| Summary: | 博士 === 國立中興大學 === 昆蟲學系所 === 107 === Nymphs of xylophagous spittlebug Poophilus costalis (Walker,1851) produce froth that covers their entire body surface. Since no mold has ever been found on this froth under natural conditions, it was speculated that there might be antibiotic substances in the froth that inhibit fungal growth. Therefore, in this study, the formation and antibiotic substance of the froth of spittlebug were carried out. Firstly, the head width, body length and development days of the nymphs were recorded, and the digestive tract and Malpighian tubules were the source tissues of this froth were confirmed. This study has shown that the froth of P. costalis can repress the growth of Fusarium oxysporum f. sp. pisi and can not repress the growth of Botrytis cinerea Person, and the source of inhibition might be the chitinase, or other antibiotic substances detected in the froth. Chitinase may be produced by the host plant, spittlebug or bacteria isolated from the froth. Three chitinases, i.e., β-N-actylglucosaminidase, endochitinase, and chitobiosidase, with specific activities of 1,759.3, 1,172.1, and 364.6 nmol p-nitrophenol/min/mg protein, respectively, have been detected in this froth. Since the Malpighian tubule is one of the froth-derived organs, the Malpighian tubule was analyzed, and the β-N-actylglucosaminidase activity was observed. Furthermore, a chitinase cDNA, PCChi (JQ806339), was cloned from the Malpighian tubules of P. costalis nymphs. The expression of this chitinase mRNA in Malpighian tubule throughout fifth instar nymph stage was confirmed. Further, the protein expression system of PCChi gene in E. coli was established, and the chitinase produced had noticeable chitobiosidase activity. Two isolates of bacteria from the froth, Stenotrophomonas maltophilia and Delftia tsuruhatensis, had high antagonstic activities against F. oxysporum f. sp. pisi and Colletotrichum gloeosporioides Penz. S. maltophilia produced 19.9, 19.1, and 1.1 nmol p-nitrophenol/min/mg of chitobiosidase, endochitinase, and β-N-actylglucosaminidase, respectively. These findings provide the possible cause of no mildew in the froth. The isolated antagonistic bacteria may have potential for development in the control of plant diseases, and the established E. coli protein expression system may serve as a reference for other protein expression in the future.
|
|---|
