Response of Wheat Seedlings to Low O2Concentrations in Nutrient Solution

Abstract

Root growth of 7-d-old wheat (Triticum aestivum cv. Gamenya) seedlings was impaired at dissolved O₂ concentrations of 0.01 and 0.055 mol m⁻³ O₂, while growth at 0.115 mol m⁻³ O₂ was the same as that in continuously aerated controls (0.26 mol m⁻³ O2). Oxygen uptake by apical (0–2 mm), expanding (2–4 mm) and expanded (10–12 mm) tissues of the roots decreased below 0.16, 0.09 and 0.05 mol m⁻³ O₂, respectively. This hierarchy is consistent with the metabolic rates of these tissues. There was a small (c. 9%) inhibition of O₂ uptake and some net synthesis of ethanol and alanine in root apices at 0.115 mol m⁻³ O₂. Significant amounts of anaerobic end-products accumulated at 0.055 mol m⁻³ O₂ and even more so at 0.01 mol m⁻³ O₂, indicating that oxidative phosphorylation was strongly inhibited. Net alanine synthesis increased in fully expanded (10–16 mm) tissues exposed to −3 O₂, and this increase was accompanied either by a proportionally smaller increase in the concentration of other free amino acids or by a net decrease in free amino acid levels excluding alanine. This suggests that alanine was synthesized as an end-product of anaerobic catabolism and did not accumulate simply because of decreased net protein synthesis. Comparing the carbon flow to CO₂, ethanol, lactate and alanine in roots at 0.01 mol m⁻³ O₂ with carbon loss as CO₂ in aerated roots suggests that carbon flow to products of metabolism was not greatly enhanced due to O₂ deficiency. This infers, but does not prove that, in wheat, generation of energy during periods of O₂ deficiency is not enhanced due to a Pasteur effect.