Activities of Enzymes Relating to Starch Synthesis and Endogenous Levels of Growth Regulators in Potato Stolon Tips During Tuberization

Changes in contents of starch and protein, and activities of enzymes involved in starch synthesis were studied during tubcrization of stolon tips of Solanum tuberosum L. cv. Irish Cobbler. Starch content and activities of phosphorylase and granule-bound starch synthctase based on fresh weight increased rapidly in the early phase (stage I, the stolon tips just before swelling; stage 2, the swelling tips; stage 3, young tubers of 0.2–0.5 cm diameter), and they all remained nearly unchanged in the later phase (stage 3 to stage 6, young tubers of 3.5 cm diameter). The content of soluble protein based on fresh weight remained unchanged. Activities of soluble starch snythetase and ADP-glucose pyrophosphorylase were not detected at stage 1 and 2, but increased at later stages. Endogenous levels of auxin, cytokinin and gibberellin were assayed for the materials at the corresponding developmental stages. Auxin content was high at stages 1 and 2, and lowered at later stages. Cytokinin content increased abruptly at stage 6. Gibberellin content was low at all stages. The internal conditions for starch deposition and tuberization in potato were discussed in regard to regulation of enzyme activities by growth regulators.     

Morphological,genetic and behavioural analyses of a hybrid zone between the ground beetles Carabus lewisianus and C. albrechti (Coleoptera,Carabidae): asymmetrical introgression caused by movement of the zone?

We analysed the putative hybrid zone between the ground beetles Carabus lewisianus Breuning and C. albrechti Morawitz from the Kanto and Tanzawa Mountains in central Honshu, Japan, using morphological, genetic, and behavioural data. Canonical discriminant analysis of three external and five genital morphological characters revealed an apparent morphological gap, suggesting restricted sympatry in the contact zone. RFLP and molecular phylogenetic analyses of the mitochondrial gene ND5 revealed that haplotypes originating from C. lewisianus introgressed extensively into C. albrechti . Fitting tanh curves to morphological (external and genital) and genetic characters showed differential cline widths and centres, suggesting stronger selection for genital morphology with narrower cline widths, and extensive introgression of the nuclear genes responsible for external characters relative to those controlling genital morphology into the range of C. albrechti . Linkage disequilibria between the morphological characters did not differ from zero, suggesting sufficient recombination occurred in the zone but the effect of small sample sizes was not negligible. Mate choice trials demonstrated that males showed a weak but not significant preference for conspecific mates. We interpret these patterns as evidence for (1) partial reproductive isolation presumably by postmating processes; (2) selection against intermediate genital morphologies, and (3) independent responses of the characters to different evolutionary forces that may cause movement of genital clines and introgression of the mitochondrial gene and external morphology. The movement of the boundaries may have resulted in the particular species distribution patterns in the study area.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 86 , 79–94.     

Trilobite taphonomy and ecology in Upper Ordovician carbonate buildups in Dalarna, Sweden

A major ecological grouping of the trilobites in the Upper Ordovician Boda Limestone buildups in Dalarna is outlined, based primarily on the modes of occurrences in the Jutjärn quarry. The so-called pockets are analysed with regard to their trilobite contents and distribution within a carbonate buildup. The pockets are of two general types. One consists of narrow opened fissures along bedding planes. The matrix of these may contain either of the peculiar blind Isocolus sjoegreni or Ityophorus undulatus , both of which appear to have been cavernous species, possibly belonging to the Bathyuracea (or Leiostegiacea). In addition, small proetids used the fissures for moulting. The other kind of pocket is a cavity largely filled with sediment from the surface of the buildup. The size is considerable, in rare cases up to many tens of cubic metres. Although the buildups housed about 90 trilobite species, each of these pockets is dominated by one or two out of seven large species. Of these, six are illaenids, the seventh the illaenid-like cheirurid Holotrachelus punctillosus. Usually only pygidia and cranidia are found. These species may have lived gregariously around the rims of the cavities. The remaining species, about 85% of the trilobite fauna, appear to have lived on the surface of the buildups. The largest group is the proetids with some 20 species (in addition to those known from pockets). Cheirurinids and lichids contribute with some 15 species each, and there are six odontopleurids. The distinctness of the 'community' is indicated by the circumstance that only three species are shared with contemporaneous level-bottom faunas in Sweden.     

