Abstract. An unknown substance(s) produced in the cotyledons of seedlings of the Japanese morning glory (Pharbitis nil) during a defined period of darkness triggers the subsequent initiation of floral buds at apical and axillary meristems. Recent studies have concentrated on characterizing molecular changes as a possible mechanism associated with its synthesis, but these have failed to eliminate interference due to lack of development unity in the sampled population and to consider different kinetic alternatives of those potential changes. The current study demonstrates that numerous age-related changes occur in polypeptides from cotyledons during growth under noninductive conditions, but that these are minimal in older seedlings selected for improved synchrony of the floral response. Polypeptides from older seedlings sampled at various times during and after a dark inductive period were examined by two-dimensional polyacrylamide gel electrophoresis (2-D PAGE). No differences associated with floral induction could be detected. The results indicate that changes in gene expression correlated with floral-induction do not occur in the abundant polypeptide fraction within the limitations of the techniques employed.Floral initiation in many plants is triggered by changes in day length, a process termed photoperiodic induction, and is believed to result from the synthesis of a substance (or substances) within the leaves and cotyledons of the induced plant (for a review see Kinet et al. 1985). Although many attempts have been made to isolate and identify this floral-inducing substance, no success has been reported to date. Changes in gene expression have been proposed as one possible mechanism regulating or accompanying the synthesis of a floralinducing substance. Recent studies have supported this hypothesis in a number of experimental systems (Kannangara et al. 1990, Lay-Yee et al. 1987a,b, Warm 1984. However, other researchers have failed to find evidence for rapid changes in gene expression during induction (Friedman et al. 1987, Kimpel and Doss I989, Ono et al. 1988), suggesting that evidence testing this hypothesis and perhaps the hypothesis itself should be critically reevaluated.We have examined polypeptides present in vivo in cotyledons of the Japanese morning glory cv. Violet during growth and floral induction. The aim of the growth studies was to catalogue age-related differences in polypeptide profiles of seedlings that are capable of responding to photoperiodic induction and to determine morphological markers (after Lamoreaux et al. 1978) that correlate with these differences as criteria for selecting populations with improved synchrony. These populations were then used to examine cotyledon polypeptides during photoperiodic induction. The goal of these studies was to confirm whether or not changes in gene expression accompany this process, as some have reported, including changes that might arise as a consequence of posttranslational modification. We find no evidence of photoinduction-specific changes in t...
