A Computational Framework for 3D Mechanical Modeling of Plant Morphogenesis with Cellular Resolution

The link between genetic regulation and the definition of form and size during morphogenesis remains largely an open question in both plant and animal biology. This is partially due to the complexity of the process, involving extensive molecular networks, multiple feedbacks between different scales of organization and physical forces operating at multiple levels. Here we present a conceptual and modeling framework aimed at generating an integrated understanding of morphogenesis in plants. This framework is based on the biophysical properties of plant cells, which are under high internal turgor pressure, and are prevented from bursting because of the presence of a rigid cell wall. To control cell growth, the underlying molecular networks must interfere locally with the elastic and/or plastic extensibility of this cell wall. We present a model in the form of a three dimensional (3D) virtual tissue, where growth depends on the local modulation of wall mechanical properties and turgor pressure. The model shows how forces generated by turgor-pressure can act both cell autonomously and non-cell autonomously to drive growth in different directions. We use simulations to explore lateral organ formation at the shoot apical meristem. Although different scenarios lead to similar shape changes, they are not equivalent and lead to different, testable predictions regarding the mechanical and geometrical properties of the growing lateral organs. Using flower development as an example, we further show how a limited number of gene activities can explain the complex shape changes that accompany organ outgrowth.     

Proteomic analysis reveals differences between Vitis vinifera L. cv. Chardonnay and cv. Cabernet Sauvignon and their responses to water deficit and salinity

The impact of water deficit and salt stress on two important wine grape cultivars, Chardonnay and Cabernet Sauvignon, was investigated. Plants were exposed to increasing salinity and water deficit stress over a 16 d time period. Measurements of stem water potentials, and shoot and leaf lengths indicated that Chardonnay was more tolerant to these stresses than Cabernet Sauvignon. Shoot tips were harvested every 8 d for proteomic analysis using a trichloroacetic acid/acetone extraction protocol and two-dimensional gel electrophoresis. Proteins were stained with Coomassie Brilliant Blue, quantified, and then 191 unique proteins were identified using matrix-assisted laser desorption ionization time of flight/time of flight mass spectrometry. Peptide sequences were matched against both the NCBI nr and TIGR Vitis expressed sequence tag (EST) databases that had been implemented with all public Vitis sequences. Approximately 44% of the protein isoforms could be identified. Analysis of variance indicated that varietal difference was the main source of protein expression variation (40%). In stressed plants, reduction of the amount of proteins involved with photosynthesis, protein synthesis, and protein destination was correlated with the inhibition of shoot elongation. Many of the proteins up-regulated in Chardonnay were of unclassified or of unknown function, whereas proteins specifically up-regulated in Cabernet Sauvignon were involved in protein metabolism.     

Stimulation of fission yeast and mouse Hop2-Mnd1 of the Dmc1 and Rad51 recombinases

Genetic analysis of fission yeast suggests a role for the spHop2–Mnd1 proteins in the Rad51 and Dmc1-dependent meiotic recombination pathways. In order to gain biochemical insights into this process, we purified Schizosaccharomyces pombe Hop2-Mnd1 to homogeneity. spHop2 and spMnd1 interact by co-immunoprecipitation and two-hybrid analysis. Electron microscopy reveals that S. pombe Hop2–Mnd1 binds single-strand DNA ends of 3′-tailed DNA. Interestingly, spHop2-Mnd1 promotes the renaturation of complementary single-strand DNA and catalyses strand exchange reactions with short oligonucleotides. Importantly, we show that spHop2-Mnd1 stimulates spDmc1-dependent strand exchange and strand invasion. Ca²⁺ alleviate the requirement for the order of addition of the proteins on DNA. We also demonstrate that while spHop2-Mnd1 affects spDmc1 specifically, mHop2 or mHop2-Mnd1 stimulates both the hRad51 and hDmc1 recombinases in strand exchange assays. Thus, our results suggest a crucial role for S. pombe and mouse Hop2-Mnd1 in homologous pairing and strand exchange and reveal evolutionary divergence in their specificity for the Dmc1 and Rad51 recombinases.     

