Intra-isolate heterogeneity of the ITS region of rDNA in Pythium helicoides

Heterogeneity of the rDNA ITS region in Pythium helicoides and the phylogenetic relationship between P. helicoides and closely related species were investigated. In PCR-RFLP analysis of the rDNA ITS region of six P. helicoides isolates investigated, including the type culture, intraspecific variation was found at the HhaI site. The total length of fragments was longer than before cutting, indicating sequence heterogeneity within isolates. Digestion of the cloned rDNA ITS region derived from seven isolates with HhaI revealed polymorphisms among and within single zoospore isolates, and variability of the region was also present among the clones derived from the same isolate. To test whether the rDNA ITS region of closely related species and other regions in the genome of P. helicoides are also variable, the rDNA ITS region of P. ultimum and the cytochrome oxydase II (cox II) gene encoded in mitochondria were sequenced. P. ultimum had little variation in the rDNA ITS region. The cox II gene sequences of both species revealed only a low intraspecific variability and no intra-isolate variation. In the phylogenic tree based on the rDNA ITS sequences, all clones of P. helicoides formed one large clade that was distinct from the clades comprising morphologically similar species, such as P. oedochilum and P. ostracodes, and was closely related to P. chamaehyphon rather than the other species.     

Genetic, proteomic and metabolic analysis of the regulation of energy storage in rice seedlings in response to drought

We used proteomic analysis to determine the response of rice plant seedlings to drought-induced stress. The expression of 71 protein spots was significantly altered, and 60 spots were successfully identified. The greatest down-regulated protein functional category was translation. Up-regulated proteins were mainly related to protein folding and assembly. Additionally, many proteins involved in metabolism (e.g. carbohydrate metabolism) also showed differences in expression. cDNA microarray and GC-MS analysis showed 4756 differentially expressed mRNAs and 37 differentially expressed metabolites. Once these data were integrated with the proteomic analysis, we were able to elucidate the metabolic pathways affected by drought-induced stress. These results suggest that increased energy consumption from storage substances occurred during drought. In addition, increased expression of the enzymes involved in anabolic pathways corresponded with an increase in the content of six amino acids. We speculated that energy conversion from carbohydrates and/or fatty acids to amino acids was increased. Analysis of basic metabolism networks allowed us to understand how rice plants adjust to drought conditions.     

Insights into the composition and assembly of the membrane arm of plant complex I through analysis of subcomplexes in Arabidopsis mutant lines

NADH-ubiquinone oxidoreductase (Complex I, EC 1.6.5.3) is the largest complex of the mitochondrial respiratory chain. In eukaryotes, it is composed of more than 40 subunits that are encoded by both the nuclear and mitochondrial genomes. Plant Complex I differs from the enzyme described in other eukaryotes, most notably due to the large number of plant-specific subunits in the membrane arm of the complex. The elucidation of the assembly pathway of Complex I has been a long-standing research aim in cellular biochemistry. We report the study of Arabidopsis mutants in Complex I subunits using a combination of Blue-Native PAGE and immunodetection to identify stable subcomplexes containing Complex I components, along with mass spectrometry analysis of Complex I components in membrane fractions and two-dimensional diagonal Tricine SDS-PAGE to study the composition of the largest subcomplex. Four subcomplexes of the membrane arm of Complex I with apparent molecular masses of 200, 400, 450, and 650 kDa were observed. We propose a working model for the assembly of the membrane arm of Complex I in plants and assign putative roles during the assembly process for two of the subunits studied.     

Habitat choice in rotifera communities of three shallow lakes: impact of macrophyte substratum and season

The distribution of rotifer communities between emergent (Typha angustifolia) and submerged (Chara tomentosa) vegetation and a comparatively open water zone were compared during the spring, summer and autumn seasons at three macrophyte-dominated lakes. This survey identified 107 rotifera species of which 58% of the taxonomical structure was common for the three examined lakes. Stoneworts with a more complicated spatial and morphological structure (having a much longer stem length than the narrow leaf cattail), supported higher rotifer densities. The stem length appeared to be the best predictor of all the macrophyte parameters and pH and chlorophyll a for the chemical variables, for explaining the variation of rotifer densities using the stepwise multiple forward regressions. The distribution of pelagic species did not differ between particular sites, which may have reflected the behavioural requirements of those rotifers. Some of them remained in the open water zone while others seeking an anti-predator refuge, gathered within macrophyte stands during the daytime. Moreover, there were nine Chara-associated species recorded and only one Typha-associated species was noted. The similarity of rotifer communities was most strongly influenced by particular habitat and season. Guest editors: S. S. S. Sarma, R. D. Gulati, R. L. Wallace, S. Nandini, H. J. Dumont & R. Rico-Martínez Advances in Rotifer Research     

Disruption of Elements Uptake due to Excess Chromium in Indian Medicinal Plants

Chromium and its compounds may cause disturbance in the nutrient level of the plants. Iron, manganese, copper, and zinc are essential nutrient elements and required for balanced growth and development of plants, but chromium uptake sometimes disturbed their concentration in plants. Therefore, in the present paper, an effort has been made to observe the effect of different levels of Cr on nutrient uptake of Phyllanthus amarus and Solanum nigrum, the medicinally important plants of indigenous systems of medicine having hepatoprotective and diuretic properties. The study revealed that Cr causes significant changes in nutrient uptake as compared to control plants. Besides, Cr-treated plants showed growth depression and decrease in fresh and dry weight too. With the increase in Cr supply, accumulation of Cr in roots was increased significantly. Concentration of manganese and zinc was also increased. However, copper concentration in both the plants seemed less affected by Cr.     

