Some Biochemical Changes Associated with Paclobutrazol-Induced Adventitious Root Formation on Bean Hypocotyl Cuttings

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Abstract
Phaseolus vulgaris hypocotyl cuttings were placed in solutions containing either 0 (controls) or 43 μM paclobutrazol for 24 h after which they were placed in peat– perlite for 8 d. Paclobutrazol more than doubled the number of roots formed on the cuttings but did not affect individual root length. Compared with controls, treated cuttings exhibited increased activities of catalase, peroxidase, polyphenol oxidase, malate dehydrogenase, protease and RNase in the base of the cuttings. These enhanced enzyme activities were particularly evident between 3 and 5 d after excision. The largest paclobutrazol-induced promotion of enzyme activity occurred with malate dehydrogenase which was increased more than 2-fold compared with the controls. In contrast, paclobutrazol reduced amylase activity in comparison to controls, suggesting that this enzyme may not be directly related to root formation. These data indicate that the enhancement of adventitious root formation by paclobutrazol is accompanied by changes in the activities of a number of enzymes which have previously been postulated to be involved in rooting. However, these changes in activity are generally greatest later in the rooting period, suggesting that they may be involved in the development rather than the initiation of roots.