Submitted to: American Society of Plant Biologists Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 8/31/2005
Publication Date: N/A
Interpretive Summary: Cytokinins are a group of plant hormones that are essential for plant development, but little is known about how a plant maintains the proper level of cytokinins necessary for normal plant growth. There are several mechanisms a plant could use to control active levels of zeatin (the most common cytokinin in plants); they could make more (biosynthesis), they could transport zeatin into or away from the tissue, or they could break down or modify zeatin so it is no longer active. This poster describes changes in plant growth and development in corn caused by altering the metabolism of zeatin. Specifically, it examines the effect of adding glucose to the zeatin molecule.
Technical Abstract: O-Glycosylation plays an important role in regulating the levels of cytokinins. O-glucosides are likely to be important in cytokinin storage and transport since they are resistant to dehydrogenases (oxidases) and can be converted back to free bases. Maize transformants harboring the bean zeatin O-glucosyltransferase (ZOG1) gene driven by the ubiquitin promoter were characterized. Modifications were observed in both vegetative and reproductive development. Transgenic plants were shorter, with higher leaf chlorophyll contents and delayed senescence. Tassels were smaller with many empty florets, lacking anthers. Ears emerged sooner than expected, about two days after tassel emergence instead of the usual seven days. These changes resulted in dramatically decreased kernel production in the field but not in the greenhouse with artificial pollination. RT-PCR, Western blotting, and cytokinin analyses quantified transgene transcription, translation, and effects on cytokinin composition. Transformants had significantly higher levels of the O-glucosides of zeatin and cis-zeatin, and also higher levels of the respective aglycones. These results suggest that increased O-glycosylation of zeatin leads to complex changes in plant development and cytokinin composition.