Assessment of alcohol dehydrogenase synthesis and aerenchyma formation in the tolerance of Sium L. species (Apiaceae) to water-logging

- Aerial-aquatic and terrestrial species of Sium show a similar response to flooding.
- High plasticity of root systems of the species is regulated by soil moisture.
- The anaerobic metabolism and aerenchyma formation coexist in the root apices.
- Anaerobic fermentation is an early systemic response of the plants to root flooding.
- Adventitious roots include longitudinal and honeycomb-like gas spaces in the cortex.

To survive and reproduce under the conditions of limited oxygen supply, plants develop morphological and biochemical features that are either constitutive or induced by flooding. We performed a comparative study of the root cortex structure and alcohol dehydrogenase (ADH) synthesis in widespread aerial-aquatic Sium latifolium and terrestrial S. sisaroideum (Apiaceae) in response to changes in the soil water content to check the hypothesis that plasticity of structural and metabolic traits may ensure survival and adaptation of these species at variable soil moisture − from aerated soil to water-logging. Plant grown under natural and experimental conditions were used for microscopy and enzyme assays. We show that the soil moisture determined changes in the root cortex structure and systemic switching-on of anaerobic fermentation in the investigated species. Water-logging of the terrestrial species S. sisaroideum induced first ADH synthesis and then development of new aerenchymatous adventitious roots that are inherent for aerial-aquatic plants of S. latifolium. Histochemical localization showed high ADH activity in the root apices. The aerenchyma in adventitious roots of both species consisted of longitudinal gas spaces in the inner cortex and enlarged intercellular spaces of a “honeycomb” type in the outer cortex. Thus, both Sium species showed complex anaerobic biochemical and structural responses to flooding, promoting the internal aeration of roots. The high plasticity of the root systems in S. latifolium and S. sisaroideum have led to their widespread distribution in nature.