to six antipodals. The degeneration of one of the synergids appears before pollination in the maturing process. The two fused polar nuclei are located in the chalazal part of the central cell. The antipodals may have secretory activities. It is suggested that the embryo sac of the sugar beet completes the maturing process independently of pollination.     

Qualitative importance of the microbial loop and plankton community structure in a eutrophic lake during a bloom of cyanobacteria

Plankton community structure and major pools and fluxes of carbon were observed before and after culmination of a bloom of cyanobacteria in eutrophic Frederiksborg Slotssø, Denmark. Biomass changes of heterotrophic nanoflagellates, ciliates, microzooplankton (50 to 140 μm), and macrozooplankton (larger than 140 μm) were compared to phytoplankton and bacterial production as well as micro- and macrozooplankton ingestion rates of phytoplankton and bacteria. The carbon budget was used as a means to examine causal relationships in the plankton community. Phytoplankton biomass decreased and algae smaller than 20 μm replacedAphanizomenon after the culmination of cyanobacteria. Bacterial net production peaked shortly after the culmination of the bloom (510 μg C liter^?1 d^?1 and decreased thereafter to a level of approximately 124 μg C liter^?1 d^?1. Phytoplankton extracellular release of organic carbon accounted for only 4–9% of bacterial carbon demand. Cyclopoid copepods and small-sized cladocerans started to grow after the culmination, but food limitation probably controlled the biomass after the collapse of the bloom. Grazing of micro- and macrozooplankton were estimated from in situ experiments using labeled bacteria and algae. Macrozooplankton grazed 22% of bacterial net production during the bloom and 86% after the bloom, while microzooplankton (nauplii, rotifers and ciliates larger than 50 μm) ingested low amounts of bacteria and removed 10–16% of bacterial carbon. Both macro-and microzooplankton grazed algae smaller than 20 μm, although they did not control algal biomass. From calculated clearance rates it was found that heterotrophic nanoflagellates (40–440 ml^?1) grazed 3–4% of the bacterial production, while ciliates smaller than 50 μm removed 19–39% of bacterial production, supporting the idea that ciliates are an important link between bacteria and higher trophic levels. During and after the bloom ofAphanizomenon, major fluxes of carbon between bacteria, ciliates and crustaceans were observed, and heterotrophic nanoflagellates played a minor role in the pelagic food web.     

Intestinal cancer development in response to oral infection with high-fat diet-induced Type 2 diabetes (T2D) in collaborative cross mice under different host genetic background effects

Mammalian Genome - Type 2 diabetes (T2D) is a metabolic disease with an imbalance in blood glucose concentration. There are significant studies currently showing association between T2D and...     

A structural investigation of the ovule in sugar beet, Beta vulgaris: Integuments and micropyle

The micropyle and the integuments of sugar beet (Beta vulgaris) ovules have been investigated by light and electron microscopy during differentiation and maturation of the ovule. The micropyle itself is formed by the inner integument which is surrounded by the outer integument at its base. The micropyle containts a fibrillar PAS+ substance and is often covered by a thin sheet or hymen. Both integuments are cuticle-covered thin sheets, each 2-few cell layers in thickness. In the outer integument an increase in starch accumulation occurs during ovule maturation and probably functions as nutrient storage for embryo development. The inner epidermis of the inner integument differentiates as the most conspicuous cell layer of the beet ovule. During growth and maturation of the ovule a system of small perinuclear vacuoles containing dense material increases steadily in these cells. At maturity this system fills up more than half of each cell and very dense material has accumulated in each vacuole. This vacuole content is highly refractive and contains tannins and/or polyphenols.     

Modified plant plasma membrane H+-ATPase with improved transport coupling efficiency identified by mutant selection in yeast

Transport across the plasma membrane is driven by an electrochemical gradient of H⁺ ions generated by the plasma membrane proton pump (H⁺-ATPase). Random mutants of Arabidopsis H⁺-ATPase AHA1 were isolated by phenotypic selection of growth of transformed yeast cells in the absence of endogenous yeast H⁺-ATPase (PMA1). A Trp-874-Leu substitution as well as a Trp-874 to Lys-935 deletion in the hydrophilic C-terminal domain of AHA1 conferred growth of yeast cells devoid of PMA1. A Trp-874-Phe substitution in AHA1 was produced by site-directed mutagenesis. The modified enzymes hydrolyzed ATP at 200–500% of wild-type level, had a sixfold increase in affinity for ATP (from 1.2 to 0.2 mM; pH 7.0), and had the acidic pH optimum shifted towards neutral pH. AHA1 did not contribute significantly to H⁺ extrusion by transformed yeast cells. The different species of aha1, however, displayed marked differences in initial rates of net H⁺ extrusion and in their ability to sustain an electrochemical H⁺ gradient. These results provide evidence that Trp-874 plays an important role in auto-inhibition of the plant H⁺-ATPase and may be involved in controlling the degree of coupling between ATP hydrolysis and H⁺ pumping. Finally, these results demonstrate the usefulness of yeast as a generalized screening tool for isolating regulatory mutants of plants transporters.     

Differential proto-oncogene mRNA induction from rats treated with peroxisome proliferators

After experimental treatment of rats with clofibrate or ciprofibrate, two peroxisomes proliferators with hypolipidemic activity, RNAs were prepared from liver, kidney, heart and brain; hybridization was done with DNA probes for c-myc and c-Ha-ras oncogenes and for cyanide insensitive Acyl CoA oxidase, a peroxisomal protein. c-myc mRNA is highly abundant in liver and at a lower extent in kidney, especially after treatment with ciprofibrate; clofibrate also allows a c-myc mRNA increase, but at a lower extent. c-Ha-ras, which is already expressed in all tested tissues from control animals, is stimulated by clofibrate and ciprofibrate treatments. Comparatively these compounds stimulate the cyanide insensitive Acyl CoA oxidase expression as well as they increase the somatic index of liver and kidney. From these experiments we suggest that hepatocarcinogenesis triggered by some hypolipidemic agents could be mediated by proto-oncogene mRNA level increase.