DIFFERENTIAL INDUCTION OF MESSENGER-RNAS FOR THE GLYCOLYTIC AND ETHANOLIC FERMENTATIVE PATHWAYS BY HYPOXIA AND ANOXIA IN MAIZE SEEDLINGS

Fructose-1,6-bisphosphate aldolase (ALD) and enolase (ENO) from the glycolytic pathway, and pyruvate decarboxylase (PDC) and alcohol dehydrogenase 2 (ADH2) from the ethanolic fermentative pathway, are enzymes previously identified as among those synthesized selectively in O-2-deficient roots of maize (Zea mays L.). The present study measured levels of transcripts representing these two pathways in 5-mm root tips, root axes (the remainder of the primary seminal root), and shoots of maize seedlings to determine how closely both pathways were co-induced and how they were modulated by changes in O-2 concentration. In hypoxic seedlings with the roots in solution sparged with 4% (v/v) O-2 (balance N-2) and the shoots in the same gaseous atmosphere, mRNAs for Pdc(1) and Adh2 in root tips both increased about 15-fold during the first 12 h, followed by a decline toward initial levels by 18 to 24 h. Message levels for Ald1 and Enol showed only small changes during hypoxia. When expression was examined under anoxia, the extent to which all four mRNAs increased in different tissues depended on whether the seedlings had been previously acclimated to hypoxia or were anoxically shocked. The results show that although all the genes examined increased expression during hypoxia and/or anoxia, they differed in the rapidity and magnitude of the response and in the time to reach maximal message levels: there was no common pattern of change of message levels for the glycolytic or for the fermentative enzymes.