ABSCISIC ACID-RESPONSIVE ELEMENT BINDING PROTEIN1 (AREB1) (i.e., ABF2) is a basic domain/leucine zipper transcription factor that binds to the abscisic acid (ABA)-responsive element (ABRE) motif in the promoter region of ABA-inducible genes. Here, we show that expression of the intact AREB1 gene on its own is insufficient to lead to expression of downstream genes under normal growth conditions. To overcome the masked transactivation activity of AREB1, we created an activated form of AREB1 (AREB1DQT). AREB1DQT-overexpressing plants showed ABA hypersensitivity and enhanced drought tolerance, and eight genes with two or more ABRE motifs in the promoter regions in two groups were greatly upregulated: late embryogenesis abundant class genes and ABA-and drought stress-inducible regulatory genes. By contrast, an areb1 null mutant and a dominant loss-of-function mutant of AREB1 (AREB1:RD) with a repression domain exhibited ABA insensitivity. Furthermore, AREB1:RD plants displayed reduced survival under dehydration, and three of the eight greatly upregulated genes were downregulated, including genes for linker histone H1 and AAA ATPase, which govern gene expression and multiple cellular activities through protein folding, respectively. Thus, these data suggest that AREB1 regulates novel ABRE-dependent ABA signaling that enhances drought tolerance in vegetative tissues.

Keywords: allelopathy, leaf litter leacheate, plant species, sandwich method. time-consuming bioassay method and could be used to screen a large number of samples.

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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

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