The Competence to flower

Prior to flowering, the cells in the SAM must first become competent to respond to a signal(s) that evokes floral initiation (McDaniel et al., 1992) . In photoperiodic flowering, this signal is produced in the leaves, which can be demonstrated by grafting of plants exposed to different day lengths .

If an apical bud is able to respond to these developmental signals then it is said to have acquired competence (McDaniel et al., 1992) .

The next stage is called determination. Once a shoot apex is determined to flower, then it will do so even after removal of leaves forming the floral stimulus. For example if a determined apex is grafted onto a vegetative shoot, which is not producing a stimulus, it will still flower (McDaniel and Hartnett, 1996) .

In some plants, such as Lolium temulentum, flowering of a determined apex is delayed in the absence of transmissible signals, although flowering still occurs. For example, even when the meristem has become determined by a long-day photoperiod signal, flowering is delayed unless gibberellic acid is supplied (Taiz and Zeiger, 2002) .

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