Nicaraguan teosinte Zea nicaraguensis, a species found in frequently flooded areas, is useful germplasm for breeding flooding-tolerant maize. Mano and Omori select flooding-tolerant lines using a library of introgression lines (ILs), each containing a chromosome segment from Z. nicaraguensis in the maize (Z. mays) inbred Mi29. The most flooding-tolerant line they identify contains a Z. nicaraguensis chromosome segment on the long arm of chromosome 4, suggesting the presence of a major quantitative trait locus (QTL) in that region. There is no significant relationship between the capacity to form constitutive aerenchyma and flooding tolerance in the ILs, indicating the presence of other factors related to flooding tolerance under reducing soil conditions.
Suaeda maritima shows morphologically different forms on high and low areas of the same salt marsh. Wetson et al. demonstrate that roots of this halophyte have a constitutively very high activity of lactate dehydrogenase (LDH) regardless of whether they are growing in aerated or severely hypoxic conditions, and not the inducible increase in activity that has been demonstrated in other plants during hypoxia. This high LDH activity is likely to be a factor in the high phenotypic plasticity observed in reciprocal transplants between high- and low-marsh field sites and in simulated tidal-flow tanks in a glasshouse.
Many wetland species form both aerenchyma and a barrier to radial oxygen loss (ROL) in roots, which enhance internal O2 diffusion to the root apex. Shiono et al. study the dynamics of these features for short or long roots of rice, Oryza sativa, when they are exposed to non-aerated conditions and find that barrier induction commences more quickly in longer roots; there are no differences in aerenchyma formation. ROL barrier induction occurs before histochemically detectable changes in putative suberin and lignin deposits can be seen, suggesting that the structural changes required for barrier functioning are subtle.