Variability ofAspergillus niger after treatment withN-methyl-N′-nitro-N-nitrosoguanidine

N-Methyl-N'-nitro-N-nitrosoguanidine influences strongly the variability of Aspergillus niger MU 90, particularly on long-term treatment. The number of spores capable of growth decreases with the duration of treatment and the number of morphological and biochemical mutants considerably increases. The highest number of mutants with increased organic acid production was obtained after a mutagenic treatment when the number of surviving spores decreased below 1%.     

Glycogen metabolism in the placenta of streptozotocin diabetic rats.

Administration of STZ prior to mating, induced significant impairment in glycogen metabolism in term rat placentae. Glycogen retention was observed in the treated placentae, while glycogen synthetase activity was reduced. The glycogenolytic pathway seemed to proceed mainly through amyloglucosidase enzyme whose activity increased threefold. Glucose-6-phosphatase showed a moderate activation, mainly in the labyrinth zone, while phosphorylase was slightly inhibited. These changes were accompanied by a decrease in placental insulin levels. The possible defensive role played by the placenta in cases of maternal hyperglycemia was postulated.     

Calcium Ions Protect Beet Root Cell Membranes against Thermally Induced Changes

The initial heat induced increase in permeability of beet (Beta vulgaris L.) root cell membranes, as measured by betacyanin efflux, is reversible. The leakage of betacyanin stopped when tissue held for 90 min at 45°C was transferred to 27°C. Stronger heat treatments, 10 min at 60°C or 150 min at 45°C, resulted in a continuous release of betacyanin indicating an irreversible change in membrane structure. Calcium ions inhibited the heat induced betacyanin efflux only if this was due to a reversible increase in permeability.     

Ultrastructure of unique plasmodesmata in Selaginella willdenowii

Summary All meristematic cells of dorsal angle meristems of Selaginella willdenowii Baker cultured in vitro possessed expanded plasmodesmata, unlike the conventional plasmodesmata which were also found in these cells. Apical tissues of stems, roots and shoots from intact plant also possessed these structures though to a lesser degree than angle meristems. Root tips and stem apices had numerous conventional plasmodesmata in their walls. The expanded plasmodesmata, with their marked symmetry, represent a unique variation of plasmodesmatal structure.This study was partially supported by NSF Grant GB 37945 to Zachary S. Wochok.     

Glycosylation in vitro of an asparagine sequon catalysed by preparations of yeast cell membranes.

Preparations of yeast cell membranes can catalyse in vitro the N-acetyl-beta-D-glucosaminylation of the asparagine sequon at residues 34--36 of bovine pancreatic ribonuclease A. The relevant glycopeptides were isolated from tryptic hydrolysates of the glycosylated ribonuclease and analysed. The donor used was UDP-N-acetyl-D-glucosamine, although the mechanism of the transfer is unknown. Mn2+ ions at concentrations of 25 mM double the activity of the enzymic transfer.     

A procedure for decreasing the level of 2,3-bisphosphoglycerate in red cells in vitro

The physiological adaptation to anemia and other hypoxic states includes an increase in the level of 2,3-bisphosphoglycerate (2,3-DPG) in the red cell. We suggest that the high level of 2,3-DPG may have adverse effects in vivo. It has been found that red cells incubated with glycolate lose 2,3-DPG at a rapid rate relative to controls. ATP is stable. Net 2,3-DPG synthesis is observed after the glycolate is removed from the cells suggesting that they are not harmed. The effect appears to be specific for glycolate since lactate, glyoxylate, glycerate, acetate, and citrate were without effect. This procedure could be used to assess the effects of decreasing the 2,3-DPG level to normal in the erythrocytes of sickle cell and other anemias.     

The specificity of the effect of 2,4-D and NAA of the growth,micromorphology, and occurrence of starch in long-termNicotiana tabacum L. Cell strains

The characteristic micromorphology of the tobaoco cell strains, or its cyclic changes in the course of the subcultivation interval can be affected by auxin composition of the medium,i.e. by the application of either 2,4-D alone, or NAA, or their combination. On omitting one of the auxins, the over-all growth of the cultures is not substantially affeoted; however, the participation of various oell types, as well as the occurrenoe of starch grains are altered. The presenoe of 2,4-D alone results in an inhibition of starch occurrence, NAA alone causes a stimulation. There is no causal dependence of the occurrence or absence of starch grains on the stimulation of elongation (volume) growth, or, on the contrary, on cell division.     

Refractoriness of ovarian adenylate cyclase to continued hormonal stimulation.

Culture of preovulatory rat follicles with luteinizing hormone, follicle-stimulating hormone or prostaglandin E2 for 24 h reduced the subsequent response of adenylate cyclase to the homologous by 80, 50 and 90%, respectively; yet follicles refractory to luteinizing hormone fully responded to follicle-stimulating hormone responded to luteinizing hormone and prostaglandin E2, and those refractory to prostaglandin E2 could be stimulated by either gonadotropin. Desensitization of the adenylate cyclase system by luteinizing hormone was achieved by hormone concentrations of 0.8--2.0 mug/ml in the medium; a lower dose of luteinizing hormone (0.4 mug/ml), though effective in stimulating adenylate cyclase, did not induce refractoriness. Prostaglandin E2 caused partial refractoriness at dose levels of 0.1--0.25 mug/ml; higher dose levels were more effective. These findings suggest that continued exposure to the preovulatory follicle to elevated levels of hormones may cause perturbations in either the interaction between the hormone and its specific receptor or in a subsequent step essential for activation of adenylate cyclase.