恶性疟原虫abstrakt同源基因的克隆及DEAD盒家族蛋白的序列分析

DEAD盒蛋白家族的ATP依赖性的RNA解旋酶类参与细胞内几乎所有的RNA代谢过程 ,在几乎所有生物的细胞生长发育过程中扮演着众多不可或缺的角色。在本实验中 ,通过PCR和探针杂交相结合的筛选方法 ,筛选恶性疟原虫 (Plasmodiumfalciparum)的基因组文库 ,克隆了FH1F———abstrakt同源基因的完整序列。通过搜索已经完成测序的恶性疟原虫基因组数据库 ,推测FH1F序列定位在第 5条染色体上。FH1F全长2 80 4bp,包含一个 1 1 6 1bp的完整阅读框 ,编码一个由 386个氨基酸组成的蛋白。对FH1F蛋白序列用BlastP进行搜索和分析以及用DNAStar与许多典型的DEAD盒蛋白序列进行比对分析 ,结果均提示FH1F蛋白应该是DEAD盒家族的一个Abstrakt蛋白。另一方面 ,用DNAStar对已知所有完整的DEAD盒蛋白进行详细的序列分析以及用Mega对这些序列进行系统发育研究的结果都显示 :DEAD盒家族的蛋白聚类成为若干不同的亚群 ;与DEAD盒蛋白的一般保守序列相比 ,Abstrakt,eIF 4A ,Vasa ,P6 8等不同亚群的DEAD盒蛋白在保守区具有各自不同的结构特征。本文对不同的DEAD盒蛋白的结构特征进行了总结并试图给出不同亚群分类上的结构标准 ,对Abstrakt蛋白在本应高度保守的位点上异常于其它DEAD盒蛋白的氨基酸残基的取代也进行了相关的初步分析     

Antioxidant levels in tissues of young and adult camels (Camelus dromedarius)

In this study, we measured the concentration of some antioxidant substances in erythrocytes hemolysate, liver, kidney and brain in young and adult camels. It has been found that the activity of the antioxidant enzymes glutathione peroxidase (GSH-Px), catalase (CAT), superoxide dismutase (SOD) and the concentration of glutathione, ascorbic acid and alpha-tocopherol are high in both young and adult camels. GSH-Px and CAT activities were higher in adult camels than in the young whereas no significant difference in the activity of SOD between young and adult camels was noticed. Glutathione was present in all tissues studied. Ascorbic acid was found to have significantly higher values in young camels. From this study it could be concluded that, as in other mammals, camel tissues contain a powerful antioxidant system. The liver has the highest contents of antioxidants and antioxidant enzymes indicating that it plays an important role in pro-oxidants detoxification. Age has a variable effect on the antioxidant system in camels.     

Evidence of field-evolved resistance to organophosphates and pyrethroids in Chrysoperla carnea (Neuroptera: Chrysopidae)

The toxicity of some of the most commonly used insecticides in the organophosphate and pyrethroid classes were investigated against different Chrysoperla carnea (Stephens) (Neuroptera: Chrysopidae) populations collected over three consecutive years (2005-2007). The populations were tested using leaf dip bioassays for residual effects and topical applications to measure the response of larvae that would come into direct contact with field application of insecticides. In leaf dip assays, the LC50 (micrograms per milliliter; 120 h) values for chlorpyrifos and profenofos were in the range of 59.3-1,023 and 180.02-1,118 respectively. The LC50 values for lambda-cyhalthrin, alphamethrin, and deltamethrin were 359.08-2,677, 112.9-923.5, and 47.81-407.03, respectively. The toxicity for the above insecticides in topical application was similar to toxicity in leaf dip assays. The susceptibility of a laboratory population, which was locally developed and designated as (Lab-PK), to deltamethrin was comparable with another susceptible laboratory population. Resistance ratios for five field populations were generally low to medium for deltamethrin, but high to very high for chlorpyrifos, profenofos, lambda-cyhalthrin and alphamethrin compared with the Lab-PK population. Our data also suggested that the five field populations had multiple resistance to two classes of insecticides. The populations showed resistance to two organophosphates tested and to lambda-cyhalthrin and alphamethrin; however, resistance to deltamethrin was only found at two locations. This pattern indicates occurrence of two divergent patterns of resistance within pyrethroids. The resistance to the insecticides was stable across 3 yr, suggesting field selection for general fitness had also taken place in various populations of C. carnea. The broad spectrum of resistance and stability of resistance to insecticides in C. carnea in the current study suggested that it could be a prime candidate for mass releases and compatible with most spray programs.     

Adsorption of Basic violet 16 from aqueous solutions by waste sugar beet pulp: kinetic,thermodynamic, and equilibrium isotherm studies

Waste sugar beet pulp has been used as adsorbent for the removal of a hazardous cationic dye, Basic violet 16, from its aqueous solution. Adsorption of the dye was studied as function of time, pH of the solution, dosage of the adsorbent, sieve size of the particles, concentration of the dye, and temperature. The initial pH of the dye solution did not affect the chemistry of the dye molecule and the surface of beet pulp. Langmuir and Freundlich adsorption isotherms were successfully employed, and on the basis of these models, the thermodynamic parameters were evaluated. Adsorption of Basic violet 16 on beet pulp was found to be an exothermic reaction. Time contact studies showed that more than 80% adsorption of the dye is achieved in less than 1 h. Kinetics investigations confirmed both pseudo-first-order and pseudo-second-order behaviors; on the other hand, it shows that the intraparticle diffusion step is not the only rate-controlling step in all concentrations.