The genus Argemone. I. Cytogenetic relationships between diploid species

Cytogenetic investigations of 5 diploid Argemone species and their hybrids were undertaken. Correlative informations on the morphology, cytology, crossability and interfertility have been secured to understand the mechanism crossability and interfertility have been secured to understand the mechanism of speciation in the genus.All species studied possess 14 bivalents, normal meiosis and perfect pollen and seed fertility.Statistical comparisons regarding two meiotic metrics (frequency of ring bivalents; chiasma frequency) between some of the species revealed significant differences.Crosses were attempted in all species combinations, and hybrids were obtained in several. On the basis of pollen and seed fertility these were classified as fortile (mexicana × subfusiformis; subjusiformis × mexicana f. leiocarpa) and semifertile (mexicana × albiflora; subjusiformis × platyceras; mexicana f. leiocarpa × platyceras) hybrids. F₁'s are intermediate, qualitatively they exhibit heterosis.Meiosis was analysed in all hybrids (pachynema; M-I, A-I) and several metrics e.g. ring bivalent frequency, chiasma frequency were taken as indices of genome affinity.It is suggested that mexicana, mexicana f. leiocarpa and subfusiformis are taxonomically close and display only allelic differentiation: albiflora and platyceras are structurally distinct from each other. Several structural changes e.g. duplications, inversions, translocations etc. were involved in their differentiation.The role of isolation barriers in maintaining species differentiation is discussed.     

AMINO ACID TRANSPORT IN NITZSCHIA OVALIS ARNOTT1,2

The marine diatom Nitzschia ovalis possesses at, least 3 amino acid uptake systems, specific for transport of acidic, polybasic, and, neutral amino acids. Maximum uptake velocity (V_max) for each, site is inversely related to the nitrogen content of the cell, and to the nitrogen available in the culture medium. Transport, of polybasic amino acids occurs throughout the course of growth in batch, culture, but the V_max increases dramatically as the culture ages and nitrogen/cell reaches a low value. K_s does not, change significantly. Acidic and neutral amino acids are taken up only by cells harvested from nitrogen-poor culture. It appears that amino acid transport is repressed by high concentrations of nitrogen in the medium. Under natural conditions, where nitrogen concentrations are low, the contribution of amino acid uptake to the nitrogen economy of Nitzschia populations may be significant.     

Polymer concentration effects on helix–coil transition widths

A theoretical study of effects of excluded volume intermolecular interactions on the sharpness of helix–coil transitions in solutions of polyamino acids or simple proteins indicates that the transition width may vary appreciably as a function of polymer concentration. The analysis is based on a second virial approximation for the excess free energy of mixing of a solution of polymers of varying degrees of helicity. The virial coefficients involved are roughly estimated on the basis of gross polymer geometry. For large N (degree of polymerization) the transition is found, typically to sharpen with increasing concentration, becoming second order and then first order at sufficiently high concentrations. The critical polymer concentration is found to be roughly of the order N^?1.2 ??₀^?1 for an “all or none” model and of order σ^1/2 N^?0.2 ??₀^?1 for a model with continuously variable degree of helicity (??₀ is the volume of a single helical molecule and σ^1/2 the normalized statistical weight of a helix–coil interface). In the second case for N ～ 10³ and σ ～ 10^?2–10^?4, the predicted critical concentration is in the range 10^?1–10^?3 g/cm.³ Comparison is made with experiments on solutions of poly(γ-benzyl-L glutamate).     

Electrical Sizing of Particles in Suspensions: III. Rigid Spheroids and Red Blood Cells

The processes involved during the passage of a suspended particle through a small cylindrical orifice across which exists an electric field are investigated experimentally for an approximate prolate spheroid in the form of two tangent, rigid spheres (ragweed pollen particles) and for fresh, human red blood cells. Oscillograms of current pulses produced by both types of particles are presented and discussed in terms of particle shape and orientation and the effects of the hydrodynamic field. It is concluded that all the particles enter the orifice with their major axes aligned parallel to the orifice axis (electric field), but that during their passage some are rotated by the hydrodynamic field. Cells with their equatorial plane perpendicular to a radius of the orifice change their orientation with respect to the electric field as they are rotated, the others do not; only in the former case is there any deformation. It is shown that the bimodal or skewed size distributions can be explained on this basis, and that size (shape factor × volume) is actually a normally distributed variable (P > 95%). The average size of samples from 10 healthy adults was found to be 102.7 μ³ with a coefficient of variation of 1.8%. For a volume of 87 μ³, this corresponds to a shape factor of 1.18, an axial ratio (assuming a perfect oblate spheroid) of 0.26, and an equivalent major axis of 8.6 μ. The effect of high electric fields on red cell size distributions is mentioned.     

An improved treatment of data for estimation of molecular weights by sephadex gel filtration

A method for analysis of elution data of proteins, obtained from Sephadex gel filtration experiments, is described. The relevant elution data from seven different proteins, with known molecular weights and Stoke's radii, were fitted into various equations relating elution parameters and molecular size parameters. It was observed that polynomial relationships represented elution data for proteins with a much greater degree of precision than linear equations. The validity of this procedure was also checked by analysing gel filtration data available in the literature and it was concluded that a better fit was obtained using polynomial relationships, provided a sufficiently large number of experimental points were available for numerical analysis. Using this method, values of 320,000 ± 7000 for the molecular weight, and (60 ± 0.4) × 10^?8 cm for the Stoke's radius of Neurospora NAD-specific glutamate dehydrogenase were calculated.