Feedbacks between nutrient cycling and vegetation predict plant species coexistence and invasion

To investigate the role of species‐specific litter decomposability in determining plant community structure, we constructed a theoretical model of the codevelopmental dynamics of soil and vegetation. This model incorporates feedback between vegetation and soil. Vegetation changes the nutrient conditions of soil by affecting mineralization processes; soil, in turn, has an impact on plant community structure. The model shows that species‐level traits (decomposability, reproductive and competitive abilities) determine whether litter feedback effects are positive or negative. The feedback determines community‐level properties, such as species composition and community stability against invasion. The model predicts that positive feedback may generate multiple alternative steady states of the plant community, which differ in species richness or community composition. In such cases, the realized state is determined by initial abundance of co‐occurring species. Further, the model shows that the importance of species‐level traits depends on environmental conditions such as system fertility.     

Characterization and purification of polymorphic arylalkylamine N-acetyltransferase from the American cockroach, Periplaneta americana.

We separated two forms of arylalkylamine N-acetyltransferase (AANAT) from various organs of the American cockroach, Periplaneta americana. Both forms of the enzyme had an equivalent molecular mass of 28 kDa. One form isolated from the testicular accessory glands had high enzyme activity at acidic pHs. The isoelectric point was 5-6 and the substrate specificity was wider than the other type. The other isolated form from female midguts had a higher level of enzyme activity at basic pHs. These findings suggested that P. americana contains polymorphic AANAT, as is the case in Drosophila melanogaster. These forms differed not only in pH specificity, and substrate specificity but in chromatographic behavior and kinetic properties. Most of the organs we examined contained a mixture of the two forms since two types of AANAT activity were separated in different chromatographic fractions when two pH conditions were used for activity measurement.     

Secretion of Mucor rennin, a fungal aspartic protease of Mucor pusillus, by recombinant yeast cells

Summary The aspartic protease gene of a zygomycete fungus Mucor pusillus was expressed in Saccharomyces cerevisiae under the control of the yeast GAL7 promoter. A putative preproenzyme with an NH₂-terminal extension of 66 amino acids directed by the gene was processed in yeast cells and the mature enzyme, whose NH₂-terminus was identical to that of the Mucor enzyme, was efficiently secreted into the medium at a concentration exceeding 150 mg/l. The enzyme secreted from the recombinant yeast was more glycosylated than the native Mucor enzyme but its enzymatic properties were almost identical with those of the native enzyme, which has been used as a milk coagulant in cheese manufacture.     

Purification of Protein Body-I of Rice Seed and its Polypeptide Composition

Protein body type one (PB-I) was isolated and purified fromdeveloping rice grain by a combination of sucrose density gradientcentrifugation and treatment with pepsin. SDS-PAGE analysisshowed that isolated PB-I contains several polypeptide groups,the largest having an apparent molecular size of 13 kDa andtwo smaller ones of 10 kDa and 16 kDa. The 13-kDa group wasfound to be composed of two polypeptides of slightly differentmolecular sizes, 13a (larger component) and 13b (smaller component).Most of the 13a and 13b polypeptides were shown to be largelyprolamins, although there were also some salt- and alcohol-insolublepolypeptides with an apparent molecular size of 13 kDa. It wasconcluded that PB-I is the accumulation site of rice prolamin.It was further estimated that the protein amount in PB-I accountedfor about 20% of the total protein of rice endosperm. (Received March 20, 1987; Accepted September 8, 1987)     

Induction and subsequent repair of DNA damage by fast neutrons in cultured mammalian cells

The induction and repair of DNA damage were studied by a DNA unwinding method in mouse L5178Y cells exposed to fast neutrons. DNA lesions induced by fast neutrons were classified into three types from their repair profiles: fast-reparable breaks (T1/2 = 3-5 min), slow-reparable breaks (T1/2 = 70 min), and nonreparable breaks. The repair rates of both fast-reparable and slow-reparable breaks were almost the same as those of corresponding damage induced by low-LET radiation. Neutrons induced a smaller amount of fast-reparable damage, an almost equal amount of slow-reparable damage, and a larger amount of nonreparable damage than those induced by equal doses of gamma rays or X rays. RBEs for fast- and slow-reparable damage were 0.3 and 0.9, respectively. The RBE for nonreparable damage was dose dependent and was 1.4 at the level of 100 breaks/10(12) Da DNA. Among the three types of lesions, only the nonreparable damage levels correlated with the linear-quadratic shape of the survival curves and with the enhanced killing effectiveness of neutrons (RBE = 1.7 at D0).     

Purification of sarcotoxin III, a new antibacterial protein of Sarcophaga peregrina

A glycine-rich antibacterial protein with a molecular mass of 7,000 termed sarcotoxin III, was purified to homogeneity from the hemolymph of third instar larvae of Sarcophaga peregrina. When the hemolymph was fractionated, this protein was recovered in the same fraction as sarcotoxin I, a group of potent antibacterial proteins that have been purified. But, it was clearly different from sarcotoxin I in amino acid composition and molecular mass. Sarcotoxin III was shown to be induced in the hemolymph in response to injury of the larval body wall.     

Infrageneric variation of the low molecular weight carbohydrate composition of the seeds of the genusVicia (Leguminosae)

The low molecular weight carbohydrate compositions of the seeds of 29 species ofVicia, namelyV. amoena, V. amurensis, V. bifolia, V. dumetorum, V. fauriei, V. japonica, V. nipponica, V. pisiformis, V. pseudo-orobus, V. sylvatica, V. unijuga, V. venosa, V. cassubica, V. orobus, V. cracca agg.,V. hirsuta, V. villosa agg.,V. tetrasperma,V. oroboides, V. sepium, V. cuspidata, V. grandiflora, V. lathyloides, V. sativa agg.,V. bithynica, V. faba, V. narbonensis, V. hybrida andV. lutea were determined by gas liquid chromatography. The carbohydrate compositions were found to be species-specific. Principal component analysis of the carbohydrate composition data showed that these species can be divided into three groups. Although, as far as the examined species were concerned, these groups were not correlated with the known subgenera, significant correlation between the groups and the known sections was detected in the subgenusVicia. The carbohydrate composition character would be important to clarify the relationships among closely related taxa of the genusVicia.