Light control of extractable nitrate reductase activity in higher plants

Light regulation of extractable nitrate reductase (NR) activity of higher plants is complicated by: 1) involvement of several photoreceptors, 2) differences in the relative importance of the several photoreceptors among species and among developmental stages of the same species, 3) two types of effects – alteration of activity of existing NR and influences on de novo synthesis of NR, and 4) differing forms of NR within the same species. The interrelationships of all of these factors are not clear. It may be that each system will have to be understood separately before a general model can be developed. Immunochemical quantification of NR from systems exposed to varied light regimes may enhance our understanding of this area. Currently few general conclusions can be made; however, we think that the following statements are true or are usually true: (1) Phytochrome influences extractable NR activity by the low irradiance response and high irradiance response in etiolated tissues. (2) In de-etiolated tissues phytochrome can influence NR activity decay at the end of a light period by the low irradiance response. (3) The phytochrome equilibrium or the absolute level of P_fr influences extractable NR activity in green tissues under white light. (4) Blue light influences extractable NR activity through phytochrome and another, unknown, blue light-absorbing pigment. Flavins may be involved in vitro in reactivation of inactivated NR. (5) Photosynthesis does not directly influence the induction of the forms of NR that require substrate and light for induction. (6) In some tissues there appears to be a close link between nitrite-reducing and nitrate-reducing capabilities. (7) Much circumstantial evidence from kinetic and protein-synthesis-inhibitor studies and the only available immunochemical data indicate that light induces de novo synthesis of NR, resulting in increased extractable activity.     

THE LIPID COMPOSITION OF THORACOSPHAERA HEIMII: EVIDENCE FOR INCLUSION IN THE DINOPHYCEAE1

The fatty acid, sterol and chlorophyll composition of the calcified, unicellular alga Thoracosphaera heimii (Lohmann) Kamptner are reported. The presence of 4,23,24-termethyl-5α-cholest-22E-en-3β-ol (dinosterol), 4,23,24-trimethyl-5α-cholest-22E-en-3-one (dinosterone) and the predominance of C₁₈, C₂₀ and C₂₂ unsaturated fatty acids, including the acid 18:5ω3, indicates that T. heimii is a dinoflagellate. The fatty acid: sterol ratio (1.3), is typical of dinoflagellates. The geochemical significance of dinosterone, the high relative concentration of 4-desmethyl-5α-stanols and the role of 23-methyl-5α-cholest-22E-en-3β-ol in the biosynthesis of dinosterol in T. heimii are also discussed.     

Phylogeny and physiology of Drosophila opsins

Phylogenetic and physiological methods were used to study the evolution of the opsin gene family in Drosophila. A phylogeny based on DNA sequences from 13 opsin genes including representatives from the two major subgenera of Drosophila shows six major, well-supported clades: The blue opsin clade includes all of the Rhl and Rh2 genes and is separated into two distinct subclades of Rhl sequences and Rh2 sequences; the ultraviolet opsin clade includes all Rh3 and Rh4 genes and bifurcates into separate Rh3 and Rh4 clades. The duplications that generated this gene family most likely took place before the evolution of the subgenera Drosophila and Sophophora and their component species groups. Numerous changes have occurred in these genes since the duplications, including the loss and/or gain of introns in the different genes and even within the Rhl and Rh4 clades. Despite these changes, the spectral sensitivity of each of the opsins has remained remarkably fixed in a sample of four species representing two species groups in each of the two subgenera. All of the strains that were investigated had R1-6 (Rhl) spectral sensitivity curves that peaked at or near 480 nm, R7 (Rh3 and Rh4) peaks in the ultraviolet range, and ocellar (Rh2) peaks near 420 nm. Each of the four gene clades on the phylogeny exhibits very conservative patterns of amino acid replacement in domains of the protein thought to influence spectral sen sitivity, reflecting strong constraints on the spectrum of light visible to Drosophila.     

CHARACTERIZATION OF TWO CHLORELLA VULGARIS (CHLOROPHYCEAE) STRAINS ISOLATED FROM WASTEWATER OXIDATION PONDS1

We report here on the characterization and isolation of two ecotypes of Chlorella vulgaris Beyerinck that coexist in wastewater reservoirs. One ecotype (C1) contains high amounts of chlorophyll b, is capable of autotrophic growth, and can utilize only a few organic solutes for growth. The second ecotype (C2) contains low amounts of chlorophyll b, requires vitamin B₁₂, and can support its growth with a broad range of organic compounds. Of the two ecotypes, the latter showed slower growth rates when light was the sole source of energy. Cells of C2-type Chlorella attained higher photosynthetic activities than C1-type cells at saturating irradiances. However, their low chlorophyll b content and lower light utilization efficiency suggest that C2-type Chlorella contains relatively low amounts of light-harvesting antennae, a disadvantage in severely light-limited ecosystems like wastewater reservoirs. We hypothesize that the two Chlorella types coexist by adopting different lifestyles: C1-type cells rely largely on their photosynthetic potential for energy conservation and growth, whereas C2-type cells may exploit their heterotrophic properties for this purpose.     

