Coated Vesicles from the Protozoan Parasite Trypanosoma brucei: Purification and Characterization

ABSTRACT. A procedure was developed to purify a coated vesicle fraction from the protozoan parasite Trypanosoma brucei. Electron microscopy revealed a difference between T. brucei coated vesicles and clathrin-coated vesicles from other eukaryotes: trypanosome vesicles were larger (100 to ISO nm in diameter) and contained an inner coat of electron-dense material in addition to the external coat. Evidence suggests that the internal coat is the parasite's variant surface glycoprotein (VSG) coat. The SDS-PAGE analysis shows the major protein of T. brucei coated vesicles has a molecular mass of 61 kD, similar to VSG; this protein was recognized in an immunoblot by anti-VSG serum. Trypanosome coated vesicles also contain a protein which comigrates with the major protein (clathrin) of coated vesicles purified from rat brains. However, this protein is a minor component and it is not serologically cross-reactive with mammalian clathrin. Immunoblot analysis demonstrated that the parasite vesicles contained host IgG, IgM, and serum albumin.     

Synchronization of Mating Reactivity Rhythms in Populations of Paramecium bursaria

Cell populations of Paramecium bursaria show arhythmic mating reactivity after exposure to constant light (LL) for more than 2 wk. After this arhythmic population is exposed to darkness for 9 h, the mating reactivity rhythm of the cell population reappears. The phases of rhythms in individual cells are synchronized to each other. When the arhythmic population in constant light is exposed to dark pulses of various durations, the first peak of the recovered mating reactivity rhythm appears 6 h after the end of the dark pulse. Thus, in the case of dark pulses to cells in LL, the transition from dark to light sets the phase of the subsequent mating reactivity rhythm. When an arhythmic population in LL is transferred to constant darkness (DD), a rhythm of mating reactivity also appears and, in this case, the first peak of the rhythm occurs 18 h after the LL to DD transition. Therefore, arhythmic populations of cells in LL can be synchronized by either a dark pulse or by transition to continuous darkness. When the arhythmic populations in LL were transferred to various light/dark (LD) cycles, the mating reactivity rhythms entrained to LD cycles of 18 to 30 h in duration. Finally, mating rhythms can also be synchronized by treatment with puromycin (400 μg/ml for 6–18 h).     

稻草—凤尾菇—蚯蚓—肉鸡食物链的氮流与能流研究

稻草养菇、菇渣喂蚓、以蚂喂鸡是通过营养关系将三个生产过程有机地连接起来,形成农业生态系统特有的食物链。关于这三个环节各自的经济效益及栽培技术方面的研究工作已经做了很多,而作为一条食物链的整体状况,主要是能流和物流状况。尚未见到更深入具体的报道。作者试图通过实验定量分析和评价该食物链中每一链节上以及整体上的氮流和能流状况,进而对其生产应用价值做一初步探讨。     

Second virial coefficient of alpha-crystallin

Light scattering studies were performed on bovine alpha-crystallin measuring the scattering intensities as a function of scattering angle, concentration, and temperature. The data yielded the molecular weight, radius of gyration, and second virial coefficient of alpha-crystallin at different temperatures. The second virial coefficient increased with increasing temperature. Both the enthalpy and entropy of solution of alpha-crystallin are positive. The Flory theta temperature was found to be 271 K.     

Do light/dark cycles of medium frequency enhance phytoplankton productivity?

It has been suggested that turbulence with the resultant light/dark cycle and light gradient through which phytoplankton move, enhances their productivity. The stationary bottle incubation technique for estimating rates of primary productivity has mainly been criticized because of bottle effects, the elimination of natural turbulence and the presence of photo-inhibition. In a series of experiments where productivity was measured over static profiles and compared to the productivity in a mixed system, no definite conclusion could be reached regarding the effect of varying light/dark cycles of medium frequency (seconds to minutes). It appeared as though the ratio of the euphotic depth to mixing depth (Z _eu/Z _m) influenced productivity more than the duration of the light/dark cycle. The static bottle incubation method gave higher integral productivities than the mixed samples at low ratio's ofZ _eu/Z _m. It is suggested that mixing has two separate, but synergistic effects i.e. it not only moves the phytoplankton cells through a light/dark cycle, but also decreases the boundary layer, which increases the rate of exchange through the cell wall of nutrients and metabolites. In doing so more nutrients are available and light could be utilized more efficiently and therefore, productivity is increased.     

Reversion of the apical hook of pea in the dark and its promotion by a red light pulse.

At the developmental stage at which the apical hook passed the 3rd and 4th nodes, dark-grown seedlings of pea ( Pisum sativum L. cv. Progress No.9) opened the hook upright and then formed a new hook above the node nearly in the opposite direction to the previous one. In cv. Alaska, in contrast, many (about 84%) seedlings closed the hook in the original direction after they partially (up to about 110°) opened it at the 3rd node, thus doing a wagging movement, while a small percentage (about 16%) of the seedlings reversed the hook direction. Exposure to red light of cv. Alaska seedlings for 10 min increased the percentage of the hook reversion up to 71% or more. The hook reversion was never observed except when the hook part passed the nodes, suggesting the involvement of the nodes in the phenomenon.     