The occurrence and properties of dihydrofolate reductase in pea seedlings

Dihydrofolate reductase (E.C. 1.5.1.3 [EC] ) was found in pea seedlingsand was partially purified by treatments with ammonium sulfate,protamine sulfate and by DEAE-cellulose column chromatography.Some properties of the enzyme were investigated. Optimum pHfor the reaction was 6.5. In the enzyme reaction, FAH₂ and NADPH₂were specifically required. MICHAELIS constants for FAH₂ andNADPH₂ were 4.3x10^–6 M and 4.0x10^–5 M, respectively.Folate antagonists such as aminopterin, methotrexate and pyrimethaminewere potent inhibitors of this enzyme. Enzyme activity was almostcompletely inhibited at a concentration of 10^–7 M of aminopterinand methotrexate and 10^–6 M of pyrimethamine. Growth of germinating pea seeds was inhibited by aminopterin,methotrexate and pyrimethamine, and it recovered significantlywith a tetrahydro-derivative of folate, CF, but not with dihydrofolicor folic acid. These results suggest that growth inhibitionof pea seedlings by these antagonists is due to inhibition ofdihydrofolate reductase in seedlings. ¹Studies on the enzymatic synthesis and metabolism of folatecoenzymes in plants IV. (For the previous paper, Part III, seeReference (21)) . Part of this paper was presented at the AnnualMeeting of the Agricultural Chemical Society of Japan held atTokyo on April 4, 1967 (Received October 8, 1969; )     

Biosynthesis of folic acid compounds in plants VI. The occurrence and properties of the dihydrofolate-synthesizing enzyme in pea seedlings

An enzyme, which catalyzes the formation of dihydrofolate fromdihydropteroic acid and L-glutamic acid, was found in pea seedlings.The enzyme was purified approximately 25-fold from the crudeextracts of pea seedlings, and its some properties were investigated.Optimum pH for the enzyme activity was found to be 8.8. Pteroicand tetrahydropteroic acids were not active as substrate. Theenzymatic reaction required as cofactors ATP, divalent (Mg²⁺or Mn²⁺) and univalent (K⁺, NH₄⁺ or Rb⁺) cations. The productwas characterized as dihydrofolic acid by bioautography. MICHAELIS constants for L-glutamic acid, ATP, dihydropteroicacid and Mg²⁺ were 7.0x10^–4, 9.0x10^–5, 3.5x10^–6and 1.2x10^–3 M, respectively. The MICHAELIS constant forMn²⁺ was 3.0x10^–4. The enzyme was inhibited by PCMB orsilver nitrate and, to some extent, by L-aspartic acid. Inhibitionby PCMB was completely reversed by addition of 2-mercaptoethanol.Enzyme activity was distributed widely among plants. The importanceof magnesium and potassium ions for enzyme catalysis is discussed. ¹For the previous paper, Part V, see Reference (30). (Received March 28, 1970; )     

Prospective Neural Areas and Their Morphogenetic Movements during Neural Plate Formation of Xenopus Embryos. I. Development of Vegetal Half Embryos and Chimera Embryos

