| Summary: | 碩士 === 國立東華大學 === 生物技術研究所 === 98 === Indole-3-acetic acid (IAA) is the major auxin in higher plants. It is synthesized in shoot apical meristems, young leaves, and developing fruits and seeds. The developmental effects of IAA include increasing the extensibility of the cell wall for cell elongation, apical dominance, promotion of lateral and adventitious roots, interaction with cytokinin for plant tissue culture and induction of vascular differentiation. Most of IAA exists as conjugated forms in plants for multiple functions, such as storing, subsequent reuse and homeostatic control of IAA, protecting free IAA from enzymatic destruction and long distance transport of IAA in vascular tissue. The metabolic mechanism of IAA in plants is far from clear, but IAA amino acid conjugates play a key intermediate in IAA-controled plant physiology and metabolism. The study of IAA amidohydrolases can help us to understand the mechanism of IAA in plant. We intended to isolate bacterial strains exhibiting significant IAA-leucine hydrolases activity from bacteria since IAA-amino acid conjugate hydrolase identified from plants were not substrate specific. We also measured the effects by IAA on the growth of the bacterial strain. First, by standard enrichment, we used N-acetyl-D, L-leucine as the sole source of carbon and nitrogen sources to cultivate a number of bacterial strains that is from the rhizosphere of weeds on the beach. The bacterial strain, labeled 7-8-1-1, was selected by TLC analysis. The strain 7-8-1-1 was a gram-positive bacterium. The crude extract of 7-8-1-1 had substrate specificity to hydrolyze IAA-Leu (N-[3-indolylacetyl]-L-leucine). The optimal pH was 6.5~7.5. It was able to produce this enzyme activity in normal growth condition without inducer, but IAA and other compound, which had the physiological activity, could inhibit the growth and reproduction of 7-8-1-1. In summary, we identified a new bacterial strain with indole-3-acetyl-L-leucine hydrolase activity which may provide a tool for experiments that will help future studies of IAA-Leu on the growth and development of plants.
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