Cell cycle inHelianthus tuberosus tuber tissue in relation to dormancy

Summary Observations are presented on the patterns of DNA synthesis and mitotic activity in medullary parenchyma cells excised from tubers ofHelianthus tuberosus in four different periods of dormancy. Dormancy break (activation) was induced byin vitro culture on media added with 2,4-dichlorophenoxyacetic acid. The cell cycle responsein vitro to different combinations of growth substances has also been investigated.The results show that remarkable changes in the timing of the first and second cell cycles and their phases occur with the progression of dormancy. With increasing time after tuber harvest, the following behaviours are observed: (i) a lengthening of the first cell cycle, chiefly due to a lengthening of the G₂ phase (G₂ is absent at the beginning of dormancy) and an increase in the time interval between the start of thein vitro culture and the onset of the first mitotic wave; (ii) an increased duration of the S phase; (iii) a remarkable reduction in the cell synchrony.These behaviours, as indicated also by their comparison with thein vitro response of the cell cycle to different hormonal treatments, seem to depend on the physiological status of the tubers at the time of explant. It is concluded that the analysis of the cell cycle is an useful tool for understanding some aspects of such a complex physiological situation as dormancy.Istituto di Mutagenesi e Differenziamento del C.N.R., Pisa, Italy, publication no. 321.     

Pentacyclic steroids,part XVI,studies on the total syntheses of racemic 1,6-dithiabenz[3,4]estra-3, 5(10),8,14-tetraen-17-one and its D-homo analogue

The total syntheses of racemic 1,6-dithiabenz[3,4]-estra-3,5(10), 8,14-tetraen-17-one [VII]and 1,6-dithiabenz-[3,4]-D-homoestra-3,5(10),8,14-tetraen-17a-one [IX]starting fron isothiochroman-4-one [I]are described.     

Nematicidal Principles from Two Species of Lamiaceae

Aqueous extracts of Ocimum sanctum and O. basilicum leaves contained compounds that killed Meloidogyne incognita larvae in 160 min. Thin layer and gas-liquid chromatography, and infrared spectrophotometry indicated that the essential oils eugenol and linalool were the active nematicidal compounds.     

Androstenedione, dehydroepiandrosterone and testosterone in ovarian vein plasma and androstenedione in peripheral arterial plasma during the bovine oestrous cycle

Catheters were placed in the carotid artery via a facial artery (n = 12) and in the ovarian vein (n = 12), and, in conjunction, electromagnetic flow meters were placed around the ovarian artery (n = 6) in cyclic beef cows. Androstenedione was quantitatively the highest and dehydroepiandrosterone the lowest of the ovarian androgens measured. Ovarian androgens were correlated positively with each other (P less than 0.05) but not with ovarian blood flow or day of the cycle. There was a trend for spikes of androgen release (ovarian vein concentration x ovarian blood flow) from the ovary to be greatest during the period of decreasing progesterone and CL regression. However, only with testosterone were spikes of release different (Days--13 to--9 less than Days -8 to -4; P less than 0.05; Day 0 = oestrus). The dynamic changes in ovarian androgens noted in this study were compatible with the concept of continuous follicular development and atresia throughout the oestrous cycle.     

Epoxidation of unsaturated fatty acids by a soluble cytochrome P-450-dependent system from Bacillus megaterium

