La dormance embryonnaire chez Taxus baccata: Influence de la composition du milieu liquide sur I'induction de la germination Par

Embryo dormancy of Taxus baccata var. fastigiata is eliminated when cultured continuously in nutritive liquid medium. An equivalent percentage of germination is obtained when the embryos are transferred to agar medium after 8 days of liquid culture. There is no morphological development of the embryo during the period in the liquid medium. But we have ascertained that water-soluble germination inhibitors present in the embryo are leached out into the medium, permitting germination. Germination is totally absent when the embryos are cultured continuously in distilled water, alone or with minerals; incidental in sucrose solution; and maximal when the medium contains sucrose and Ca²⁺ or K⁺ ions. The extent of germination on agar medium depends upon the composition of the liquid medium in which the embryos are cultured for the initial 8 days. But this preliminary culture in the liquid medium does not always remove the endogenous inhibitors, irrespective of its composition. This can be achieved only in the presence of sucrose; and this process can be made more effective by the addition of Ca²⁺ ions.     

Field catches of Oxythyrea cinctella using visual and olfactory cues

Diurnal flower‐visiting scarabs (Coleoptera: Scarabaeidae, Cetoniinae) use visual and olfactory stimuli when locating possible feeding sites. In field trapping experiments in Turkey, testing different colours and floral volatile compounds, a combination of fluorescent yellow colour and a blend of 2‐phenylethanol and (±)‐lavandulol leads to the highest number of Oxythyrea cinctella (Schaum) being caught. Trap catches of O. cinctella with respect to the individually presented visual or olfactory cues are significantly lower than to a combination of the two. The closely‐related O. funesta, a sibling species in the Oxythyrea genus, is also known to be caught by the same colour‐volatile combination. When applied together in a high capture‐capacity trap, the fluorescent yellow colour and the binary floral odour blend may provide a suitable means of monitoring population changes of O. cinctella, which indicates their potential use in agriculture.     

Biomechanical capabilities influence postural control strategies in the cat hindlimb

During postural responses to perturbations, horizontal plane forces generated by the cat hindlimb are stereotypically directed either towards or away from the animal's center of mass, independent of perturbation direction. We used a static, three-dimensional musculoskeletal model of the hindlimb to investigate possible biomechanical determinants of this "force constraint strategy." We hypothesized that directions in which the hindlimb can produce large forces are preferentially used in postural control. We computed feasible force sets (FFSs) based on hindlimb configurations of three cats during postural equilibrium tasks and compared them to horizontal plane postural force directions. The grand mean FFS was bimodal, with maxima near the posterior-anterior axis (-86+/-8 degrees and 71+/-4 degrees ), and minima near the medial-lateral axis (177+/-8 degrees and 8+/-8 degrees ). Experimental postural force directions clustered near both maxima; there were no medial postural forces near the absolute minimum. However, the medians of the anterior and posterior postural force direction histograms in the right hindlimb were rotated counter-clockwise from the FFS maxima (p<0.05; Wilcoxon signed-rank test). Because the posterior-anterior alignment of the FFS is consistent with a hindlimb structure optimized for locomotion, we conclude that the biomechanical capabilities of the hindlimb strongly influence, but do not uniquely determine the force directions observed in the force constraint strategy. Forces used in postural control may reflect a balance between a neural preference for using forces in the directions of large feasible forces and other criteria, such as the stabilization of the center of mass, and muscular coordination strategies.     

Conversion of Phosphatidyl Choline to Phosphatidic Acid in Freeze Injured Rye and Wheat Cultivars

The effect of exposure to freezing temperature (?15°C) on leaf phospholipid composition of hardened rye (Secale cereale L.) and hardened wheat cultivars (‘Miranovskaja 808’, ‘Bezostaja 1’, ‘Short Mexican’ and ‘Penjamo 62’), which differ in their resistance to frost, was investigated. Hardening took place under natural conditions. All the seedlings attained an equal level of linolenic acid in their leaves during hardening. Exposure to freezing temperatures resulted in a loss of phosphatidyl choline and accumulation of phosphatidic acid in the leaves. The ratio of phosphatidic acid to phosphatidyl choline, but not the level of poly-unsaturated fatty acids in the leaves, was related to their ability to survive at low temperatures. As freezing injury is caused by the formation of ice crystals in both extra- and intracellular space, it is probable that the plasma membranes of the investigated cultivars differed with respect to their water permeability. It is concluded that the plants, depending on the degree of their resistance to cold, produce an unknown substance of lipidic nature upon exposure to cold, with the aid of which they adjust the transitional state of their membranes to the prevailing temperature and, at the same time, facilitate the efflux of water from the cells.     

Differential accessibility of DNA in extended and condensed chromatin to pancreatic DNase I

Pancreatic DNase I has been used to study the interaction between DNA and chromosomal proteins in extended and condensed chromatin fractions isolated from mouse and Chinese hamster livers. It was found that DNase digests extended chromatin at a faster rate than condensed chromatin, and the evidence suggests that the chromosomal proteins are more tightly complexed to the DNA in condensed than in extended chromatin. This difference in DNA-protein interaction in extended and condensed chromatin may be related to the functional difference which characterizes these fractions, and might be one of the factors underlying the production of bands on metaphase chromosomes.     

Fluorescence microscopy of mycobacteria in pleural effusions

The diagnostic advantage of fluorescence microscopy (FM) of Papanicolaou-stained cytological specimens obtained by bronchoscopy has been described previously. This study was designed to evaluate the method's diagnostic benefit in cytological preparations of pleural effusions in cases of active pulmonary tuberculosis. In contrast to bronchial material there is no advantage in cytological evaluation of pleural effusions by FM.