This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via Web of Science (52) Citing Articles via Google Scholar Google Scholar Articles by Thomson, C. J. Articles by Greenway, H. Search for Related Content PubMed PubMed Citation Articles by Thomson, C. J. Articles by Greenway, H. Agricola Articles by Thomson, C. J. Articles by Greenway, H.

Environmental and Stress Physiology

Metabolic Evidence for Stelar Anoxia in Maize Roots Exposed to Low O₂ Concentrations ¹

Crop & Pasture Sciences, School of Agriculture, University of Western Australia, Nedlands, Western Australia 6009 Australia

This investigation presents metabolic evidence to show that in 4- to 5-day-old roots of maize (Zea mays hybrid GH 5010) exposed to low external O₂ concentrations, the stele receives inadequate O₂ for oxidative phosphorylation, while the cortex continues to respire even when the external solution is at zero O₂ and the roots rely solely on aerenchyma for O₂ transport. Oxygen uptake rates (micromoles per cubic centimeter per hour) declined at higher external O₂ concentrations in excised segments from whole roots than from the isolated cortex; critical O₂ pressures for respiration were greater than 0.26 moles per cubic meter O₂ (aerated solution) for the whole root and only 0.075 moles per cubic meter O₂ for the cortex. For plants with their shoots excised and the cut stem in air, ethanol concentrations (moles per cubic meter) in roots exposed to 0.06 moles per cubic meter O₂ were 3.3 times higher in the stele than in the cortex, whereas this ethanol gradient across the root was not evident in roots exposed to 0 moles per cubic meter O₂. Alanine concentrations (moles per cubic meter) in the stele of roots exposed to 0.13 and 0.09 moles per cubic meter O₂ increased by 26 and 44%, respectively, above the levels found for aerated roots, whereas alanine in the cortex was unchanged; the increase in stelar alanine concentration was not accompanied by changes in the concentration of free amino acids other than alanine. For plants with their shoots intact, alcohol dehydrogenase and pyruvate decarboxylase activities (micromoles per gram protein per minute) in roots exposed to 0.13 moles per cubic meter O₂ increased in the stele by 40 to 50% over the activity in aerated roots, whereas there was no appreciable increase in alcohol dehydrogenase and pyruvate decarboxylase activity in the cortex of these roots. More convincingly, for roots receiving O₂ solely from the shoots via the aerenchyma, pyruvate decarboxylase in the cortex was in an "inactive" state, whereas pyruvate decarboxylase in the stele was in an "active" state. These results suggest that for roots in O₂-free solutions, the aerenchyma provides adequate O₂ for respiration in the cortex but not in the stele, and this was supported by a change in pyruvate decarboxylase in the cortex to an active state when the O₂ supply to the roots via the aerenchyma was blocked.

This article has been cited by other articles:

				W. Armstrong, T. Webb, M. Darwent, and P. M. Beckett Measuring and interpreting respiratory critical oxygen pressures in roots Ann. Bot., January 1, 2009; 103(2): 281 - 293. [Abstract] [Full Text] [PDF]

				C. D. HANBURY and B. J. ATWELL Growth Dynamics of Mechanically Impeded Lupin Roots: does Altered Morphology Induce Hypoxia? Ann. Bot., October 1, 2005; 96(5): 913 - 924. [Abstract] [Full Text] [PDF]

				A. Wiengweera and H. Greenway Performance of seminal and nodal roots of wheat in stagnant solution: K+ and P uptake and effects of increasing O2 partial pressures around the shoot on nodal root elongation J. Exp. Bot., September 1, 2004; 55(405): 2121 - 2129. [Abstract] [Full Text] [PDF]

				K. L. Bologa, A. R. Fernie, A. Leisse, M. Ehlers Loureiro, and P. Geigenberger A Bypass of Sucrose Synthase Leads to Low Internal Oxygen and Impaired Metabolic Performance in Growing Potato Tubers Plant Physiology, August 1, 2003; 132(4): 2058 - 2072. [Abstract] [Full Text] [PDF]

				K. P. Ismond, R. Dolferus, M. De Pauw, E. S. Dennis, and A. G. Good Enhanced Low Oxygen Survival in Arabidopsis through Increased Metabolic Flux in the Fermentative Pathway Plant Physiology, July 1, 2003; 132(3): 1292 - 1302. [Abstract] [Full Text] [PDF]

				J. T. van Dongen, U. Schurr, M. Pfister, and P. Geigenberger Phloem Metabolism and Function Have to Cope with Low Internal Oxygen Plant Physiology, April 1, 2003; 131(4): 1529 - 1543. [Abstract] [Full Text] [PDF]

				E. I. BOAMFA, P. C. RAM, M. B. JACKSON, J. REUSS, and F. J. M. HARREN Dynamic Aspects of Alcoholic Fermentation of Rice Seedlings in Response to Anaerobiosis and to Complete Submergence: Relationship to Submergence Tolerance Ann. Bot., January 2, 2003; 91(2): 279 - 290. [Abstract] [Full Text] [PDF]

				K. E. Koch, Z. Ying, Y. Wu, and W. T. Avigne Multiple paths of sugar-sensing and a sugar/oxygen overlap for genes of sucrose and ethanol metabolism J. Exp. Bot., February 1, 2000; 51(90001): 417 - 427. [Abstract] [Full Text]