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Chapter
8 |
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Amino
Acids
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| Amino acids, the building blocks of proteins
in all organisms, play additional roles in plants. For
example, amino acids serve as precursors to plant hormones
and serve to transport nitrogen from sources to sinks.
As such, the control of amino acid synthesis in plants
affects many aspects of growth and development. Additionally,
the synthesis of essential amino acids in plants and amino
acid composition of seeds relate indirectly to animal
nutrition. Thus, understanding the pathways that control
amino acid synthesis in plants has significance with regard
to basic research on the control of metabolic pathways
as well as practical implications. Although amino acid
biosynthetic pathways have been well worked out in microbes,
the situation in plants is less well defined, in part
because of additional unique complexities. For example,
in many instances, plants have multiple isoenzymes that
catalyze biosynthetic reactions. These isoenzymes may
be localized in distinct organelles or distinct cell types.
Defining each step in an amino acid biosynthetic pathway
and determining how each step is regulated are some of
the key aspects of current research in amino acid biosynthesis
in plants. This chapter highlights examples in which molecular,
genetic, and biochemical approaches have been combined
to elucidate the steps of these pathways in plants and
to understand the regulation of these pathways at the
level of gene regulation and beyond. Plant mutants in
amino acid biosynthetic enzymes have shown that the synthesis
of amino acids in vivo affects numerous diverse processes,
including photorespiration, hormone biosynthesis, and
plant development. Use of transgenic approaches has revealed
the feasibility of manipulating amino acid biosynthesis
pathways in plants, with applications to engineering herbicide
resistance, altering amino acid composition in seed, and
altering resistance to photoinhibition. Thus, although
they are products of primary metabolism, amino acids also
control many diverse aspects of plant growth and development. |
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