IS LONG-TERM HYPOXIA MET BY THE PASTEUR EFFECT IN ROOTS OF WHEAT SEEDLINGS

It has been argued, whether or not the Pasteur effect occurs in plant tissues as a response to long-term hypoxia. To study this question roots of wheat seedlings (Triticum aestivum L. cv. Alcedo) were analysed following acclimation to oxygen shortage by a prior 6-d-cultivation in a nitrogen-flushed nutrient solution. A Pasteur Quotient of approximately one suggested the absence of a significant Pasteur effect. This conclusion was supported by finding an accumulation of soluble carbohydrates. A progressive adaptation of hypoxically pretreated wheat roots was indicated by measurements under low oxygen tension of 2 kPa, when half of the produced carbon dioxide was generated by fermentation (Gas exchange Quotient, GQ approximate to 2.1) with no apparent increase in the glycolytic substrate flux. The remaining oxygen uptake was even higher in hypoxically grown roots than in the aerobically grown control specimens. When whole seedlings were placed in oxygen-free conditions for 2 h, roots of seedlings pretreated hypoxically suffered a 50% loss in the concentration of ATP, while 90% of the ATP was lost in roots transferred from an aerated solution directly into an anaerobic environment. This was interpreted as an improvement in hypoxia tolerance by minimising the fermentation rate (low PQ) but in particular the ATP requirements by metabolic arrest strategies.