Ultrastructure of the developing pigment strand of rice (Oryza sativa L.) in relation to its role in solute transport

Summary The developing pigment strand of rice (Oryza sativa L.) was studied by conventional electron microscopy and also by use of thick sections post-fixed with zinc iodide and osmium (ZIO).When the rice caryopsis achieves maximum length, a suberised adcrusting wall layer is laid down over the original primary walls of the pigment strand. Concomitant with suberin deposition a proliferation of tubular endoplasmic reticulum occurs in the cytoplasm giving rise to numerous interconnected vesicles which bear ribosomes. The vesicles in the general cytoplasm retain their ribosomes while those close to the wall become smooth and contain an electron-opaque granular material which is eventually deposited to the outside of the plasmalemma. This granular material may be the precursor(s) from which suberin is polymerised. The suberised wall attains about six times the width of the original primary wall and plasmodesmata, which traverse both primary wall and suberised wall layers, become greatly elongated.Lipid bodies increase in both size and frequency during development, eventually coalescing to form a complete plug across the pigment strand and occluding the symplast of this tissue. The significance of these ultrastructural observations is discussed in relation to the previously demonstrated role of the pigment strand as a translocation pathway for water and assimilates during grain filling.Abbreviations ER endoplasmic reticulum - ZIO zinc iodide-osmium fixation     

Nitrogen Oxyanion-dependent Dissociation of a Two-component Complex That Regulates Bacterial Nitrate Assimilation

Nitrogen is an essential nutrient for growth and is readily available to microbes in many environments in the form of ammonium and nitrate. Both ions are of environmental significance due to sustained use of inorganic fertilizers on agricultural soils. Diverse species of bacteria that have an assimilatory nitrate/nitrite reductase system (NAS) can use nitrate or nitrite as the sole nitrogen source for growth when ammonium is limited. In Paracoccus denitrificans, the pathway-specific two-component regulator for NAS expression is encoded by the nasT and nasS genes. Here, we show that the putative RNA-binding protein NasT is a positive regulator essential for expression of the nas gene cluster (i.e. nasABGHC). By contrast, a nitrogen oxyanion-binding sensor (NasS) is required for nitrate/nitrite-responsive control of nas gene expression. The NasS and NasT proteins co-purify as a stable heterotetrameric regulatory complex, NasS-NasT. This protein-protein interaction is sensitive to nitrate and nitrite, which cause dissociation of the NasS-NasT complex into monomeric NasS and an oligomeric form of NasT. NasT has been shown to bind the leader RNA for nasA. Thus, upon liberation from the complex, the positive regulator NasT is free to up-regulate nas gene expression.     

The ability of pancreatic polypeptides (APP and BPP) to return to normal the hyperglycaemia, hyperinsulinaemia and weight gain of New Zealand obese mice.

Intraperitoneal injections of avian pancreatic polypeptide (APP) and bovine pancreatic polypeptide (BPP) are capable of returning to normal the hyperinsulinaemia, hyperglycaemia and weight gain of New Zealand obese mice. The lag glucose tolerance also becomes indistinguishable from normal. The mechanism whereby these polypeptides cause reversion is not known. Reversion can also be brought about by the intraperitoneal implantation of islets from white mice into New Zealand obese animals. The implanted islets secrete mouse pancreatic polypeptide. We conclude that the New Zealand obese syndrome arises from a genetic lack of mouse pancreatic polypeptide. We suggest that in humans a lack of pancreatic polypeptide might manifest as a syndrome analogous to that found in New Zealand obese mice.     

Seawater temperature and sublethal coral bleaching in Jamaica

Permanent study sites were established at 6 m, 12 m and 18 m on the West Fore Reef at Discovery Bay, Jamaica. Colonies of Montastrea annularis, Porites astreoides, Porites porites and Agaricia spp. were assessed for presence and extent of bleached tissue at two month intervals between October 1986 and September 1987. In 98% of all corals exhibiting a bleaching response, less than 25% of the colony appeared pale. In the remaining 2%, more than 25% of the tissue appeared pale. M. annularis, P. astreoides and Agaricia spp. showed a significant positive correlation between the percent of colonies exhibiting a partial bleaching response and seawater temperature. There was no significant difference in the percentage of colonies bleached between the three depths. M. annularis and Agaricia spp. exhibited a significantly higher percentage of colonies bleached than P. astreoides and P. porites. For M. annularis 15% of coral colonies studied showed 1–2 cm² randomly seattered patches of pale tissue which remained constant throughout the study. The partial bleaching patterns observed in this study were never lethal and are considered, in part, to be a response to seasonal variations in seawater temperature. Study location: Discovery Bay Marine Laboratory, P.O. Box 35, Discovery Bay, Jamaica, W. Indies     

Growth of an adherent continuous cell line entrapped in a peg/alginate matrix

Summary CHO-K1 cells, an anchorage-dependent line, were entrapped in beads prepared from a Na alginate/polyethylene glycol mixture and grown, through successive passages, to an average maximum density of 4.5×10⁷ viable cells/g of bead. Cell growth and viability was unaffected by repeated alginate re-solubilization and reformation of the gel beads through five passages.     

