The induction of biplanar growth in fern gametophytes in the presence of RNA base analogues.

The RNA base analogues, 5-fluorouracil, 2-thiouracil, and 8-azaguanine, inhibit the growth of Dryopteris borreri, but do not prevent the transition from filamentous to biplanar growth. Transition, which occurs only when the filament has developed to 4 or 5 cells, may be considerably delayed, due to inhibition of filamentous growth, but it always occurs when the critical cell number of the filament is reached. Furthermore, the inhibitors show only a marginal differential effect on biplanar compared to filamentous growth when the growth rates are determined from kinetic studies. It is suggested that the selective effects previously reported may result from the experimental techniques used, coupled with the actual growth characteristics of the gametophyte.