Dichroism of Photosensitive Pigment in Rhabdoms of the Crayfish Orconectes

Microspectrophotometric measurements of isolated crayfish rhabdoms illuminated transversely show that their photosensitive absorption exhibits a dichroic ratio of 2 in situ. The major absorption axis matches the axial direction of the closely parallel microvilli comprising the receptor organelle. Since these microvilli are regularly oriented transversely in about 24 layers, with the axes of the microvilli at 90° in alternate layers, transverse illumination of a properly oriented rhabdom displays alternate dichroic and isotropic bands. Because all the microvilli from any one cell share the same orientation, the layers of microvilli constitute two sets of orthogonal polarization analyzers when illuminated along the normal visual axis. Furthermore, since the dichroic ratio is 2 and transverse absorption in isotropic bands is the same as that in the minor absorbing axis of dichroic bands, the simplest explanation of the analyzer action is that the absorbing dipoles of the chromophores, as in rod and cone outer segments, lie parallel to the membrane surface but are otherwise randomly oriented. The rhabdom's functional dichroism thus arises from its specific fine structural geometry.     

Quantitative succinate-dehydrogenase histochemistry

Summary In enzyme histochemistry formazan production can be used as a measure for oxidative enzyme activity. The formazan deposits can be measured quantitatively per cell with a scanning and integrating microspectrophotometer. Optimal conditions are described for the estimation of histochemical succinate dehydrogenase activity in sections of fish bodymusculature and mouse soleus and plantaris muscle. It is shown that when proper measuring conditions are choosen a ditetrazolium salt (TNBT) can be used in quantitative enzyme histochemistry and that the optimal conditions for the histochemical succinate dehydrogenase reaction in muscle fibres of fish and mouse muscle are somewhat different for these two species. The differences in pH, temperature and succinate sensitivity are the most prominent.     

Effect of maternal diet on offspring coping styles in rodents: a systematic review and meta‐analysis

Maternal nutrition can have long‐term effects on offspring morphology, physiology and behaviours. However, it is unclear whether mothers ‘program’ offspring behavioural coping strategy (proactive/reactive) according to the predicted nutritional quality of their future environment. We conducted a systematic review on this topic and meta‐analytically synthesized relevant experimental data on mice and rats (46 studies). We included data from experiments where dams were subjected to caloric restriction, protein restriction or overfeeding around gestation and subsequently measured offspring activity, exploration, or anxiety. Overall, little evidence existed for effects of maternal nutrition on the three investigated behavioural traits. The high heterogeneity observed in the data set suggests that maternal programming may sometimes occur. However, because offspring had access to a balanced diet before testing, behaviours may have been reprogrammed. Our results may indicate that reprogrammed behaviours could ameliorate negative effects associated with sub‐optimal nutrition in early life. Further, our systematic review revealed clear knowledge gaps and fruitful future research avenues.     

Physiological differences and changes in global DNA methylation levels in <Emphasis Type="Italic">Agave angustifolia</Emphasis> Haw. albino variant somaclones during the micropropagation process

Key message

Global DNA methylation changes caused by in vitro conditions are associated with the subculturing and phenotypic variation in Agave angustifolia Haw.

Abstract

While the relationship between the development of albinism and in vitro culture is well documented, the role of epigenetic processes in this development leaves some important questions unanswered. During the micropropagation of Agave angustifolia Haw., we found three different phenotypes, green (G), variegated (V) and albino (A). To understand the physiological and epigenetic differences among the somaclones, we analyzed several morphophysiological parameters and changes in the DNA methylation patterns in the three phenotypes during their in vitro development. We found that under in vitro conditions, the V plantlets maintained their CAM photosynthetic capacity, while the A variant showed no pigments and lost its CAM photosynthetic ability. Epigenetic analysis revealed that global DNA methylation increased in the G phenotype during the first two subcultures. However, after that time, DNA methylation levels declined. This hypomethylation correlated with the appearance of V shoots in the G plantlets. A similar correlation occurred in the V phenotype, where an increase of 2 % in the global DNA methylation levels was correlated with the generation of A shoots in the V plantlets. This suggests that an “epigenetic stress memory” during in vitro conditions causes a chromatin shift that favors the generation of variegated and albino shoots.

