Journal of Experimental Botany, Vol. 52, No. 360, pp. 1507-1517,
July 1, 2001
© 2001 Oxford University Press
Original Papers |
Evidence for down-regulation of ethanolic fermentation and K+ effluxes in the coleoptile of rice seedlings during prolonged anoxia
1 Faculty of Agriculture, The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia, 6009, Australia
2 Institute of Agrobiological Genetics and Physiology, Jiangsu Academy of Agricultural Sciences, Nanjing, 210014, People's Republic of China
Ethanolic fermentation, the predominant catabolic pathway in anoxia-tolerant rice coleoptiles, was manipulated in excised and ‘aged’ tissues via glucose feeding. Coleoptiles with exogenous glucose survived 60 h of anoxia, as evidenced by vigorous rates of K+ and phosphate net uptake and growth of roots and shoots when re-aerated. In contrast, coleoptiles without exogenous glucose showed net losses of K+ and phosphates starting 12 h after anoxia was imposed and these did not recover fully when re-aerated after 60 h of anoxia. Ethanol production (µmol g-1 FW h-1) declined from about 7.5 during the first 12 h of anoxia to 5 or 2.2 after 48–60 h, in coleoptiles with or without exogenous glucose, respectively. Carbohydrate concentrations changed only slightly in anoxic coleoptiles with exogenous glucose due to net glucose uptake at 2.6 µmol g-1 FW h-1. Ethanolic fermentation, and therefore ATP production, may have been down-regulated after an initial period of acclimation to anoxia in coleoptiles with exogenous glucose. Maintenance requirements for energy were assessed to be 3.4–7.6-fold lower in these anoxic coleoptiles than published estimates for non-growing aerated leaf tissues. A modest part of the required economy in energy consumption would have been derived from diminished ion transport; anoxia reduced K+ and phosphate net uptake by 70–90% in these coleoptiles. K+ efflux was 10-fold lower in anoxic than in aerated coleoptiles with exogenous glucose. Using the unidirectional efflux equation, the membrane permeability to K+ was estimated to be 17-fold lower in anoxic than in aerated coleoptiles, presumably due to predominantly closed K+ channels.
Key words: Energy maintenance requirement, ethanolic fermentation, membrane permeability, potassium, phosphate, solute net uptake or loss.
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