Figure 11.

A summary of the low-fluence R light effect on the transport and biosynthesis of IAA. In dark-grown seedlings, IAA biosynthesis is high at the top of the hypocotyl and is low in the lower part of the hypocotyl. IAA synthesized in the top section moves basipetally in the PAT stream to supply free IAA to lower hypocotyl regions. When seedlings were exposed to R light, IAA biosynthesis at the top section increased, and IAA transport in the adjacent hypocotyl region also increased to move newly synthesized IAA to the lower hypocotyl regions, which maintained a constant free IAA level at the top section and increased free IAA in the lower portion of the hypocotyl. [See online article for color version of this figure.]