Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The molecular structures of peanut peroxidases from the cell suspension culture medium have been well characterized. The aim of present work is to investigate some of the physiological roles of these peroxidases, namely the functions in growth.;Specific polyclonal antibodies against both anionic and cationic peroxidases were produced by affinity chromatography. Immunological assays showed virtually no cross-reactivity between these antibodies and other compounds. The peroxidases from peanut cell suspension culture medium had {dollar}>{dollar}80% immunological homologies with those from cultured cells and hypocotyls as determined by Ouchterlony gel diffusion, western blot and competitive ELISA. Based on these homologies both the purified peroxidases from the medium and the antibodies against them were used for the study of the physiological functions of peroxidases in cultured cells and hypocotyls.;An increase of peroxidase quantity and activity in the hypocotyl segments was correlated with the inhibition of growth by meta-fluoro-tyrosine (MFT) added to the culture medium. A further linkage between growth and peroxidases has been clarified through the enhancement of growth by antibodies and the inhibition of growth by peroxidases.;MFT reduced the synthesis of cationic peroxidase less than that of total proteins. On the other hand, the half live of cationic peroxidase was increased by MFT. These two effects are assumed to be the cause of the increase of cationic peroxidase quantity and activity in the tissues treated with MFT. It was also determined that the synthesis and the degradation of peroxidases were regulated at transcriptional and translational levels.;Possible biochemical mechanisms for the regulatory role of peroxidases in growth were investigated. Peroxidases catalyzed the in vivo and in vitro oxidative couplings of cell wall polymer-linked tyrosine, ferulic acid and coniferyl alcohol. In this way, peroxidases mediate the crosslinkings of extensins and polysaccharides in the cell wall, and thus control the rheology and elongation of the cell wall. By using isolated cell walls and specific antibodies it was indicated that the cationic peroxidase played a major role for in vivo couplings. No difference in the affinity of anionic and cationic peroxidases for the phenol substrates was revealed by enzyme kinetic studies. Peroxidases were found to mediate the metabolism of IAA and ascorbate, which regulates growth. The anionic peroxidase had a higher affinity for IAA and ascorbate as well as a higher Vmax in the peroxidation of IAA and ascorbate.;The cell wall-association of most cationic isozyme and the cytoplasm-association of most anionic isozyme were visualized by immunogold labelling. This is consistent with the dominant role of the cationic isozyme in the elongation of the cell wall, and with the principal action of anionic isozyme in the cytoplasm-located IAA and ascorbic acid peroxidation.



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