The Influence of Temperature on Nitrate Reductase Activity of Agrostis palustris and Cynodon dactylon

The influence of temperature was studied in relation to nitrate reductase activity of creeping bentgrass (Agrostis palustris Huds. cv. ‘Toronto’) a cool season grass and bermudagrass (Cynodon dactylon L. cv. ‘Tifgreen’) a warm season grass. Maximum nitrate reductase activity of both species occurred at 20°C. The nitrate reductase level in bentgrass leaves was reduced when grown at 35°C while bermudagrass leaves were relatively unaffected. The activity per se of the bentgrass enzyme preparation was inhibited rather than synthesis of the enzyme.     

RNA-dependent DNA Polymerase in Human Lymphocytes during Gene Activation by Phytohaemagglutinin

RNA-DEPENDENT. DNA polymerase an activity initially thought to be unique to RNA tumour viruses^1–3, is now known to be present in normal human lymphocytes⁴, which are differentiated and seldom divide in vivo or in culture. The addition of phytohaemagglutinin (PHA) or other mitogens (including appropriate antigens) transforms lymphocytes into actively proliferating cells⁵. Several enzymes which function in gene activation and DNA replication specifically increase in activity during this transformation^6,7. We now report that RNA-dependent DNA polymerase also behaves in this way.     

The Influence of Atrazine, Benzyladenine, and the Embryonic Axis on Chlorophyll Synthesis in Cucumber and Squash Cotyledons

Excision of the embryonic axis prior to 3 1/2 days of germination in the dark followed by 8-h of light decreased the total chlorophyll content of cucumber cotyledons but not squash cotyledons. Benzyladenine stimulated the accumulation of chlorophyll in the cotyledons of intact embryos and excised cotyledons in both cucumber and squash. Gibberellic acid had no effect. Atrazine inhibited chlorophyll formation in excised squash cotyledons. Benzyladenine also increased the carotenoid and xanthophyll content in the cotyledons from intact squash seedlings. The results suggest that pigment synthesis in cotyledons may be controlled by a number of substances produced in the embryonic axis and that cytokinin-like benzyladenine can simulate the action of one of them.     

Polyingression, an Important Morphogenetic Movement in Chick Gastrulation

Three lines of evidence are presented to support the conceptthat polyingression represents a major morphogenetic movementin the genesis of the primary hypoblast, definitive endodermand the mesoderm layers in chick gastrulation. Colchicine treatedembryos produce a primary hypoblast layer thereby indicatingthat cell proliferation in the posterior marginal zone and elsewherein the early embryo does not make a necessary contribution tohypoblast formation. Scanning electron microscopy provides morphologiccomplementary evidence that polyingression from the epiblastis a principal source of cells for the hypoblast. Finally, themorphology of cells with acetylcholinesterase activity suggeststhat this enzyme is related to release of cells from the epiblastso that ingression can occur.     

Functional analysis of mouse keratin 8 in polyoma middle T-induced mammary gland tumours

Keratin 8 and 18 are commonly used as tumorigenic markers for various types of carcinomas. They are known to be involved in cell migration, cell invasiveness, plasminogen activity and drug and radiation resistance. To ascertain a potential function for simple epithelium keratins in mammary adenocarcinoma in vivo, keratin-8-deficient mice (mK8) were mated with transgenic mice carrying the middle T oncogene driven by the MMTV promoter. The resulting mK8 knockout and control progeny carrying the middle T transgene developed mammary gland tumours with the same incidence. However, the onset of palpable mammary gland tumours occurred earlier in mK8 mutant than in control mice. This effect was prominent in males where the onset in control animals is delayed overall, because of the lower hormonal inducibility of the MMTV promoter. Metastatic foci were observed in the lungs of all females and of a few males, idependently of the genotype. Histological analysis revealed no morphological differences of the tumorigenic cells in primary tumours nor in metastatic foci. As expected, keratin 8 was absent in the mK8 tumours. Keratin 7 (mK7), keratin 18 (mK18) and keratin 19 (mK19) protein were observed in both primary and metastatic foci. These results constitute the first in vivo analysis of the role of simple epithelium keratins in mammary carcinogenesis. It demonstrates that the latency, but not the incidence nor the morphological features, of PyV middle T-induced mammary gland tumours is affected by keratin 8 deficiency