Development of a Heat-Inducible Gene Expression System Using Female Gametophytes of Arabidopsis thaliana

Female gametophyte (FG) is crucial for reproduction in flowering plants. Arabidopsis thaliana produces Polygonum-type FGs, which consist of an egg cell, two synergid cells, three antipodal cells and a central cell. Egg cell and central cell are the two female gametes that give rise to the embryo and surrounding endosperm, respectively, after fertilization. During the development of a FG, a single megaspore produced by meiosis undergoes three rounds of mitosis to produce an eight-nucleate cell. A seven-celled FG is formed after cellularization. The central cell initially contains two polar nuclei that fuse during female gametogenesis to form the secondary nucleus. In this study, we developed a gene induction system for analyzing the functions of various genes in developing Arabidopsis FGs. This system allows transgene expression in developing FGs using the heat-inducible Cre-loxP recombination system and FG-specific embryo sac 2 (ES2) promoter. Efficient gene induction was achieved in FGs by incubating flower buds and isolated pistils at 35�C for short periods of time (1–5 min). Gene induction was also induced in developing FGs by heat treatment of isolated ovules using the infrared laser-evoked gene operator (IR-LEGO) system. Expression of a dominant-negative mutant of Sad1/UNC84 (SUN) proteins in developing FGs using the gene induction system developed in this study caused defects in polar nuclear fusion, indicating the roles of SUN proteins in this process. This strategy represents a new tool for analyzing the functions of genes in FG development and FG functions.

Foaming Polystyrene with Mixtures of Carbon Dioxide and HFC-134a

Mixtures of blowing agents are becoming widely used in the industry either for economical reasons or for achieving better control of processing conditions. Despite the fact that they are commonly used for foaming, the literature is fairly scarce on that particular subject and the fundamentals are not very well understood. This work studies the effect of blending carbon dioxide and 1,1,1,2-tetrafluoroethane (HFC-134a) in polystyrene. Ultrasonic monitoring and online rheology provided information on the solubility and plasticizing effect of the gases. Results show that, on an equivalent molar basis, HFC-134a is slightly more soluble than CO2 and is a more effective plasticizer. Moreover, HFC-134a generates foam samples with a higher nucleation density than CO2 using similar processing conditions. Blending the two gases generates nucleate cell densities, which are intermediate to the pure gases but do not follow a log-additivity rule. It is hypothesized that blending gases affect their mutual diffusion coefficients, which in turn, largely dictates the final foam morphology.

Jania (Corallinales, Rhodophyta) in southern Australia

The coralline algal genus Jania Lamouroux (tribe Janieae, subfamily Corallinoideae, family Corallinaceae) contains six species on southern Australian coasts: J. micrarthrodia Lamouroux, J. pulchella (Harvey) comb. nov., J. pusilla (Sonder) Yendo, J. verrucosa Lamouroux, and two new species, J. minuta and J. parva. These species are segregated primarily on vegetative characters pertaining to fronds, intergenicula, branching, medullary organisation, and substrate preference, with reproductive features used in some cases. Four of the species are, as far as known, endemic to southern Australia: J. minuta, J. pawa, J. pulchella, and J. pusilla. Jania minuta and J. rnicrarthrodia have evolved a unique short-segmented morphology, with intergenicula containing only one or two tiers of medullary cells each. Jania micrarthrodia is a common and conspicuous epiphyte and variable in morphology depending on degree of water movement. In J. minuta, tetrasporangia are replaced by unusual sporangia, each comprised of a large two-nucleate cell, bracketed by small, uninucleate apical and basal cells. This species also forms distinctive multicellular propagules. Jania parva has delicate fronds with dichotomies that tend to diverge widely; only bisporangial and gametangial plants have been found. Jania pulchella has two types of intergenicula, 'janioid' intergenicula which in fertile plants contain conceptacles, and basal compressed and lobed 'cheilosporoid' intergenicula; it is transferred from Cheilosporum pulchellum Harvey. Jania pusilla is usually epiphytic on Cystophora spp., and has small fronds with broad intergenicula. Jania verrucosa, the most robust species, forms dense tufts on low intertidal rocks in southern Australia and in other subtropical or temperate regions.

