Dominance among fruits/sinks and the search for a correlative signal

The present problems with hormonal signals transferring dominance effects are reviewed and, as a new hypothesis, it is stated that the sequence of sink development may establish the dominance effect. ‘Primigenic dominance’ (PD) is suggested to describe this kind of correlative inhibition, in which the earlier developed sink inhibits later developed organs. New results show that the polar IAA export of the earlier developed sink inhibits the IAA export of later developed sinks. This ‘autoinhibition’ occurs at ‘junctions’, where auxin streams from various sinks meet. It is suggested that this depressed IAA‐export of the subordinated fruit/sink acts as the signal that leads to inhibited development. This hypothesis avoids some of the problems related with other hypotheses, such as the requirement of a multidirectional signal. Primigenic dominance is a unifying hypothesis, which can be applied to most correlative dominance phenomena in the plant. Primigenic dominance is less complicated than the traditional ‘apical dominance’ (AD) hypothesis, because it does not require secondary messengers.