Pentose Phosphate Pathway as a Major Component of Induced Respiration of Carrot and Potato Slices

When washed at moderate temperatures, slices of many underground storage organs show a steady rise in their rate of respiration until it reaches a value two to five times that of freshly cut tissue. Laties (3) has recently reviewed our knowledge of these changes in respiration. In accordance with his suggestion, the respiration which develops gradually on washing will be referred to as induced respiration. It is important to distinguish between this induced respiration and any immediate increase in respiration caused by cutting the whole organ. Stiles and Dent (9) and Turner and Hanly (10) have reported the development of such an induced respiration in washed slices of carrot tissue. In a previous paper (1) we have shown that in freshly cut carrot tissue glucose is oxidized through both the Embden-Meyerhof-Parnas (EMP) glycolytic pathway and the pentose phosphate (PP) pathway, and that it is possible to alter the relative contributions of these two pathways to glucose oxidation. On indirect evidence, Laties (4) has suggested that the development of induced respiration involves qualitative as well as quantitative changes in the respiration. In view of our knowledge of the respiratory pathways in freshly cut carrot tissue it was worthwhile to examine the pathways of glucose oxidation in washed tissue. This paper describes some further characteristics of the basal and induced respiration in carrot tissues and presents evidence that the development of the induced respiration was accompanied by an increase in the proportion of glucose oxidized through the PP pathway. Evidence is also presented that a similar increase in the activity of the PP pathway accompanied the development of the induced respiration of slices of potato tubers.