Mechanisms of morphological adaptation of roots to waterlogging in gramineous plants

Abstract

Roots of gramineous plants can be morphologically adapted to waterlogging in soil, where dissolved oxygen concentrations are extremely low. To adapt to such conditions, some gramineous plants develop lysigenous aerenchyma, which is formed by the creation of gas spaces as a result of death and the subsequent lysis of some cells, in the root cortex. Internal transport of oxygen from shoots to roots through aerenchyma is essential for plants to survive under waterlogged conditions. Although it is well known that the gaseous phytohormone ethylene is involved in induction of aerenchyma formation, the detail molecular mechanisms underlying inducible aerenchyma formation remained to be elucidated. Previously, we identified genes associated with aerenchyma formation in maize roots by using a microarray analysis combined with laser microdissection, and found that the expression of genes encoding generation/ scavenging of reactive oxygen species is confined to cortical cells. This suggests that reactive oxygen species are involved in inducible aerenchyma formation in gramineous plants. Recently, we showed that adventitious roots of wheat seedlings that emerge under waterlogged conditions have thicker root diameters and larger air spaces (i.e., aerenchyma) than adventitious roots that emerge under aerobic conditions. Therefore, the thicker root diameters would contribute to the transport of oxygen from shoots to roots. In this article, we summarize recent advances in understanding the molecular mechanisms of aerenchyma formation in gramineous plants, and discuss the mechanisms for morphological adaptation of roots of gramineous plants to waterlogging in soil.