Inversion of gravitropism by symmetric blue light on the clinostat

Gravitropic stimulation of maize (Zea mays L.) seedlings resulted in a continuous curvature of the coleoptiles in a direction opposing the vector of gravity when the seedlings were rotated on a horizontal clinostat. The orientation of this response, however, was reversed when the gravitropic stimulation was preceeded by symmetric preirradiation with blue light (12.7 mol photons·m^–2). The fluence-response curve of this blue light exhibited a lower threshold at 0.5 mol·m^–2, and could be separated into two parts: fluences exceeding 5 mol·m^–2 reversed the direction of the gravitropic response, whereas for a range between the threshold and 4 mol·m^–2 a split population was obtained. In all cases a very strong curvature resulted either in the direction of gravity or in the opposite orientation. A minor fraction of seedlings, however, curved towards the caryopsis. Furthermore, the capacity of blue light to reverse the direction of the gravitropic response disappeared with the duration of gravitropic stimulation and it depended on the delay time between both stimulations. Thistonic blue-light influence appears to be transient, which is in contrast to the stability observed fortropistic blue-light effects.This work was supported by the Deutsche Forschungsgemeinschaft.     

Stomatal response to humidity in sugarcane and soybean: effect of vapour pressure difference on the kinetics of the blue light response

Abstract. The effect of atmospheric humidity on the kinetics of stomatal responses was quantified in gas exchange experiments using sugarcane ( Saccharum spp. hybrid) and soybean ( Glycine max ). Pulses of blue light were used to elicit pulses of stomatal conductance that were mediated by the specific blue light response of guard cells. Kinetic parameters of the conductance response were more closely related to leaf-air vapour pressure difference (VPD) than to relative humidity or transpiration. Increasing VPD significantly accelerated stomatal opening in both sugarcane and soybean, despite an approximately five-fold faster response in sugarcane. In contrast, the kinetics of stomatal recovery (closure) following the pulse were similar in the two species. Acceleration of opening by high VPD was observed even under conditions where soybean exhibited a feedforward response of decreasing transpiration (E) with increasing evaporative demand (VPD). This result suggests that epidermal, rather than bulk leaf, water status mediates the VPD effect on stomatal kinetics. The data are consistent with the hypothesis that increased cpidermal water loss at high VPD decreases the backpressure exerted by neighbouring cells on guard cells. allowing more rapid stomatal opening per unit of guard cell metabolic response to blue light.     

Sensitive detection of mycoplasmalike organisms in field-collected and in vitro propagated plants of Brassica, Hydrangea and Chrysanthemum by polymerase chain reaction

A polymerase chain reaction (PCR) protocol, previously designed for amplification of a DNA fragment from aster yellows mycoplasmalike organism (MLO), was employed to investigate the detection of MLO DNA in field-collected and in vitro micropropagated plants. PCR with template DNA extracted from symptomatic, naturally-infected samples of Brassica, Chrysanthemum and Hydrangea, each yielded a DNA band corresponding to 1.0 Kbp. However, no DNA product was observed when either infected Ranunculus (with phyllody disease) or Gladiolus with (symptoms of ‘germs fins’) was used as source of template nucleic acid for PCR; further experiments indicated absence of target DNA in the case of Ranunculus and the presence of substances in Gladiolus which inhibited the PCR. The MLO-specific DNA was detected by PCR using less than 95 pg of total nucleic acid (equivalent to total nucleic acid from 1.9, ug tissue) in the case of field-collected Hydrangea and less than 11.4 pg of nucleic acid (equivalent to total nucleic acid from 19 ng of tissue) in the case of field-collected Brassica. The findings illustrate highly sensitive detection of MLOs in both field-grown and in vitro micropropagated infected plants.     

Mitochondrial malate dehydrogenase from watermelon: sequence of cDNA clones and primary structure of the higher-plant precursor protein

The isolation and sequence of a cDNA clone encoding the complete mitochondrial malate dehydrogenase (mMDH) of watermelon cotyledons is presented. Taking advantage of the polymerase chain reaction technology partial cDNA clones from the central part, the 3 part and the 5 part of the mRNA were obtained with oligonucleotides based on directly determined amino acid sequences. Subsequently, two complete cDNA clones for mMDH were synthesized with a sense primer corresponding to the nucleotide sequence of the amino terminal end of pre-mMDH and two antisense primers corresponding to the major alternative adenylation sites found in the mRNA.The amino acid residues for substrate and cofactor binding identified by X-ray crystallography for pig heart cytoplasmic MDH are conserved in the 320 amino acid long mature higher-plant mMDH. A presequence of 27 amino acids is present at the amino terminal end of the precursor protein.