The effect of niacin related compounds on the growth of various plant seedlings was investigated during 10 days after sowing. The most effective compound was cinchomeronic acid (CA : pyridine-3, 4-dicarboxylic acid) with radish seedling and the relative growth rate of the stem was 2.18 at 10 mM as compared to that of the control. No effect was observed with nicotinic acid, nicotinamide, etc. To obtain the fundamental data for solving the action mechanism of CA, following experiments were carried out. The cell size of the stem was changed dramatically when CA was width was about the half as compared to that of the control sample on the microphotograph. Incorporation of CA into the plant body was investigated by using [^<14>C] CA. As the results, the total amount of incorporated CA was increased with the growth and the amount in a stem part was 5 times higher than that in a leaf part. After incubating [3, 4, 7, 8-^<14>C] CA with the cell-free extract from radish seedling, the reaction mixture was analyzed with radio-HPLC and no radio active peak other than CA was observed on the chromatogram. And also no peak except CA was observed in the extract from radish seedling grown on the medium containing [^<14>C] CA. Hence, CA may not be metabolized in the plant body and shows the effect by itself not by it's metabolite. The effect of various plant hormones on the growth of radish seedling was investigated. As the result, only 3-indolebutyric acid and 3-indoleacetic acid has slight effect. CA is known as a chelating agent, so the effect of EDTA on the plant growth was investigated. The result showed that no promoting effect was observed with it. So, the growth-promoting effect of CA may not be due to the chelating action of CA.
