Developmental manipulation of the circadian pacemaker in the cockroach: relationship between pacemaker period and response to light

Abstract Previous research has shown that fundamental properties of the circadian pacemaker that drives the rhythm of locomotor activity in the cockroach Leucophaea maderae L. are permanently altered by exposure of animals to 22 or 26 h light cycles during post-embryonic development (Barrett & Page, 1989; Page & Barrett, 1989). The present results document differences between animals exposed to either constant darkness (DD) or constant light (LL) during postembryonic development in the free-running period, the phase shifting response to light pulses, and the response to an LL to DD transition of the adult pacemaker. In addition, the changes in pacemaker period and in the phase shifting response that result from raising animals in several different lighting conditions are shown to be strongly correlated. The data suggest there is a developmentally labile interdependence between the period of the pacemaker and its sensitivity to light.     

Comparative body size relationships in pocket gophers and their chewing lice

In this paper, we use the method of independent contrasts to study body size relationships between pocket gophers and their chewing lice, a host-parasite system in which both host and parasite phylogcnies are well studied. The evolution of body size of chewing lice appears to be dependent only on the body size of their hosts, which confirms the 1991 findings of Harvey and Keymer. We show that there is a positive relationship between body size and hair-shaft diameter in pocket gophers, and that there is also a positive relationship between body size and head-groove width in chewing lice. Finally, we show a positive relationship between gopher hair-shaft diameter and louse head-groove width. We postulate that changes in body size of chewing lice are driven by a mechanical relationship between the parasite's head-groove dimension and the diameter of the hairs of its host. Louse species living"on larger host species may be larger simply because their hosts have thicker hairs, which requires that the lice have a wider head groove. Our study of gopher hair-shaft diameter and louse head-groove dimensions suggest that there is a 'lock-and-key' relationship between these two anatomical features.     

Streptovaricins inhibit Focus Formation by MSV (MLV) Complex

We recently reported that the streptovaricins inhibit the reaction by which DNA is transcribed from the RNA template resident in murine leukaemia virions (MLV)¹. The reports^{2, 3} which first indicated that this DNA polymerase is present in oncogenic RNA viruses have been confirmed and extended^4–8. The enzyme provides a mechanism whereby an RNA virus can insert stable genetic information into a host chromosome. Gallo and co-workers described an RNA dependent DNA polymerase in lymphoblastic leukaemic cells which was inhibited by N-demethylrifampicin⁹ and this antibiotic, together with a number of other rifamycin derivatives, also inhibited the oncogenic viral DNA polymerase¹⁰. Like the streptovaricins, the rifamycins are ansa macrolide antibiotics (Fig. 1).     

Generic Criteria for Flabellula,Rugipes and Hyalodiscus,With Descriptions of Species*

SYNOPSIS. Six strains of amoebae isolated from freshwater habitats and having broad, flattened locomotive forms were studied in clonal cultures, with attention to trophic structure, nuclear division, cyst structure in those strains which formed cysts, some aspects of cytochemistry, and other characteristics. Three strains were found to belong to the genus Flabellula, one being identified as F. platypodia (Gläser, 1912) and the other 2 as F. mira Schaeffer, 1926. The new species Rugipes placidus is described. One strain, identified as belonging to the species originally called Amoeba actinophora Auerbach, 1855, is re-described as Hyalodiscus actinophorus, and a similar strain is described as H. actinophorus var. minor n. var. All 3 strains of Flabellula had the unusual type of mitotic figure reported by Gläser for F. platypodia but not previously studied with the Feulgen technic. The genus Rugipes has the mitotic pattern more common to small amoebae and is distinguished from Flabellula partly on that basis. Both strains of Hyalodiscus have division figures of this common type. Of the strains included in this investigation, only R. placidus and H. actinophorus formed cysts in culture. The cysts of neither species were viable after one year at room temperature and humidity. The status of Rugipes as distinct from Flabellula is discussed. The genus Hyalodiscus is interpreted in a manner compatible with the original definition of Hertwig and Lesser and is included within the order Amoebida. The strains of this genus isolated have a doubly contoured, strongly PAS-positive covering over the endoplasmic hump. Some criteria for the taxonomy of amoebae are evaluated in the light of work reported in this and 2 previous papers.     

