Potential Role of Elicitins in the Interaction between Phytophthora Species and Tobacco

The potential role of extracellular elicitor proteins (elicitins) from Phytophthora species as avirulence factors in the interaction between Phytophthora and tobacco was examined. A survey of 85 Phytophthora isolates representing 14 species indicated that production of elicitin is almost ubiquitous except for isolates of Phytophthora parasitica from tobacco. The production of elicitins by isolates of P. parasitica correlated without exception with low or no virulence on tobacco. Genetic analysis was conducted by using a cross between two isolates of P. parasitica, segregating for production of elicitin and virulence on tobacco. Virulence assays of the progeny on tobacco confirmed the correlation between production of elicitin and low virulence.     

Characterization of a Phytoplasma Associated with Pear Decline in Iran

Symptoms of pear decline (PD) were observed in several pear growing regions of Iran. Pear trees with typical symptoms of PD from Estahban (Fars Province) were examined for phytoplasma infection using polymerase chain reaction (PCR) assay. Graft inoculation of healthy pear trees with scions from diseased trees resulted in production of PD symptoms and transmission of phytoplasma as verified by PCR. Target DNA was amplified from symptomatic pear trees with fO1/rO1, an apple proliferation (AP) group-specific primer pair. Physical and putative restriction fragment length polymorphism (RFLP) analyses of fO1/rO1 primed PCR products showed profiles corresponding to AP group, 16SrX-C subgroup ( Candidatus Phytoplasma pyri). Percent similarity values and phylogenetic analysis of fO1/rO1 primed sequences confirmed that, as a member of AP subclade, Estahban PD phytoplasma has a closer relationship to PD and peach yellow leaf roll phytoplasmas than to AP ( Ca . Phytoplasma mali) and European stone fruit yellows ( Ca . Phytoplasma prunorum) phytoplasmas. This is the first report of PD phytoplasma in the eastern Mediterranean.     

Quick Decline of Macadamia Trees: Association with Phytophthora capsici

Some macadamia trees in commercial orchards in Hawaii showing quick decline syndrome had bleeding from the trunk. Phytophthora capsici was isolated from c. 67% of such sites, and was shown to kill branches of artificially-inoculated healthy macadamia trees. The pathogen was detected in both diseased and apparently healthy bark and isolated from wood 80 mm away from the bark. Results suggest that trunk infection by P. capsici may lead to girdling and rapid decline, and attract insects which then cause some bleeding by making wounds at the sites of recent infection.     

The Role of Phytophthora cryptogea and Waterlogging in Root Rot Kiwifruit

A 48 h or 96 h period of waterlogging induced a partial rotting of the root system of 18 month old potted kiwifruit cuttings. However, root regeneration compensated for the loss of damaged roots and the plants remained healthy. Inoculation with Phytophthora cryptogea under low soil moisture conditions caused a small amount of root rotting (11 %) and regeneration of the roots occurred. Root rot was significantly increased when inoculations were combined with extended periods of waterlogging. Root rot incidence was highest (89 %) in inoculated plants exposed to periods of 96 h waterlogging. Regeneration did not occur with any of these plants and consequently, the shoot systems were severely damaged.     

Species of Phytophthora and Pythium as Nematode-destroying Fungi

Pythium monospermum,, P. aphanidermatum, and Phytophthora palmivora were found to be capable of destroying certain nonstylet-bearing nematodes through endozoic parasitism by hyphae from ingested zoospores. Hyphae of P. monospermum parasitized nematode eggs but could not capture or otherwise prey upon living nematodes. We suggest that endoparasitism of free-living nematodes may be common among Oomycetes in nature.     

