Abstract
Auxin is a phytohormone important for vascular differentiation, and its apical-basal polar transport is believed to be necessary for the formation of a continuous vascular strand. We previously reported that an auxin transport inhibitor, NPA prevented tracheary element (TE) differentiation from isolated Zinnia mesophyll cells on cellular level. Interestingly, exogenously supplied auxin overcame its prevention. In this study, we first investigated the effect of NPA on establishment of polarity during TE differentiation. NPA prevented cell elongation in association with TE differentiation, and secondary wall thickenings which starts from one end of developing TEs. We also measured auxin accumulation in cultured Zinnia cells with labeled NAA. As a result, total auxin was increased by NPA treatment, but the level of free auxin was rather decreased in NPA treated cells. Based on these results, mechanism by which NPA inhibits TE differentiation will be discussed.
