Secondary aerenchyma formation and root growth response of soybean (Glycine max) seedlings under flooded conditions.

Most of wetland species can develop their roots into flooded soils because of the presence of longitudinal aerenchyma channels that facilitates oxygen diffusion from shoot to root tips. This tissue is called as primary aerenchyma because it is formed in fundamental tissues. It is also formed in rice root, consequently rice plants can grow well in paddy field. On the other hand, it is considered that most of mesophytes such as field crops cannot grow under flooded and excess moisture conditions because of their low ability to develop aerenchyma. However, we found that soybean plants could develop aerenchyma and grow well in flooding compared with other leguminous crops such as Vigna and Phaseolus species. This type of aerenchyma, which is consisted of white spongy tissue filled with gas space and is differentiated from secondary meristem (phellogen), is called assecondary aerenchyma. It plays a role in supplying oxygen from the aerial parts to the flooded roots and nodules. In our recent study, it was observed that there was a wide range of varietal differences on secondary aerenchyma formation and adventitious root development in soybean seedlings under flooding. Although the research for secondary aerenchyma in soybean plants is on the way, it may be able to breed soybean varieties with flooding tolerance.