Response of Plant Hormone bioassay to Paclobutrazol

Abstract

Quantitative estimation of a known or suspected biologically active substance (such as a hormone or drug) by measuring its effect on a living organism in standard conditions is known as bioassay. The interaction of gibberellic acid (GA3) and paclobutrazol (PBZ) in lettuce hypocotyl bioassay and 6-benzyl aminopurine (BAP) and paclobutrazol in radish cotyledon enlargement test that paclobutrazol counteracts gibberellin activity when applied exogenously. The radish cotyledon enlargement at low concentration without counteracting BAP action. The reduction of growth to be counteracting of gibberellin activity by paclobutrazol as well as its cytokinin well activity at lower concentration which indicate concentration of gibberellins activity as evidence by their respective bioassay in the present investigation. Paclobutrazol slightly increased radish cotyledon growth at low concentration (up to 0.01 ppm) and could not counteract the growth caused by 1.0 ppm BAP at its 0.001 to 1.0 ppm concentrations suggesting independent effect of paclobutrazol to that of BAP. Furthermore, the activity of paclobutrazol was tested in corn root curvature test and it was found that PBZ concentrations from 0.001 to 10.0 ppm linearly increased the percentage of corn roots showing more than 90° curvature. Therefore, suggession that PBZ conutracted GA3, induced growih and also as IAA and cytokinin at lower concentration0.001 to 100ppm.