Classic experiments suggested that a floral stimulus, florigen, could move across a graft from an induced plant to a noninduced plant and trigger flowering. Recent evidence using Arabidopsis has recently shown that florigen is probably

A) a phytochrome molecule that is activated by red light.
B) a protein that is synthesized in leaves, travels to the shoot apical meristems, and initiates flowering.
C) a membrane signal that travels through the symplast from leaves to buds.
D) a second messenger that induces Ca⁺⁺ ions to change membrane potential.
E) a transcription factor that controls the activation of florigen-specific genes.