Effects of Green Light on the Chloroplasts of Spinach Leaf Discs

The development and photosynthetic capacity of chloroplastsformed in green light in cultured spinach leaf discs has beenstudied. At intensities of 4 to 6 mW cm^–2 green lightstimulates chloroplast replication to about the same extentas white, blue, and red light. However, practically no chloroplastreplication occurs in discs grown in low intensity green orwhite light but considerable chloroplast growth takes place.Ultrastructural studies have shown that these chloroplasts,which can be two to five times the area of control plastids(high intensity white light), have an essentially normal thylakoidsystem. Double isotope labelling experiments have establishedthat the synthesis of chloroplast ribosomal-RNA is similar incontrols and in discs grown in low intensity green or whitelight. On a per unit chlorophyll basis the CO₂ fixation rateof spinach discs grown in low intensity green (or white) lightsaturates with increasing light intensity or increasing CO₂concentration at values well below control discs. In this respecttheir photosynthetic characteristics bear a similarity to thoseof shade plants.     

New Inhibitor of Phosphodiesterase with Anti-bronchoconstrictor Properties

IN earlier work on the synthesis of isosteres of purine and in particular of theophylline (I), a series of triazolopyrimidines was found which could protect guinea-pigs against histamine bronchospasm. One compound (II) was also found to be active in certain cases of human asthma but it was found to be of no practical value because it had a tendency to cause nausea and vomiting. But because there is at present no adequate treatment for asthma, we undertook to prepare related substances which retain the activity but which are free of the defect: Thus we produced 3-acetamido-6-methyl-8-n-propyl-s-triazolo [4,3a] pyrazine (III; R=CO.Me;I.C.I.58,301 (ref. 3)). This substance is only in the early stages of clinical study in man, but we report here the chemical, biological and biochemical properties that led to its selection.     

Response of nematode communities after large‐scale ice‐shelf collapse events in the Antarctic Larsen area

Owing to large‐scale ice‐shelf disintegration events, the Antarctic Larsen A and B areas recently became ice‐free. During the ANT‐XXIII/8 Polarstern campaign, this region was sampled for the first time. Our study is the first to investigate benthic communities in this area and their response to the collapse of ice shelves in the Antarctic. The nematofauna appears to be strongly influenced by the sudden ice‐cover removal, although its response differs from that of the macro‐ and megabenthos. Our results indicate that precollapse, sub‐ice communities were impoverished and characterized by low densities, low diversity and high dominance of a few taxa. This might still be visible at a station located deep inside the Larsen B embayment, where Halomonhystera was dominant. Post‐collapse recolonization of the ‘inner’ stations, i.e. those located furthermost from the former ice‐shelf edge, is believed to be a long‐time process. At the time of sampling, community structure at the inner stations was not or only slightly influenced by colonization, and might be structured by local environmental conditions. Our results indicate that a locally increased food supply after ice‐cover removal could provoke a faster, local response of the nematode assemblages compared with the response due to recolonization. Thalassomonhystera is recognized as an opportunist, taking advantage of increased food supply at inner stations A_South and B_North. Communities living close to the former ice‐shelf edge are believed to be at an intermediate or late stage of succession, with a dominance of Microlaimus, a common Antarctic genus and quick colonizer. Densities here were comparable with those at other Antarctic stations, whereas they were considerably decreased at the inner stations. In general, the collapse of the Larsen ice shelves initially has a positive effect on the shelf nematode fauna in the area, both in terms of abundance and diversity.     

Anther Culture of Lolium temulentum, Festuca pratensis and Lolium x Festuca Hybrids. II. Anther and Pollen Development In Vivo and In Vitro

The various pathways of pollen development were investigatedin cultured anthers of Lolium temulentum, Festuca pratensisand the L. multiflorum x F. pratensis hybrid ‘Elmet’.In all three, development from the vegetative cell was the predominantpathway of pollen callus development. However, there were characteristicdifferences in the behaviour of the generative cell. In L. temulentumit remained attached to the pollen wall and degenerated, whereasin F. pratensis it divided. In ‘Elmet’ it detachedfrom the pollen wall and remained undivided. Both polarizedand unpolarized partitioned calluses were observed. Developmentof the fusion product of the vegetative and generative nucleiwere also observed in anthers of L. temulentum. Anomalous grainswere not found to be major source of pollen calluses. Sections of anthers of L. temulentum were used to investigatethe origin of S pollen grains, the small pale-staining grainswhich denote pollen dimorphism. Such grains form out of contactwith the tapetum and are therefore determined before or duringmeiosis (i.e. before harvest of anthers for culture). Sectionswere also used to demonstrate the influence of the durationof pretreatment on the development of the middle layer of theanther wall. Festuca pratensis, Lolium temulentum, Lolium x Festuca, anther culture, haploid, microspore, pollen     

