Studies on the Endoplasmic Reticulum : IV. Its Form and Distribution during Mitosis in Cells of Onion Root Tip

Cells of onion and garlic root tips were examined under the electron and phase contrast microscopes after fixation in KMnO₄. Special attention was focused on the distribution and behavior of the endoplasmic reticulum (ER) during the several phases of mitosis. Slender profiles, recognized as sections through thin lamellar units of the ER (most prominent in KMnO₄-fixed material), are distributed more or less uniformly in the cytoplasm of interphase cells and show occasional continuity with the nuclear envelope. In late prophase the nuclear envelope breaks down and its remnants plus cytoplasmic elements of the ER, which are morphologically identical, surround the spindle in a zone from which mitochondria, etc., are excluded. During metaphase these ER elements persist and concentrate as two separate systems in the polar caps or zones of the spindle. At about this same time they begin to proliferate and to invade the ends of the spindle. The invading lamellar units form drape-like partitions between the anaphase chromosomes. In late anaphase, their advancing margins reach the middle zone of the spindle and begin to fray out. Finally, in telophase, while elements of the ER in the poles of the spindle coalesce around the chromosomes to form the new envelope, the advancing edges of those in the middle zone reticulate at the level of the equator to form a close lattice of tubular elements. Within this, which is identified as the phragmoplast, the earliest signs of the cell plate appear in the form of small vesicles. These subsequently grow and fuse to complete the separation of the two protoplasts. Other morphological units apparently participating in mitosis are described. Speculation is provided on the equal division or not of the nuclear envelope and the contribution the envelope fragments make to the ER of the new cell.     

Effect of Phenolic Acids and Esters on Respiration and Reproduction of Bacteria in Urine

Vanillic, syringic, gallic, and protocatechuic acids, methyl-p-hydroxybenzoate, and propyl-p-hydroxybenzoate generally inhibited respiration in vitro of Escherichia coli, Proteus vulgaris, Pseudomonas aeruginosa, and Aerobacter aerogenes in human urine. In the absence of any other available carbon source, certain of the phenolic compounds were utilized. Reproduction was generally suppressed in urine buffered to pH 7, 5.6, 4.5, and 4.0. The phenolic compounds were used in the range of 0.11 to 0.99 μmole/ml.     

Somaclonal variation in soybean plants regenerated from tissue culture

Callus cultures of soybean (Glycine max (L.) Merr.) genotypes PI 88788, PI 438489B, and cultivar Bedford were initiated in vitro from seedling explants consisting of the cotyledonary node plus epicotyl from germinated mature seed. Plants were regenerated from these callus cultures and subsequently evaluated for qualitative variation in three to four subsequent generations. Variant phenotypes observed that have not been previously reported from tissue culture include lanceolate leaves, leaf variegation (chimeral variegated plants), pod variegation on otherwise normal plants, and change in growth habit from indeterminate to determinate. The lanceolate leaf, chimeral variegated plant, and change from indeterminate to determinate growth habit characters were inherited through at least three generations (R₀-R₂), and segregation occurred in each generation. Pod variegation was inherited through the two generations tested thus far and segregation occurred in each generation. No variation was observed in control plants derived from normal seed. Variants appeared more frequently in regenerants from PI 88788 and PI 438489B than from Bedford. These results confirm and extend the finding that certain tissue culture techniques may be used to induce novel plant formation from somatic tissue of soybean.Missouri Agricultural Experiment Station, University of Missouri, Columbia, Missouri, USAMention of tradenames does not constitute a guarantee or warranty of the product by University of Missouri or USDA-ARS and does not imply their approval to the exclusion of other products.     

A new chondrodystrophy mutation in Japanese quail (Coturnix japonica)

A second form of hereditary chondrodystrophy (ch-2) has been discovered in a selected line of Japanese quail, Coturnix japonica. This form of chondrodystrophy is autosomal and recessive, characterized by an overall shortening and bending of the long bones of the wings and legs, slight dwarfing of the trunk, bulging of the eyes, flattening of the head, and a parrot beak. The shortened long bones vary in regard to the amount of bending from nearly straight to bends of up to 90 degrees in the midshaft region. In severe cases, the bend is evident as a protuberance of the skin. Affected embryos usually survive the 18-day incubation period. Several have hatched, but most survived no longer than 4 days after hatching. Only one female has survived long enough to lay eggs. Testcrosses indicated that this mutation is not allelic to micromelia.     

Sites of Tubulin Polymerization in PC 12 Cells

The site at which tubulin enters into polymer in the neuritic process is a very important datum in terms of our understanding of the mechanism of transport of the microtubular cytoskeleton out the axon. If the form of tubulin being transported out the axon is the microtubule, then assembly of tubulin into microtubules should occur at or near the cell body; if, however, the form of tubulin transported is free tubulin dimer, then assembly can occur at any free microtubule end out the neurite. We have injected a fluorescent analog of tubulin into differentiated PC 12 cells and used differential extraction protocols to extract free dimer but not microtubules. We have imaged these cells before and after extraction by low-light-level video fluorescence microscopy and have used image analysis to examine the sites of tubulin incorporation into polymer or other unextracted components as a function of time. We find that tubulin in the distal reaches of the neurite is found initially as monomer and that its appearance in the unextracted component occurs later. This pattern of appearance of fluorescent tubulin initially in the soluble fraction and later in the unextractable component is qualitatively similar to that reported by other workers for biotinylated tubulin, but we see a larger gap between the rates of appearance in soluble fraction and in polymer. Quantitative analysis of fluorescence intensities in the two compartments with distance out the neurite reveals substantial variation between different neurites: In some neurites, the pattern of variation of unextracted/total tubulin suggests that tubulin enters into the unextracted component primarily near the cell body and that this unextracted component moves out the neurite with time, and in other neurites it suggest that monomer adds into microtubule ends staggered out the neurite. In no case do we see a pattern suggesting that distal addition predominates. These analyses of fluorescence intensities in extracted and unextracted neurites suggest that both transport of polymerized microtubules and monomer addition onto staggered microtubule ends occur in PC12 neurites and that in individual neurites one or the other of these two behaviors may predominate.