Revision of the theory of phototropism in plants: a new interpretation of a classical experiment

Went's classical experiment on the diffusion of auxin activity from unilaterally illuminated oat coleoptile tips (Went 1928), was repeated as precisely as possible. In agreement with Went's data with theAvena curvature assay, the agar blocks from the illuminated side of oat (Avena sativa L. cv. Victory) coleoptile tips had, on an average, 38% of the auxin activity of those from the shaded side. However, determination of the absolute amounts of indole-3-acetic acid (IAA) in the agar blocks, using a physicochemical assay following purification, showed that the IAA was evenly distributed in the blocks from the illuminated and shaded sides. In the blocks from the shaded and dark-control halves the amounts of IAA were 2.5 times higher than the auxin activity measured by theAvena curvature test, and in those from the illuminated half even 7 times higher. Chromatography of the diffusates prior to theAvena curvature test demonstrated that the amounts of two growth inhibitors, especially of the more polar one, were significantly higher in the agar blocks from the illuminated side than in those from the shaded side and the dark control. These results show that the basic experiment from which the Cholodny-Went theory was derived, does not justify this theory. The data rather indicate that phototropism is caused by the light-induced, local accumulation of growth inhibitors against a background of even auxin distribution, the diffusion of auxin being unaffected.Abbreviation IAA indole-3-acetic acid     

Thiol-directed immobilization of recombinant IgG-binding receptors

A genetic engineering approach is described for directed immobilization of IgG-binding receptors to a thiol-containing matrix using a single cysteine residue. The cysteine residue is introduced into the C-terminal part of receptors based on staphylococcal protein A. Receptors containing one, two or five IgG-binding domains were produced in Escherichia coli and subsequently immobilized on thiopropyl-Sepharose. A high amount, 5 mumol/ml gel (45 mg/ml), of recombinant receptor could be rapidly immobilized to the solid support and both the gel and the immobilized receptor could be regenerated by reduction and oxidation reactions. The gel was used for affinity purification of human IgG and analysis of IgG-binding capacity at different amounts of immobilized recombinant protein show the same maximal IgG-binding capacity (20-25 mg/ml) for all three immobilized receptors. However, at low substitution grade of receptors, the immobilized receptor molecules were shown to bind one (Z-Cys) and two (ZZ-Cys) IgG molecules, respectively. These results demonstrate that the immobilized protein molecules are in a functionally active form and that a two-domain receptor can bind two molecules of IgG without steric hindrance. Interestingly, the five-domain receptor (ZV-Cys), with a structure similar to native protein A, can only bind approximately two IgG molecules, despite the five-domain structure of the molecule.     

Investigation of transport-associated phosphorylation of sugar in yeast mutants (snf3) lacking high-affinity glucose transport and in a mutant (fdp1) showing deficient regulation of initial sugar metabolism

Pool-labeling experiments with 2-deoxyglucose in derepressed cells of the yeastSaccharomyces cerevisiae confirmed the previously reported results pointing to the possible existence of transport-associated phosphorylation of sugar. In yeast mutants containing a disruption or an inactivating point mutation in thesnf3 gene, which codes for the high-affinity glucose carrier, no evidence for transport-associated phosphorylation of 2-deoxyglucose was observed. If transport-associated phosphorylation in yeast exists, it is apparently not mediated by the low-affinity glucose carrier. Mediation by the high-affinity carrier would fit with the known requirement of an active kinase for high-affinity sugar transport. A mixed type of uptake in cells having both carriers would explain many of the problems associated with the 2-deoxyglucose pool-labeling experiments. Since mutants that have only low-affinity glucose transport are not deficient in the glucose-induced RAS-mediated cAMP signal, transport-associated phosphorylation of glucose is not required for or involved in the induction of the signal. The yeastfdp mutant, which dies on media containing fermentable sugars because of overaccumulation of sugar phosphates, also did not show any evidence for the existence of transport-associated phosphorylation. The same was true for the double mutantfdp snf3. The latter also showed the typicalfdp phenotype, indicative that the lethality on media containing fermentable sugar is owing to aberrant regulation of low-affinity transport. The high protein kinase activity in thefdp mutant does not appear to be responsible for the absence of evidence for transport-associated phosphorylation, because another mutant with high protein kinase activity, thebcy mutant, displayed normal transport behavior.     

