Aerenchyma formation and radial O₂ loss along adventitious roots of wheat with only the apical root portion exposed to O₂ deficiency

Abstract

This study investigated aerenchyma formation and function in adventitious roots of wheat ( Triticum aestivum L.) when only a part of the root system was exposed to O 2 deficiency. Two experimental systems were used: (1) plants in soil waterlogged at 200 mm below the surface; or (2) a nutrient solution system with only the apical region of a single root exposed to deoxygenated stagnant agar solution with the remainder of the root system in aerated nutrient solution. Porosity increased two-to three-fold along the entire length of the adventitious roots that grew into the water-saturated zone 200 mm below the soil surface, and also increased in roots that grew in the aerobic soil above the water-saturated zone. Likewise, adventitious roots with only the tips growing into deoxygenated stagnant agar solution developed aerenchyma along the entire main axis. Measurements of radial O 2 loss (ROL), taken using root-sleeving O 2 electrodes, showed this aerenchyma was functional in conducting O 2. The ROL measured near tips of intact roots in deoxygenated stagnant agar solution, while the basal part of the root remained in aerated solution, was sustained when the atmosphere around the shoot was replaced by N 2 . This illustrates the importance of O 2 diffusion into the basal regions of roots within an aerobic zone, and the subsequent longitudinal movement of O 2 within the aerenchyma, to supply O 2 to the tip growing in an O 2 deficient zone.

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.…”

Respuesta de las plantas a estrés por inundación. Una revisión

“…En trébol blanco (Trifolium repens), Huber et al (2009) encontraron que bajo condiciones de inundación la porosidad de la raíz incrementa 60% en comparación con condiciones de buen drenaje. Igualmente, las raíces de plantas de trigo que son expuestas a inundación presentan de cuatro a cinco veces más porosidad que las de plantas crecidas en suelos bien drenados (Malik et al, 2003).…”

“…El aerénquima puede ser constitutivo en especies tolerantes a inundación como el arroz (Oriza sativa L.) o su formación puede ser inducida por factores como presencia de zonas deficientes de O 2 , el transporte interno de ácido 1-aminociclopropano-1-carboxílico, precursor del etileno, o la acumulación de etileno en el suelo (Malik et al, 2003).…”

“…Además, el aerénquima ayuda al crecimiento y producción de raíces en condiciones de anoxia (Aguilara et al, 1999;Malik et al, 2003). Bajo inundación también se incrementa la proporción de raíces nodales con aerénquima, facilitando la difusión de O 2 y la elongación de la raíz (Suralta y Yamauchi, 2008).…”

“…La inundación inhibe la actividad de enzimas como la β-D-glucosidasa y la fosfatasa, involucradas en JIMéNEZ S./MORENO F./ MAGNITSKIY los ciclos del carbono, nitrógeno, fósforo y azufre (Xiao-Chang y Qin, 2006) y se aumenta la concentración de etileno (Malik et al, 2003). Estas condiciones cambiantes en el suelo generan efectos negativos en el crecimiento y desarrollo de las plantas.…”