Effects of anti-auxins on secondary aerenchyma formation in flooded soybean hypocotyls

In flooded hypocotyl of soybean (Glycine max), cell division in phellogen and the elongation of these cells are enhanced, and thereby a secondary aerenchyma with high porosity is produced. Auxin controls cell division and cell elongation in many plants, so we studied its role in secondary aerenchyma development. Soybean plants with fully expanded unifoliolate leaves were flooded for 6 d with solutions (100 μM each) of seven anti-auxins. TIBA, NPA, HFCA, 1-NOA, or CHPAA did not restrict the secondary aerenchyma formation, while MH moderately suppressed the aerenchyma development, and PCIB strongly inhibited the development of phellogen and secondary aerenchyma. However, the endogenous IAA concentrations in the flooded hypocotyls did not increase or decrease relative to the controls until 72 h, when a secondary aerenchyma was observed. From these results, it is unclear whether auxin plays an important role in the process of secondary aerenchyma formation under flooding.