Effects of a Plant Growth Regulator 4,4,4–Trifluoro–3–(indole–3–)–butyric Acid on Thickening Growth of Radish Hypocotyl

Effects of a synthesized plant growth regulator 4,4,4–trifluoro–3–(indole–3–)–butyric acid (TFIBA) on thickening growth of radish hypocotyls were investigated. The thickening growth of radish hypocotyls, which are the edible part, was stimulated by TFIBA applied to the seeds before transplanting. The fresh weight of the hypocotyls in the seedlings treated with 10－4mol L－1 (10－4M) TFIBA solution significantly increased during cultivation in a growth chamber for 28 days as compared to that in the control. However, such significant increase was not observed in the seedlings treated with 10－5mol L－1 (10－5M) TFIBA solution. The fresh weight and maximal diameter of hypocotyls in the seedlings treated with TFIBA solution of 10－4M and 10－5M were significantly increased by 30–50 % as compared to those of the control at 35 days after transplanting when the seedlings were cultured in a green house under natural light and temperature conditions. The length of hypocotyls in the seedlings treated with 10－4M and 10－5M TFIBA increased approximately 20–50 % during the early growth stage as compared to that in the control. The fresh and dry weight of the shoots in the seedlings was apparently increased by treatment with 10－4M and 10－5M TFIBA solutions at 35 days after transplanting. These results suggest that TFIBA stimulates hypocotyl elongation and total photosynthetic activity in the shoots and results in promotion of thickening growth of the hypocotyls.