Submitted to: Journal of Plant Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/23/2002
Publication Date: 8/30/2003
Citation: MUHITCH, M.J. DISTRIBUTION OF THE GLUTAMINE SYNTHETASE ISOZYME GSP1 IN MAIZE (ZEA MAYS). JOURNAL OF PLANT PHYSIOLOGY. 2003. v. 160. p. 601-605. Interpretive Summary: Developing corn seeds receive nutrients through their pedicels, the neck-like structure that attaches them to the cob. Pedicels are also important ports of entry into the seed for various disease organisms. We have previously developed a genetic system to make proteins within the pedicle to inhibit fungal disease. In the course of the research, it was realized that the genetic system also causes protein accumulation in additional corn tissues. Therefore, we examined numerous corn tissues to find the full extent of where this system will produce proteins. The protein accumulates in only minor amounts in tassels, anthers, kernel glumes, ear husks, cobs and stalks, and not at all in pollen. This research reassures us that the genetic system being developed to reduce fungal disease and mycotoxin contamination of corn seeds should not effect the corn plant or consumers in unintentional negative ways.
Technical Abstract: Higher plants contain families of glutamine synthetase (GS) isozymes. In maize (Zea mays L.), GSp1, the predominant GS isozyme of the developing kernel, is abundant in the pedicel and pericarp, but absent from the endosperm and embryo. Determination of GSp1 tissue distribution in vegetative tissues has been limited thus far to root and leaves, where the isozyme was found to be absent. However, the promoter from the gene encoding GSp1 has been shown to drive reporter gene expression not only in the maternal seed-associated tissues in transgenic maize plants, but also in the anthers, husks and pollen. These observations warranted a more thorough examination of the distribution of the native GSp1 among the non-seed tissues of maize. In the current report, chromatographic evidence is presented that GSp1 resides in immature tassels, dehiscing anthers, kernel glumes, ear husks, cobs and stalks of maize plants, but not in mature, shedding pollen grains. RNA blot analysis confirmed these biochemical data. In stalks, GSp1 increases in the later stages of ear development, suggesting that it plays a role in nitrogen remobilization during grain fill.