Graduate Thesis Or Dissertation

 

Cytokinin O-glycosyltransferases : biochemical characteristics in vitro and developmental regulation in transgenic plants Public Deposited

Downloadable Content

Download PDF
https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/rv042w35v

Descriptions

Attribute NameValues
Creator
Abstract
  • Cytokinins are plant hormones regulating cell division and differentiation. Most developmental events from germination, vegetative morphogenesis to seed and fruit set are influenced by cytokinins. t,ns-Zeatin is the major natural occurring cytokinin. Its isomer, cis-zeatin, and its derivatives are usually present in low quantities and have traditionally been considered as adjunct components due to their low biological activity. Glycosylation of cytokinins occurs frequently and O- glycosylation genes of t,ns-zeatin have been cloned in our lab. Determining the function of O-glycosides and the regulation of gene expression are part of a larger on-going project. Current literature indicates that cis-zeatin derivatives occur as predominant cytokinins in specific organs of certain plant species, such as chickpea seeds, potato tubers and rice roots. These observations, together with the recent cloning of maize genes encoding 0-glucosyltransferses preferring cis-zeatin to transzeatin, suggest that cis-zeatin may have a more important role than currently recognized. Within the long-term objective of understanding the possible role of cis-zeatin in plant development and the function and regulation of cytokinin O-glycosylation, this study was undertaken to contribute to two specific areas, the characterization of two cis-zeatin O-glucosyltransferases (cisZOG1 and cisZOG2) and determining promoter activity of a t,ans-zeatin O-xylosyltransferase gene (ZOXI) in transgenic plants. Open reading frames (ORFs) of the cisZOG1 and cisZOG2 were cloned into expression vectors and large quantity of recombinant enzymes was obtained. Substrate specificity and reaction properties of cisZOG1 and cisZOG2 were examined. The optimal pH of the enzymatic reaction is about 7.5. The Km for ciszeatin is about 46μM for cisZOG1 and 96μM for cisZOG2. UDP-glucose (UDPGlc), the sugar donor, has Kms of 0.1 and 0.59mM for cisZOG1 and cisZOG2, respectively. The Km values were within the expected range of cytokinin metabolism enzymes. The affinity of these enzymes to cis-zeatin was 11 fold higher than tins-zeatin. Competition experiments with other cytokinins indicated that cis-zeatin riboside, and thidiazuron are strong inhibitors while t,ns-zeatin, kinetin and N⁶-benzyladenine are slightly inhibitory. These findings, combined with detecting substantial amounts of cis-zeatin derivatives in all tissues, suggest specific metabolic pathways for cis-zeatin in maize. The regulation of trans-zeatin O-glycosylation gene expression was studied using an available sequence of ZOX1 (zeatin O-xylosyltransferase) containing the promoter fused with the reporter gene GUS (p-glucuronidase). Transgenic tobacco and Arabidopsis containing the pZOX1::GUS and control constructs (superpromoter::GUS and no promoter::GUS) were generated. Reporter gene activity mediated by pZOX1 was observed in immature seeds of transgenic tobacco as expected of the promoter in its native host, Phaseolus. In vegetative tissues, pZOX1 mediates gene expression only in trichomes and stem hairs. As the formation of these tissues from epidermal cells involves a switch in cell division plane as well as endoduplication, the expression of zeatin O- glycosylation genes in native hosts may be related to transient reduction of active cytokinins to accommodate alternating cydes of rapid duplication and rest. The absence of pZOX1::GUS activity in transgenic Arabidopsis may indicate a difference in required transcription factors between this model plant and tobacco and legumes. The results and plant materials will serve as useful information and materials to further explore the induction of gene expression by hormones and environmental cues.
Resource Type
Date Available
Date Issued
Degree Level
Degree Name
Degree Field
Degree Grantor
Commencement Year
Advisor
Committee Member
Academic Affiliation
Non-Academic Affiliation
Subject
Rights Statement
Publisher
Peer Reviewed
Language
Digitization Specifications
  • File scanned at 300 ppi (Monochrome, 256 Grayscale, 24-bit Color) using Capture Perfect 3.0.82 on a Canon DR-9080C in PDF format. CVista PdfCompressor 4.0 was used for pdf compression and textual OCR.
Replaces
Additional Information
  • description.provenance : Made available in DSpace on 2012-08-13T22:15:00Z (GMT). No. of bitstreams: 1VeachYeonjinKim2003.pdf: 2670230 bytes, checksum: 4c6176cde965b44f2c50fbf21e7068ad (MD5) Previous issue date: 2002-06-12
  • description.provenance : Submitted by Sergio Trujillo (jstscanner@gmail.com) on 2012-08-13T20:37:14ZNo. of bitstreams: 1VeachYeonjinKim2003.pdf: 2670230 bytes, checksum: 4c6176cde965b44f2c50fbf21e7068ad (MD5)
  • description.provenance : Approved for entry into archive by Patricia Black(patricia.black@oregonstate.edu) on 2012-08-13T22:13:18Z (GMT) No. of bitstreams: 1VeachYeonjinKim2003.pdf: 2670230 bytes, checksum: 4c6176cde965b44f2c50fbf21e7068ad (MD5)
  • description.provenance : Approved for entry into archive by Patricia Black(patricia.black@oregonstate.edu) on 2012-08-13T22:15:00Z (GMT) No. of bitstreams: 1VeachYeonjinKim2003.pdf: 2670230 bytes, checksum: 4c6176cde965b44f2c50fbf21e7068ad (MD5)

Relationships

Parents:

This work has no parents.

In Collection:

Items