Studies of the Mechanism by which Daminozide (B9) Inhibits Stomatal Opening

The mechanism by which the synthetic growth retardant daminozide(B9) inhibits stomatal opening has been investigated, and itsaction compared with that of the naturally occurring growthhormone, abscisic acid. The inhibition of stomatal opening bylow concentrations of daminozide in normal air is largely reversedin CO₂-froe air, suggesting that the main effect is due to anincrease in internal CO₂ concentratiom This is supported byobservations of a raised level of CO₂ compensation in treatedleaves. The CO₂-independent light reaction of stomata does,however,also appear to be inhibited by dammozide. Higher concentrationscause damage to cells of the epidermis, and such effects couldalso be found in normal practical use of the growth retardant. The mechanism of action of daminozide on stomata has littlein common with that of abscisic acid, which does not operateby increasing the internal CO₂ concentration and does not inducecellular damage. Daminozide cannot be recommended for practicaluse as an antitrans-pirant because of its mechanism of action,which is likely to cause a decrease in the efficiency of wateruse.