A comparison of the effects of mechanically-induced stress,ethephon and silver thiosulphate on the growth of cauliflower seedlings

Mechanically-induced stress (MIS) was applied to cauliflower seedlings by brushing with paper for 1.5 minutes each day. With the possible exception of the effect on leaf 1 thickness, none of the growth responses induced by MIS were significantly nullified by spraying the seedlings with the ethylene inhibitor, silver thiosulphate (STS). The ethylene-releasing compound, ethephon, induced some changes in cauliflower growth similar to those caused by MIS, such as reduced shoot and leaf 1 weight, a reduction in cotyledon and leaf 1 area, and an increase in the thickness of leaves 1 and 2. However, other effects of ethephon were different from those of brushing. Petiole length and diameter and the weight and area of leaf 2 were reduced by brushing but generally increased by ethephon. STS reversed, at least partially, most of the ethephon effects on growth, thus demonstrating that it acts as an inhibitor of ethylene action in cauliflower.The results are discussed in relation to the possible endogenous control of MIS growth responses by endogenous ethylene and auxin.