Diffusion of Fe(II) from an iron propagation cage and its effect on tissue iron and pigments of macroalgae on the cage

Iron propagation cages were settled on sand and/or rock beds in coastal areas of Hokkaido. The cage was oxidized by dissolved oxygen and the released Fe(II) diffused into the seawater around the cage. Fe(II) concentrations in the range of 10–50 nM were detected within a 20-m distance around the cage. For comparison, in the Japan Sea, the total iron concentration is less than 2 nM.Laminaria japonica was grown in an indoor semi-continuous culture system. The critical Fe level for maintaining maximum growth, and the subsistence Fe level for survival were measured. The concentrations obtained were 14–21 and 8 g Fe g^–1 tissue, respectively. Iron found inL. japonica growing on rocks and/or rock beds in the Japan Sea was close to the subsistence level. However, the Fe level inL. japonica on the cage in the Japan Sea was considerably higher. The concentrations of chlorophyll-a and fucoxanthin collected from the cage were significantly higher for sporophytes, demonstrating that iron is a very important element for the growth of seaweeds.     

Effects of atmospheric SO2 on Azolla and Anabaena symbiosis

The water fern Azolla pinnata R. Br. was fumigated for 1 week with either 25, 50 or 100 nl 1⁻¹ SO₂. The symbiosis of Azolla with Anabaena azollae (spp.) was severely damaged by atmospheric SO₂ even at concentrations as low as 25 nl 1⁻¹, with significant reductions in growth, reduction of C₂H₂, NH₃ assimilation, protein synthesis, and heterocyst development. These disturbances appear to be mainly responsible for the extreme sensitivity of this fern to atmospheric SO₂. Changes in violaxanthin/antheraxanthin and epoxy-lutein/lutein ratios also indicate that free radical products are induced by atmospheric SO₂. These results suggest that the Azolla-Anabaena symbiotic system is a very responsive and reliable lower plant model to study the detailed effects of total sulphur deposition upon the balances between various important plant metabolic processes.     

The effects of enhanced ozone and enhanced carbon dioxide concentrations on biomass, pigments and antioxidative enzymes in spruce needles (Picea abies L.)

During one growing period, 5-year-old spruce trees (Picea abies L., Karst.) were exposed in environmental chambers to elevated concentrations of carbon dioxide (750 cm³ m^?3) and ozone (008 cm³ m^?3) as single variables or in combination. Control concentrations of the gases were 350cm³ m^?3CO₂ and 0.02 cm³ m ^?3 ozone. To investigate whether an elevated CO₂ concentration can prevent adverse ozone effects by reducing oxidative stress, the activities of the protective enzymes superoxide dismutase, catalase and peroxidase were determined. Furthermore, shoot biomass, pigment and protein contents of two needle age classes were investigated. Ozone caused pigment reduction and visible injury in the previous year's needles and growth reduction in the current year's shoots. In the presence of elevated concentrations of ozone and CO₂, growth reduction in the current year's shoots was prevented, but emergence of visible damage in the previous year's needles was only delayed and pigment reduction was still found. Elevated concentrations of ozone or CO₂ as single variables caused a significant reduction in the activities of superoxide dismutase and catalase in the current year's needles. Minimum activities of superoxide dismutase and catalase and decreased peroxidase activities were found in both needle age classes from spruce trees grown at enhanced concentrations of both CO₂ and ozone. These results suggest a reduced tolerance to oxidative stress in spruce trees under conditions of elevated concentrations of both CO₂ and ozone.     

Changes in the spectral absorption of cone visual pigments during the settlement of the goatfish Upeneus tragula: the loss of red sensitivity as a benthic existence begins

The goatfish Upeneus tragula undergoes an abrupt metamorphosis at settlement when the pelagic larvae begin a reef-associated benthic mode of life. A microspectrophotometric investigation of the retinal visual pigments was carried out on fish prior to, during, and following settlement. It was found that the visual pigment in the long wavelength-absorbing member of the double cones in the dorsal retina changed rapidly from a rhodopsin with a wavelength of maximum absorption (max) of 580 nm to that of 530 nm. The second member of the double cones always had a rhodopsin with the max absorbing at shorter wavelengths. Prior to settlement the average for this class of cones was 487 nm whereas during and immediately following the settlement period the max recorded from individual outer segments was found to vary between 480 nm and 520 nm, with two possible classes of cone absorbance emerging within this range. These two classes of absorbance had average max values of 487 and 515 nm. The average max of the paired cone classes in one larger wild-settled fish were found to be at 506 nm and 530 nm. No change was detected in the max of the single cones or the rods which were always found to have a max of about 400 nm and 498 nm respectively. The loss of the redabsorbing pigment occurred over the same time scale as the metamorphosis of morphological features associated with the settlement process. It is thought that the loss of this visual pigment is associated with the change in light environment of the fishes as they leave the surface waters to begin a benthic mode of life in deeper water.Abbreviations AIMS Australian Institute of Marine Science - ANOVA Analysis of variance - IR infra-red - max wavelength of maximum absorption - MSP microspectrophotometer - NA numerical aperture - SL standard length     

Design considerations for two-stage enrichment clinical trials

When there is a predictive biomarker, enrichment can focus the clinical trial on a benefiting subpopulation. We describe a two-stage enrichment design, in which the first stage is designed to efficiently estimate a threshold and the second stage is a “phase III-like” trial on the enriched population. The goal of this paper is to explore design issues: sample size in Stages 1 and 2, and re-estimation of the Stage 2 sample size following Stage 1. By treating these as separate trials, we can gain insight into how the predictive nature of the biomarker specifically impacts the sample size. We also show that failure to adequately estimate the threshold can have disastrous consequences in the second stage. While any bivariate model could be used, we assume a continuous outcome and continuous biomarker, described by a bivariate normal model. The correlation coefficient between the outcome and biomarker is the key to understanding the behavior of the design, both for predictive and prognostic biomarkers. Through a series of simulations we illustrate the impact of model misspecification, consequences of poor threshold estimation, and requisite sample sizes that depend on the predictive nature of the biomarker. Such insight should be helpful in understanding and designing enrichment trials.