upon Tyne, England Receiv-ed March 8. 1967. Sumiitmary. Young seedlings of buckwheat (Fagopyrum escidentium) respire in air with an RQ of unity. Analysis of respiratory substrates coupled with a study of the utilization of acetate-14C and glucose-_4C suggest that both the Embden-Meyerhof-Parnas, tricarboxylic acid and pentose phosphate sequences participate in the total respiratory catabolism.In anoxia CO, dropped to one third of the aerobic rate and ethanol accumulated to only about one half the rate of CO, output on a molar basis. Smaller amounts of lactate, succinate and free amino acids (particularly alanine and y-aminobutyric acid) accumulated, carboxylic acids decreased and there were initial increases in pyruvate and a-ketoglutarate. The observed changes are consistent with residual tricarboxylic acid and pentose phosphate cycle activity in anoxia and may account for the excess CO2 production over ethanol accumulation. CO, ethanol and lactate production did not account for all of the carbohydrate consumed in anoxia.Relative rates of carbon loss w-ere measured in air and in atmospheres containing 3.5 %, 2.1 %, 1.3 % and 0.6 % oxygen. The extinction point of anaerobic metabolism was 1.5 %.On return to air from anoxia the CO2 output increased and the RQ rose from 0.8 to 1.0 over the first 2-hour period. Ethanol. lactate and succinate were colsullmed and other constituents returned to their previous aerobic level. Some of these changes suggest a rather slow resumption of tricarboxylic acid cycle activity on return to air.Carbon loss as CO, in air was greater than the carbon loss as CO2 at the extinction point. Carbon loss in anoxia as CO, ethanol and lactate was similar to carbon loss at the extinction point. Assessed in this orthodox manner buckwheat seedlings shoNv no Pasteur effect but the complex nature of the changes in levels of metabolic substrates and intermediates do not allow firm conclusions to be draw^n on the effects of oxygen on the rates of glycolysis and other respiratory processes.In earlier work on the respiratory iiietabolism of germinating buckwheat seedlings Leach (t1) measured CO., outputs in air (N) and in pure nitrogen (I) and hence determined I/N quotients for the moment of transfer from aerobic to anaerobic conditions. The values were all close to 0.33 and Leach inferred that at the mnoment of transition the complete oxidation of carbohydrate to CO, and w ater was replaced by fermentation to yield CO.. and Later, Ranson ( 18) measured the rates of both ethanol accumulation and CO., output in young buckwheat seedlings on first-transfer to anoxia. Values obtained for the I/N quotients were again near 0.33 but the ethanol/CO, quotients were between 0.5 and 0.6. Thus, for these buckwheat seedlings the rate of carbon loss in CO, evolved and ethanol accumulated in anoxia was less than the carbon loss as CO. in air.Thomas (22) argued that a truer assesstnent of the effect of oxygen in conserving respiratorv substrate in plant tissues would be made by a comparison of the anaerobic car...
Simimary. Changes in levels of glcolytic and some related respiratory intermediates in young seedlings of buckwheat (Fagopyrum esculentuim) following transfer A) from air to anoxia, B) from air to 1.5 % 0, C) from 1.5 % O, to anoxia and D) from anoxia to air, are recorded and discussed in relation to other measurements made with these seedlings.On transfer from air to anoxia the changes are similar to those recorded for pea seeds in which it is inferred that glycolysis is faster in anoxia than in air. The results with buckwheat however can be explained in terms of a decreased rate of glycolysis in anoxia. An alternative hypothesis is developed which states that glycolysis is faster in anoxia than in air and that it is the contribution of the pentose phosphate cycle to the total respiratory catabolism which decreases as the oxygen concentration is reduced towxards zero.The transienit changes in concentrations of some glycolvtic and related intermediates which occur on transfer from air to anoxia have been described for pea seeds (1) and rhododendron leaves (3). In both of these plant organs the carbon loss in anoxia, measured as CO, evolved and ethanol and lactate accumulated, exceeds the carbon loss as CO2 in air, and the changes observed in concentrations of each glycolytic intermediate exhibit marked similarities in the 2 organs. For the peas, it has been inferred that there is a faster rate of carbohydrate breakdown in anoxia than in air and, based on the observed changes in levels of the respiratory intermediates on transfer from air to anoxia, a hypothesis has been developed to explain an increased rate of glycolysis following the transfer. A central feature of this hypothesis is that the sugar-phosphorylating and other glycolytic enzymes are located in an organized structure which is effectively more permeable to ADP than to ATP (1,2).In buckwheat seedlings the rate of carbon loss in anoxia, measured as CO9 evolved and ethanol and lactate accumulated, is less than the carbon loss as CO2 in air (4). It was therefore of some interest to compare the changes in levels of glycolytic and related intermediates on transfer from air to anoxia with those observed in peas and rhododendron leaves. In many respects the changes observed in buckwheat 1 The work described in this paper was supported by a Grant-in-aid from the Science Research Council to S. L. Ranson proved to be similar to those in peas and rhododendron leaves even though the rate of carbon loss, assessed as described above, decreased in buckwheat on transfer to anoxia but increased in pea and rhododendron.Consequently, measurements were made of the changes in glycolytic intermediates in the seedlings on transfer from air to the extinction point of fermentation (1.5 % oxygen) and from the extinction point to anoxia. At the extinction poinlt, ethanol and lactate accumulation are suppressed and the respira-,tory metabolism remains, apparently, wholly aerobic. Carbon loss as CO2 at the extinction point is nevertheless only 50 to 60 % of the carbon loss in ...
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