Correlation Between the Molecular Structure and the Biological Activity of Co-ARIS, a Cofactor for Acrosome Reaction-Inducing Substance

Two components in the egg jelly are required for inducing the acrosome reaction in starfish; a sulfated glycoprotein called acrosome reaction-inducing substance (ARIS) and its cofactor called Co-ARIS. Three distinct molecules were isolated as the major Co-ARIS' and designated as Co-ARIS' I, II and III. Structural analysis of Co-ARIS' revealed that they are steroidal saponins comprising a sulfated steroid and a pentasaccharide chain. Co-ARIS' I and II differ only in the steroidal side chain. In the presence of ARIS, each Co-ARIS induced the acrosome reaction with a maximal effect at 100–200 μM (Co-ARIS I) or 25–50 μM (Co-ARIS' II and III). Mixtures of Co-ARIS' I, II and III were more effective than the individuals. The activity of Co-ARIS was considerably reduced by solvolytic desulfation but was not affected at all by periodate oxidation. Reduction by NaBH₄ decreased the activity of Co-ARIS I and enhanced that of Co-ARIS II. Treatment of Co-ARIS III with NaBH₄ did not affect the activity as anticipated from its structure. These results suggest that the sulfate moiety and the side chain of steroid are important for the activity of Co-ARIS. The saccharide chain, however, seems not necessarily to be strictly specified for the activity.     

Indispensability of Iron-bound Chick Transferrin for Chick Myogenesis in Vitro

Myotrophic activity of highly purified chick transferrins (Tfs) to chick primary myogenic cells has been studied in a culture medium containing horse serum. Iron-binding to Tfs is indispensable for the activity. The removal of iron from Tfs gives rise to a complete loss of the activity and it is restored by iron-rebinding depending on the amount of bound iron. This result, combined with other physicochemical and immunological data, strongly, confirms that the myotrophic activity is exerted by the Tfs themselves, not by a contaminating material(s). It has been found that culture medium containing horse Tf which seems inadequate for the study of the biological effects of Tfs is, however, suitable for studies on chick Tfs, since horse Tf is inactive in promoting chick myogenesis. Terminal sialic acid residues are unrelated to myotrophic activity since Tfs with different numbers of residues (0, 1, and 2 moles/Tf molecule) are comprable in their activities. The mechanism of Tf action on cells and contradictions among previous papers as to the requirement of Tf for cell growth have been discussed from the viewpoint of an iron-donor with class-specificity.     

Mesophyll conductance decreases in the wild type but not in an ABA‐deficient mutant (aba1) of Nicotiana plumbaginifolia under drought conditions

Under drought conditions, leaf photosynthesis is limited by the supply of CO₂. Drought induces production of abscisic acid (ABA), and ABA decreases stomatal conductance (g_s). Previous papers reported that the drought stress also causes the decrease in mesophyll conductance (g_m). However, the relationships between ABA content and g_m are unclear. We investigated the responses of g_m to the leaf ABA content [(ABA)_L] using an ABA‐deficient mutant, aba1, and the wild type (WT) of Nicotiana plumbaginifolia. We also measured leaf water potential (Ψ_L) because leaf hydraulics may be related to g_m. Under drought conditions, g_m decreased with the increase in (ABA)_L in WT, whereas both (ABA)_L and g_m were unchanged by the drought treatment in aba1. Exogenously applied ABA decreased g_m in both WT and aba1 in a dose‐dependent manner. Ψ_L in WT was decreased by the drought treatment to ?0.7 MPa, whereas Ψ_L in aba1 was around ?0.8 MPa even under the well‐watered conditions and unchanged by the drought treatment. From these results, we conclude that the increase in (ABA)_L is crucial for the decrease in g_m under drought conditions. We discuss possible relationships between the decrease in g_m and changes in the leaf hydraulics.     

