Enzymic mechanism of starch synthesis in ripening rice grains VI. Isozymes of starch synthetase

The DEAE-cellulose column chromatography has shown two differentforms of starch synthetase, which are referred to as fractionsI and II in extracts of rice seeds (non-waxy and waxy varieties)harvested at the milky stage. Similarly treated leaf extractsof rice (non-waxy) and maize (non-waxy) also demonstrate dieexistence of two major isozyme fractions. In all enzyme preparationstested, ADP-glucose was the sole glucosyl donor and UDP-glucosewas totally inactive. Rechromatography, on a DEAE-cellulosecolumn, of two enzyme fractions (I and II) separated from non-waxyrice seed extracts did not alter their elution patterns. Someof their enzymic properties were compared, in particular, theirglucosyl-acceptor (primer) specificities. Regardless of potentamylase activities in the two fractions, notable differenceswere observed in that fraction I utilized the long-chain oligosaccharides[maltododecaose] and various types of high molecular -glucansmore readily than fraction II. However, short-chain oligosaccharides[maltose, maltotriose and maltotetraose] were utilized morereadily by fraction II than by fraction I. A possible role forthe two starch synthetase isozymes in starch synthesis in plantcells is discussed. (Received January 5, 1971; )     

Carbon dioxide balance of a tropical peat swamp forest in Kalimantan, Indonesia

Tropical peatlands, which coexist with swamp forests, have accumulated vast amounts of carbon as soil organic matter. Since the 1970s, however, deforestation and drainage have progressed on an enormous scale. In addition, El Niño and Southern Oscillation (ENSO) drought and large‐scale fires, which grow larger under the drought condition, are accelerating peatland devastation. That devastation enhances decomposition of soil organic matter and increases the carbon release to the atmosphere as CO₂. This phenomenon suggests that tropical peatlands have already become a large CO₂ source, but related quantitative information is limited. Therefore, we evaluated the CO₂ balance of a tropical peat swamp forest in Central Kalimantan, Indonesia, using 3 years of CO₂ fluxes measured using the eddy covariance technique from 2002 through 2004. The forest was disturbed by drainage; consequently, groundwater level (GL) was reduced. The net ecosystem CO₂ production (NEP) measurements showed seasonal variation, which was slightly positive or almost zero in the early dry season, and most‐negative late in the dry season or early the rainy season. This seasonality is attributable to the seasonal pattern of climate, tree phenology and fires. Slightly positive NEP resulted from smaller ecosystem respiration (RE) and larger gross primary production (GPP) under conditions of high photosynthetic photon flux density (PPFD) and large leaf area index (LAI). The most‐negative NEP resulted from smaller GPP and larger RE. The smaller GPP was related to high vapor pressure deficit (VPD), small LAI and low PPFD because of smoke from fires. The larger RE was related to low GL. Annual NEP values were estimated respectively as −602, −382 and −313 g C m⁻² yr⁻¹ for 2002, 2003 and 2004. These negative NEP values show that the tropical peat swamp forest, disturbed by drainage, functioned as a CO₂ source. That source intensity was highest in 2002, an ENSO year, mainly because of low PPFD caused by dense smoke emitted from large fires.     

PRESENCE OF THREE ACTIN TYPES IN SKELETAL MUSCLE OF CHICK EMBRYOS

The types of actin present during development of skeletal muscle in chick embryos were investigated by various electrophoretic methods. The proportions of the actin types in the tissue were estimated by a novel method involving separation of actin bands by electrophoresis, staining of the bands with Coomassie Brilliant Blue R–250, extraction of dye and measurement of its absorbance.
Results showed that α-, β- and γ-actins were all present in embryonic skeletal muscle and were assembled into myofibrils. However, β- and γ-actins disappeared from myofibrils as muscle development proceeded. In embryonic muscle, the proportions of the three actin types in the soluble and myofibril fractions were different: their amounts were in the order β>γ>α in the soluble fraction, and α>β>γ in the myofibril fraction.     

