Biological activities of gibberellin biosynthesis-related substances in the barley endosperm test

The biological activities of various gibberellin biosynthesis-relatedsubstances; mevalonic acid, kaurene derivatives, steviol, GA₁₈,GA₃₈, GA₂₃, GA₂₈ and GA₃, were examined using the barley endospermtest, with the "paper disc method", which responds to a verysmall amount of gibberellin. Mevalonic acid was inactive. Kaurene was slightly active andits activity levelled off at a relative small dosage. Thoughthe activity of kaurenol after a short period was similar tothat of kaurene after a longer period, the former showed anoptimum curve of activity after a longer period. Kaurenoic acid,steviol and GA₁₈ also showed an optimum activity curve, aftera short period in which the highest activity increased in thesequence given. The activities of GA₃₈, GA₂₃ and GA₃ were foundto be high after a very short period, increasing in the sequencegiven and linearly with an increase in dosage although GA₂₈was very slightly active after a longer period. (Received October 26, 1974; )