Allometric growth and adaptive value of exaggerated body parts in the larvae of Gratiana spadicea (Klug) (Coleoptera: Chrysomelidae)

1. Larvae of tortoise beetles present exaggerated body parts in association with an abdominal shield, which is made of faeces and exuviae that are deposited on the urogomphi throughout ontogeny. Growth trajectories and scaling relationships of these functional structures associated with the shield, if any, are unknown. 2. This study of Gratiana spadicea first tested, under field conditions, whether there is adaptive value associated with the shield regarding protection against predation and sunlight. Then, under laboratory conditions, the growth trajectory and allometric relationships among body parts were investigated, including scoli, individual and apparent furcae, and shield. The influence of food deprivation on the development of these structures was also determined. 3. Findings from previous studies were confirmed, suggesting that the adaptive value assigned to the shield is related to protection against predators. The present study demonstrated for the first time that the shield acts as a parasol in cassidines, decreasing the exposure of their larval body to sunlight. The scoli and apparent furca are exaggerated structures of G. spadicea, the development of which involves allometric growth and greater energetic investment (positive allometry) during ontogeny. There was proportionally less energetic investment for somatic construction of individual furca (negative allometry) due to the accumulation of the exuviae. 4. The possible consequences, in terms of developmental costs and survivorship benefits associated with the evolution of such exaggerated structures, are discussed.     

Population cytogenetics of aphidicolin-induced fragile sites

Summary Chromosome fragile sites are inducible by aphidicolin in cultured human lymphocytes. To assess the frequency and distribution of these common fragile sites in the general population, a cytogenetic survey was performed on 126 subjects, 59 males and 67 females, whose age ranged from 1 day to 72 years. Common fragile sites, induced by aphidicolin, were widespread and showed a remarkably different sensitivity among individuals; age influenced the overall frequency of fragile sites. Moreover, both age and sex seemed to modulate the expression of specific fragile sites. In our population, the most common fragile sites were: 3p14, 16q23, Xp22, 6q26, 1p31, 4q31, 1p22, 7q22, 2q33, 3q27, 2q31, 7q32, 14q24, 10q22, 5q31, 2q37, 6p21.     

The influence of poly(ethylene glycol) 6000 on spermine-induced aggregation of liposomes.

Poly(ethylene glycol) 6000 affected the aggregation of mixed liposomes induced by spermine. It lowered the concentration of spermine causing 50% maximal aggregation, accelerated the rate and increased the extent of aggregation. The effect was inversely proportional to the density of the acidic phospholipid in the vesicles. These effects were not due either to poly(ethylene glycol) 6000-induced permanent structural modification of the liposome or increased binding of spermine to the vesicles. These findings are discussed in relation to a decreased hydration force caused by the ability of poly(ethylene glycol) 6000 to alter the water of hydration of the phospholipid polar groups in the liposome.     

Diurnal rhythmicity of mammalian DNA-dependent RNA polymerase activities I and II: dependence on food intake

Diurnal variations of DNA-dependent RNA polymerase activities I and II have been found in rats maintained under controlled feeding schedules. RNA polymerase I has two peaks of activity in a 24-hours cycle: one 6 hours after the onset of dark period and a second one in the middle of the light period. Polymerase II shows only one peak coinciding with the first one of polymerase I. These diurnal fluctuations are not present in the liver of rats denied food on the day of the experiment. Both polymerases do not exibit different optima for divalent metal ions and ionic strength in the different feeding conditions studied.     

Thaimycins,new anthelmintic and antiprotozoal antibiotics produced by Streptomyces michiganensis var. amylolyticus var. nova

Summary A new microorganism, isolated in our laboratories and identified as Streptomyces michiganensis var. amylolyticus var. nova is described.Thaimycins can be obtained by submerged fermentation of this microorganism on a suitable culture medium.Three new related compounds, thaimycins A, B and C have been obtained and characterized by their physical and chemical properties.Data on the antiprotozoal and anthelmintic activities in vitro as well as in vivo are reported.     

Lipid Peroxidation. Definition of Experimental Conditions for Selective Study of the Propagation and Termination Phases

To find experimental conditions to selectively study the propagation phase of lipoperoxidation we studied the lipoperoxidation, catalyzed by FeCl₂, of liposomes in a buffering condition where Fe²⁺ autoxidation and oxygen active species generation does not occur. Liposomes from egg yolk phosphatidylcholine. prepared by vortex mixing, do not oxidize Fe²⁺: on the contrary they oxidize Fe²⁺ when prepared by ultrasonic irradiation. Dimyristoyl phosphatidylcholine liposomes prepared by ultrasonic irradiation do not oxidize Fe²⁺. During sonication polyunsaturated fatty acid residues autoxidize and lipid hydroperoxides (LOOH) are generated. Only when LOOH are present in the liposimes Fe²⁺ oxidizes and its rate of oxidation depends on the amount of LOOH in the assay. The reaction results in the generation of both LOOH and thiobarbituric acid reactive material (TBAR): it is inhibited by butylated hydroxytoluene and has a acidic pH optimum; it is not inhibited by catalase and OH' scavengers. The reaction studied. thus, appears to be the chain branching and propagation phase of lipoperoxidation. When we studied the dependence of Fe²⁺ oxidation, LOOH and TBAR generation on FeCl₂ concentration, we observed that at high FeCl₂ concentrations the termination phase of lipoperoxidation was prevalent. Thus. by selecting the appropriate FeCl₂ concentration the proposed experimental system allows study of either the propagation or the termination phase of lipoperoxidation.     

Biochemical and immunological studies of three genetic variants of 3-phosphoglycerate kinase 2 from the mouse

Three electrophoretic variants of 3-phosphoglycerate kinase 2 (PGK-2A, PGK-2B, and PGK-2C) were purified from DBA/2J, C3H/HeJ, and C57L/J mice, respectively. PGK-2C exhibits only 2% of the specific activity of PGK-2A and PGK-2B in the reaction leading to the formation of 1,3-diphosphoglycerate. Compared to PGK-2A and PGK-2B, PGK-2C exhibits broader coenzyme specificity and lower K_ms for substrate and coenzymes. Incubation at 45C revealed that PGK-2B is more heat stable than either PGK-2A or PGK-2C. Enzyme immunoinactivation and double immunodiffusion studies showed that mice carrying any one of these three PGK-2 alleles have similar amounts of proteins for PGK-1 and PGK-2 in testes. The results of these studies suggest that low PGK-2C activity in C57L/J mice is a result of a structural rather than a regulatory gene mutation.