Changes in the Activities of Aldolase and of D-Glyceraldehyde-3-Phosphate Dehydrogenase during the Mitotic Cycle in Microspores of Lilium longiflorum

Microspores of Lilium longiflorum were isolated at various stages of development surrounding the mitotic interval and were analyzed for changes in the activities of D-glyceraldehyde-3-phosphate dehydrogenase and aldolase. Fructose 1,6 diphosphate was used as substrate. Activities were measured by the increase in optical density due to the reduction of diphosphopyridine nucleotide. It was found that mitosis occurs during the minimal activity of both aldolase and D-glyceraldehyde-3-phosphate, thus indicating that heightened glycolytic capacity is not necessarily related to mitosis. It was also found that soluble-SH levels were highest when the enzymes were least active. It appeared, therefore, that the "—SH enzymes" are not necessarily activated intracellularly by high concentrations of soluble thiol. These results are discussed in connection with the theory that soluble-SH compounds stimulate glycolysis and in this way initiate mitosis.     

Two classes of pollen-specific, heat-stable proteins in Lilium longiflorum

Several floral organ-specific proteins in lily anthers do not accumulate to detectable levels until just before anthesis. Antisera were raised against three of these proteins. designated LLA, in pollen of Lilium longiflorum Thunb. cv. Snow Queen. Monospecific antibodies were further prepared from antisera to investigate the specificity and distribution of these proteins during development. In an effort to study the function of these gene products, pollen protein was heat-treated at 90°C for 10 min. Monospecific anti-LLA-32 and -23 antibodies recognized two of these heat-stable proteins with molecular masses of 32 and 23 kDa. Accumulation of the two proteins in anther development was correlated with desiccation that occurred naturally in the pollen. Immunob-lot analyses of total protein from floral and vegetative organs confirmed that both LLA-32 and -23 proteins were pollen-specific. The proteins showed consistent patterns of expression during development and their levels decreased when pollen germinated. The properties of the two proteins differed in responsiveness to both polyethylene glycol 8000 and abscisic acid, and in solubility characteristics. Analysis of amino acid composition indicates that both LLA-32 and -23 proteins are rich in glutamic acid/glutamine and glycine, a characteristic of heat-stable proteins. However, LLA-23 has more polar amino acid residues with a polarity of 57%, two-fold higher than that of the LLA-32. Immunoblot analyses showed that LLA-32 and -23 proteins were immunologically unrelated to the dehydrin-like protein in lily seeds. It concluded that the two classes of pollen-specific proteins have some features in common with each other and with dehydrins. but that each is distinct.     

Dynamics of Cell Redifferentiation in Dictyostelium mucoroides

During migration of a D. mucoroides slug, prespore cells at the immediate edge of the prespore-prestalk junction advance into the prestalk region in approximately 1.5 min. Redifferentiation of the prespore into prestalk cells occurs during this period. Evidence that the cells redifferentiated required autoradiographic, electron microscopic, and staining techniques. These methods determined that glycoprotein synthesis declined; prespore vesicles, the organelles found specifically in prespore cells, were degraded; and staining was reduced during this developmental transition into prestalk cells.     

Dissociating Two Stages of Preparation in the Stop Signal Task Using fMRI

Often we must balance being prepared to act quickly with being prepared to suddenly stop. The stop signal task (SST) is widely used to study inhibitory control, and provides a measure of the speed of the stop process that is robust to changes in subjects’ response strategy. Previous studies have shown that preparation affects inhibition. We used fMRI to separate activity that occurs after a brief (500 ms) warning stimulus (warning-phase) from activity that occurs during responses that follow (response-phase). Both of these phases could contribute to the preparedness to stop because they both precede stop signals. Warning stimuli activated posterior networks that signal the need for top-down control, whereas response phases engaged prefrontal and subcortical networks that implement top-down control. Regression analyses revealed that both of these phases affect inhibitory control in different ways. Warning-phase activity in the cerebellum and posterior cingulate predicted stop latency and accuracy, respectively. By contrast, response-phase activity in fronto-temporal areas and left striatum predicted go speed and stop accuracy, in pre-supplementary motor area affected stop accuracy, and in right striatum predicted stop latency and accuracy. The ability to separate hidden contributions to inhibitory control during warning-phases from those during response-phases can aid in the study of models of preparation and inhibitory control, and of disorders marked by poor top-down control.     