自噬发生中的ROS调节机制

活性氧是细胞代谢中产生的有很强反应活性的分子,易将邻近分子氧化,并参与细胞内多种信号转导途径,对相关生理过程进行调控．自噬是真核细胞通过溶酶体机制对自身组分进行降解再利用的过程,在细胞应激及疾病发生等过程中发挥重要作用．本文对活性氧和自噬相关调节进行分类介绍,根据新近研究进展,从活性氧参与的自噬性死亡、自噬性存活以及线粒体自噬3方面探讨了相关信号转导机制,对活性氧作为信号分子参与的自噬调控途径做一总结和介绍．     

Phylogenetic Analysis of Clinically Relevant Fusarium Species in Iran

Mycopathologia - Fungi of the genus Fusarium are well known as major plant pathogens but also cause a broad spectrum of human infections. Sixty-three clinical isolates, collected during...     

Collophora hispanica,a New Pathogen and Potential Threat to the Almond Industry in Iran

Trunk diseases are potential threats for almond productivity and longevity worldwide, including Iran. In a recent survey on fungal species associated with trunk diseases of almonds in north‐western Iran, Collophora isolates (tentatively identified as Collophora hispanica) were recovered with high frequency from wood samples with internal necrosis and brown to black vascular streaking of almond trees showing symptoms of decline. However, the pathogenic potential of Collophora isolates on almond trees in Iran remains unproven. In this study, the identity of the isolates was further confirmed as C. hispanica based on a combination of morphological data and sequence data of ITS‐rDNA region, and pathogenicity of C. hispanica isolates on almond was evaluated using excised shoot method and in greenhouse experiments. Collophora hispanica isolates induced lesions statistically different from the control, in both excised shoot method and greenhouse assays. Significant differences were observed among the isolates in the length of the lesion induced on wood. Collophora hispanica should be considered as the main trunk pathogens of almond trees in north‐western region of Iran. The distribution and host range of this new pathogen on almond remains to be studied.     

The Role of Autophagy during Development of the Oomycete Pathogen Phytophthora infestans

Phytophthora infestans is a highly destructive plant path- ogen that causes late blight disease in plants such as potato and tomato （Fry and Goodwin, 1997）. As a typical oomycete, the primary infective propagule of P. infestans is the sporangium, which can either germinate directly or release biflagellate zoospores that encyst and germinate on the host subsequently （Grenville-Briggs et al., 2005）. Due to abundant formation of the sporangia and prolific sporulation, P. infestans can spread quickly in the host tissues and cause extensive necrosis of the infected plants （Kamoun and Smart, 2005）.     

ROS 的信息分子功能

ROS在机体内主要由NADPH氧化酶系统产生,ROS作为信息分子对细胞功能如细胞生长,转化,凋亡,转录和衰老的调节及相关信息传递等方面的研究,在90年代后期有了明显的进展。并从细胞内环境的氧化还原状态变化和蛋白质的氧化修饰角度初步探讨了ROS参与信息传递的机理。     

Decline of Clear-Water Rotifer Populations in a Reservoir: The Role of Resource Limitation

The relative importance of and changes in resource limitation of herbivorous rotifers were assessed during the clear-water phase in the Rímov Reservoir, Czech Republic, using in situ manipulative experiments. Resource limitation was tested experimentally as the difference in population growth rate (Δr) among various experimental treatments on four occasions. The reservoir community of rotifers was exposed to three treatments: (i) control, (ii) diluted and (iii) diluted and fertilized. Significant responses to these experimental manipulations were shown by Synchaeta spp., Polyarthra spp. and Keratella cochlearis. Growth rate was usually highest during the spring rotifer maximum and decreased during the clear water phase. The highest intensity of food limitation (expressed as ‚Chlorophyll-a’ limitation) was found in Synchaeta spp. K. cochlearis had low food limitation during the spring peak, high food limitation during the second experiment and low food limitation, again, during the later experiment. In contrast, Polyarthra spp. had the same Chlorophyll-a limitation throughout the whole experimental period. Linear regression was used to estimate the relative proportion of Δr variability explained by Chlorophyll-a concentration and rotifer density in all of the experiments. Chlorophyll-a concentration explained 89, 97 and 92% of the resource limitation in Synchaeta spp., Polyarthra spp. and K. cochlearis, respectively. The proportion of variability explained by rotifer density-dependent factors was lower: 60% for Synchaeta spp. and 68 % for Polyarthra spp.     

