Carbohydrate Metabolism of Rice Seedlings Grown in Oxygen Deficient Solution

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Abstract
Atwell, B. J. and Greenway, H. 1987. Carbohydrate metabolism of rice seedlings grown in oxygen deficient solution.—J. exp. Bot. 38: 466–478. Rice seedlings (Oryza sativa L.) were grown in the dark for up to 4 d in solutions containing various concentrations of O2. The rate of depletion of the endosperm was most rapid in aerated solution (0·25 mol O2 m–3), largely due to the inhibition of growth of seedlings at very low O2 concentrations. Earlier suggestions that there is a deficit of sugars for growth and energy generation in O2 deficient coleoptiles were tested. Coleoptiles, shaking in aerated solution, respired about one-third of the endogenous sugars to CO2 and incorporated the rest into structural compounds. In contrast, the proportion of carbon which went to growth in anoxia was very low. Consistent with these results, endogenous sugar levels were generally highest at low O2 concentrations. Even so, coleoptiles grown and tested as low as 0·03 mol O2 m–3 showed appreciable metabolism of exogenous 14C-glucose to CO2, soluble and insoluble compounds, suggesting that a minimal O2 supply was sufficient to sustain some growth. Furthermore, glucose feeding caused little or no rise in O2 uptake or tissue sugar levels. Similarly, the specific activity of the evolved CO2 was not markedly different in coleoptiles growing at 0·03 and 0·25 mol O2 m–3 Further evidence was obtained to show that endogenous substrates were adequate for growth and respiration at both low and high O2 concentrations. Exogenous glucose and malate did not stimulate O2 uptake at any stage of growth in aerated coleoptiles. There was sufficient endogenous substrate to sustain a 35–45% rise in O2 uptake induced by uncoupling and enrichment with O2. Exogenous glucose did not stimulate growth of intact seedlings at any O2 concentration.