Hydrogen cyanide and embryonal dormancy in apple seeds

Embryos of apple ( Malus domestica Borh. cv. Antonówka) were treated with 1 m M gaseous HCN for 6 h and cultured under a 12 h photoperiod. HCN pretreatment stimulated germination, increased the length of hypocotyls, shortened the main root and decreased the percentages of seedlings with asymmetrically grown as well as with asymmetrically greened cotyledons. High activity of β-cyanoalanine synthase (EC 4.4.1.9) and a sharp increase in cyanogen content during embryo culture suggested very low levels of endogenous HCN. despite the activity of HCN releasing enzymes. The obtained data allow us to postulate an important role for cyanide in the regulatory complex controlling dormancy in apple seeds. Experiments with respiratory inhibitors indicated, however, that HCN pretreatment affected neither the alternative electron transport pathway nor residual respiration.     

The effect of fish predation on Cyclops life cycle

Two populations of Cyclops abyssorum tatricus studied in neighbouring alpine lakes in Tatra Mountains (southern Poland) differed in their life cycles. In the lake with planktivorous fishes, Cyclops was typically monocyclic, with highly synchronized reproduction during two winter months, while in the fishless lake its reproduction was asynchronous and continued for six months. Direct and indirect effects of fish predation on Cyclops life cycles are discussed.     

Cytochromec oxidase fromParacoccus denitrificans in Triton X-100: Aggregation state and kinetics

Cytochromec oxidase fromParacoccus denitrificans was homogenously dispersed in Triton X-100. Using gel exclusion chromatography and sucrose gradient centrifugation analysis a molecular weight of the detergent-protein complex of 155,000 was determined. After subtraction of the bound detergent (111 mol/mol hemeaa ₃) a molecular weight of 85,000 resulted, which agreed well with the model of a monomer containing two subunits. This monomer showed high cytochromec oxidase activity when measured spectrophotometrically in the presence of Triton X-100 (V _max=85 s^–1). The molecular activity, plotted according to Eadie-Hofstee, was monophasic as a function of the cytochromec concentration. AK _m of 3.6×10^–6 M was evaluated, similar to theK _m observed in the presence of dodecyl maltoside [Naeczet al. (1985).Biochim. Biophys. Acta 808, 259–272].     

Persistence of cell cycle times over many generations as determined by heritability of colony sizes of ras oncogene-transformed and non-transformed cells

Abstract. The persistence of cell lifetimes during about 10 successive cell generations was investigated by comparing the number of cells in primary colonies and in secondary colonies derived from primary colonies. Primary colonies were grown from single cells for 3 or 4 days (a time equivalent to an average of five cell generations) and the number of cells in each primary colony determined. Cells in each primary colony were dispersed to initiate secondary colonies, grown for the same time, and the number of cells in secondary colonies determined. Several criteria were used to compare primary and related secondary colonies, the most informative was found to be regression and correlation coefficients between number of cells in primary colonies and mean numbers of cells in related secondary colonies. For two non-transformed mouse fibroblast cell lines, NIH 3T3 and BALB 3T3, the regression and correlation coefficients of cell number in primary and secondary colonies were positive. This suggests inheritance of cell lifetimes over many cell generations. After the addition of an activated ras oncogene (human cellular Harvey ras , or viral Kirsten ras ) some regression and correlation coefficients changed in magnitude but all remained positive. Comparison of experimental data and the results of computer simulations suggest that several models of inheritance of cell lifetimes are not adequate to explain the results, including a model of independence between lifetimes of mother and daughter cells and the common model that describes daughter cells as inheriting the lifetime of their mother with deviation. Simulations do suggest that cell lifetimes are inherited within clones as deviation from the lifetime of the initial cell, and that the ras oncogene does not destroy persistence within clones but does increase heterogeneity of cell lifetimes.