Landscape Variation in Tree Species Richness in Northern Iran Forests

Mapping landscape variation in tree species richness (SR) is essential to the long term management and conservation of forest ecosystems. The current study examines the prospect of mapping field assessments of SR in a high-elevation, deciduous forest in northern Iran as a function of 16 biophysical variables representative of the area’s unique physiography, including topography and coastal placement, biophysical environment, and forests. Basic to this study is the development of moderate-resolution biophysical surfaces and associated plot-estimates for 202 permanent sampling plots. The biophysical variables include: (i) three topographic variables generated directly from the area’s digital terrain model; (ii) four ecophysiologically-relevant variables derived from process models or from first principles; and (iii) seven variables of Landsat-8-acquired surface reflectance and two, of surface radiance. With symbolic regression, it was shown that only four of the 16 variables were needed to explain 85% of observed plot-level variation in SR (i.e., wind velocity, surface reflectance of blue light, and topographic wetness indices representative of soil water content), yielding mean-absolute and root-mean-squared error of 0.50 and 0.78, respectively. Overall, localised calculations of wind velocity and surface reflectance of blue light explained about 63% of observed variation in SR, with wind velocity accounting for 51% of that variation. The remaining 22% was explained by linear combinations of soil-water-related topographic indices and associated thresholds. In general, SR and diversity tended to be greatest for plots dominated by Carpinus betulus (involving ≥ 33% of all trees in a plot), than by Fagus orientalis (median difference of one species). This study provides a significant step towards describing landscape variation in SR as a function of modelled and satellite-based information and symbolic regression. Methods in this study are sufficiently general to be applicable to the characterisation of SR in other forested regions of the world, providing plot-scale data are available for model generation.     

The Role of Reactive Oxygen Species in Mitochondrial Permeability Transition

We have provided evidence that mitochondrial membrane permeability transition induced by inorganic phosphate, uncouplers or prooxidants such as t-butyl hydroperoxide and diamide is caused by a Ca²⁺-stimulated production of reactive oxygen species (ROS) by the respiratory chain, at the level of the coenzyme Q. The ROS attack to membrane protein thiols produces cross-linkage reactions, that may open membrane pores upon Ca²⁺ binding. Studies with submitochondrial particles have demonstrated that the binding of Ca²⁺ to these particles (possibly to cardiolipin) induces lipid lateral phase separation detected by electron paramagnetic resonance experiments exploying stearic acids spin labels. This condition leads to a disorganization of respiratory chain components, favoring ROS production and consequent protein and lipid oxidation.     

Detection of Aflatoxin in Aspergillus Species Isolated from Pistachio in Iran

To estimate the incidence contamination of fresh pistachio nuts by aflatoxigenic fungi in Iran, nut samples were collected from pistachio orchards in Kerman, Rafsanjan and Isfahan regions. Out of the 200 Aspergillus isolates obtained, 11 species were identified as A. alliaceous, A. candidus, A. flavus, A. niger, A. niveus, A. ochraceus, A. parasiticus, A. tamari, A. terreus, A. unguis and A. wentii. For detection of aflatoxin production ability of the isolates, three target genes, namely aflR, aflJ, and omtB, used in PCR amplification. In all the examined cases, the degenerate primer designed for amplification of omtB gene, named omtBII, was able to amplify an expected 611 bp fragment in aflatoxigenic isolates in this study and yielded the same result as those obtained from TLC analysis and fluorescence ability by application of methylated β‐cyclodextrin in culture media. Using this procedure the significant incidence of aflatoxin‐producing aspergilli was confirmed in pistachio nuts produced in different regions of Iran. The results indicated that PCR method described here, in combination with fluorescence assay, is a reliable and simple confirmatory test for monitoring pistachio nuts contaminated with aflatoxinogenic aspergilli.