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The effect of lepidimoide (Na 2-O-rhamnopyranosyl-4-deoxy-α-L-threo-hex-4-enopyranosiduronate) and its free carboxylic acid (hereafter referred as lepidimoic acid), on senescence in oat (Avena sativaL. cv. Victory I) leaf segments in the dark was studied. Lepidimoic acid inhibited loss of total chlorophyll in excised oat leaf segments during the initial phase of senescence. The loss of total chlorophyll was also retarded in the presence of 10 μmol/L kinetin. Lepidimoic acid preserved chlorophyll content synergistically with kinetin. Lepidimoide (Na salt) preserved chlorophyll content in the absence or presence of kinetin to a similar extent as did lepidimoic acid. These facts suggest that lepidimoide causes, especially in cooperation with cytokinin, a retardation of leaf senescence as characterized by the loss of total chlorophyll in the leaves.

The cDNA fragments of auxin-binding protein (ABP1) were isolated by degenerated-primer mediated reverse transcription-polymerase chain reaction (RT-PCR) from dicotyledonous plant species, i.e. cress, mung bean, pea, radish and soybean, and monocotyledonous species, i.e. oat and rice. Cloned abp 1cDNA fragments were sequenced and compared with known abp 1clones from A. thaliana, maize, strawberry and tobacco at the amino acid level. In all plant species studied, the amino acid sequences of newly isolated abp 1clones were highly conserved at two regions (region A: Thr-Pro-Ile-His-Arg-His-Ser-Cys-Glu-Glu-Ile/Val-Phe-Ile/Thr/Val-Val-Leu/Pro/Val-Lys-Gly-Xaa-Gly-Thr-LeuAy; region B: His-Glu-Asp-Leu-Gln-Phe/Val-Leu-Asp/Val-Ile/Val-Ile-Ser-Arg-Pro-Pro), which were previously reported to be important for auxin-binding. On the other hand, some putative residues of amino acids in the region between regions A and B could be found to be specific in dicot and monocot species, respectively. Southern-blot analysis indicated a small abp 1gene family in all species studied. Northern-blot analysis indicated that the size of abp 1mRNA transcripts in all species studied was conserved at approximately 850bp. The phyloge-netic tree of ABP1 was analyzed by the UPGMA method.