The Effect of the Site of Nitrogen Assimilation on Plant Growth
Lexa, Matej
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https://hdl.handle.net/2142/77334
Description
Title
The Effect of the Site of Nitrogen Assimilation on Plant Growth
Author(s)
Lexa, Matej
Issue Date
1999
Doctoral Committee Chair(s)
Cheeseman, John M.
Department of Study
Civil Engineering
Discipline
Environmental Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Agriculture, Agronomy
Biology, Ecology
Biology, Genetics
Environmental Sciences
Biology, Plant Physiology
Language
eng
Abstract
The allocation of biomass and nutrients to roots and shoots is an important process that affects the morphology of a growing plant and dictates its capacity for photosynthesis, nutrient uptake and other key physiological processes. Plants growing on NO3- differ in the proportion of NO3- reduced in their roots and leaves. The importance of a particular reduction site for the plant is not clear, however. Simulation models suggest that root reduction of NO3 - might increase biomass and nutrient allocation to the root, and possibly result in other growth changes. Understanding the effects of root or shoot NO3- reduction will provide a better understanding of the existing variability in the site of NO 3- reduction in different species and of its physiological and ecological significance.
In this dissertation, I have explored this question experimentally. My approach was to obtain plants with NO3- reduction mostly in the roots or mostly in the leaves, measure growth and biomass allocation parameters of those plants when grown on NO3-, and compare them to growth of wild-type (WT) plants and nitrate reductase deficient mutants. Two techniques were used to manipulate the site of NO 3- reduction: (i) grafting and (ii) genetic transformation. Grafted wildtype and nitrate reductase-deficient pea plants adapted to changes in the location of NO3- reduction. The results support the idea of rapid mixing of metabolite pools and provide evidence for shoot to root signalling of nitrogen status. Utilizing tissue-specific promoters, plants were created with altered levels of nitrate reductase in roots and shoots. The results showed that transformation of WT plants with nia2 tobacco gene resulted in greater alterations in NRA than the transformation of the corresponding double mutant. Changes in growth and co-suppression-like leaf chlorosis was the most frequent outcome, often causing a lowering or disappearance of NRA. A negative correlation between the ratio of root and shoot reduction of nitrate and the root shoot ratio of transformed plants was found. The possible reasons for differences between the two approaches are discussed.
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