Manipulation of ethanol production in anoxic rice coleoptiles by exogenous glucose determines rates of ion fluxes and provides estimates of energy requirements for cell maintenance during anoxia

Ethanol production by anoxic, excised, 7-10 mm tips of rice coleoptiles was manipulated using a range of exogenous glucose concentrations. Such a dose-response curve enabled good estimates at which level of ethanol production (and hence by inference ATP production), injury commenced and also allowed assessments of energy requirements for maintenance in anoxia. Rates of net uptake or loss of K+ and P by these excised coleoptile tips were related to rates of ethanol production (r(2) of 0.59 and 0.68, respectively). At 72 h anoxia, ATP levels in excised tips were similar at 0, 2.5, and 50 mol m(-3) exogenous glucose, despite large differences in the inferred rates of ATP production. At 96 h anoxia, tips without exogenous glucose had low ATP concentrations; these may be the cause or the consequence of cell injury. In tips without glucose, injury was indicated by losses of K+ and Cl- between 72-96 h anoxia, and during the first hour after re-aeration, while later than 1 h after re-aeration, rates of net uptake were substantially lower than for re-aerated tips previously in anoxia with exogenous glucose. Between 96 h and 124 h anoxia, ion losses from tips without exogenous glucose increased while recovery of net uptake after re-aeration was very sluggish and incomplete. The energy requirement for maintenance of health and survival of anoxic coleoptile tips, expressed on a fresh weight basis, was lower than for three other anoxia-tolerant plant tissues/cells, studied previously. However, the energy requirement on a protein basis was assessed at 1.4 mu mol ATP mg(-1) protein h(-1) and this value is 2.6-5.4-fold higher than for the other plant tissues/cells. Yet, this requirement was still only 58-88% of the published values for aerated tissues. The reason for this relatively high ATP requirement per unit protein in anoxic rice coleoptiles remains to be elucidated.