Genetic Recombination in Coprinus. IV. a Kinetic Study of the Temperature Effect on Recombination Frequency

At the restrictive conditions (35 degrees under continuous light) Coprinus lagopus is unable to initiate premeiotic S phase which takes place normally within 8-10 h of karyogamy. A shift-up to the restrictive conditions causes an arrest of the basidiocarps at this critical stage. A prolonged arrest causes a reversal to mitosis (Lu 1974b). Incubation of basidiocarps at the restrictive conditions before this critical stage causes no increase in recombination frequency (R.F.) in the loci studied. An arrest of 4 h at the critical stage still causes no R.F. increase, but 12-13 h and 18-19 h arrests cause increases of 50% and 90% over the controls, respectively. Thus R.F. can be increased even before the cells are fully committed to meiosis.-A 3-h heat treatment at the beginning of S phase (or 8 h before karyogamy) also causes some (30%) increase in R.F. while the same treatment at late S phase (or 3 h before karyogamy) causes a substantial (164%) increase in R.F. over the controls. A 3-h heat treatment before S phase causes no increase in R.F.-Pachytene is also responsive to temperature treatments (Lu 1969). The maximum R.f. increase is 100% by heat and 220% by cold treatment. The shortest time that can cause the maximum increase in recombination by high temperature is 3 h and that by cold treatment is 7 h. These durations are correlated with the length of the pachytene stage under the treatment conditions. The kinetic data show that the increase in R.F. caused by high and low temperatures follows two-hit kinetics and their rate of increase is almost identical. The higher increase in R.F. by low temperature can be attributed to the increased duration of pachytene and therefore R.F. is a function of time. The longer the homologous chromosomes are held together, the higher the recombination frequency.     

The problem of carotenoid biosynthesis in the taxonomy of genera Rhodotorula and Rhodosporidium

This report presents results in the composition of major carotenoids of various coloured mutants of the genusRhodotorula and of mating types of the genusRhodosporidium. The separation of carotenoid intermediates was carried out by thin layer chromatography using Silufol 254 Kavalier and the determination of eluated spots by spectrophotometry. There was found no difference in carotenoid composition of both mating typesa and α of individual species of the genusRhodosporidium. The vegetative and sexual reproduction ofRhodotorula andRhodosporidium can be separated from the carotenogenesis using 10^?4 mol diphenylamine. It was concluded that lycopene could be the intermediate to mono- and dicyclic carotenoids; in the case of partial inhibition of the dehydrogenation step the direct cyclization of neurosporene to β-zeacarotene can be expected. An unknown compound, probably lycopersene was found and was considered to be the precursor of phytoene. Phytoene and phytofluene were proved in all studied samples. Nutritional conditions (vitamins, sulfur amino acids, etc.) are able to shift the ratios between major carotenoids. Rhodotorula aurantiaca strains were observed to be auxotrophic mutants of various characters and the existence of this species as independent one, was denied.     

A nuclease from Neurospora crassa specific for d(A-T) rich regions in double stranded DNA

A nuclease from N. crassa has been prepared to the hydroxylapatite stage of purification described by Rabin and Fraser (1). It degrades single stranded DNA in an essentially exonucleolytic process. It does not give any appreciable acid soluble material with double stranded DNA as substrate. This shows its high degree of specificity towards single stranded DNA.     

Comparison of the mutagenic activity of N-ethyl- N-nitrosourea and N-methyl- N’- nitro- N- nitrosoguanidine inLens esculenta

Mutagenic activity of N-ethyl-N-nitrosourea (ENU) and of N-methyl-N’-nitro-N--nitrosoguanidine (MNG) in lentil was studied. The highest proportion of segregating progenies with chlorophyll mutants and chimeric plants was 34.8% from the total number of analysed offsprings, ENU being applied in this case in the concentration of 0.005% for 20 h at 18 to 19 °C. When MNG was applied in the concentration of 0.001 % for 10h at 22 to 23 °C the proportion was 5.1%. Progenies segregating two or more chlorophyll mutants originated with ENU only; their relative frequencies varied from 1.4% to 7.1%. The number of different types of mutants or of their combinations segregating at the same time in the same progeny was shown to be dependent with the two agent tested on the mutagenic activity of the concentration used. The most efficient concentration of ENU induced the total of 8 different mutants at the same time, together with a combination of two or three mutant types in the same progeny. With MNG no combination of chlorophyll mutants in the same progeny was ever found simultaneously. The greatest number of mutants corresponding to 1 progeny M₁ was 0.53 when ENU was applied; with MNG the maximum values were approximately ten times lower. The maximum number M₂ of chlorophyll mutants and chimeric plants was 3.58% with ENU and 0.23 with MNG.     

On the interaction of growth retardants with IAA and kinetin

In the pea test a highly positive response to the treatment with IAA reversed to a negative one or became 5 to 6 times weaker when CCC was applied together with IAA. In cultivating pea seedlings, following their decapitation, for two days in a 0.25 per cent CCC solution and then in water, growth of their cotyledonous axillaries (cotylaries) were inhibited. This inhibitive action of CCC could be made ineffective when the seedlings, following two-days’ cultivation in the CCC solution, were grown further in kinetin solutions (0.37–3 mg per 1). Cotylaries of decapitated pea seedlings, when grown in kinetin solutions were inhibited. With kinetin solutions of 6–12 mg/l a strong inhibition also occured in the growth of roots at the apical parts of which spherical swellings were developing. The CCC supplied to the roots of intact etiolated pea seedlings is translocated acropetally into the stem at a rate of about 5 cm per hour. Decapitation of the plant causes retardation of this transport, yet a coat of 0.00001–1% IAA or kinetin paste produces acceleration of the stream. Existence of an antagonism between CCC and IAA, demonstrated earlier, was found holding true also for B-9 (N, N-dimethyl-aminesuccinamic acid) and IAA, as the inhibitive action of B-9, 0.06% solution on the growth of lettuce hypocotyls was reduced to a highly significant degree when the plants were supplied with B-9 together with IAA at a concentration of 10 mg/l.     

UV sensitivity of germinating culture ofBacillus cereus

The spores ofBacillus cereus can be germinated in reasonable synchrony in rich media. The survival of germinating cells after UV irradiation is strongly affected by repair. When plating on mineral agar a linear decrease of survival is obtained between 20–60 min of germination, whereas the survival on nutrient agar shows only minor fluctuations. The difference in survival on these two media which reached 1–2 orders of magnitude is due mostly to the shape of the shoulder on the survival curve. Survival on mineral agar may be increased by postincubation in complex media or by preincubation in mineral media. It was concluded that repression and derepression of biosynthetic pathways was responsible for the different efficiency of repair.