Publication Date

2000

Document Type

Dissertation/Thesis

Degree Name

M.S. (Master of Science)

Department

Department of Biological Sciences

LCSH

Curly-topages||Sugar beet--Diseases and pests||Photosynthesis

Abstract

Beet Curly Top Virus (BCTV) is a geminivirus causing serious losses in crop yield in the Southwestern U.S. BCTV is spread by a leafhopper insect vector and has a wide dicot host range, spreading systemically via phloem tissue. Earlier work indicated that BCTV infection may indirectly damage phloem tissue; however, its effects on sucrose translocation in the plant have not been examined before. Our research has focused on the effect of BCTV infection on photosynthesis and carbon allocation in sugarbeet plants. We have worked with two varieties of sugarbeet, Z-10 and 9BB6090, as well as two viral strains, Logan and CFH, and a Mock control. Ten weeks after infection we found that photosynthetic rates were lower in plants infected with BCTV Logan when compared to Mock control plants. Lower photosynthetic rates were associated with decreased chlorophyll levels as well as reduced activity of RuBP carboxylase/oxygenase (Rubisco), the primary CO2 fixing enzyme. The Z-10 variety showed lower Rubisco activity overall when compared to the 9BB6090 sugarbeet variety, which is more resistant to the virus. BCTV infection caused changes in assimilate partitioning, illustrated by dramatically higher sucrose levels in the 9BB6090 Logan-infected plant. Corresponding free glucose levels were also higher for Logan-infected plants of both varieties. Because of the seven-fold sucrose increase in Logan-infected plants, we investigated the ability of BCTV-infected plants to translocate exogeneously supplied 14C-sucrose. The results showed that Z-10 BCTV-infected plants transported less sucrose into the petiole. The high levels of sucrose in BCTV-infected leaves were associated with reduced cytoplasmic fructose 1,6-bisphosphatase (FBPase) activity in BCTV Logan and BCTV CFH infected plants for both varieties. Chloroplastic FBPase activity was only reduced in the Z-10 variety. Sucrose phosphate synthase (SPS) rates did not show any significant change in Mock-control plants or BCTV-infected plants. We propose that the damage to phloem tissue caused by BCTV infection reduces the transport of sucrose. The resulting buildup of sucrose and glucose may result in feedback effects causing down-regulation of genes encoding chlorophyll and Rubisco subunits levels and certain sucrose-producing enzymes.

Comments

Includes bibliographical references (pages [99]-103)

Extent

viii, 103 pages

Language

eng

Publisher

Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

Media Type

Text

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