Diversity in root aeration traits associated with waterlogging tolerance in the genus Hordeum

Abstract

Growth, root aerenchyma, and profiles of radial O2 loss (ROL) along adventitious roots were evaluated in 35 'wild' Hordeum accessions and cultivated barley (H. vulgare L. ssp. vulgare) when grown in stagnant nutrient solution (deoxygenated and containing 0.1% agar). When grown in stagnant solution, accessions from wetland and 'intermediate' habitats were superior, compared with accessions from non-wetland habitats, in maintaining relative growth rate, tillering, and adventitious root mass. Constitutive aerenchyma formation in adventitious roots was ≥�10% in 22 accessions (cf. H. vulgare at 2%). When grown in stagnant solution, aerenchyma was ≥� 20% in the adventitious roots of 14 accessions (cf. H. vulgare at 12%). Variation among the accessions in the volume of aerenchyma formed when grown in aerated or stagnant solution was not determined by the waterlogging regime of the species' natural habitat. However, the genus Hordeum comprises four genomes and when grown in stagnant solution accessions with the X genome formed, on average, 22% aerenchyma in adventitious roots (50 mm behind apex), whereas those with the H genome averaged 19%, and those with the Y or I genomes averaged 16 and 15%, respectively. Sixteen accessions formed a barrier to ROL in the basal region of adventitious roots when grown in stagnant solution. The formation of a barrier to radial O2 loss was predominant in accessions from wet habitats, and absent in accessions from non-wetland habitats. In addition, this trait was only present in accessions with the X or H genomes. The combination of aerenchyma and a barrier to ROL enhances the longitudinal diffusion of O2 within roots towards the apex. The possibility of a link between having a barrier to ROL and the X or H genomes in Hordeum species might, in future studies, enable a genetic analysis of this important trait.

Differences in Vegetative Growth Response to Soil Flooding between Common and Tartary Buckwheat

“…Formation of aerenchyma in roots under soil fl ooding is thought to be an adaptive trait (Mustrough and Albrecht, 2003;Setter and Waters, 2003). There is a correlation between tolerance to fl ooding and aerenchyma formation in wheat (Huang et al, 1994a) but not in Hordeum (Garthwaite et al, 2003). Further investigation will be needed on the biochemical and structural adaptation in roots to understand the fl ooding tolerance of common and Tartary buckwheat.…”

Acclimation to soil flooding — sensing and signal-transduction

“…In contrast, lysigenous aerenchyma can develop in both mature and in newly-developing roots (although older wheat roots were not capable to form aerenchyma (Thomson et al, 1990)), and its presence often depends on environmental stimuli. Many crop species, such as wheat (Triticum aestivum -Huang et al, 1994;Boru et al, 2003;Malik et al 2003), barley (Hordeum vulgare -Bryant, 1934;Garthwaite et al, 2003), maize (McPherson, 1939;Drew et al, 1979;Konings and Verschuren, 1980), sunflower (Kawase, 1979), and rice (Jackson et al, 1985b), form lysigenous aerenchyma. This is probably the reason why so little research has been done on the regulation of schizogenous aerenchyma formation (Jackson and Armstrong, 1999), whereas the inducible signal-transduction pathway of lysigenous aerenchyma has gained far more attention, particularly by using maize root aerenchyma as a model.…”

Waterlogging tolerance and capacity for oxygen transport in Brachypodium distachyon (Bd21)

“…In Oryza sativa (rice) and Hordeum marinum, suberin and/or lignin in the outer part of roots are thought to contribute to the barrier (Garthwaite et al 2008, Kotula et al 2009a, Kotula et al 2009b, Ranathunge et al 2011 can be detected ). These strategies for acclimating to waterlogged conditions are found in several wetland plants, including rice (Justin and Armstrong 1991, Colmer et al 1998, Colmer et al 2006, Rumex palustris (Visser et al 1995, Visser et al 2000 and H. marinum (Garthwaite et al 2003, Garthwaite et al 2008). However, other crops, such as wheat (McDonald et al 2001b), barley (Garthwaite et al 2003) and maize (Zea mays) (Drew et al 1979, Abiko et al 2012b, can form aerenchyma and newly formed roots, but cannot form an ROL barrier.…”

“…These strategies for acclimating to waterlogged conditions are found in several wetland plants, including rice (Justin and Armstrong 1991, Colmer et al 1998, Colmer et al 2006, Rumex palustris (Visser et al 1995, Visser et al 2000 and H. marinum (Garthwaite et al 2003, Garthwaite et al 2008). However, other crops, such as wheat (McDonald et al 2001b), barley (Garthwaite et al 2003) and maize (Zea mays) (Drew et al 1979, Abiko et al 2012b, can form aerenchyma and newly formed roots, but cannot form an ROL barrier. These crops are more sensitive to waterlogging than wetland plants.…”