The anaerobic response of the maize primary root has been a well characterized phenomenon (Sachs et al. Cell 20:761-769, 1980). Phillip Kelley in our lab has recently identified the functions of 3 more anaerobic proteins besides the already known alcohol dehydrogenase and pyruvate decarboxylase. All of them turned out to be related to glycolysis. The 55,000 dalton anaerobic protein (ANP55) corresponded to glucose phosphate isomerase (JBC, 1984, in press). And both the 35,500 and 33,000 dalton anaerobic proteins (ANP35.5 & ANP33) were recognized by the antiserum raised against fructose-1,6-diphosphate aldolase (submitted to JBC). We have further observed that the two forms of aldolase were not only serologically related, but the balance of their expression was controlled by the oxygen tension of the environment. Pulse label experiments showed that ANP35.5 was the predominant form of the two aldolases under aerobic condition. However, when roots were transferred into anaerobic environment, ANP33 became the major form accounting for more than 70% of the S35-methionine incorporation into aldolase. The mechanism and biological significance of this subtly regulated phenomenon remain to be determined. The two forms of aldolase are not likely to be the result of transcription from two different genes, since only one restriction fragment can be detected in genomic Southern blots probed with the DNA clone of aldolase (Sarah Hake, unpubl. hybrid select translation data). At this point, we favor the hypothesis of post-translational modification or breakdown of one form into the other. Preliminary evidence indicated that, in the presence of protease inhibitor (PMSF) during extraction, only the higher molecular weight form of aldolase could be detected (Kelley and Freeling, ms. submitted). This being true, we have indirect evidence for the anaerobic "induction" of a protease that clips aldolase.
Che-Hong Chen and Michael Freeling
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