HPLC测定中药百合中2个甾体皂苷的含量

首次建立百合中2个甾体皂苷的高效液相色谱含量测定方法.采用Shim-pack VP-ODS (4.6 mm×250mm,5μm)色谱柱,甲醇-水梯度洗脱,流速1.0 mL/min,检测波长205 nm.化合物1和2的线性范围及相关系数分别为:1.03 ～10.30ug(r=0.9998)和1.26～12.56 μg(r=0.9999);平均回收率分别为100.59％和99.97％.该方法操作简便,结果准确,重现性好,可用于百合中2个甾体皂苷的含量测定,为建立和完善中药百合药材的质量控制方法提供依据.     

Stabilizing Effect of Cannibalism in a Two Stages Population Model

In this paper we build a prey–predator model with discrete weight structure for the predator. This model will conserve the number of individuals and the biomass and both growth and reproduction of the predator will depend on the food ingested. Moreover the model allows cannibalism which means that the predator can eat the prey but also other predators. We will focus on a simple version with two weight classes or stage (larvae and adults) and present some general mathematical results. In the last part, we will assume that the dynamics of the prey is fast compared to the predator’s one to go further in the results and eventually conclude that under some conditions, cannibalism can stabilize the system: more precisely, an unstable equilibrium without cannibalism will become almost globally stable with some cannibalism. Some numerical simulations are done to illustrate this result.     

Single-Stage Carbon Replicas of Microspores

Single-stage surface replicas of treated or fresh pollen grains can be made ready for the electron microscope in 1.5 hr. The microspores are discharged into a drop of 50% acetone on a 1 cm square of cleaved mica and air dried. Carbon is evaporated to a film thickness of 35 mμ during rotation of the mica support. The carbon film and microspores are parted from the mica with water and heated in 2-aminoethanol at 145-155 C for 10 min to 3 hr. The replicas are then washed 5 min or longer on water at 90 C and picked up on electron microscope grids. The resulting self-shadowed surface replica can be immediately observed by electron microscopy.     

Movement of Amyloplasts in the Root Cap Cells of Geotropically Sensitive Roots

The root cap of Lepidium sativum under our culture conditions was found to contain 7 (or occasionally 8) storeys of starch-containing cells. In the youngest one (or two) of these storeys the amyloplasts are small and the cells appear embryonic. In the 6 non-embryonic storeys the amyloplasts are large. Upon inversion of the root, the amyloplasts in the 3 youngest of the 6 non-emhryonic storeys start falling toward the opposite end of the cell at about 72 μ per h (at 21 C), hut they maintain this speed for only 6 to 12 min, after which they virtually come to a stop. As a result, it takes 10 to 12 min before any of the amyloplasts get approximately as close to the ceiling as they were to the floor before the inversion; and this is true only of the 2 youngest of the non-embryonic storeys. When the root is placed horizontal, whether coming from the normal or the inverted position, the amyloplasts reach the lower, longitudinal wall in 15 min or less. The positions of the amyloplasts in the cells of the 3 oldest starch-containing storeys are erratic and show little, if any, dependency on the preceding time of inversion.     

Redifferentiation of dedifferentiated human chondrocytes in high-density cultures

The ommatidia in the ventral two-thirds of the compound eye of male Pieris rapae crucivora are not uniform. Each ommatidium contains nine photoreceptor cells. Four cells (R1-4) form the distal two-thirds of the rhabdom, four cells (R5-8) approximately occupy the proximal one-third of the rhabdom, and the ninth cell (R9) takes up a minor basal part of the rhabdom. The R5-8 photoreceptor cells contain clusters of reddish pigment adjacent to the rhabdom. From the position of the pigment clusters, three types of ommatidia can be identified: the trapezoidal (type I), square (type II), and rectangular type (type III). Microspectrophotometry with an epi-illumination microscope has revealed that the reflectance spectra of type I and type III ommatidia peak at 635 nm and those of type II ommatidia peak at 675 nm. The bandwith of the reflectance spectra is 40-50 nm. Type II ommatidia strongly fluoresce under ultra-violet and violet epi-illumination. The three types of ommatidia are randomly distributed. The ommatidial heterogeneity is presumably crucial for color discrimination.     