Relationships among Key deer, insect herbivores, and plant quality

Deer can have severe effects on plant communities, which in turn can affect insect communities. We studied the effects of Key deer herbivory on the incidence of insect herbivores that occur within deer habitats in the lower Florida Keys, within the National Key Deer Refuge (NKDR). We analyzed plant chemistry (tannins, nitrogen) and surveyed for the occurrence of insects (above the browse tier) among plant species that were either deer-preferred or less-preferred. Results indicated higher levels of foliar tannins on islands with fewer Key deer and larger amounts of foliar nitrogen on islands with a high density of Key deer. Consequently, leaf miners were significantly more abundant on islands with high deer density, irrespective of deer-preference of plant species. On islands with a high deer density, incidence of leaves damaged by chewing insects was lower on preferred plant species but greater on less-preferred species than on islands with fewer deer. No apparent patterns were evident in the distribution of leaf gallers among plant species or islands with different deer density. Our results imply that plant nutrition levels—either preexisting or indirectly affected by deer deposition—are more important than plant defenses in determining the distribution of insect herbivores in the NKDR. Although high densities of the endangered Key deer have negative effects on some plant species in the NKDR, it seems Key deer might have an indirect positive influence on insect incidence primarily above the browse tier. Further research is warranted to enable fuller understanding of the interactions between Key deer and the insect community.     

The effect of flow turbulence on plant growth and several growth regulators in Egeria densa Planchon

The effects of turbulence velocity on Egeria densa Planchon was studied for 12 weeks using mechanically oscillating grid-generated turbulence without mean flow. The root-mean-square of the turbulence velocity fluctuations (u′) ranged from 1.62 ± 0.44 to 2.86 ± 0.8 cm s⁻¹ (high turbulence), 1.36 ± 0.2 to 1.86 ± 0.78 cm s⁻¹ (medium turbulence) and 0.67 ± 0.12 to 0.81 ± 0.16 cm s⁻¹ (low turbulence). The control was subjected to gentle manual mixing once a day. Shoot elongation was significantly reduced with increasing turbulence intensity, and the endogenous indole acetic acid (IAA) concentration was significantly decreased with increasing turbulence intensity and exposure time. The plants exposed to high turbulence showed a 64.6% decrease in endogenous IAA concentration compared to the control, while it was decreased only 26.9% in plants exposed to low turbulence. IAA and cytokinin catabolism was increased, and there was an increase in the hydrogen peroxide concentration of the tissues, which triggered peroxidase activity. The total chlorophyll and chlorophyll a content decreased with the time of exposure. Although the flow turbulence negatively affected plant growth and metabolism, all of the plants survived for the experimental period.     

The PDZ-GEF Gef26 regulates synapse development and function via FasII and Rap1 at the Drosophila neuromuscular junction

Guanine nucleotide exchange factors (GEFs) are essential for small G proteins to activate their downstream signaling pathways, which are involved in morphogenesis, cell adhesion, and migration. Mutants of Gef26, a PDZ-GEF (PDZ domain-containing guanine nucleotide exchange factor) in Drosophila, exhibit strong defects in wings, eyes, and the reproductive and nervous systems. However, the precise roles of Gef26 in development remain unclear. In the present study, we analyzed the role of Gef26 in synaptic development and function. We identified significant decreases in bouton number and branch length at larval neuromuscular junctions (NMJs) in Gef26 mutants, and these defects were fully rescued by restoring Gef26 expression, indicating that Gef26 plays an important role in NMJ morphogenesis. In addition to the observed defects in NMJ morphology, electrophysiological analyses revealed functional defects at NMJs, and locomotor deficiency appeared in Gef26 mutant larvae. Furthermore, Gef26 regulated NMJ morphogenesis by regulating the level of synaptic Fasciclin II (FasII), a well-studied cell adhesion molecule that functions in NMJ development and remodeling. Finally, our data demonstrate that Gef26-specific small G protein Rap1 worked downstream of Gef26 to regulate the level of FasII at NMJs, possibly through a βPS integrin-mediated signaling pathway. Taken together, our findings define a novel role of Gef26 in regulating NMJ development and function.     

不同密度格木幼林的土壤理化与林下植被特征

为探索适合格木(Erythrophleum fordii)人工林在幼龄阶段的种植密度,在不同林分密度(2 m×1 m、2 m×2 m、2 m×3 m、3 m×3 m)的6 a生格木人工林下设置标准样地,采用土壤质量评价和灰色关联度等方法,探究不同密度下格木幼林的土壤理化与林下植被特征。结果表明,密度2 m×3 m下的林木胸径、树高最优,较最低水平高16.7%、27.9%;土壤总孔隙度最大,全N、硝态N、铵态N含量最高,灌木草本多样性最高。相关性分析表明土壤化学性质对灌木草本的多样性影响最大。不同林分密度下格木幼林土壤理化性质及林下植物多样性有显著差异,因此,选择合适的林分密度对人工林土壤肥力的可持续利用及林分的经营培育至关重要。