Manipulation of IAA-Oxidase Activity and Auxin-Deficiency Symptoms in Intact Cotton Plants with Manganese Nutrition

Cotton (Gossypium hirsutum L. cv. Deltapine 15) seedlings were grown in solution culture in which the Mn²⁺ level was varied. Following an initial period, a series of shifts in manganese nutrition were employed, each lasting 14 days. Appearance was observed and fresh weight, IAA oxidase (IAAO), peroxidase and IAAO inhibitor levels were determined. After the initial 3 weeks of treatment, growth was negatively correlated with IAAO (or peroxidase) activity. All shifts in manganese nutrition resulted in predicted changes in IAAO activity, growth and plant appearance during a second 2-week period of the experiment. Continuously deficient plants exhibited highest leaf abscission and IAA oxidase activity, and lowest growth of all treatments. Plants shifted from deficient to control levels of Mn²⁺ exhibited a marked decline in IAAO activity, increase in growth and absence of leaf abscission. Plants shifted from borderline deficiency to deficient Mn²⁺ exhibited a major increase in IAAO activity, reduction in growth and extensive leaf abscission. Control and borderline toxicity plants maintained normal IAAO activity, growth, and appearance. During a final 2-week period, symptom expression was intensified. In particular, the initial borderline deficiency plants shifted to deficient levels of Mn²⁺ abscised most of those leaves that expanded after the shift in treatment. In addition, shifts of some plants to toxic Mn²⁺ levels during the third phase of the experiment produced a complete cycle of manipulation. Plants initially deficient in Mn²⁺ with high IAAO and low growth recovered growth and declined in IAAO when shifted to control Mn²⁺ and then suffered severe inhibition of growth and toxicity symptoms when shifted to high Mn²⁺. In all cases changes in enzyme activity, growth, leaf abscission and similar symptoms were most strongly expressed in the youngest tissue or that with the greatest potential for growth during the interval of a particular treatment. Since total growth, IAAO, leaf abscission, internode length and similar symptoms were consistently manipulated in both directions (increase or decrease in intensity or degree) by raising or lowering Mn²⁺ levels in the plant culture medium, we conclude that there is a causal relationship between IAAO and these responses that involves destruction of auxin.     

Global and regional importance of the tropical peatland carbon pool

Accurate inventory of tropical peatland is important in order to (a) determine the magnitude of the carbon pool; (b) estimate the scale of transfers of peat‐derived greenhouse gases to the atmosphere resulting from land use change; and (c) support carbon emissions reduction policies. We review available information on tropical peatland area and thickness and calculate peat volume and carbon content in order to determine their best estimates and ranges of variation. Our best estimate of tropical peatland area is 441 025 km² (～11% of global peatland area) of which 247 778 km² (56%) is in Southeast Asia. We estimate the volume of tropical peat to be 1758 Gm³ (～18–25% of global peat volume) with 1359 Gm³ in Southeast Asia (77% of all tropical peat). This new assessment reveals a larger tropical peatland carbon pool than previous estimates, with a best estimate of 88.6 Gt (range 81.7–91.9 Gt) equal to 15–19% of the global peat carbon pool. Of this, 68.5 Gt (77%) is in Southeast Asia, equal to 11–14% of global peat carbon. A single country, Indonesia, has the largest share of tropical peat carbon (57.4 Gt, 65%), followed by Malaysia (9.1 Gt, 10%). These data are used to provide revised estimates for Indonesian and Malaysian forest soil carbon pools of 77 and 15 Gt, respectively, and total forest carbon pools (biomass plus soil) of 97 and 19 Gt. Peat carbon contributes 60% to the total forest soil carbon pool in Malaysia and 74% in Indonesia. These results emphasize the prominent global and regional roles played by the tropical peat carbon pool and the importance of including this pool in national and regional assessments of terrestrial carbon stocks and the prediction of peat‐derived greenhouse gas emissions.