Abstract

Dowco 242 (D-242) is a new growth regulator synthesized by the Dow Chemical Company, U.S.A. It is a derivative of a quaternary ammonium compound. The extent of the inhibitory effects of D-242 on plant growth are dependent upon: (1) Stage of plant growth-the retardative effect of this chemical on stem growth decreases with the age of the plant. (2) Tissue of plant-stem tissues and root tissues show different responses to treatment by D-242. Root growth, unlike the stem elongation, was not reduced by the chemical. Except for initial leaf expansion, the leaf number as well as the leaf area was not altered by treatment with D-242. (3) Concentration of D-242 used-the higher the concentration of D-242 utilized, the more the growth of the stem was inhibited, and a longer time was needed to reach its maximal growth. D-242 caused the reduction of stem growth because of the declination of GA3 content in plant. There is a conflict in the relationship between the GA3 content and peroxidase activity on plant growth. It seems that the peroxidase, which causes the oxidative destruction of IAA, may be enhanced or de-repressed by decreases of GA3 content in plant. Therefore, it may be concluded that the reason D-242 retards the stem growth of plants is due to the decrease of GA3 and IAA content in plants.