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Ultrastructure of jelly fig achenes and purification, characterization, and antifungal activity analysis of a chitinase in the pericarp of achenes
本研究證實愛玉瘦果的果皮中含有一酸性幾丁質酶，在酸性的環境下皆具有酵素活性，其優異的生化特性與穩定結構，使之能耐高溫60℃達數小時之久，酵素活性不減，儲存於4℃低溫下近一年其酵素活性仍超過八成；又愛玉幾丁質酶針對含有幾丁質的植物病原真菌之細胞壁作用，可以將水果倉儲病原菌-炭疽病菌(Colletotrichum gloeosporioides)之病原孢子殺死，以防止成熟的水果表面產生變黑腐爛的病徵，對於蓮霧果腐病的病原菌(Rhizopus stolonifer)與十字花科蔬菜立枯絲核病菌(Rhizoctonia solani)菌絲之生長，亦有很好的抑制效果；此外對於番茄葉黴病菌(Fulvia fulva)及十字花科黑斑病(Alternaria brassicicola) 孢子之發芽，也有不錯的抑制功效；綜合上述研究成果，發現愛玉幾丁質酶具有耐熱與抗黴的特性，頗有研發成為防黴劑的潛能。
Ultrastructure of jelly fig achenes and purification, characterization, and antifungal activity analysis of a chitinase in the pericarp of achenes Jelly fig (Ficus awkeotsang Makino) is a unique plant growing in Taiwan. There are no further researches and discussions about the jelly fig except for a clue to congealing of jelly curd and some improvement of planting methods during that time. There is also no morphological and structural information with regard to jelly fig achenes. This research focuses on the basic studies of jelly fig. Although the congealed mechanism of jelly curd has been discovered, it is still unknown where the gelled pectin and pectin methylesterase are present in the achene. Detail structures of the jelly fig achene and subcellular locations of its pericarpial proteins are still unclear. Therefore, this research utilized microscopic observation, enzyme immunoassay, and immunogold labeling to reveal the unsolved questions. The pericarp of jelly fig achene has only 3-4 layers of living cells and about five layers of death cell's conformations. A large cell layer and a small cell layer compose of the outer and inner layers of seed coat, which has its own unique pigment. Like other dicotyledons, an embryo and an endosperm exist in the seed. These cells contain abundant protein bodies and oil bodies. Pectin methylesterase and chitinase are present in the cytoplasm of live pericarpial cells. The content of pectin methylesterase is more than that of chitinase. The pectin lies mainly on the cell wall of the endosperm in the seed. Water extract of jelly fig achenes contains the pericarpial pectin methylesterase and endospermous pectin. The interaction between pectins and pectin methylesterases produces the low methoxyl pectins and then these pectins link with cations, to form the solid state of jelly curd. A chitinase was found in the pericarpial extract of jelly fig achene. This chitinase possess excellent biochemical characteristics and stable structure; it maintains fully activity after treated at 60 degrees centigrade for several hours. Most plant pathogens contain chitin in their cell walls. The spore germination of Colletotrichum gloeosporioides, the major postharvest pathogen of mango, papaya and many other fruits in Taiwan, was inhibited and killed by this chitinase. In addition, the spore germination of Fulvia fulva, and Alternaria brassicicola was also suppressed by the chitinase. The mycelial growth of Rhizoctonia solani AG-4 and Rhizopus stolonifer was strongly inhibited by the jelly fig chitinase as well. According to the above results, jelly fig chitinase has the thermostable and antifungal activity, and due to such kinds of traits, the jelly fig chitinase may be a potential fungicide in the future. Keywords : jelly fig, achene, chitinase, fungus, thermostable, pericarp.
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