Reaction of Certain Solanaceous and Asteraceous Plant Species to Inoculation with Phytophthora infestans in Cameroon

Experiments were conducted to detect potential hosts of Phytophthora infestans, causal agent of potato late blight among weeds occurring in Cameroon. Isolates of P. infestans isolated from garden huckleberry (Solanum scabrum), potato (S. tuberosum) and tomato (S. lycopersicon) were inoculated on detached leaves of 12 solanaceous and 14 asteraceous species collected from the potato agroecosystem in the western highlands of Cameroon. Isolates of P. infestans from huckleberry and potato infected the same host plants as well as gboma eggplant (S. macrocarpon) and two asteraceous weeds; Billy goatweed (Ageratum conyzoides) and Dichrocephala (Dichrocephala integrifolia). Inoculum from potato caused late blight symptoms on haemorrhage plant (Aspilia africana); while inoculum from tomato resulted in late blight on worowo (Solanecio biafrae). This is the first report of late blight infection on S. macrocarpon, A. conyzoides, Sol. biafrae and Asp. africana in Cameroon. The research results indicate that some asteraceous and solanaceous weeds may be alternative hosts of P. infestans in the potato agroecosystem.     

Cambium Formation in Wounded Solanaceous Stems

When stems of certain Solanaceous species are wounded the internalphloem strands that lie near to the damaged surface become enlargedthrough cell division, and some of them develop a vascular cambium.This ‘internal cambium’ forms phloem inwards andxylem outwards; it is thus in inverted orientation. Such a structuredoes not occur in the normal stem of any Solanaceous plant.Further, during the regeneration of a cambial cylinder afterwounding, the regenerating cambium may turn inward to meet woundedinternal phloem strands. Where this happens, subsequent secondarythickening leads to the formation of thin tubes of cambium runningradially through the xylem and forming a limited amount of enclosedphloem which connects the internal and external phloem systemsof the stem. The jpositions in which these cambia arise are explicable bythe ‘gradient induction’ hypothesis of cambial regeneration,but not by the ‘free surfacfe’ and ‘cambialring’ theories.     

茄属生物碱的研究进展

甾体生物碱(SA)主要是茄属植物体内的一种次级代谢产物。它复杂的结构多样性决定了生物活性的多样性。它的合成途径也比较复杂,尚不十分清楚。以生物碱类化合物的化学结构为基础,对近几年来茄属生物碱的研究现状进行了简要综述。主要论述了茄属生物碱的化学结构、含量分布、生理活性以及与茄属生物碱合成途径相关的分子生物学研究。并分析了茄属生物碱今后的发展方向。以期为以后研究糖苷生物碱的生物合成途径、毒性机制、药理学作用等奠定一定的基础。     

Certain Aspects of the Sexuality of Two Species of Chlamydomonas

SUMMARY. When older cultures (18 days old) of Chlamydomonas eugametos were mated, zygote formation occurred under conditions similar to those devised for C. moewusii. Young (6 days old) cultures of the former did not mate when the nitrogen concentration of the medium was high (0.03% NH₄NO₃). In confirmation of the work of Sager and Granick, it was found that low nitrogen concentrations, produced by decreasing the concentration of NH₄NO₃ in the original medium, by increasing the intensity of the illumination, or by using old cultures, enhanced gametogenesis in C. eugametos. It has also been demonstrated that the two species are compatible with one another, even under conditions which are unfavorable for gametogenesis in C. eugametos alone.     

病毒诱导烟草的基因沉默

病毒诱导基因沉默是利用RNA介导病毒防卫机制的一项技术。构建含有目的基因片段的人工改造病毒载体,通过农杆菌侵染导致植物内源目的基因沉默。为建立病毒诱导基因沉默体系,选用烟草脆裂病毒（TRV）和烟草为实验材料。构建了八氢番茄红素去饱和酶基因（PDS）的基因沉默病毒载体,病毒载体侵染结果显示目的基因PDS沉默导致烟草幼苗出现光漂白现象。采用RT-PCR的方法检测目的基因PDS的沉默效果,结果显示PDS基因mRNA被显著降解。该体系的建市有利于将来对植物基因进行高通量功能分析。     

Virus-induced permeability transition in mitochondria

Isolated rat liver mitochondria undergo permeability transition after supplementation with a suspension of tobacco mosaic virus. Four mitochondrial parameters proved the opening of the permeability transition pore in the inner mitochondrial membrane: increased oxygen consumption, collapse of the membrane potential, release of calcium ions from mitochondria, and high amplitude mitochondrial swelling. All virus-induced changes in mitochondria were prevented by cyclosporin A. These effects were not observed if the virus was treated with EGTA or disrupted by heating. Protein component of the virus particle in the form of 20S aggregate A-protein, or helical polymer, as well as supernatant of the heat-disrupted virus sample, had no effect on mitochondrial functioning. Electron microscopy revealed the direct interaction of the virus particles with isolated mitochondria. The possible role of the mitochondrial permeability transition pore in virus-induced apoptosis is discussed.     

