Root Rot of Trifolium subterraneum Induced by Fusarium solani

A fungus disease of Trifolium subterraneum, previously unknown in South Africa, was identified as Fusarium root rot caused by F. solani (Mart.) Sacc. Diseased plants were severely stunted. The characteristic internal root discolouration observed in the field, is described. The disease occurred mainly between Swellendam and Humansdorp in the southern and south-eastern Cape Province. The subterranean clover fields inspected were between 95 and 100 % infected with the root rot disease. T. repens and T. pratense were also susceptible.     

Dissociation of copulation from ovulation in pregnant rabbits

Experiments were designed to determine why copulation in the pregnant rabbit does not terminate pregnancy while treatment with ovulatory doses of luteinizing hormone (LH) human chorionic gonadotropin (hCG) or luteinizing hormone-releasing hormone (LHRH) is known to do so. Pregnant rabbits (Day 8) were mated or were injected with hCG (25 IU/doe) or LHRH (1, 10 micrograms/kg). Serial blood samples were collected over the next 72 h and analyzed for content of LH, follicle-stimulating hormone (FSH) and progesterone. At sacrifice, uteri and ovaries from these animals were examined for viability of the embryos and for signs of recent ovulation. Injection of hCG or LHRH into pregnant animals led to ovulation and to patterns of LH, FSH and progesterone secretion like those which precede ovulation in estrous rabbits. However, mating the pregnant does did not lead to ovulation or to any changes in the circulating hormones. To investigate whether the elevated levels of progesterone during pregnancy were responsible for the dissociation of coitus from ovulation, nonpregnant rabbits were injected with progesterone (2 mg/kg) and then mated or injected with hCG or LHRH. In virtually every respect, the numbers of ovulations and the patterns of hormone secretion in the progesterone-treated, nonpregnant rabbits mimicked those observed in the 8-day pregnant animals; injection of hCG or LHRH caused ovulation and hormonal surges while hCG caused ovulation only. Mating did not lead to ovulation or any change in blood levels of LH, FSH or progesterone. Taken together, the results show that the elevated circulating levels of progesterone, characteristic of pregnancy, are probably responsible for the dissociation of copulation from gonadotropin release in pregnant rabbits.     

The processing and collaborative assay of a reference endotoxin

A preparation of Escherichia coli bacterial endotoxin, the latest of successive lots drawn from bulk material which has been studied in laboratory tests and in animals and humans for suitability as a reference endotoxin, has been filled and lyophilized in a large number of vials. Details of its characterization, including stability studies, are given. A collaborative assay was conducted by 14 laboratories using gelation end-points with Limulus amebocyte lysates. Approximate continuity of the unit of potency with the existing national unit was achieved. The lot was made from the single final bulk but had to be freeze-dried in five sublimators. An assessment was therefore made for possible heterogeneity. The results indicate that the lot can be used as a large homogeneous quantity. The advantages of using it widely as a standard for endotoxins are discussed.     

CYTOKINESIS AND PLASMODESMATA IN ULOTHRIX1

Cytokinesis essentially similar to that of vascular plants occurs in Ulothrix, an unbranched filamentous green alga. Plasmodesmata, similar to those of vascular plants, but different from those of many other algae, are also present. Cell plate formation and plasmodesmata also occur in Stigeoclonium, a branched green alga.     

Inhibition of Transformation of Bacillus subtilis by Heavy Metals

Mercuric ions, as well as organomercuric ions and cadmium ions, can inhibit deoxyribonucleic acid-mediated transformation in Bacillus subtilis 168 without decreasing the viability of the total population. Differences in the inhibition of transformation by mercuric ions are identifiable on a temporal and concentration dependence basis. Sensitivity to low concentrations (9.2 x 10(-8) M) appears early in the uptake of deoxyribonucleic acid before the transformed markers have become insensitive to deoxyribonuclease. Resistance to "low concentrations" of Hg(2+) is kinetically indistinguishable from the requirement for magnesium in the transformation process. This inactivation is not reversed by the mercury-binding compound glutathione. Sensitivity to mercuric ions at a higher concentration (5.52 x 10(-7) M) occurs after the donor deoxyribonucleic acid has become insensitive to deoxyribonuclease. These complex interactions between mercuric ions and the process of transformation are discussed.     

Application of mobilities in electromagnetic fields to the determination of kinetic parameters

Changes in electrophoretic and/or electromagnetophoretic mobilities during the course of biochemical reactions are related to first order rate constants of those reactions. By linearization of the mobility/reaction-coordinate relations, a method for the determination of rate constants is suggested, an assessment being made of some likely advantages and limitations of this approach to kinetic problems.     

Tryptophan Biosynthesis in Cell Cultures of Nicotiana tabacum

Some of the general features of the pathway for l-tryptophan biosynthesis in cell cultures of Nicotiana tabccum var. Wisc. 38 have been investigated. The results of both isotope competition and direct-labeling experiments show that shikimic acid, anthranilic acid, indoleglycerol phosphate, and indole can serve as precursors to l-tryptophan in these cells, indicating that, in terms of its biochemical intermediates, the pathway is similar to that described for the bacteria and fungi.     

Temporal expression of different pathways of 1-arginine metabolism in healing wounds

Arginine can be metabolized by inflammatory cells through at least two pathways. One is an oxidative l-arginine deiminase (OAD) that results in the formation of citrulline and reactive nitrogen intermediates. The other is arginase, which determines the production of ornithine and urea. The temporal expression of these pathways in an experimental wound model (s.c. implanted polyvinyl alcohol sponges in the rat) was investigated by examining the concentrations of amino acids and of nitrite in fluids obtained from the sponges 6 h to 15 day after implantation. These analyses revealed two distinct periods during which the arginine concentration in the fluids was markedly below plasma levels. During the early period (less than 3 days after sponge implantation) wound fluid contained more citrulline and nitrite than at any other time, suggesting OAD activity. In contrast, ornithine accumulated in the fluids during the late decrease in arginine concentration that extended beyond day 3, during which time the wound fluid also contained a high arginase activity. This time-dependent expression of different pathways of arginine metabolism in wounds was confirmed in sponge cultures containing [guanido-14C]-l-arginine. Cells contained in sponges harvested less than 48 h after implantation metabolized labeled arginine mainly to labeled citrulline, whereas labeled urea was produced during culture of sponges harvested after this time. The low arginine content of wound fluid did not appear to be rate limiting for the expression of OAD in late sponges because no OAD activity was evidenced when 4 mM arginine was added to the cultures. These results indicate that the OAD pathway is expressed in this model predominantly during the early, polymorphonuclear leukocyte-predominant, phase of repair. At this time, the reactive nitrogen intermediates resulting from the metabolism of arginine may mediate some of the events characteristic of early inflammation, including microbiostasis, vasodilation, and inhibition/reversal of platelet aggregation. In turn, the late suppression of this pathway and the catabolism of arginine through arginase may promote macrophage function within wounds.