queen substance A pheromone secreted by queen
bees and given to worker bees that controls them from
producing more queens.
quiescent center A region of cells behind the root cap
that contains a population of mitotically inactive cells;
precedes the organization of a root meristem and con-
tains high levels of the enzyme ascorbic acid oxidase,
which may suggest a mechanism that links gene expres-
sion with patterning. It is the region in the apical meris-
tem that has little activity, and cells rarely divide or do so
very slowly. However, cells can be encouraged to divide
bywounding of the root. The quiescent center (QC) con-
sists of a small group of cells at the tip called the initials.
It is the initials that divide very slowly and create the qui-
escent center. Cells around the QC divide rapidly and
form the majority of the cells of the root body.282 queen substance