Effects of training at simulated altitude on performance and muscle metabolic capacity in competitive road cyclists

Differences between the effects of training at sea level and at simulated altitude on performance and muscle structural and biochemical properties were investigated in 8 competitive cyclists who trained for 3-4 weeks, 4-5 sessions/week, each session consisting of cycling for 60-90 min continuously and 45-60 min intermittently. Four subjects, the altitude group (AG), trained in a hypobaric chamber (574 torr = 2300 m above sea level), and the other four at sea level (SLG). Before and after training work capacity was tested both at simulated altitude (574 torr) and at sea level, by an incremental cycle ergometer test until exhaustion. Work capacity was expressed as total amount of work performed. Venous blood samples were taken during the tests. Leg muscle biopsies were taken at rest before and after the training period. AG exhibited an increase of 33% in both sea level and altitude performance, while SLG increased 22% at sea level and 14% at altitude. Blood lactate concentration at a given submaximal load at altitude was significantly more reduced by training in AG than SLG. Muscle phosphofructokinase (PFK) activity decreased with training in AG but increased in SLG. All AG subjects showed increases in capillary density. In conclusion, work capacity at altitude was increased more by training at altitude than at sea level. Work capacity at sea level was at least as much improved by altitude as by sea level training. The improved work capacity by training at altitude was paralleled by decreased exercise blood lactate concentration, increased capillarization and decreased glycolytic capacity in leg muscle.     

The Upper Cave at Zhoukoudian and the origins of the Mongoloids

The best evidence for identifying the inhabitants of northeast Asia in the terminal Pleistocene or early Holocene periods is provided by the human burials from the Upper Cave at Zhoukoudian, and in particular the “Old Man”. Apart from the Minatogawa finds on Okinawa, all Late Pleistocene human remains from East Asia that are reasonably well published are poorly preserved and often have equivocal dates. Since the time the Upper Cave was excavated it has been supposed that the human remains were the link between “Peking Man” and the modern Mongoloid complex. We have carried out multivariate analyses of the “Old Man” cranium employing new measurements of Weidenreich's cast of the skull and comparative data from Howells' survey of modern human groups. Despite our expectations the analyses have not shown the “Old Man” to be closely linked with the Mongoloids. Considering all the evidence available we conclude that the common belief of a close biological relationship between the people buried in the Upper Cave and the modern Mongoloids is not yet adequately demonstrated. Of crucial importance in interpreting the Upper Cave burials is their antiquity, which is still commonly thought to be in the order of at least 18 000 years. We believe that recent C-14 dates of about 11 000 years, determined from animal bones, indicate the earliest possible date for the burials. The time span between the Upper Cave burials and the earliest known modern Mongoloids in north China is in the order of about 4–5000 years. It is possible that a major population shift has occurred in north China between the terminal Pleistocene and the mid Holocene, when farming first appears. If this is so, the Upper Cave people may not have been closely allied to the Mongoloid groups that now inhabit East Asia and the Americas.     