INDUCTION OF THE ACROSOME REACTION ON THE EGG SURFACE OF DE-JELLIED SEA URCHIN EGGS BEFORE AND AFTER FERTILIZATION*

The capacity of the surface of sea urchin eggs to induce the acrosome reaction was assayed by estimating the rate of acrosome reaction of supernumerary spermatozoa in the presence of variously treated eggs before and after fertilization. DTT-disruption of the vitelline coat did not eliminate the acrosome reaction-inducing capacity. This capacity was retained after fertilization in eggs of both H. pulcherrimus and A. crassispina. The acrosome reaction-inducing capacity of the eggs was markedly decreased by treatment with trypsin. The low capacity of the trypsin-treated eggs was maintained after fertilization in H. pulcherrimus, but in A. crassispina the capacity returned to the pre-trypsin treatment level after fertilization. Fertilized eggs from which the fertilization membrane was mechanically removed retained the inducing capacity to a considerable extent, independent of the presence or absence of the hyaline layer, but the capacity diminished rapidly as cleavage proceeded. It was concluded from these data that the acrosome reaction of spermatozoa actually occurred at the surface of de-jellied eggs and that the inducing substance resides in the plasma membrane in addition to the fertilization membrane. A chemical difference between the inducing substance of egg surface and jelly substance is discussed.     

FINE STRUCTURE OF LOACH OOCYTES DURING MATURATION IN VITRO

The morphological changes during in vitro maturation of Misgurnus anguillicaudatus oocyte are described. The process of oocyte maturation can be divided into three provisional stages based on morphological events. Fully-grown, immature oocytes are opaque yellowish-white. The morphological characteristics of their ooplasm are the existence of annulate lamellae, a mass of long mitochondria and an electron dense layer beneath the vitelline surface. Three hr after a 1 hr exposure to corticosterone, these structures disappear and the cortical ooplasm becomes semi-transparent. In this stage of the maturation process (Stage I), the germinal vesicle, without a nucleolus, moves toward the animal pole, and scattered cytoplasmic inclusions approach the vitelline surface. Six hr after exposure to the hormone (Stage II), the whole ooplasm becomes semi-transparent and large yolk platelets are seen in the animal pole region. Tubular endoplasmic reticula develop throughout the ooplasm and some cortical alveoli (CA) become aligned beneath the vitelline surface. Nine hr after exposure to the hormone (Stage III), the oocyte chorion separates from the follicle cells. Most CA align beneath the vitelline surface and cytoplasm accumulates in the cortical region of the animal hemisphere.     

CONJUGATED ECDYSONE IN THE EGGS OF THE SILKWORM, BOMBYX MORI

A high activity of molting hormone (ecdysone) was detected in the extract of unfertilized, diapausing and developing silkworm eggs. The active substance in the diapause eggs behaved as a highly polar molecule at partitioning between n -butanol and water, and also in TLC. The majority of the activity seems to be due to a conjugated ecdysone, since the polar active substance was changed to a less polar substance upon treatment with "snail enzymes".     

Effects of pH on the Fertilization Response of the Medaka Egg

The effects of changing the intra- and extracellular pH on the cortical reaction and sperm penetration into eggs were examined in Oryzias latipes. When eggs were inseminated in a saline adjusted to various pH values with different buffers, fertilization took place normally over a wide range of external pH (pH₀) from about 6 to 10 with a peak at 7 to 8.5. The primary causes of the reduced fertilization were impaired motility or immobility of the spermatozoa in the acidic saline and the swelling of the chorion in the alkaline saline. A rise in the intracellular pH (pH_i) shortly after commencement of the cortical reaction was found by monitoring the color of a pH indicator micro-injected into the cytoplasm. The experimental results obtained by microinjection of various pH buffers (pH 4–12) suggest that the intracellular membrane fusion of the plasma membrane with the cortical alveolar membrane (CABD) is affected by the acidic pH_i while the propagation of the CABD and the intercellular membrane fusion between the plasma membranes of the egg and the spermatozoon are affected by the acidic pH₀.     

TRANSCELLULAR BIOSYNTHESIS OF CYSTEINYL LEUKOTRIENES BY KUPFFER CELL—HEPATOCYTE COOPERATION IN RAT LIVER

We previously proposed that an enzymatic cooperation between Kupffer cells and hepatocytes may play an important role in cysteinyl leukotriene (LT) production in rat liver. Anin vitrotranscellular synthesis cysteinyl LTs by a Kupffer cell—hepatocyte coculture system was characterized here. Kupffer cells alone, with A23187 stimulation, did not generate cysteinyl LTs until supplemented either with isolated hepatocytes or with LTC₄synthase and glutathione, indicating that Kupffer cells can synthesize LTA₄but not convert it into LTC₄. In contrast, hepatocytes converted the LTA₄into cysteinyl LTs and further degraded the cysteinyl LTs. Cysteinyl LT production by the Kupffer cell—hapatocyte coculture system was optimized by addition of 1–3% serum albumin to the culture and by bringing the cell—cell distance closer to less than 3μ. Tumour necrosis factor also stimulated cysteinyl LT production by the coculture system. From these results, it is expected that the Kupffer cell—hepatocyte transcellular system for cysteinyl LT production actually functionsin vivo.