Virus-induced necrosis in white cabbage

Turnip mosaic virus was found to be a major cause of internal necrosis in white cabbage. The extent of the disorder in heads in store could be correlated with the severity of virus symptoms on the outer leaves of the plants in the field.     

Virus-induced gene silencing in plants

Virus-induced gene silencing (VIGS) is a technology that exploits an RNA-mediated antiviral defense mechanism. In plants infected with unmodified viruses the mechanism is specifically targeted against the viral genome. However, with virus vectors carrying inserts derived from host genes the process can be additionally targeted against the corresponding mRNAs. VIGS has been used widely in plants for analysis of gene function and has been adapted for high-throughput functional genomics. Until now most applications of VIGS have been in Nicotiana benthamiana. However, new vector systems and methods are being developed that could be used in other plants, including Arabidopsis. Here we discuss practical and theoretical issues that are specific to VIGS rather than other gene "knock down" or "knockout" approaches to gene function. We also describe currently used protocols that have allowed us to apply VIGS to the identification of genes required for disease resistance in plants. These methods and the underlying general principles also apply when VIGS is used in the analysis of other aspects of plant biology.     

Virus-induced gene silencing in tomato

We have previously demonstrated that a tobacco rattle virus (TRV)-based vector can be used in virus-induced gene silencing (VIGS) to study gene function in Nicotiana benthamiana. Here we show that recombinant TRV infects tomato plants and induces efficient gene silencing. Using this system, we suppressed the PDS, CTR1 and CTR2 genes in tomato. Suppression of CTR1 led to a constitutive ethylene response phenotype and up-regulation of an ethylene response gene, CHITINASE B. This phenotype is similar to Arabidopsis ctr1 mutant plants. We have constructed a modified TRV vector based on the GATEWAY recombination system, allowing restriction- and ligation-free cloning. Our results show that tomato expressed sequence tags (ESTs) can easily be cloned into this modified vector using a single set of primers. Using this vector, we have silenced RbcS and an endogenous gene homologous to the tomato EST cLED3L14. In the future, this modified vector system will facilitate large-scale functional analysis of tomato ESTs.     

Hypoxia-Induced Reactive Oxygen Species Cause Chromosomal Abnormalities in Endothelial Cells in the Tumor Microenvironment

There is much evidence that hypoxia in the tumor microenvironment enhances tumor progression. In an earlier study, we reported abnormal phenotypes of tumor-associated endothelial cells such as those resistant to chemotherapy and chromosomal instability. Here we investigated the role of hypoxia in the acquisition of chromosomal abnormalities in endothelial cells. Tumor-associated endothelial cells isolated from human tumor xenografts showed chromosomal abnormalities, >30% of which were aneuploidy. Aneuploidy of the tumor-associated endothelial cells was also shown by simultaneous in-situ hybridization for chromosome 17 and by immunohistochemistry with anti-CD31 antibody for endothelial staining. The aneuploid cells were surrounded by a pimonidazole-positive area, indicating hypoxia. Human microvascular endothelial cells expressed hypoxia-inducible factor 1 and vascular endothelial growth factor A in response to either hypoxia or hypoxia-reoxygenation, and in these conditions, they acquired aneuploidy in 7 days. Induction of aneuploidy was inhibited by either inhibition of vascular endothelial growth factor signaling with vascular endothelial growth factor receptor 2 inhibitor or by inhibition of reactive oxygen species by N-acetyl-L-cysteine. These results indicate that hypoxia induces chromosomal abnormalities in endothelial cells through the induction of reactive oxygen species and excess signaling of vascular endothelial growth factor in the tumor microenvironment.     

Regulation of Mitosis in Living Cells. I. Mitosis under Controlled Conditions

A quantitative method has been devised to study mitosis in vitro by phase contrast and polarization microscopy. Mitosis in cell-wall-free endosperm cells of Haemanthus kathrinar Baker (the African blood lily) has been divided into 18 arbitrary stages or events. The time course for the various stapes, as well as the percentage of cells that proceed from one stage to another during a four hour observation period, are presented. Cells that were in prophase when selected for study proceeded from nuclear membrane breakdown to melaphase in 60 minutes and remained in melaphase for 30 minutes. Only 13 minutes was required to proceed from onset of anaphase to mid-anaphasc. Mid-anaphase provides a clear and precise baseline for determining the time required for succeeding stages to appear. The cell plate made its appearance 40 minutes after mid-anaphase and was completely formed 20 minutes later. The nuclear membranes also became evident at this latter time and nucleoli were visible 30 minutes later. Thus, the average time for a cell observed initially in prophase to proceed from nuclear membrane breakdown to formation of two daughter cells was just over three hours. A high percentage of cells that were in late prophase or later stages of mitosis at the time of initial observation completed mitosis during the observation period. The effect of the length of time a cell is subjected to experimental conditions upon its subsequent behaviour is assessed. These results form the basis for future studies of the effects of chemicals, particularly herbicides, upon cells in mitosis as observed in vitro by phase contrast and polarization microscopy.