In previous publications from this laboratory we have described a soluble, partially purified cytochrome P-450-dependent monooxygenase complex that, in the presence of NADPH and O2, catalyzes the monohydroxylation of long chain fatty acids, alcohols, and amides at the omega -1, omega -2, and omega -3 positions. We have now found that this preparation catalyzes the epoxidation as well as the hydroxylation of palmitoleic acid and a variety of other monounsaturated fatty acids. The experimental results reported here strongly support the concept that both hydroxylation and epoxidation are catalyzed by an identical cytochrome P-450 complex utilizing the same active and binding sites. Furthermore, for saturating levels of these substrates, the rate-limiting step in oxygenation does not appear to involve substrate structure. Thus, although the position and geometry of the double bond may dramatically affect the rate of epoxidation relative to hydroxylation, the combined rate of substrate oxygenation is essentially a constant independent of this ratio. Finally, we propose and present evidence for an enzyme-substrate binding model that involves polar binding of the carboxyl terminus and strong hydrophobic binding and sequestering of the terminal methyl group of the fatty acid. The three methylene carbons adjacent to the methyl group are positioned in a set geometry around the active site but the midchain region of a monounsaturated fatty acid is relatively free to interact or bind loosely with the enzyme surface in a variety of conformations. Depending on fatty acid structure, one or more of these conformations can bring the unsaturated center close enough to the active site to permit epoxidation of the double bond.     

Structural preferences for the binding of chromium nucleotides by beef heart mitochondrial ATPase

The mono- and bidentate forms of adenosine 5'-diphosphate, chromium (III) salt (CrADP) were separated using Sephadex G-10 column chromatography. The isomeric purity of the two forms was monitored using high voltage electrophoresis and column chromatography. The same techniques were employed to assess the purity of the mono-, bi-, and tridentate forms of adenosine 5'-triphosphate, chromium (III) salt (CrATP). Distinct differences in the interaction of beef heart mitochondrial ATPase with the various isomers of chromium nucleotides were seen in kinetic studies. Monodentate CrADP was a competitive inhibitor of the ATP hydrolysis activity of both purified ATPase and submitochondrial particles. However, when ITPase activity was examined, noncompetitive inhibition was observed. The bidentate isomer of CrADP did not affect ATPase activity. Enzymatic synthesis of the transition state analog of ATP synthesis and hydrolysis, Pi-CrADP occurred exclusively with the monodentate isomer of CrADP. It was also found that only the mono- and tridentate forms of CrATP were potent inhibitors of ATP hydrolysis by beef heart mitochondrial ATPase. These results are discussed in terms of possible ATP synthesis and hydrolysis mechanisms.     

A conjugative 'plasmid' lacking autonomous replication

Attempts were made to isolate open and covalently closed circular DNA from strains containing the IncJ plasmids. All of the methods tried were unsuccessful. It was shown that the IncJ plasmid R391 can integrate into the Escherichia coli K12 chromosome and can mobilize chromosomal markers from a single origin in an orientated manner. It is proposed that the IncJ plasmids are integrated in the chromosome for most, if not all, of their existence and this explains the inability to isolate plasmid DNA from strains containing them.     

Host modification of Sindbis virus sialic acid content influences alternative complement pathway activation and virus clearance

Previous studies have shown that Sindbis virus, an enveloped alphavirus of the togavirus group, activates the alternative complement pathway in the absence of detectable antiviral immunoglobulin. The present studies examined the role of the host-determined sialic acid content of Sindbis virus on activation of the alternative complement pathway. Purified Sindbis virus grown in baby hamster kidney (BHK-SV) and in mosquito (MOSQ-SV) cells yielded virus with 10.2 and less than 2.0 nmol sialic acid/mg viral protein, respectively. Sindbis virus deficient in sialic acid (2.0 nmol sialic/mg) was also produced by treating the BHK-SV with neuraminidase (NANase-SV). When MOSQ-SV or NANase-SV was incubated in either C4DGPS or C2DHS, each consumed significantly more C3 than did BHK-SV, indicating that the ability of Sindbis virus to activate the alternative pathway is inversely related to its sialic acid content. Studies in vivo showed that virus deficient in sialic acid (MOSQ-SV) was cleared from the blood of mice much more efficiently than was virus rich in sialic acid (BHK-SV), after i.v. inoculation. Furthermore, when animals were depleted of C3 through C9 by cobra venom factor (CoVF) treatment, no differences in the clearance of high and low sialic acid-containing viruses were observed. Thus both the activation in vitro and complement-dependent clearance in vivo are significantly affected by the host-determined sialic acid content of Sindbis virus.