SPECIES RICHNESS OF FRESHWATER GASTROPOD COMMUNITIES IN CENTRAL NORTH AMERICA

Species richness of freshwater gastropod communities (SR) wasexamined at 429 sites in central North America. Lakes and riversshowed the highest SR values, as did habitats with organic substrates,shale and clay. SR was significantly correlated with speciesrichness of aquatic macrophytes, particularly in lotic habitats.Of the 8 water chemistry variables examined, SR in the studyarea as a whole was significantly positively correlated withinorganic phosphorus, chloride, total alkalinity, total dissolvedsolids and pH, and inversely correlated with dissolved organicmatter. Stepwise multiple regression analyses showed that contributionsof the respective chemical variables varied in different typesof water bodies. Different variables interacted in their effectson SR. In all cases more than half of the variability in SRremained unexplained by the chemical variables examined. Manyfactors apparently influence SR, their relative importance varyingwith situation. (Received 24 October 1986;     

A PANEL PERFORMANCE PROCEDURE IMPLEMENTED IN R

Monitoring performance is essential for the efficient use of a sensory panel both during training and while carrying out product assessments. We present a concise procedure to monitor panel performance based on classical statistical methods. The program includes tests for the ability to discriminate between products, repeatability of assessments, scale use, agreement between panelists and a principal component analysis map of panelist means across attributes. The algorithm is implemented in R – a state‐of‐the‐art, freely available statistical software package. The program output is summarized in graphs and tables. This easily applicable panel performance procedure is aimed at improving sensory practice, especially in areas where the use of highly complex systems is not feasible.     

UV effects on stoichiometry and PUFAs of Selenastrum capricornutum and their consequences for the grazer Daphnia magna

1. The effect of ultraviolet (UV) radiation (280–400 nm) on fatty acid composition and elemental ratios of carbon (C), nitrogen (N) and phosphorus (P) of a unialgal culture of the chlorophyte Selenastrum capricornutum was investigated. Algae were cultured in the presence or absence of UV radiation and were subsequently fed to Daphnia magna to assess potential effects of UV on zooplankton fatty acid composition, growth and reproduction. 2. Algal growth rate was substantially reduced by UV radiation, probably because of a severe inhibition of photosynthetic efficiency (measured as optimal quantum yield). 3. Algae exposed to UV radiation had a significantly reduced content of 18 : 1 n‐9, while C18 polyunsaturated fatty acids (PUFAs) were higher under UV radiation. These observations point at an increased demand for and synthesis of PUFAs under UV stress. 4. The C : P and N : P ratios showed a remarkable decrease in UV‐exposed cells primarily owing to an increased uptake of P. The nutritional quality in terms of both fatty acid composition and stoichiometry was therefore higher in the UV treatment relative to the control. 5. Despite the UV‐induced changes in nutritional quality of S. capricornutum, no significant effects on D. magna growth or reproduction were detected. The fatty acid composition of Daphnia fed on UV irradiated algae showed a significantly lower content of 18 : 1 n‐9, but no changes in the essential PUFAs.     

Importance of colour in the reaction of passerine predators to aposematic prey: experiments with mutants of Pyrrhocoris apterus (Heteroptera)

Persistent questions concerning the warning coloration of unpalatable insects address whether the bright aposematic colour itself or its combination with a species-specific dark pattern is the key factor in their protection against insectivorous birds, and how chromatic polymorphism originates and is maintained in aposematics. In the present study, these questions were tested experimentally, using the birds Parus major , Parus caeruleus , Erithacus rubecula , and Sylvia atricapilla as predators, and chromatically polymorphic firebug Pyrrhocoris apterus : red wild form, white, yellow, and orange mutants (all four of them with the same black melanin pattern, the mutants differing in colour of pteridine pigments only) and the nonaposematic brown-painted wild form as prey. The results show that a specific colour is essential for the birds to recognize the specific aposematic prey; the melanin pattern is not sufficient. White mutants were no better protected than nonaposematic firebugs; red wild-type and orange mutants were equally well protected against all bird species; and the reaction of birds to yellow mutants was species-specific. An evolutionary scenario of 'recurrent recessive mutations' is formulated to explain the origin of colour polymorphism in some aposematics.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 143–153.