Mode of Action of some Stimulants of the Hatching Enzyme Secretion in Fish Embryos*

Mode of action of two stimulants of the hatching enzyme secretion, electric current (AC) and potassium cyanide, was analyzed by applying them to Medaka embryos in the presence or absence of suppressants of nervous system-mediated secretion, tetrodotoxin or MS–222. Electric current (AC) stimulated the secretion of the hatching gland of the embryos that had been treated with these suppressants, while potassium cyanide did not. These results strongly suggest that electric current acts as a stimulant of hatching enzyme secretion directly on the gland cell itself, while potassium cyanide stimulates the secretion indirectly, probably through nervous system of the embryo. In the present experiments, it was also shown that Ca²⁺ and ionophore, X-537A, when applied directly to the hatching gland extracellularly, induced a marked secretion-associated morphological change of the gland cells instantaneously. However, it was found that chum salmon prolactin did not induce the secretion-associated morphological changes in the hatching gland cells when it was applied directly to the gland cells in situ or indirectly through embryonic circulation.     

DIFFERENTIATION OF ACTIVITY PATTERNS IN THE SUPRAHYOID MUSCLES DURING SWALLOWING OF FOODS WITH FIVE TASTE QUALITIES

Activity patterns of the suprahyoid muscles were examined using a new analytical technique. The suprahyoid activities were recorded during swallowing of tasteless foods and foods with taste qualities (sweet, salty, sour, bitter and umami). The technique involved: (1) division of cumulative integrated suprahyoid activities from each swallow into 10 equal sections and (2) assignment of individually sectioned activities to a standardized timescale as T_P (from T₁₀To T₁₀₀; relative time for P% of the cumulative electromyogram) to enable comparison of data from different trials. Three significant differences were found in T _p between the following foods: tasteless and sour, tasteless and bitter, and sour and umami. However, the differences were not repeatedly confirmed. These results suggest that gustatory signals from food tastes affect differentially the activity patterns of the suprahyoid muscles during pharyngeal swallowing, although the effect is not permanent. This method may be used to measure taste impressions in infants and in certain disabled subjects.     

How does flowering magnitude affect seed survival in Shorea pilosa (Dipterocarpaceae) at the predispersal stage in Malaysia?

General flowering (GF), a supra-annual, irregular fluctuation in flowering and seeding at the community level, is a phenomenon unique to the tropical rainforests of South-East Asia. To test the animal pollination and predator satiation hypotheses, which are the main hypotheses that attempt to explain the ultimate cause of GF, we conducted a bagging experiment after the flowering of Shorea pilosa (Dipterocarpaceae). Seed survival at the predispersal stage was divided into two stages (1–30 days and > 30 days after flowering) and we compared the results between treatments and between GF and non-GF periods using a survival analysis. Survival during the GF period at both stages was significantly higher than during non-GF periods, suggesting that both hypotheses were supported and that synchronous flowering with GF benefits the reproductive success of S. pilosa .     

The Expression of Tyrosinase,Tyrosinase-Related Proteins 1 and 2 (TRP1 and TRP2), the Silver Protein,and a Melanogenic Inhibitor in Human Melanoma Cells of Differing Melanogenic Activities

The expression of various melanogenic proteins, including tyrosinase, the tyrosinase-related proteins 1 (TRP1) and 2 (TRP2/DOPAchrome tautomerase), and the silver protein in human melanocytes was studied in six different human melanoma cell lines and compared to a mouse derived melanoma cell line. Analysis of the expression of tyrosinase, TRP1, TRP2, and the silver protein using flow cytometry revealed that in general there was a positive correlation between melanin formation and the expression of those melanogenic enzymes. Although several of the melanoma cell lines possessed significant activities of TRP2, the levels of DOPAchrome tautomerase in extracts of human cells were relatively low compared to those in murine melanocytes. Melanins derived from melanotic murine JB/MS cells, from melanotic human Ihara cells and HM-IY cells, from sepia melanin, and from C57BL/6 mouse hair were chemically analyzed. JB/MS cells, as well as Ihara cells and HM-TY cells, possessed significant amounts of 5,6-dihydroxyindole-2-carboxylic acid (DHICA) derived melanins, this being dependent on the activity of TRP2. Kinetic HPLC assays showed that 5,6-dihydroxyindole (DHI) produced during melanogenesis was metabolized quickly to melanin in pigmented KHm-1/4 cells, whereas DHI was stable in amelanotic human SK-MEL-24 cells. A melanogenic inhibitor that has been purified from SK-MEL-24 cells that suppressed oxidation of DHI in the presence or absence of tyrosinase, but had no effect on DHICA oxidation. The sum of these results suggest that the expression of melanogenic enzymes as well as the activity of a melanogenic inhibitor are critical to the production of melanin synthesis in humans.     

