The role of plant growth-promoting rhizobacteria (PGPR) in adaptation of plants in extreme environments is not yet completely understood. For this study native bacteria were isolated from rhizospeheric arid soils and evaluated for both growth-promoting abilities and antagonistic potential against phytopathogenic fungi and nematodes. The phylogentic affiliation of these representative isolates was also characterized. Rhizobacteria associated with 11 wild plant species from the arid soil of Almadinah Almunawarah, Kingdom of Saudi Arabia (KSA) were investigated. From a total of 531 isolates, only 66 bacterial isolates were selected based on their ability to inhibit Fusarium oxysporum, and Sclerotinia sclerotiorum. The selected isolates were screened in vitro for activities related to plant nutrition and plant growth regulation as well as for antifungal and nematicidal traits. Isolated bacteria were found to exhibit capabilities in fix atmospheric nitrogen, produce ammonia, indoleacetic acid (IAA), siderophores, solubilize phosphate and zinc, and showed an antagonistic potential against some phytopathogenic fungi and one nematode species (Meloidogyne incognita) to various extent. Isolates were ranked by their potential ability to function as PGPR. The 66 isolates were genotyped using amplified rDNA restriction analysis (ARDRA) and 16S rRNA gene sequence analysis. The taxonomic composition of the representative genotypes from both rhizosphere and rhizoplane comprised Bacillus, Enterobacter and Pseudomonas. Out of the 10 genotypes, three strains designated as PHP03, CCP05, and TAP02 might be regarded as novel strains based on their low similarity percentages and high bootstrap values. The present study clearly identified specific traits in the isolated rhizobacteria, which make them good candidates as PGPR and might contribute to plant adaption to arid environments. Application of such results in agricultural fields may improve and enhance plant growth in arid soils.
The direct effects of phytohormones (auxin and kinetin) and root diffusates on the surface lipophilicity of the plant parasitic nematodes Globodera rostochiensis and Meloidogyne incognita were investigated. The fluorescent lipid probe AF18 (5-N(octodecanoyl) aminofluorescein) was used to detect surface changes. Root diffusates increased AF18 uptake by G. rostochiensis while it had no effect on M. incognita. Kinetin and auxin decreased AF18 uptake in G. rostochiensis, while they had the opposite effect on M. incognita. Auxin/kinetin ratio was also found to be important in triggering the surface changes, especially at high concentrations. Whether plant nematodes have auxin and/or kinetin binding proteins is discussed as well as the mechanism behind the surface lipophilicity changes due to root diffusates and phytohormones.
In this paper we describe the effect of poly-L-lysines of different molecular weight on the schistosomula. In the control sample, the schistosomula of Schistosoma mansoni take up fluorescent Texas Red conjugated to bovine serum albumin (TxR-BSA) into the gut. Following slight damage by 24.0 kDa poly-L-lysine, a high proportion of schistosomula take up fluorescent TxR-BSA into the excretory system. Subsequently, the dye diffused into the bodies of the schistosomula. We suspected that this diffusion involved the process of endocytosis so we investigated this with the use of endocytosis inhibitor, Latrunculin A. Addition of the endocytosis inhibitor Latrunculin A following poly-L-lysine treatment inhibited gut uptake of TxR-BSA as well as the diffusion of excretory-ingested TxR-BSA molecules.
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