Silver staining of the lampbrush chromosomes ofTriturus cristatus carnifex

Lampbrush chromosomes fromTriturus cristatus carnifex were stained using the ammoniacal silver staining (AgAS) technique. Many of the recognized marker structures proved to be silver positive, plus between six and fifteen lateral loop pairs. None of the stained loop pairs corresponded to known sites of the nucleolus organizers, although the extrachromosomal nucleoli were silver positive. The ammoniacal silver staining technique does not demonstrate the specificity for active ribosomal cistrons in lampbrush chromosomes that it does in a wide variety of mammalian mitotic chromosomes.     

The response of development rate to temperature in the univoltine cranefly,Tipula subnodicornis Zetterstedt

Summary The cranefly, Tipula subnodicornis, emerges as an adult in the spring and has an annual life-cycle in the British Isles. This is maintained partly through the presence of a winter diapause but the response of development rate to temperature also acts to preserve the timing of the cycle. During development under constant temperature conditions in the laboratory the optimum temperature (taken as the temperature which promoted the most rapid development) dropped from 25°C, or above, in the egg stage to below 20°C in the late larval stages. It is suggested that at the warmer, southern limits of the geographical range rapid early development may be compensated by a retardation in late larval growth. In addition, the response of growth rate to change in temperature was small in the fourth, final, instar and resulted in low Q ₁₀ values; 2.4 between 7° and 10°C, 1.5 between 10° and 15°C and 0.9 between 15° and 20°C. As the fourth instar comprises the greater part of the growth period, this has the effect of minimising the effect of temperature differences which are the result of differences of latitude or altitude. Even at optimum temperatures the growth period was prolonged and larvae in the field do not reach maximum weight, and the photosensitive stage, until late autum when short daylength promotes diapause. Subsequent development in the spring, before pupation and during the pupal period, showed a reversion to the higher Q ₁₀ figures of the early stages in development.The development of final instar Tipula subnodicornis larvae is contrasted with that of Tipula melanoceros. Tipula melanoceros emerges as an adult in September and it is likely that it has an egg diapause. Consequently larval development is confined to a short period between April and late July and growth must be rapid during this period. Under constant temperature conditions in the laboratory the growth of final instar larvae showed a marked contrast to that of Tipula subnodicornis in that the response to temperature was large and remained positive over a wider temperature range.     

The enzymic degradation of lipids resulting from physical disruption of cucumber (Cucumis sativus) fruit

Homogenization of fresh tissue from cucumber fruits results in a loss of endogenous lipid catalysed by acyl hydrolase enzymes. Deacylation of lipids is not accompanied by accumulation of free fatty acids. The levels of both saturated (mainly palmitic) and polyunsaturated (linoleic and linolenic) fatty acids in the lipids are reduced. Losses of the major acyl lipid constituents of cucumber (triacylglycerols and phospholipids) are mainly responsible for the observed hydrolysis. Triacylglycerol acyl hydrolase (lipase), phospholipase D and polar lipid acyl hydrolase enzyme activities were demonstrated. It is suggested that hydrolytic attack on endogenous lipids is the initial event on disruption of cucumber tissue, in the formation of lipid degradation products, amongst which are the volatile carbonyl compounds responsible for the characteristic flavour of cucumber.     

Prophage Induction in Escherichia coli (Lambda) by N-Nitrosamines

Carcinogenic N-nitrosamines were tested for their ability to induce λ in a lysogenic strain of Escherichia coli K-12 (58-161 F⁺). Dimethylnitrosamine, di-n-propylnitrosamine, methyl-n-propylnitrosamine, and N-nitrosopiperidine were shown to be inducers of prophage.     

The Genetics of Dopa Decarboxylase in DROSOPHILA MELANOGASTER I. Isolation and Characterization of Deficiencies That Delete the Dopa-Decarboxylase-Dosage-Sensitive Region and the α-Methyl-Dopa-Hypersensitive Locus

A detailed cytogenetic investigation of 16 overlapping deficiencies in the 36C-40A region on the left arm of the second chromosome (2L) in Drosophila melanogaster is reported. These deficiencies permit a localization of both the dopa-decarboxylase-dosage-sensitive region and the α-methyl-dopa-hypersensitive locus, l(2)amd, to the same region, 37B10-37C7.     

Isolation of cell cycle mutants of Physarum polycephalum

Summary Asynchronous amoebal cultures of temperature-sensitive mutants of Physarum polycephalum were examined cytologically, and two cell cycle mutants were identified. Genetic analysis indicated that each mutant carried a single mutation that was expressed in both amoebal and plasmodial phases. Thus it is possible to isolate cell cycle mutations expressed in plasmodia by initial isolation and analysis of amoebal mutants, a quicker procedure than the alternative of isolating plasmodial mutants directly. The two mutants were studied further by measuring nuclear DNA contents and synthesis of macromolecules. Both mutants gave results consistent with a block in nuclear division.