Import of 14C-Photosynthate by Developing Leaves of Sugarcane

Sink-to-source transition was studied in developing sugarcane (Saccharum interspecific variety L62–96) leaves. Fully-expanded, mature sugarcane leaves were fed ¹⁴CO₂ for 20 minutes, incorporating about 617 Bq. After five hours the leaves of each plant were cut into 1-cm-length segments that were weighed and then placed in scintillation cocktail for counting. All leaves younger than the leaf fed ¹⁴CO₂ imported labeled photoassimilate. Three to four leaves had both importing and non-importing regions within the blade and a distinct transition region between them. A transition region was observed in leaves which had expanded to between 30 and 90 % of final blade length. Radioactivity per gram fresh weight was calculated as a measure of sink strength. Sink strength was greatest in the youngest leaf and declined with leaf age. The results of this study indicate that 1) import of photosynthate by developing sugarcane leaves occurs over a longer span of developmental ages than in dicotyledonous leaves and 2) the actual tissue region undergoing transition within such a leaf can be resolved as narrow zone between the importing and non-importing regions.     

The response of isoprene emission rate and photosynthetic rate to photon flux and nitrogen supply in aspen and white oak trees

Isoprene is the primary biogenic hydrocarbon emitted from temperate deciduous forest ecosystems. The effects of varying photon flux density (PFD) and nitrogen growth regimes on rates of isoprene emission and net photosynthesis in potted aspen and white oak trees are reported. In both aspen and oak trees, whether rates were expressed on a leaf area or dry mass basis, (1) growth at higher PFD resulted in significantly higher rates of isoprene emission, than growth at lower PFD, (2) there is a significant positive relationship between isoprene emission rate and leaf nitrogen concentration in both sun and shade trees, and (3) there is a significant positive correlation between isoprene emission rate and photosynthetic rate in both sun and shade trees. The greater capacity for isoprene emission in sun leaves was due to both higher leaf mass per unit area and differences in the biochemical and/or physiological properties that influence isoprene emission. Positive correlations between isoprene emission rate and leaf nitrogen concentration support the existence of mechanisms that link leaf nitrogen status to isoprene synthase activity. Positive correlations between isoprene emission rate and photosynthesis rate support previous hypotheses that isoprene emission plays a role in protecting photosynthetic mechanisms during stress.     

Characterization of inositolpolyphosphate binding to myocardial membranes

Although it is well-accepted that the phosphatidylinositol signalling transduction pathway, producing inositol-1,4,5-P3 (InsP₃) and inositol-1,3,4,5-P₄ (InsP4) as second messengers, functions in heart muscle, virtually nothing is known about the roles of the higher inositol polyphosphates such as inositolhexakisphosphate (InsP₆). This study demonstrates that InSP₆ has the ability to bind intracellularly, with different binding characteristics, to different myocardial membranes. Binding to purified sarcoplasmic reticulum (SR) membranes, purified sarcolemmal (SL) membranes as well as to viable mitochondria were characterized. Binding to all these membranes display high as well as low affinity binding sites, with differing affinities. Kd values of binding to SR were 32 and 383 nM, to SL 61 and 1312 nM, while those of mitochondrial binding were 230 and 2200 nM respectively.InsP₄ binding was also investigated and displayed the following characteristics: to SR, one low affinity binding site (Kd = 203 nM) and to SL, a high as well as a low affinity binding site with Kd values of 41 and 2075 nM respectively. Presence of InsP₃, the second messenger for SR calcium release, at concentrations of 1 nM, elevated the binding of InsP₄ to SR and SL by a mean of 30% and 20% respectively.Fractionation of SR and SL membranes on sucrose density gradients, after solubilization with CHAPS, indicated that InsP₆ bound to two separate protein peaks in both these membranes, while InsP₄ bound to only one. In SR membranes, InsP₄ bound preferentially to a protein separating at high sucrose density while it bound to a protein separating at low sucrose density in SL membranes.     

