Auxin depletion from leaf primordia contributes to organ patterning

Significance Stem cells not only initiate organs, but may also contribute to organ patterning, at least in the shoot apex of flowering plants: classical microsurgical experiments imply that the shoot apical meristem promotes development of the leaf adaxial side, i.e., the upper side. In this study, we show the existence of a transient low auxin zone in the adaxial side that contributes to adaxial development. We further find that this adaxial low auxin zone results from auxin transport from leaves to the shoot apex. Thus, it is not a positive signal from stem cells, but departure of a signaling molecule from primordia to stem cells, that delivers polarity information—opposite to what is generally assumed.