The γ-crystallin gene families: Sequence and evolutionary patterns

Summary The -crystallin proteins consist of two topologically equivalent domains, each built up out of two similar motifs. They are encoded by a gene family, which already contained five members before the divergence of rodents and primates. A further gene duplication took place in each lineage. To analyze the pattern of evolution within this gene family, the coding sequences of six human genes, six rat genes, and four mouse genes were compared. Between species, a uniform rate of evolution of all regions of the protein is seen. The ratio of synonymous to nonsynonymous substitution in the human/rat or human/mouse comparison is much lower than the ratio when rat and mouse are compared indicating that the -crystallin proteins are better conserved in the rodent lineage. Within species, the regions encoding the two external motifs I and III of the protein show a greater extent of nonsynonymous substitution than the regions encoding the two internal protein motifs II and IV. The low extent of synonymous substitution between the second exons (encoding motifs I and II) of the rat -crystallin genes suggests the frequent occurrence of gene conversion. In contrast, a high extent of synonymous substitution is found in exon 3 (encoding motifs III and IV) of the rat genes. The same phenomenon is seen within the human gene family. The frequencies of occurrence of the various dinucleotides deviate less from those predicted from the frequencies of occurrence of each individual nucleotide in the second exons than in the third exons. The sequences of the third exons are significantly depleted in CpG, ApA, and GpT and enriched in CpT and GpA.     

Cellular and molecular markers of anteroposterior and dorsoventral organisation in the vitellogenic follicles of adult Sarcophaga bullata (Diptera) and dorsoventral orientation of follicles in the ovary

Summary Polar organisation in the follicles of adult Sarcophaga bullata is reflected in the nurse cell-oocyte axis and in the orientation of the two polar cell pairs in the follicular epithelium. The internal organisation of the nurse cell chamber contributes to polarity but not to dorsoventral asymmetry. Dorsoventral asymmetry is correlated with the eccentric position of the germinal vesicle and the orientation of the polar cell pairs; no other follicle cell specialisations are seen. In an ovary, follicles are preferentially orientated with the dorsal side to the centre of the ovary. Cytoskeletal and some haemolymph proteins are molecular markers of polarity. Thus, in pre-vitellogenic stages, tubulin immunoreactivity is higher in the oocyte than in the nurse cells, actin immunoreactivity is the same over the cystocytes and larval serum proteins are restricted to the poles. During vitellogenesis, both actin and tubulin become more concentrated in the nurse cells and larval serum protein 1 accumulated in the polar cells during border cell migration when yolk polypeptides also accumulate in the oocyte. At the end of vitellogenesis a lipophorin is taken up by the oocyte. No molecular marker of dorsoventral asymmetry was identified.     

A nomenclature for the genes encoding the chlorophylla/b-binding proteins of higher plants

We propose a nomenclature for the genes encoding the chlorophylla/b-binding proteins of the light-harvesting complexes of photosystem I and II. The genes encoding LHC I and LHC II polypeptides are namedLhca1 throughLhca4 andLhcb1 throughLhcb6, respectively. The proposal follows the general format recommended by the Commision on Plant Gene Nomenclature. We also present a table for the conversion of old gene names to the new nomenclature.     

Induction of mutation in V79 Chinese hamster cells by tetrachlorohydroquinone, a metabolite of pentachlorophenol

Tetrachlorohydroquinone (TCHQ) and tetrachlorocatechol (TCC), two metabolites of the environmental mutagen and carcinogen pentachlorophenol, were tested without exogenous activation in V79 Chinese hamster cells for the induction of mutation at the hypoxanthine phosphoribosyl transferase (HPRT) locus to 6-thioguanine resistance (TGr) and at the Na/K-ATPase locus to ouabain resistance (OuaR). Treatment was for 24 h at 37 degrees C. TCHQ produced statistically significant increases in the frequency of TGr mutants. The lowest observed effective dose (LOED) was 20 microM, where the relative cloning efficiency was 63%. The relationship between the dose of TCHQ and the frequency of TGr mutants was approximately linear over the range of 0-60 microM with an estimated slope (+/- 95% confidence limits) of 1.1 +/- 0.3 mutants per 10(6) clonable cells per microM. At the highest tested dose of TCHQ, 60 microM, the relative cloning efficiency was reduced to 7%. In contrast to TCHQ, TCC was unable to induce TGr mutants at doses up to 120 microM. The relative cloning efficiency at this dose was 5%. Both TCHQ and TCC were unable to induce OuaR mutants. The results suggest that TCHQ is at least partly responsible for the genotoxic activity of pentachlorophenol. TCHQ can produce reactive oxygen species, which may cause large genetic damage such as deletions, resulting in mutation to TGr but not to OuaR.