The effects of gibberellin A3, photoperiod, and age on vegetative growth and flowering inCosmos bipinnatusvar. Sensation

摘要

Plants ofCosmos bipinnatusCav. 'Sensation' (a quantitative short-day plant) were grown continuously under conditions favorable or unfavorable for flowering, and some plants in each group were treated with gibberellic acid (GA3). Morphological and anatomical observations revealed that GA3promoted floral initiation under non-inductive long days but not as efficiently as inductive short days, as judged by the rate of apical transition to the reproductive state. GA3did not influence the total number of plants that flowered but did increase height growth. Plants treated with GA3had a normal percentage of initiation, but a much lower developmental rate. Macroscopic recognition of flowering was not possible until the inflorescence stage of the apex.Floral apices ofCosmosare formed by the transition of previously vegetative apices, the apex passing into an intermediate stage typical of most plants held under non-inductive conditions. Transitional, prefloral, and inflorescence stages follow. The formation of an intermediate stage may account for many of the conflicting results observed in physiological studies since there is a great variation in response rate depending on age of plant and stage of the apex at the start of the experiment. Anatomical observations support the findings that although GA3promotes floral initiation inCosmoswhen applied under non-inductive conditions, floral development may not continue, thus resulting in an apparent lack of response. This may also be true of many other plants considered "non-responsive" to GA3under non-inductive conditions.