| The medicinal plant plants are not only highly ornamental,some of them could be edible.In addition,there are many more species have high medical value and also can be used as industrial raw materials and plant pesticides,which providing abundant raw materials for pharmaceutical and chemical industry.The Gongga Mountain Region located on the eastern fringe of Qinghai-Xizang Plateau in China with complicated natural conditions and capricious climate provided a habitat for a great variety of Rhododendrons.As far as we know,the genera Rhododendron in Gongga Mountain Region included 2 subgenera and 79 species(including 4 varieties and 2 subspecies).In this study,culture-independent and culture-dependent approaches were employed to assessed the diversity of endophytic actinobacteria of Rhododendron that collected from Gongga Mountain Region.161 endophytic actinobacteria strains were isolated using five actinobacteria-selective media from surface sterilized stems,leaves and flowers of Rhododendron.Based on morphological characteristic,76 representative isolates were selected to analyzed 16S rRNA gene sequence.According to the phylogenetic analysis,71%isolates were belonged to the Streptomyces genera,the remainder belonged to genera Pseudonocardia,Nocardiopsis,Cellulosimicrobium,Brevibacterium,Brachybacterium,Celluomonas,Nocardioides,Rhodococcus,Nakamurella,Gordonia,Micromonospora,Actinoplanes.The diversity of the uncultured actinobacteria from the Rhododendron were investigated by PCR-DGGE.The results revealed that uncultural endophytic actinobacteria included 18 generas,which were belonged to genera Frankia,Blastococcus,Sanguibacter,Friedmanniella,Cellulomonas,Nakamurella,Mycobacterium,Streptomyces,Humicoccus,Corynebacterium,Pseudonocardia,Jatrophihabitans,Microbacterium,Nocardioides,Micrococcus,Geodermatophilus,Leifsonia,Arthrobacter.The above results showed the Rhododendron possessed abundant endophytic actinobacteria.The results of antimicrobial activity of 76 endophytic actinobacteria exhibited 81.6%of stains showed antimicrobial activity against at least one indicator organism.In addition,30.3%?46.1%?13.2%of isolates carried the genes encoding type ? polyketide synthases,type ? polyketide synthases,nonribosomal peptide synthetase and showed high diversity.The confrontation growth method tested separation strain antibacterial activity,using specific primers amplification method analyzed separation strains which had polyketide biosynthase,and nonribsomal peptide synthetase,to explore its potential function synthesis of natural products.The results showed that 81.6%representative strains had diffierent antibacterial activity against 9 indicator organisms,and endophytic actinobacteria isolated from the Rhododendron plants in Gongga Mountain Region had broad-spectrum antimicrobial activity and potential natural product diversity,which further proved that endophytic actinobacteria are valuable reservoirs of novel bioactive compounds.In order to analyze the plant growth promoting(PGP)activity,IAA,phosphate solubilization,siderophore and cellulose degradation of endophytic actinobacterial isolates were tested.The results showed 50%,63.2%,28.9%,and 31.6%of the isolates possessed capability of IAA,siderophore,phosphate solubilization and cellulose degradation production,respectively.We also detected the resistance of endophytic actinobacteria,and the results indicated that different endophytic actinobacteria showed different degrees of resistance to salinity,pH,and drought.Between the salinity of 0%-7%,pH=6-10 and the concentration of PEG was 0%-25%,most of endophytic actinobacterial isolates could grow,which revealed that the endophytic actinobacteria can grow in the disadvantageous environment.Compared to control plants,the plant height,root length,fresh weight,dry weight were increased by 18.8%and 5.87%?47.33%and 40.29%?48.99%and 51.68%?47.37%and 47.37%,respectively,under individual treatment strain SICAUZR27 and SICAUZR28,and that treatment strain SICAUZR27 exhibited significant promoting effects on plant growth.In this study,the endophytic actinobacterial diversity of the Rhododendron were investigated by using cultured-and uncultured protocols,which will convenient to study and utilized the endophytic actinobacterias resources of the Rhododendron growing in Gongga Mountain Region. |
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