Mechanisms of Central Die-back of Reynoutria japonica in the Volcanic Desert on Mt. Fuji. A Stochastic Model Analysis of Rhizome Growth

Reynoutria japonica (Polygonaceae) is a pioneer clonal herbcolonising the volcanic desert on Mt. Fuji (height 3776 m),central Japan; establishment of secondary successional speciesoccurs only in the central die-back parts of the clonal standsofR. japonica. Clonal stands were excavated and the morphologyand growth pattern of the rhizomes were investigated with specialreference to the mechanisms of central die-back. Four morphologicalparameters, length of mother rhizomes, and number, branchingpositions and branching angle of daughter rhizomes on respectivemother rhizomes were measured or counted, and their roles inrhizome growth were examined employing a stochastic computersimulation model of the whole stand development. The simulationsclarified that, of these four parameters, the branching anglewas the most influential determinant of the whole pattern ofshoot distribution and that the central die-back was producedwhen the mean branching angle was 40° or smaller. Theseresults strongly infer that the onset of central die-back iscaused intrinsically byR. japonica itself by having the meanbranching angle of 40°. The adaptive significance of thegrowth pattern is discussed in relation to resource acquiringand habitat exploitation strategies of this species. Below-ground morphology; branching angle; central die-back; clonal plant; computer simulation; Japanese knotweed;Reynoutria japonica Houttuyn; rhizome growth pattern     

Spatial heterogeneity of trophic pathways in the invertebrate community of a temperate bog

Summary 1. To examine spatial heterogeneity of trophic pathways on a small scale (<5 m diameter), we conducted dual stable isotope (δ¹³C and δ¹⁵N) analyses of invertebrate communities and their potential food sources in three patchy habitats [sphagnum lawn (SL), vascular‐plant carpet (VC) and sphagnum carpet] within a temperate bog (Mizorogaike Pond, Kyoto, Japan). 2. In total, 19 invertebrate taxa were collected from the three habitats, most of which were stenotopic, i.e. collected from a single habitat. Amongst the habitats, significant variation was observed in the isotopic signatures of dominant plant tissues and their detrital matter [benthic particulate organic matter (BPOM)], both of which were potential organic food sources for invertebrates. Site‐specific isotopic variation amongst detritivores was found in δ¹³C but not in δ¹⁵N, reflecting site‐specificity in the isotopic signatures of basal foods. The eurytopic hydrophilid beetle Helochares striatus was found in all habitats, but showed clear site variation in its isotopic signatures, suggesting that it strongly relies on foods within its own habitat. 3. The most promising potential foods for detritivores were the dead leaf stalks of a dominant plant in the VC and BPOM in the SL and carpet. An isotopic mixing model (IsoSource version 1.3.1) estimated that aquatic predators rely on unknown trophic sources with higher δ¹³C than detritus, whereas terrestrial predators forage on allochthonous as well as autochthonous prey, suggesting that the latter predators might play key roles in coupling between habitats. 4. Our stable isotope approach revealed that immobile detritivores are confined to their small patchy habitats but that heterogeneous trophic pathways can be coupled by mobile predators, stressing the importance of habitat heterogeneity and predator coupling in characterising food webs in bog ecosystems.     

DIFFERENTIATION OF SUPRAHYOID ACTIVITY PATTERNS DURING SWALLOWING OF UMAMI-TASTING FOODS

In the preceding study, the present authors differentiated the activity patterns of the suprahyoid (SH) muscles during pharyngeal swallowing of tasty and tasteless foods by using “T_P” values that assigned activity of electromyograms (EMG) to a standardized time scale. In the present study, we calculated not only the T_P values but also the In_P values (by subtracting the preceding T_P‐10 values from T_P) to analyze activity patterns of the SH EMG during pharyngeal swallowing of foods dissolved in unitary (monosodium glutamate [MSG] and disodium inosine‐5′‐monophosphate [IMP]) and binary (MSG + IMP) “umami‐” tasting solutions of low and high concentration. We found that SH activity patterns differed slightly between low and high concentration of unitary and binary umami‐tasting foods, but that SH activity patterns measured while swallowing umami‐tasting foods did not differ from those measured while swallowing sweet‐ or salty‐tasting foods, or tasteless food.