Cyclic Changes in Chloroplast Structure in Synchronized Euglena gracilis*

SYNOPSIS. In populations of Euglena gracilis strain Z synchronized by cultivation on a repetitive light-dark cycle, chloroplasts undergo cyclic changes in structure. During most of the light period chloroplasts are relatively compact with closely appressed lamellae; during the dark (division) period the chloroplasts become quite distended. This change persists for at least one cycle even when the cells are left in continuous light, suggesting that the periodicity may be related more to the age of the cell than to a direct effect of light. In addition, the pyrenoid in synchronized cells has a transient existence, being present only in the first half of the light period.     

Transmission of broad bean stain virus and Echtes Ackerbohnenmosaik-Virus to field beans (Viciajaba) by weevils

Sitona lineatus and Apion vorax were the two most common species of weevil on field beans (Vicia faba minor) at Rothamsted between 1970 and 1974. In glasshouse tests, A. vorax was a much more efficient vector than 5. lineatus of broad bean stain virus (BBSV) and Echtes Ackerbohnenmosaik-Virus (EAMV), and both species transmitted EAMV more often than BBSV. Five other species of Apion transmitted the viruses infrequently or not at all. S. lineatus adults transmitted no more often after 8–16 days on infected plants than after 1–2 days. Some A. vorax adults transmitted EAMV, but not BBSV, after feeding on infected leaves for a few minutes. After 4 days on infected plants, A. vorax sometimes remained infective for the following 8 days. No A. vorax collected from woodland plants in spring was infective with BBSV or EAMV, but 4% from bean crops containing seed-borne infection carried BBSV and 17% carried EAMV. BBSV and EAMV were recovered from triturated weevils, but not from weevil haemolymph. Possibly the viruses are transmitted as contaminants of the mouthparts or by regurgitation during feeding, but A. vorax was observed to regurgitate only when anaesthetized. BBSV and EAMV were not transmitted by aphids (Aphis fabae and Acyrthosiphon pisum), nor by pollen beetles {Meligethes spp.). Field observations suggest that infected seed is the main source of BBSV and EAMV in spring-sown crops, and that crops grown from virus-free seed, and isolated from infected crops by 250–500 m, remain free of infection for most of the season.     

Zaire butterflies and faunal diversity in the tropics

Samples of butterflies were collected along the Zaire River from its source to Kisangani and in the Ituri region. The number of species flying in the same area has been estimated wherever possible, and the degree of faunal similarity at different sites. The number of species increases as one proceeds north from 50–100 to 100–150, and the fauna is separable into two groups. The difference in faunal composition and diversity is related to the southern boundary of the rain forest. The comparative poorness of the butterfly fauna in tropical Africa compared to tropical South America is discussed, with reference to the parallel difference in the bird faunas of the two continents.     

Studies on the Respiratory Physiology of Euglena gracilis Cultured on Acetate or Glucose

SYNOPSIS. The glyoxylate cycle operates at a high level in Euglena gracilis when acetate is the only carbon source, and at a low level when glucose is the only carbon source, as indicated by activities of malate synthase. Altho glucose causes a moderate repression of some of the enzymes of the glyoxylate cycle, it neither represses nor inhibits malate synthase. The specific activity of the malic enzyme was about 5-fold greater in acetate-grown Euglena than in glucose-grown cells, but the absolute rate of CO₂ fixation was about twice as great in cells grown on glucose. The respiratory quotient was unity regardless of substrate.     

Argon,xenon, hydrogen,and the oxygen consumption and glycolysis of mouse tissue slices

The effects of xenon, argon, and hydrogen on the aerobic and anaerobic metabolism of mouse liver, brain, and sarcoma slices have been investigated. Xenon was found to alter the rates of metabolism of these tissues in a manner almost identical with helium. The gas increased the rate of oxygen consumption in all three tissues and significantly depressed that of anaerobic glycolysis in brain and liver. The depression of glycolysis in sarcoma was less pronounced and not highly significant. Although both the magnitude and statistical significance of the effects observed with argon were much smaller, there was a seeming adherence to the general pattern established by xenon and helium. Hydrogen while remaining essentially ineffective insofar as oxygen uptake was concerned, depressed glycolysis in both liver and brain slices but did not significantly affect sarcoma slices. The following points are stressed in the Discussion: (1) the magnitude and direction of effects exerted by helium, argon, xenon, hydrogen, and nitrogen do not conform with the relative values of molecular weight, density, and solubility of these gases; (2) the effect of these gases on tissue metabolism does not necessarily parallel that exerted upon the whole organism.     

Fitness of insularia morphs of the peppered moth Biston betularia

In recent years the industrial melanic carbonaria morph in the moth Biston betularia (L.) has decreased rapidly in frequency in Britain as air pollution has decreased. The intermediate melanic insularia has shown a variable response. We have estimated the fitness of insularia, compared with the other two morphs, for several data sets. As a rule its fitness lies between that of carbonaria and typical, but nearer to typical and sometimes very close to it. The intermediate position is expected if fitness relates directly to phenotype. The results suggest that insularia may continue polymorphic while carbonaria is likely to disappear. The past high frequency of insularia in South Wales may have been due to an initial increase in insularia frequency before carbonaria reached the region. Differences in dynamics of frequency change in insularia and carbonaria are evidence against induction, which has sometimes been invoked to explain the spread of melanism in this species.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 359–366.