DNA base composition of Microcyclus species and organisms of similar morphology

Summary From studies of the DNA base composition of Microcyclus species, it is concluded that the genus is to be regarded as a taxonomically heterogeneous group. This agrees with morphological observations of the different species.     

The interaction of aflatoxins with purines and purine nucleosides

From measurements of thermal hyperchromicity and the behaviour of an aflatoxin-DNA mixture on a Sephadex column it was concluded that aflatoxin B(1) is capable of weak binding to single-stranded DNA. The interactions of the aflatoxins (B(1), G(1) and G(2)) with nucleosides result in difference spectra and suggest that the purine bases and the amino group play a role in the binding of all the aflatoxins to DNA.     

Golgi apparatus mediated polysaccharide secretion by outer root cap cells of Zea mays

Summary In the outer cap cells of roots of Zea mays, secretion is accompanied by hypertrophy of dictyosome cisternae with formation of large secretory vesicles. Vesicle contents are subsequently released from the protoplast by fusion of the vesicle membrane with the plasma membrane. The secreted material, a highly hydrated polysaccharide, was localized intracellularly by the periodic acid-Schiff reaction. Under appropriate conditions, the product moves outward through the cell wall after discharge from the protoplast, and appears as a droplet adhering to the root tip. Under conditions where the secretory product accumulates at the inner wall surfaces, no external droplet is formed.The secretory activity has an active phase that is sensitive to metabolic inhibitors and influenced by temperature (Q₁₀>2), and a passive phase that is independent of temperature, insensitive to metabolic inhibitors but sensitive to osmotic agents. The active phase is characterized by a temperature-independent periodicity (3 hours). Sucrose supplied to the growth medium increases the amount of polysaccharide secreted. Polysaccharide synthesis, segregation into vesicles, and discharge from the protoplast are assumed to require active metabolism; the step involving extrusion of polysaccharide through the cell wall region appears to be a passive process influenced by the degree of hydration of the polysaccharide and by cell turgor.Purdue University Agricultural Experiment Station Journal Paper No. 2967; Charles F. Kettering Research Laboratory Contribution No. 261.     

The Endoplasmic Reticulum and the Golgi Structures in Maize Root Cells

Maize root tips were fixed in potassium permanganate, embedded in epoxy resin, sectioned to show silver interference color, and studied with the electron microscope. All the cells were seen to contain an endoplasmic reticulum and apparently independent Golgi structures. The endoplasmic reticulum is demonstrated as a membrane-bounded, vesicular structure comparable in many aspects to that of several types of animal cells. With the treatment used here the membranes appear smooth surfaced. The endoplasmic reticulum is continuous with the nuclear envelope and, by contact at least, with structures passing through the cell wall. The nuclear envelope is characterized by discontinuities, as previously reported for animal cells. The reticula of adjacent cells seem to be in contact at or through the plasmodesmata. Because of these contacts the endoplasmic reticulum of a given cell appears to be part of an intercellular system. The Golgi structures appear as stacks of platelet-vesicles which apparently may, under certain conditions, produce small vesicles around their edges. Their form changes markedly with development of the cell.