Carbohydrate Metabolism of Rice Seedlings Grown in Oxygen Deficient Solution

Atwell, B. J. and Greenway, H. 1987. Carbohydrate metabolismof rice seedlings grown in oxygen deficient solution.—J.exp. Bot. 38: 466–478. Rice seedlings (Oryza sativa L.) were grown in the dark forup to 4 d in solutions containing various concentrations ofO₂. The rate of depletion of the endosperm was most rapid inaerated solution (0·25 mol O₂ m^–3), largely dueto the inhibition of growth of seedlings at very low O₂ concentrations.Earlier suggestions that there is a deficit of sugars for growthand energy generation in O₂ deficient coleoptiles were tested. Coleoptiles, shaking in aerated solution, respired about one-thirdof the endogenous sugars to CO₂ and incorporated the rest intostructural compounds. In contrast, the proportion of carbonwhich went to growth in anoxia was very low. Consistent withthese results, endogenous sugar levels were generally highestat low O₂ concentrations. Even so, coleoptiles grown and testedas low as 0·03 mol O₂ m^–3 showed appreciable metabolismof exogenous ¹⁴C-glucose to CO₂, soluble and insoluble compounds,suggesting that a minimal O₂ supply was sufficient to sustainsome growth. Furthermore, glucose feeding caused little or norise in O₂ uptake or tissue sugar levels. Similarly, the specificactivity of the evolved CO₂ was not markedly different in coleoptilesgrowing at 0·03 and 0·25 mol O₂ m^–3 Further evidence was obtained to show that endogenous substrateswere adequate for growth and respiration at both low and highO₂ concentrations. Exogenous glucose and malate did not stimulateO₂ uptake at any stage of growth in aerated coleoptiles. Therewas sufficient endogenous substrate to sustain a 35–45%rise in O₂ uptake induced by uncoupling and enrichment withO₂. Exogenous glucose did not stimulate growth of intact seedlingsat any O₂ concentration. Key words: Rice seedlings, carbohydrate metabolism, oxygen deficient solution