Polycation-Cell Surface Interactions and Plasma Membrane Compartments in Mammals. Interference of Oligocation with Polycationic Condensation

At lower concentrations, polyarginine, polylysine, protamine, histones H 1, H2A, H2B and H3 cause lysis of human erythrocytes, whereas at higher concentrations inner histones are not hemolytic but induce only surface condensation and alterations in the cell-shape. Antibody coated erythrocytes treated with polyarginine result in ghost-like spheres having globular bodies 1 μm in diameter on the surface. Human fibroblasts and lymphocytes, and Ehrlich ascites cells treated with polyarginine also form surface globular bodies similar in size. Nucleate cell-poly-arginine mixtures with lower polycation doses result in cytolysis, while higher polycation doses produce pyknosis of the cell surface accompanied by reorganization of a membrane-like structure. Changes in spectrofluorometric values result from 1,6 -diphenyl-1,3,5-hexatrien binding to cell lipids, match the plasma membrane alterations. Reciprocal shake incubation am plifies and/or conditions these polycation-induced alterations. The homogeneity of pyknotic surface bodies and the apparent polycationic membrane reorganization requiring oscillatory friction forces suggest the preexistence of a multizonal glycocalyx distribution corresponding to plasma membrane compartments. The possible role of this compartmentalization in receptor and membrane recycling, as well as the involvement of reversible catalytic-like polycation condensation in macromolecular changes are discussed.

The fate and origin of the nuclear envelope during and after mitosis in Amoeba proteus. I. Synthesis and behavior of phospholipids of the nuclear envelope during the cell life cycle.

The synthesis and behavior of Amoeba proteus nuclear envelope (NE) phospholipids were studied. Most NE phospholipid synthesis occurs during G2 and little during mitosis or S. (A. proteus has no G1 phase). Autoradiographic observations after implantation of [3-H] choline nuclei into unlabeled cells reveal little turnover of NE phospholipid during interphase but during mitosis all the label is dispersed through the cytoplasm. Beginning at telophase all the label is dispersed through the cytoplasm. Beginning at telophase all the NE phospholipid label returns to the daughter NEs. This observation, along with the finding that no NE phospholipid synthesis occurs during mitosis or S, indicates that no de novo NE phospholipid production is required for newly forming NEs. Similarlyemetine, at concentrations that inhibit 97 percent of protein synthesis, does not prevent the post mitotic formation of NEs, suggesting that previously manufactured proteins are used in making new NEs. If a nucleus containing labeled NE phospholipids is transplanted into an unlabeled nucleate cell and the cell is allowed to grow and divide, the resultant four nuclei are equally labeled. This finding supports, but does not prove (see next paragraph), the conclusion that there probably is no continuity of the A. proteus NE during mitosis. When a phospholipid-labeled nucleus is implanted into a cell in mitosis, the grafted nucleus is not induced to enter mitosis. There is, however, a marked increase in the turnover of that nucleus's NE phospholipids with no apparent breakdown of the NE; this indicated that the mitotic cytoplasm possesses a factor that stimulates NE phospholipid exchange with the cytoplasm. That enhanced turnover is not accompanied by visible structural alteration makes less certain the earlier conclusion that no NE continuity exists during mitosis. Perhaps the most important finding in this study is that there are present, at restricted times in the cell cycle, factors capable of inducing accelerated exchange of structural components without microscopically detectable disruptions of structure.

THE CELL IN STARVATION: PHYSIOLOGICAL AND CHEMICAL OBSERVATIONS

Observations made on Amoeba proteus during total inanition revealed the following changes: Dry weight declined progressively, but at a decreasing rate to about 45 per cent of the initial levels when determined in surviving members of a dying population. Protein fell to about 70 per cent of the initial level. A hexane-alcohol extractable component fell during early starvation then rose to about its initial absolute level in the dying cells. While initially most of this component is probably lipide, it is not certain that other materials are not extracted during cell degeneration. Survival as a function of cell size was studied. No advantage in survival was apparent for any size class. Nucleate cell "halves" likewise showed no survival time differential, unlike a highly significant decrease in the survival of enucleate portions. The maintenance of the initial variance about the mean population weight (after hexane-alcohol extraction) during starvation, likewise supports the idea that survival depends largely on concentration parameters.