Cross-modal identification: Effects of contingent changes in the stimulus series

Two computer controlled experiments in an olfactory cross-modal matching task, using two-component odour mixtures matched against bar diagrams, were designed so that stimulus presentation was contingent upon the recent performance of the subject; stimuli that were relatively poorly (in experiment 1) or well (in experiment 2) matched were more frequently presented. Analysis shows that the autoregressive structure of the performance is modified by such contingent presentation and that there is a weak relationship between transmitted information in matching and the time series structure of the matching errors. It is suggested that the process is nonlinear.     

A model describing photosynthesis in terms of gas diffusion and enzyme kinetics

Summary A model predicting net photosynthesis of individual plant leaves for a variety of environmental conditions has been developed. It is based on an electrical analogue describing gas diffusion from the free atmosphere to the sites of CO₂ fixation and a Michaelis-Menten equation describing CO₂ fixation. The model is presented in two versions, a simplified form without respiration and a more complex form including respiration. Both versions include terms for light and temperature dependence of CO₂ fixation and light control of stomatal resistance. The second version also includes terms for temperature, light, and oxygen dependence of respiration and O₂ dependence of CO₂ fixation.The model is illustrated with curves based on representative values of the various environmental and biological parameters. These curves relate net photosynthesis to light intensity, [CO₂], [O₂], temperature, and resistances to CO₂ uptake. The shape of the [CO₂]-net photosynthesis curves depends on the total diffusion resistance to CO₂ uptake and the Michaelis constant for CO₂ uptake. The curves range from typical Michaelis-Menten to Blackman types.The model is combined with a model of leaf energy exchange permitting simultaneous estimation of net photosynthesis and transpiration. The combined model is illustrated with curves relating transpiration to photosynthesis under a wide variety of environmental conditions. Environmental regimes yielding maximum efficiency of water use are identified for the given assumptions and biological parameters.     

Ethical considerations in prenatal diagnosis.

Prenatal diagnostic testing raises a number of important ethical issues, some related to diagnostic testing in general and others related to the special circumstances of pregnancy. These issues are most effectively addressed in the context of a broader understanding of the goals of prenatal diagnosis. Our dual obligations--to the pregnant woman and to the fetus--have an important influence on the goals of testing. Testing seldom leads to treatment beneficial to the fetus, but more often can be beneficial to the pregnant woman, particularly if the information provided enhances her ability to make sound decisions about reproductive matters. The process of prenatal diagnostic testing can, however, limit a woman''s sense of control over the decisions made about her pregnancy. It can also provide an opportunity for third parties to become involved in what are usually considered private matters. It is therefore important that the process of testing include adequate counseling and follow-up and that the patient''s confidence be respected. As prenatal diagnostic technology expands, both in terms of patients to be tested and diagnoses to be sought, society will face difficult questions concerning access to testing and the justification for its use.     

THE PHYSICAL AND CHEMICAL ENVIRONMENT OF THE DEVELOPING EMBRYO OF PINUS RESINOSA

The relationship between changes in soluble protein, hexose sugar, total lipid concentration, and osmotic potential occurring in gametophytic supernatant of Pinus resinosa Ait. during in vivo embryogenesis was measured. The effects of varying sucrose levels of culture medium on in vitro embryo and gametophyte development were examined. Increases in embryo volume, and fresh and dry weight of the female gametophyte during in vivo embryogenesis coincide with increasing levels of soluble protein, hexose sugar, and total lipid in the gametophytic supernatant. In contrast, osmotic potential of the supernatant increased only slightly between the zygote and proembryo stages of embryo development, and remained constant thereafter. Gametophytes plus embryos grown in vitro achieved dry weights approaching those of in ovulo gametophytes on media containing levels of sucrose up to 21%. Gametophytes on media with sucrose concentrations up to 21% also resembled normal in ovulo gametophytes in appearance. However, embryo development appeared to be suspended on treatment media containing from 9% to 21% sucrose, while embryos degenerated on media with constant sucrose levels of 3% and 6%. A treatment medium containing approximately 12% sucrose would provide an osmotic environment that duplicates that found in ovulo. While greater sucrose levels promoted more normal gametophyte development in Pinus resinosa, we failed to achieve complete development of the embryo in vitro. Conclusions and implications drawn from these results are discussed.