Plant Growth-regulating Activities of 4-Methoxybenzophenones

4-Methoxybenzophenones showed diverse plant growth-regulating actions; inhibition of shoot and root growth, induction of chlorosis, and a disturbance in phototropism or geotropism. No clear relationship was found between the inhibitory activities and Hammett’s σ of the substituents. A brief discussion of the relationship between the growth-inhibitory activity and the absorption wavelength explains the mode of action.