A Developmental Study of Essential Amino Acid Biosynthesis in Chloroplasts

点击翻译按钮获取中文摘要

This project focuses on the developmental regulation of essential aspartate-family amino acid metabolism in chloroplasts of higher plants. The hypothesis being tested is that the following parameters will be tested to determine how they vary during leaf development: 1) the level and intracellular distributions of amino acids, 2) the permeability of the chloroplast envelope to amino acids and 3) the activities of key enzymes of essential amino acid production. Purified chloroplasts prepared from leaves of barley plants at various stages of development are used to determine concentrations of amino acids in chloroplasts and other cellular compartments throughout development, to measure the transport of aspartic acid and the metabolically related amino acids, lysine, threonine, methionine and isoleucine, into chloroplasts from leaves of varying ages, and to isolate the enzymes aspartate kinase, homoserine dehydrogenase and dihydrodipicolinate synthetase from plastids of different age tissues and relative catalytic activities. Antibodies also will be raised to the enzymes and variations in enzyme levels will be confirmed by immunological methods. In the last decade it has become clear that the chloroplast is the main site, if not the sole site, for the biosynthesis of the nutritionally essential aspartate-family amino acids in plant leaves. During the development of plant leaves, the requirement for the production of these and other amino acids changes. This research explores whether the capacity of chloroplasts to synthesize the essential aspartate-derived amino acids varies during leaf development, so that chloroplast development and its regulation can be better understood. These studies will further provide information regarding the nature and regulation of essential amino acid biosynthesis. Given that deficiency of two of the aspartate-derived amino acids is a main factor contributing to human malnutrition, new information regarding the regulation of their synthesis is of particular interest.