CHANGES IN THE AMOUNT OF GIBBERELLIN-LIKE SUBSTANCES IN THE SEEDLING OF PHARBITIS NIL WITH SPECIAL REFERENCE TO EXPANSION OF COTYLEDON

Two gibberellin-like substances were separated chromatographicallyfrom the ethanol-extract of germinating cotyledons of Pharbitisnil. In the dark-grown seedling, these substances in the cotyledonincreased in amount gradually with the slow increase in freshweight and area of the tissue, and attained, 4 days after sowing,a maximum level of 0.03 µg gibberellin A₃ equivalent pera couple of cotyledon; in the light-grown seedling, they increasedrapidly with the rapid increase in the fresh weight and area,and attained a maximum content of 0.07 µg gibberellinA₃ equivalent per cotyledon on the 6th day. When the etiolatedseedling was exposed to light, the amount of the gibberellin-likesubstances in the cotyledon increased in parallel with openingof the hypccotyl hook and expansion of the cotyledon. The openingof the hook and increase of the substances occurred in red lightas well as in far-red. Relatively small amounts of the gibberellin-like substanceswere also contained in the germinating hypocotyl and root. The growth of cotyledonary disks was promoted by gibberellinA₃ and the gibberellin-like substances from the expanding cotyledon. The dwarf rice seedling and dwarfs 1, 3 and 5 of maize respondedto the gibberellin-like substances, but dwarf Pharbitis didnot. (Received August 20, 1963; )