Anoxia tolerance of the rhizomes of three Japanese Iris species with different habitat

The Japanese Iris species, Iris laevigata Fisch., I. ensata Thunb., and I. sanguinea Hornem., have different habitat. However, the physiological basis that can explain the difference in the habitat is not clear. In the present study, the responses in rhizomes to anoxic conditions in the three Iris species were determined. Rhizomes of I. laevigata and I. ensata, which prefer shallow-water areas or wetlands, survived 28 days of anoxia, but those of I. sanguinea, which typically grows on dry land, could not. The activity of alcohol dehydrogenase, a key enzyme in the energy metabolism under anoxia, was detected during anoxic incubation of rhizomes of all the three Iris species, but continued to increase for 28 d only in I. laevigata. Moreover, a substantial increase in the ethanol content of rhizomes was observed only after 7 d of anoxic incubation of I. sanguinea. Although the content of sucrose and storage polysaccharides in the rhizomes of both I. laevigata and I. sanguinea decreased during incubation, the decrease was more pronounced in the latter under anoxia. These results suggest that I. laevigata and I. ensata are successfully adapted to aquatic environment owing to the tolerance of their rhizomes to low-oxygen conditions through the maintenance of energy metabolism.