The Shrunken gene on chromosome 9 of Zea mays L is expressed in various plant tissues and encodes an anaerobic protein.

The Shrunken gene, located on the short arm of chromosome 9 of Zea mays, encodes the enzyme sucrose synthase (EC 2.4.1.13). The gene is known to be expressed in the endosperm of the developing maize kernel and seems to be involved in sucrose breakdown prior to starch synthesis. We have analyzed different tissues of the maize plant for transcripts of the Shrunken gene and have found rather high transcription rates in the etiolated shoot and the primary root of the germinating kernel. If the etiolated seedlings are illuminated, the transcript level drops by about 95% in the greening plant parts (1st and 2nd leaves) which are active in photosynthesis. A very low transcript level is found in mature green leaves where sucrose is formed from products of photosynthesis via a separate pathway. Upon anaerobic stress of the young seedling, the level of Shrunken transcripts increases 10 and 20 times in shoot and root tissue respectively. Apparently anaerobic induction supersedes the negative control that is observed after illumination in the 1st and 2nd leaves. From the experiments outlined here we conclude that the anaerobic protein 87 (ANP87, Hake et al. 1985) is encoded by the Shrunken locus. While the expression of the Shrunken gene varies in different tissues and in response to external stimuli, transcription of the second sucrose synthase (B) gene seems to be irresponsive to anaerobic stress and to be expressed at a similar low level in all of the tissues examined.