The use of constitutive nuclear oncoproteins to count neurons in the enteric nervous system of the guinea pig

Immunohistochemical double labelling of the enteric nervous system of the guinea pig ileum was performed with a monoclonal antibody (anti-MYC 033) directed against a peptide sequence of the human c-Myc protein together with antibodies directed against either the neuron-specific antigens neuron-specific enolase or PGP 9.5 or the glia-specific marker S-100 to demonstrate that anti-MYC 033 labelled the nuclei of all enteric neurons but not glia. This strategy was also employed to demonstrate that another anti-c-Myc monoclonal anti-body, anti-MYC 070, labelled the nuclei of all neurons and glia, as well as perhaps all other cells in these preparations. A polyclonal antiserum raised against a peptide sequence of the human c-Fos protein (anti-FOS 4) was shown to label the identical nuclei as anti-MYC 033. The ganglionic density of nuclei labelled by anti-FOS 4 was found to be similar to previous measures of the ganglionic density of neurons. Double labelling with anti-MYC 033 and an antiserum directed against vasoactive intestinal polypeptide was performed to reexamine the ganglionic density of neurons that express this neuropeptide. Our results suggest that the ganglionic density of these neurons might be less than previously determined.     

Germline and somatic mosaicism in a female carrier of Duchenne muscular dystrophy

The family of a male with Duchenne muscular dystrophy (DMD) and a deletion within the dystrophin gene has been studied. Polymerase chain reaction analysis of ectopic mRNA from peripheral blood T+B lymphocytes and the use of (CA) _n repeat polymorphisms in and around the deleted region showed the proband's mother to be both a germline mosaic and a somatic mosaic for the deletion seen in her son. The mutation therefore occurred as a mitotic event early in embryogenesis.     

Water stress,temperature, and light effects on the capacity for isoprene emission and photosynthesis of kudzu leaves

Kudzu (Pueraria lobata (Willd) Ohwi.) is a vine which forms large, monospecific stands in disturbed areas of the southeastern United States. Kudzu also emits isoprene, a hydrocarbon which can significantly affect atmospheric chemistry including reactions leading to tropospheric ozone. We have studied physiological aspects of isoprene emission from kudzu so the ecological consequences of isoprene emission can be better understood. We examined: (a) the development of isoprene emission as leaves developed, (b) the interaction between photon flux density and temperature effects on isoprene emission, (c) isoprene emission during and after water stress, and (d) the induction of isoprene emission from leaves grown at low temperature by water stress or elevated temperature. Isoprene emission under standard conditions of 1000 mol photons·m^-2·s^-1 and 30°C developed only after the leaf had reached full expansion, and was not complete until up to two weeks past the point of full expansion of the leaf. The effect of temperature on isoprene emission was much greater than found for other species, with a 10°C increase in temperature causing a eight-fold increase in the rate of isoprene emission. Isoprene emission from kudzu was stimulated by increases in photon flux density up to 3000 mol photons·m^-2·s^-1. In contrast, photosynthesis of kudzu was saturated at less than 1000 mol·m^-2·s^-1 photon flux density and was reduced at high temperature, so that up to 20% of the carbon fixed in photosynthesis was reemitted as isoprene gas at 1000 mol photons·m^-2·s^-1 and 35°C. Withholding water caused photosynthesis to decline nearly to zero after several days but had a much smaller effect on isoprene emission. Following the relief of water stress, photosynthesis recovered to the prestress level but isoprene emission increased to about five times the prestress rate. At 1000 mol photons·m^-2·s^-1 and 35°C as much as 67% of the carbon fixed in photosynthesis was reemitted as isoprene eight days after water stress. Leaves grown at less than 20°C did not make isoprene until an inductive treatment was given. Inductive treatments included growth at 24°C, leaf temperature of 30°C for 5 h, or witholding water from plants. With the new information on temperature and water stress effects on isoprene emission, we speculate that isoprene emission may help plants cope with stressful conditions.     

