In order to elucidate the allelopathic effect of leaf litter leachates under laboratory conditions, a modified 'sandwich method', which places leaves between two layers of agar, was used. Fifty mg of leaves was used per 10 cm 2 cell. Agar concentrations at 0.5-1.0% were the best for gel support in determining radicle and hypocotyl elongation of lettuce. The optimum incubation time for bioassay was three days after imbibition onset. Among 20 typical tree species in Asia, Cymbopogon citratus and Derris scandens showed the strongest inhibitory activity determined by the sandwich method, followed by Piper betle, Tamarindus indica, and Gliricidia sepium. This bioassay seems to be a reliable method for screening allelopathic activity from leaf litter leachates.Keywords: allelopathy, leaf litter leachate, sandwich method.identify allelochemiclas in situ. However, the elucidation of allelochemicals and their involvement in the allelopathy phenomenon are difficult because of the lack of route-specific bioassay methodologies. From this viewpoint, we were developing several bioassay and assessment methods in order to explore route-specific identification of allelochemicals under laboratory conditions. Previously we reported on the assessment procedure referred to as the 'plant-box method' to evaluate allelopathy through root exudates (Fujii 1992). In this article, the laboratory-based assessment method for allelopathy through fallen leaves from trees, crops and weeds is reported. Leaf litter leachates play an important role in natural conditions, and in practical farming systems such as mulching by leaf litter. Mulching with straw is a common traditional farming system in the Japanese 'Shiki-wara'. The aim of this work was to evaluate the allelopathic activity from leaf litter leachates, which was placed between two layers of agar, using the sandwich method. MATERIALS AND METHODS Selection of gel-supportTo select a suitable gelling material, we tested several compounds such as agar, kaolinite, silica gel, gelatin and

This study deals with individual and species variations in the converting activity of methotrexate (MTX) to 7-hydroxymethotrexate in animals and humans. When MTX 7-hydroxylase was assayed in six human liver cytosols, a 48-fold range of intersubject variation of the activity was observed. The variations were correlated to the concentrations of aldehyde oxidase activity in human subjects assayed with benzaldehyde as a substrate. Species differences of liver MTX 7-hydroxylase activity were also observed. The activity was highest in rabbits, followed by rats, hamsters, and monkeys but was undetectable in dogs. Strain differences of MTX 7-hydroxylase activity based on aldehyde oxidase activity were also observed in rats and mice. The results suggest that aldehyde oxidase functions as MTX 7-hydroxylase in livers of animals and humans, and the observed differences of MTX 7-hydroxylase activity are due to variations in the amount of aldehyde oxidase present.

Photoperiodic sensitivity in heading of Echinochloa oryzicola Vasing., an obligate weed in flooded rice, was determined with 20 strains originally collected in nine countries from 7S to 44N. Plants of the strains were grown under 12, 14 and 16-hr photoperiods at 25C and the days to heading after sowing were recorded to classify them in photoperiod sensitivity by the duration of the basic vegetative phase (BVP) and photosensitive phase (PSP). The strains originally collected in the temperate region above 30N were classified into those with either weak or strong sensitivity. A geographical cline was apparent among them and the strains from higher latitude exhibited heading earlier under 14-hr photoperiod. All of the seven strains from the subtropical and tropical regions below 30N had a PSP of less than 30 days and were classified among those with photoperiod insensitivity. It is likely that this trait of E. oryzicola is advantageous for its wider adaptability in diverse rice cropping systems in these regions.

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