Respiratory metabolism in buckwheat seedlings

Abstract

Young seedlings of buckwheat (Fagopyrum esculentum) respire in air with an RQ of unity. Analysis of respiratory substrates coupled with a study of the utilization of acetate-(14)C and glucose-(14)C suggest that both the Embden-Meyerhof-Parnas, tricarboxylic acid and pentose phosphate sequences participate in the total respiratory catabolism.In anoxia CO(2) dropped to one third of the aerobic rate and ethanol accumulated to only about one half the rate of CO(2) output on a molar basis. Smaller amounts of lactate, succinate and free amino acids (particularly alanine and gamma-aminobutyric acid) accumulated, carboxylic acids decreased and there were initial increased in pyruvate and alpha-ketoglutarate. The observed changes are consistent with residual tricarboxylic acid and pentose phosphate cycle activity in anoxia and may account for the excess CO(2) production over ethanol accumulation. CO(2), ethanol and lactate production did not account for all of the carbohydrate consumed in anoxia.Relative rates of carbon loss were 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 CO(2) output increased and the RQ rose from 0.8 to 1.0 over the first 2-hour period. Ethanol, lactate and succinate were consumed 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(2) in air was greater than the carbon loss as CO(2) at the extinction point. Carbon loss in anoxia as CO(2), ethanol and lactate was similar to carbon loss at the extinction point. Assessed in this orthodox manner buckwheat seedlings show no Pasteur effect but the complex nature of the changes in levels of metabolic substrates and intermediates do not allow firm conclusions to be drawn on the effects of oxygen on the rates of glycolysis and other respiratory processes.