Selective Axonal Argentaffin Staining in Rat Central Nervous System after Protein Mercuration

The mercury-silver (Hg-Ag) argentaffin technique, known to stain specifically proteins in the lateral components of triads/diads in striated muscle cells, was applied to the central nervous system of adult rats. Following fixation in glutaraldehyde, axons in white and gray matter were selectively stained, but not perikarya or their proximal axon and dendrites. Neural tissues were postfixed 24 hr in 5% (w/v) mercuric acetate in 2% (v/v) acetic acid in distilled water, stained for 12-24 hr in darkness at 37-43 C with ammoniacal silver nitrate solution, freshly prepared by adding concentrated ammonia to 60% (w/v) silver nitrate solution until a small amount of silver oxide precipitate remained undissolved. Samples were then washed with freshly prepared 5% (w/v) sodium sulfite and distilled water. All steps were carried out using dark-colored glass flasks. Samples were dehydrated with ethanol and embedded in Paraplast or Poly Bed. Electron microscopy showed the silver-reducing protein inside the axons. Methylation abolished Hg-Ag axonal reactivity indicating that carboxyl groups were necessary for silver staining. Proteins with solubility properties characteristic of neurofilament proteins were involved in Hg-Ag staining. In the cerebellum the plexus of parallel fibers in the molecular layer were not stained, while basket cell axonal processes reacted intensely. The method appears to distinguish neuronal protein variants related to cytotypic differences in cytoskeletal neurofilaments.     

The evolution and ecology of multiple antipredator defences

Prey seldom rely on a single type of antipredator defence, often using multiple defences to avoid predation. In many cases, selection in different contexts may favour the evolution of multiple defences in a prey. However, a prey may use multiple defences to protect itself during a single predator encounter. Such “defence portfolios” that defend prey against a single instance of predation are distributed across and within successive stages of the predation sequence (encounter, detection, identification, approach (attack), subjugation and consumption). We contend that at present, our understanding of defence portfolio evolution is incomplete, and seen from the fragmentary perspective of specific sensory systems (e.g., visual) or specific types of defences (especially aposematism). In this review, we aim to build a comprehensive framework for conceptualizing the evolution of multiple prey defences, beginning with hypotheses for the evolution of multiple defences in general, and defence portfolios in particular. We then examine idealized models of resource trade-offs and functional interactions between traits, along with evidence supporting them. We find that defence portfolios are constrained by resource allocation to other aspects of life history, as well as functional incompatibilities between different defences. We also find that selection is likely to favour combinations of defences that have synergistic effects on predator behaviour and prey survival. Next, we examine specific aspects of prey ecology, genetics and development, and predator cognition that modify the predictions of current hypotheses or introduce competing hypotheses. We outline schema for gathering data on the distribution of prey defences across species and geography, determining how multiple defences are produced, and testing the proximate mechanisms by which multiple prey defences impact predator behaviour. Adopting these approaches will strengthen our understanding of multiple defensive strategies.     

Characterization of hemocytes from the marine amphipod Parhyale hawaiensis (Dana 1853): Setting the basis for immunotoxicological studies

Hemocytes are circulating blood cells that play a crucial function in amphipods and other crustacean immune systems. The hemocytes of the marine tropical amphipod Parhyale hawaiensis have been used for the evaluation of DNA damage and micronuclei, but they have not been characterized in the scientific literature. The aim of this study was to describe the hemolymph cells of P. hawaiensis and study their phagocytotic activity. Basic dyes were used to differentiate the cell types and the presence of lipids. The total hemocyte counts (THCs) and the proportion and sizes of the hemocyte types were determined. Hemolymph was exposed to Escherichia coli for verification of the presence of phagocytosis. Three cell types, all containing lipids, were identified in P. hawaiensis: granulocytes (oval shape, 13.4 × 7.6 μm), semi-granulocytes (oval shape, 14.1 × 7.2 μm), and hyalinocytes (round shape, 9.6 × 7.2 μm). Those three cell types were found in different percentages in males (64.8%, 31.1%, and 4.2%) and females (70.1%, 28.2%, and 1.7%). THCs for males were 9007 ± 3800 cells per individual and 4695 ± 1892 cells per individual for females. The cells of E. coli were phagocytized by the hemocytes. Our findings increased the knowledge of hemocytes in P. hawaiensis and is a step forward in using hemocyte-based immune responses as an endpoint in ecotoxicology.