     

Evaluation of quick disintegrating calcium carbonate tablets

The purpose of this investigation was to develop a rapidly disintegrating calcium carbonate (CC) tablet by direct compression and compare it with commercially available calcium tablets. CC tablets were formulated on a Carver press using 3 different forms of CC direct compressed granules (Cal-Carb 4450, Cal-Carb 4457, and Cal-Carb 4462). The breaking strength was measured using a Stokes-Monsanto hardness tester. The disintegration and dissolution properties of the tablets were studied using USP methodology. The calcium concentration was determined by an atomic absorption spectrophotometer. Scanning electron microscopy was used to evaluate the surface topography of the granules and tablets. Breaking strength of Cal-Carb 4450, Cal-Carb 4457, and Cal-Carb 4462 tablets was in the range of 7.2 to 7.7 kg, as compared with a hardness of 6.2 kg and 10 kg for the commercially available calcium tablets Citracal and Tums, respectively. The disintegration time for the tablets presented in the order earlier was 4.1, 2.1, 1.9, 2.9, and 9.7 minutes, respectively. The dissolution studies showed that all formulations released 100% of the elemental calcium in simulated gastric fluid in less than 20 minutes. In summary, this study clearly demonstrated that quick disintegrating CC tablets can be formulated without expensive effervescence technology.     

Species evenness and productivity in experimental plant communities

In nature, plant biomass is not evenly distributed across species, and naturally uncommon species may differ from common species in the probability of loss from the community. Understanding relationships between evenness and productivity is therefore critical to understanding changes in ecosystem functioning as species are lost from communities. We examined data from a large multi-site grassland experiment (BIODEPTH) for relationships between evenness of species composition (proportional abundance of biomass) and total biomass of communities. For plots which started with the same and even species composition, but which diverged in evenness over time, those with lower evenness had a significantly greater biomass. The relationship between evenness and biomass across all plots was also negative. However, for communities where the most common species represented one of the three largest species in monoculture at that site (inclusion of a large dominant species), the relationship was neutral. Path analyses indicated that three paths contributed to this negative relationship. First, higher species richness decreased evenness, but increased biomass (primarily through an increase in maximum plant size). Contrary to predictions, maximum plant size had either no effect on evenness, or a positive effect (in year 3 plots with a large dominant species), thereby reducing this relationship. In year 2, large variation among species in plant size (as measured in monoculture) both decreased evenness and increased biomass, thus increasing the strength of the negative relationship between evenness and biomass. However, the former effect was only found in plots with a large dominant species, the latter only in plots without a large dominant species. When species richness, maximum plant size, and variation in size were accounted for, in year 2 evenness positively affected biomass in plots that included a large dominant species. Our results are consistent with the view that naturally uncommon species may be unaffected by (or even benefit from) the presence of a large naturally common species, and that uncommon plants may have little ability to increase productivity in the absence of such a species. We conclude that the observed negative relationship between evenness and biomass resulted from multiple direct and indirect effects, the relative strength of which depended in part on the presence of large dominant species.     

Cooperative Hunting and its Relationship to Foraging Success and Prey Size in an Avian Predator

Aplomado falcons (Falco femoralis) often hunt in pairs when chasing birds; 29% of 349 hunts observed in eastern Mexico involved mated pairs of falcons simultaneously chasing the same prey animal; and 66% of 100 hunts of birds were tandem pursuits. Although true cooperative hunting is uncommon in birds of prey, hunts by pairs of Aplomado falcons consistently showed signs of cooperative behavior such as use of a simple coordinative signal, and some division of labor between participating individuals. Pairs were more than twice as successful as solo falcons hunting birds (44% vs. 19%), however, there was no evidence that cooperative hunting increased the range of feasible prey sizes. The frequent use of cooperative foraging in this and similar species may relate to necessities of efficient nest defense, and food and nest procurement in savannas inhabited by a diversity of nest-site predators.     

Synthesis of 1α,25-dihydroxyvitamin D2, its 24 epimer and related isomers,and their binding affinity for the 1,25-dihydroxyvitamin D3 receptor

The synthesis of 1α-25-dihydroxyvitamin D₂ and of several stereoisomers (5,6-trans and 1β-hydroxy isomers and the 24R-epimers of these compounds) was reported. Synthesis was accomplished from two different starting materials, 25-hydroxyvitamin D₂ and 25,25-ethylenedioxy-26-norvitamin D₂, and involved C-1-hydroxylation via 3,5-cyclovitamin D intermediates. Synthetic 1α,25-dihydroxyvitamin D₂ was found to be identical with the biologically generated natural product. An analysis of the binding affinity of the synthetic products for the 1α,25-dihydroxyvitamin D₃ receptor protein showed that isomerization of the 5,6 double bond from cis to trans, or epimerization of the 24-methyl group from S to R, reduced ligand binding to the receptor only slightly, while both changes together led to a 100-fold reduction of binding affinity. The epimerization of the 1-hydroxy function from 1α to 1β attenuated binding dramatically (ca. 1000-fold).