水稻游离小孢子培养最新研究进展

水稻小孢子培养技术不但可用来生产单倍体植株和加倍单倍体植株,而且可望成为转基因的理想受体系统。目前转基因技术、分子杂交技术与小孢子培育技术的有机结合已成为加快水稻育种速度的有效途径。本文从水稻小孢子分离纯化、影响愈伤组织或胚状体发生的因素以及植株再生三个方面综述了水稻游离小孢子培养的最新研究进展。最后就水稻小孢子培育技术急需解决的问题进行了讨论,并对小孢子培育技术发展前景进行了展望。     

Amyloplasts as possible statoliths in gravitropic protonemata of the moss Ceratodon purpureus

The kinetics of gravitropism and of amyloplast sedimentation were studied in dark-grown protonemata of the moss Ceratodon purpureus (Hedw.) Brid. The protonemata grew straight up at a rate of 20–25 m·h^– in nutrient-supplemented agar. After they were oriented to the horizontal, upward curvature was first detected after 1–1.5 h and reached 84° by 24 h. The tip cells exhibited an amyloplast zonation, with a tip cluster of nonsedimenting amyloplasts, an amyloplast-free zone, and a zone with pronounced amyloplast sedimentation. This latter zone appears specialized more for lateral than for axial sedimentation since amyloplasts sediment to the lower wall in horizontal protonemata but do not fall to the basal wall in vertical protonemata. Amyloplast sedimentation started within 15 min of gravistimulation; this is within the 12–17-min presentation time. The data support the hypothesis that some amyloplasts function as statoliths in these cells.This work was supported by the National Aeronautics and Space Administration grant NAGW-780. We thank Professor E. Hartmann and J. Schwuchow for providing Ceratodon cultures, Dr. John Z. Kiss and Jeff Young for valuable discussions, and Professor Rainer Hertel (University of Freiburg, FRG) for bringing this material to our attention.     

The Mechanism of Phagocytosis: Two Stages of Engulfment

Despite being of vital importance to the immune system, the mechanism by which cells engulf relatively large solid particles during phagocytosis is still poorly understood. From movies of neutrophil phagocytosis of polystyrene beads, we measure the fractional engulfment as a function of time and demonstrate that phagocytosis occurs in two distinct stages. During the first stage, engulfment is relatively slow and progressively slows down as phagocytosis proceeds. However, at approximately half-engulfment, the rate of engulfment increases dramatically, with complete engulfment attained soon afterwards. By studying simple mathematical models of phagocytosis, we suggest that the first stage is due to a passive mechanism, determined by receptor diffusion and capture, whereas the second stage is more actively controlled, perhaps with receptors being driven toward the site of engulfment. We then consider a more advanced model that includes signaling and captures both stages of engulfment. This model predicts that there is an optimum ligand density for quick engulfment. Further, we show how this model explains why nonspherical particles engulf quickest when presented tip-first. Our findings suggest that active regulation may be a later evolutionary innovation, allowing fast and robust engulfment even for large particles.     

The Mechanism of Phagocytosis: Two Stages of Engulfment

Despite being of vital importance to the immune system, the mechanism by which cells engulf relatively large solid particles during phagocytosis is still poorly understood. From movies of neutrophil phagocytosis of polystyrene beads, we measure the fractional engulfment as a function of time and demonstrate that phagocytosis occurs in two distinct stages. During the first stage, engulfment is relatively slow and progressively slows down as phagocytosis proceeds. However, at approximately half-engulfment, the rate of engulfment increases dramatically, with complete engulfment attained soon afterwards. By studying simple mathematical models of phagocytosis, we suggest that the first stage is due to a passive mechanism, determined by receptor diffusion and capture, whereas the second stage is more actively controlled, perhaps with receptors being driven toward the site of engulfment. We then consider a more advanced model that includes signaling and captures both stages of engulfment. This model predicts that there is an optimum ligand density for quick engulfment. Further, we show how this model explains why nonspherical particles engulf quickest when presented tip-first. Our findings suggest that active regulation may be a later evolutionary innovation, allowing fast and robust engulfment even for large particles.     