Development of animal cap-less Xenopus gastrulae was examined. In vegetal halves from which the animal cap was removed 0.6 mm above the blastopore, an apparently normal array of craniocaudal structures developed. Histological examination showed differentiation of central nervous system (CNS) structures in the cap-less embryos, but differentiation of sensory organs, such as a lens and ear vesicle in only a few embryos. Only the dorsal midline of the embryos was covered with epidermis, and its lateral-ventral areas consisted of bare endoderm and mesoderm. The development of animal cap was also investigated by exchanging the animal cap of X. laevis embryos with that of X. borealis embryos, which can be distinguished by quinacrine fluorescence staining. The central nervous system of chimera embryos consisted mainly of X. laevis cells stained homogeneously with quinacrine but a small number of punctately-stained X. borealis cells was in the anterior tip of the forebrain. Cells of the lens and ear vesicle were punctately stained. More than two-thirds of the epidermal area consisted of punctately-stained cells and only the dorsal midline of the posterior head- and trunk-epidermis consisted of homogeneously-stained cells.
Areas of the prospective central nervous system and their movement during embryogenesis of Xenopus are discussed.     

Reflections on the Limits of Science and Technology

SYNOPSIS. Exuberance over insights gained in the infant fieldof genetics early this centuryled scientists to extrapolatebeyond their data to heredity of behavioral traits in people.Oneof the direct consequences was the incarceration of Americansand Canadians of Japanese ancestry during World War II as enemyaliens. Drawing on this personal experience of the misapplicationof science, I describe the process of scientific indoctrinationand blindness to the limitations of this way of knowing. Thisled to my attempt to demystify science through the electronicmedia. Only recently have I come to understand that two assumptionsthat impelled me to use television in the first place are wrong.The first was that with access to more information about science,the general public would be in a position of making better informeddecisions on issues involving science and technology. The problemis that we are overwhelmed with information and most peoplelack the ability to distinguish meaningful "signal" (i.e., credibleinformation) from background "noise" (i.e., garbage). We believein phantoms created by the acceptance of anything because itexists as print or television programs. My second assumption had been that we need a mechanism to doan in-depth "cost/benefit" analysis of new technologies beforethey are actually made available. But history reveals that thebenefits of new technologies are immediate and obvious whilethe costs are usually hidden and completely unpredictable. But in the rush to exploit new scientific insights we ignorethe fact that science must lookat nature in isolated bits andpieces. Knowledge gained in fragments does not yield an understandingof the greater context from which the pieces are taken. Witheach new discovery, we itch to apply it, forgetting how muchwe have yet to learn. Our attempts to manipulate nature areoften illusions of control created by our ability to overpowernature by brute strength. In the area of genetic engineering,this could be truly disastrous.     

Stimulation of Spermatid Phosphofructokinase by Fructose 2,6-Bisphosphate from Rat Testes

Effect of fructose 2, 6-bisphosphate on 6-phosphofructokinase (ATP: D-fructose-6-phosphate 1-phosphotransferase, EC 2.7.1.11) in spermatid extract from rat testes was studied. Fructose 2, 6-bisphosphate stimulated the enzyme greatly by increasing its affinity for fructose 6-phosphate and relieving the inhibition by ATP. Fructose 2, 6-bisphosphate (0.8 μM) was required for 50% activation of 6-phosphofructokinase (PFK). In addition, fructose 2, 6-bisphosphate, AMP and fructose 6-phosphate acted cooperatively to stimulate the activity of PFK. This stimulation may play an important role in the regulation of glycolysis in spermatids of rat testes.     

Respiration of Sea Urchin Spermatozoa in the Presence of a Synthetic Jelly Coat Peptide and Ionophores

Sperm respiration and motility of the sea urchin Hemicentrotus pulcherrimus were studied at pH 6.8 in the presence of a synthetic jelly peptide (Gly-Phe-Asp-Leu-Asn-Gly-Gly-Gly-Val-Gly) and monovalent cationic ionophores. The synthetic peptide stimulated sperm respiration and motility to the level of that found in normal sea water (pH 8.2) with half-maximal stimulation at approximately 100 pM. Monensin and valinomycin also stimulated sperm respiration with half-maximal effects at 7 μM and 0.7 μM, respectively. The stimulation of sperm respiration by the peptide and monensin was dependent on external Na⁺, but was not dependent on the osmolarity of the suspending medium. Approximately 50 mM Na⁺ was required for half-maximal respiratory responses to the peptide and monensin.