Two possibilities have been considered to explain regulation by the axis:
(1) Specific regulatory substances move from the axis to the storage organs or
tissues where enzyme formation occurs, i.e., a hormonal mechanism. This
explanation invokes a system similar to the one in certain cereal grains, where
the embryo regulates enzyme production in the aleurone layer through the action
of gibberellins that it secretes. (2) The axis is a sink, drawing off the products of
reserve mobilization in the cotyledons or endosperm, which would otherwise
arrest continued enzymatic activity by feedback inhibition mechanisms. What is
the evidence for these two possibilities?