Amyloplasts and Starch Characterization in High Lysine Barley Mutant

Starch granules of Notch-2 high lysine barley mutant are small, irregular in shape and show a virtual loss of birefringence and a higher gelatinization temperature, compared to parent NP-113. Starch polymer of Notch-2 is qualitatively different from parent, as evidenced by X-ray diffractograms. There is a higher incidence of V-pattern at early development as also at maturity in mutant as compared to parent. Intensities corresponding to B-pattern are present at early development in both parent and mutant. B-pattern persists at maturity in mutant, while it is replaced by A-pattern in parent. Amyloplasts of mutant are modified in contrast to normal, oblong amyloplasts of parent. Modified amyloplasts show loss of grana, increased granulation and lipid droplets. Extensive lipid complexing with starch polymers in mutant is indicated and possible commercial and nutritional potentials speculated.     

小麦的小孢子培养

小孢子培养是在花药培养的基础上发展起来的一种高效再生体系,其在植物育种中的作用一直受到关注.但是,由于培养技术的限制,小麦(Triticum aestivum)小孢子培养还未能推广应用.近年来小麦小孢子培养发展很快,展现出广阔的应用前景.     

Two Stages in Neurite Formation Distinguished by Differences in Tubulin Metabolism

Abstract: Changes in tubulin solubility during neurite formation were studied biochemically using rat dorsal root ganglion neurons in culture. When fractionated with Ca²⁺-containing buffer at low temperature, a considerable proportion of total cellular tubulin was recovered in the insoluble fraction. We designated this cold/Ca²⁺-insoluble tubulin (InsT) and distinguished it from cold/Ca²⁺-soluble tubulin (SoIT). From the relative amount of InsT, neurite formation was found to proceed through two distinct stages. The first 6 days after plating (stage 1) in which the proportion of InsT increased dramatically (from 5 to 60%) coincided with neurite outgrowth. In the following period (stage 2), a constant level of InsT was maintained, whereas neurite maturation took place. Pulse-labeling experiments further revealed that the two stages differed significantly in terms of tubulin metabolism. High rates of synthesis as well as conversion from SoIT to InsT were observed in stage 1, whereas stage 2 was characterized by a decrease in both of these rates and an increase in the rate of degradation. The results show for the first time the coordinated changes in tubulin metabolism that underlie the process of neurite formation.     

Movement of Amyloplasts in the Statocytes of Geotropically Stimulated Roots. The Pre-Inversion Effect

Previously inverted Lepidium roots were placed in a horizontal position and the amyloplasts in the statocytes of the root cap allowed to fall through their entire range of movement across the cell. Under these conditions the amyloplasts first follow a mainly downward course for 6 to 8 min at a speed between 0.5 and 0.8 μm per min. For the next 10 min they move slightly more slowly in a direction away from the apical end of the cell, still sinking somewhat, but without reaching the plasmalemma along the lower wall. Previous experiments have shown that conditions assumed to allow the amyloplasts to slide parallel to the longitudinal cell walls are those that give rise to the largest geotropic curvatures. Such conditions are for instance (1) stimulation at 135° (root tips pointing obliquely upward) and (2) inversion of roots for 16 min followed by stimulation at 45°. Treatments assumed not to permit extensive sliding of the amyloplasts produce smaller geotropic curvatures, namely (3) stimulation at 45° without pre-inversion and (4) inversion followed by stimulation at 135°. The location of the amyloplasts after these four kinds of treatment has now been determined on photomicrographs and the assumptions concerning the paths and extent of sliding of the amyloplasts confirmed. Observations on electron micrographs showed that under all conditions the amyloplasts are separated from the plasmalemma by other organelles, such as ER, nucleus or vacuoles. In roots rotated for 15 min parallel to the horizontal axis of the klinostat at 2 rpm, the amyloplasts are not clumped together as densely as in normal, inverted or stimulated roots, but they are not scattered over the entire cell volume. The statolith function of the amyloplasts is discussed in view of these and other observations.