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Ion transport in seminal and adventitious roots of cereals during O₂ deficiency

Colmer, Timothy David, Greenway, Hank
Journal of experimental botany 2011 v.62 no.1 pp. 39-57
cortex, ion channels, rhizosphere, energy, ions, nutrient deficiencies, stele, ion transport, nutrient uptake, oxidative phosphorylation, adventitious roots, soil, wheat, root growth, nutrient solutions, flooded conditions, xylem, root shoot ratio, hypoxia, shoots
O₂ deficiency during soil waterlogging inhibits respiration in roots, resulting in severe energy deficits. Decreased root-to-shoot ratio and suboptimal functioning of the roots, result in nutrient deficiencies in the shoots. In N₂-flushed nutrient solutions, wheat seminal roots cease growth, while newly formed adventitious roots develop aerenchyma, and grow, albeit to a restricted length. When reliant on an internal O₂ supply from the shoot, nutrient uptake by adventitious roots was inhibited less than in seminal roots. Epidermal and cortical cells are likely to receive sufficient O₂ for oxidative phosphorylation and ion transport. By contrast, stelar hypoxia-anoxia can develop so that H⁺-ATPases in the xylem parenchyma would be inhibited; the diminished H⁺ gradients and depolarized membranes inhibit secondary energy-dependent ion transport and channel conductances. Thus, the presence of two transport steps, one in the epidermis and cortex to accumulate ions from the solution and another in the stele to load ions into the xylem, is important for understanding the inhibitory effects of root zone hypoxia on nutrient acquisition and xylem transport, as well as the regulation of delivery to the shoots of unwanted ions, such as Na⁺. Improvement of waterlogging tolerance in wheat will require an increased capacity for root growth, and more efficient root functioning, when in anaerobic media.