An enzymic site of inhibition of gibberellin biosynthesis by Amo 1618 and other plant growth retardants.

\Wirwille and M1itchell reported that apl)lications of 2'-isoprol)vl-4'(trimethv lammllonium chloride) -5'methylphenvl piperidine-1-carboxvlate (Amo 1618) (fig 1, I) to several types of flowNering plants led to ani abnormial growth habit characterized by shorter stemiis and initernodes (17). Amo 1618 is one of the mllost active of several carbamate esters containiing a q uarternarv ami-moniiumii group which prodluce this effect (12). Cathey has recently reviewed the physiological effects of these and other plant growAlth retardants (2). Sachs et al. ( 15 ) have showni that tl)l)licationi of Amo 1618 leads to a (Irastic redluction of miiitotic activity in the subapical meristem of vegetative, rootedI cuttinigs of (Chr'ysaulic,nuim mnorifoli111. Iln this case. as in numtierouis other ilnstanices rel)orted ill the literature, adde(d gibberellins partly or comllpletely overcome the actioni of plallt growtlh retardanits. [see (2) for a review]. Kend(le, Ninnemann alnd Lang (11) have providled evidence for the proposal that at least somiie of these plant growth retardlants miiay functioln b1 inhibiting the prodtlction of gibberellins in the plant. This proposal was based iniitially on their demonstrationi that the addition of .\m1