Published online by Cambridge University Press: 12 June 2017
The herbicides 2,6-dichlorobenzonitrile (dichlobenil), 7-oxabicyclo-(2.2.1)heptane-2,3-dicarboxylic acid (endothall), and 3,5-dibromo-4-hydroxybenzonitrile (bromoxynil) were examined for their influence on the activity and synthesis of proteolytic enzyme(s) in the cotyledons of squash (Cucurbita maxima Duchesne) seedlings. None of these herbicides affected the activity per se of the isolated proteolytic enzyme(s). The presence of the herbicides in the culture solution during germination caused different effects on the development of the proteolytic activity in the cotyledons for each of the three herbicides. Dichlobenil reduced the development of the activity in both the excised cotyledons and the cotyledons of intact embryos. This inhibition was overcome in part by the addition of benzyladenine to the culture solution. The inhibition of hormone synthesis or export by the embryonic axis caused by dichlobenil could explain the observed results. Endothall inhibited the development of the proteolytic activity in the cotyledons of the intact embryo treatment but had little effect on the excised cotyledons. Benzyladenine did not reverse this inhibition. The effect of endothall resembled the inhibition caused by actinomycin D, possibly indicating that endothall interfered with ribonucleic acid metabolism. Bromoxynil inhibited the proteolytic enzyme(s) development in the cotyledons of intact embryos but not in the excised cotyledons. This inhibition was partly overcome by benzyladenine. These results suggest that bromoxynil not only interferes with the hormonal control mechanism but also proteinase synthesis.