SPORE ULTRASTRUCTURE OF THE MYXOMYCETE PHYSARUM POLYCEPHALUM

Spores of the true slime mold Physarum polycephalum were examined at several stages of their development by means of scanning and transmission electron microscopy. The spores were globose, spine-covered structures produced within a sporangium enclosed in a tough, noncellular peridium. Cytologically, the spore represented a typical eukaryotic cell, having discrete organelles similar to spores of other myxomycetes. The presence of dictyosomes, helical filaments, and microbodies in these cells, as well as the further elucidation of the cell wall and the “polysaccharide-containing” areas, represent new contributions to the ultrastructure of the myxomycete spore. Of special interest were observations of metaphase nuclei just prior to spore cleavage, interphase nuclei in young spores, and nuclei in mature spores containing synaptonemal complexes. These observations indicate that in Physarum polycephalum mitosis occurs just prior to spore cleavage, and meiosis takes place after spore cleavage.     

LIMITED DNA SYNTHESIS IN THE ABSENCE OF PROTEIN SYNTHESIS IN PHYSARUM POLYCEPHALUM

Actidione (cycloheximide), an antibiotic inhibitor of protein synthesis, blocked the incorporation of leucine and lysine during the S phase of Physarum polycephalum. Actidione added during the early prophase period in which mitosis is blocked totally inhibited the initiation of DNA synthesis. Actidione treatment in late prophase, which permitted mitosis in the absence of protein synthesis, permitted initiation of a round of DNA replication making up between 20 and 30% of the unreplicated nuclear DNA. Actidione treatment during the S phase permitted a round of replication similar to the effect at the beginning of S. The DNA synthesized in the presence of actidione was replicated semiconservatively and was stable through at least the mitosis following antibiotic removal. Experiments in which fluorodeoxyuridine inhibition was followed by thymidine reversal in the presence of actidione suggest that the early rounds of DNA replication must be completed before later rounds are initiated.     

多头绒泡菌细胞核周期的电镜研究

多头绒泡菌PhysarumpolycophalumSchw的营养生长阶段为没有细胞壁的原生质团（合胞体）,内部众多的细胞核进行着同步的核内有丝分裂,本文电镜下研究了细胞核在有丝分裂周期中的结构变化。有丝分裂前期,染色质经松散改组和集缩形成染色体,核仁由中央移向边缘,并在近核膜处解体;中期核膜不消失,在核内形成纺锤体,核仁解体后的物质是不规则状散在于核内;有丝分裂后核膜的破裂处重新愈合,染色体解集缩成染色质,分散的核仁物质逐渐合并形成新的核仁。     

THE EFFECT OF ACTIDIONE ON MITOSIS IN THE SLIME MOLD PHYSARUM POLYCEPHALUM

Actidione, reportedly a specific inhibitor of protein synthesis, was found to reduce the incorporation of labeled amino acids into proteins of the slime mold Physarum polycephalum without drastically inhibiting the incorporation of nucleic acid precursors into RNA. This inhibitor was found to completely block the ensuing mitosis if it was added at any time between telophase and late prophase. Plasmodia given Actidione in late prophase (about the time of nucleolar dissolution) went on through telophase to reconstruction even though nuclear amino acid incorporation was drastically reduced during that period.     

FIBRILLAR DIFFERENTIATION IN A MICROPLASMODIUM OF THE SLIME MOLD PHYSARUM POLYCEPHALUM

The motility of Physarum polycephalum microplasmodia depends upon the conditions under which they are cultured. To investigate the relation between protoplasmic streaming and filamentous structures observed in the cytoplasm, microplasmodia were collected from shaken cultures, agar plates and shaken cultures of the organism which had previously been plate-cultured.
No sign of streaming could be found in materials in shaken culture, even in those which were shaken after they had once been motile on an agar plate. The immotile microplasmodia in both cases failed to contain any filamentous structures.
Microplasmodia on agar plates were motile, showing vigorous peripheral movements (projection of pseudopods) and inner protoplasmic streaming. In the motile organisms two types of filamentous structures were observed: loose networks just inside the plasma membrane of rounded pseudopods with smooth surfaces; and compact, straight bundles beneath the pseudopods or in much deeper locations.     

多头绒泡菌中动蛋白的免疫化学鉴定

动蛋白(kinesin)是一种微管系统的运动蛋白(motor protein),它能通过水解ATP将化学能转化为机械能,推动微管产生运动.微管系统作为一种主要的细胞骨架存在于所有真核细胞中,它们对于维持细胞形态,细胞的分裂,染色体的运动及细胞内的物质运输起着重要作用.细胞质力蛋白(dynein)和动蛋白是公认的推动这类运动的运动蛋白.自从1985年Vole首次在鱿鱼大轴突(squidgiant axon)中发现动蛋白以来,人们先后在许多种动物细胞中发现有动蛋白存在,甚至在低等真核生物棘状变形虫,盘基网柄茵和高等植物烟草花粉管中发现有动蛋白的存在.研究结果表明,动蛋白参与了真核细胞中的许多重要生命活动,如细胞中的细胞器及囊泡的运动,染色体排裂和分离等运动.动蛋白很可能是普通存在于所有真核细胞中的一种运动蛋白.多头绒泡菌(Physarum poly-cephalum)属于粘菌纲(Myxomycetes)的一种低等真核生物,它表现出许多显著的细胞运动特征如原生质团迁移,细胞质的穿梭运动(shuttle streaming)等,是研究非肌细胞运动和收缩蛋白的经典材料.在多头绒泡菌胞质中也具有微管系统,它们构成其纺锤丝等,参与染色体的运动及其它胞质运动,但至今国内外尚无人证明其中有与微管作用的运动蛋白——动蛋白的存在,作者利用抗牛脑动蛋白的单克隆抗体,     

多头绒泡菌染色体构建过程的形态学研究

以同步核内有丝分裂的多头绒泡菌(Physarum polycephalum)原质团为材料,在有丝分裂周期中连续取材,按常规方法制备超薄切片,在电镜下研究了染色体形态构建的整个过程。有丝分裂前期,首先是G_2期凝集的染色质块逐渐解集缩成为松散状,染色质在松散的同时逐渐改组成直径为80～150nm的松散染色线结构。接着是在松散的染色线上形成一些电子密度高的集缩区,随着集缩区的增多和扩展,染色线缩短变粗,最后形成直径300～350nm的染色体。上述两个过程各需30min左右。与上述过程同时发生的是,核仁由中央位置逐渐移向边缘,前期50min左右时在近核膜处呈团块状解体。染色体形态构建的整个过程约需1h,可分为染色质的松散改组和集缩两个连续的步骤,25～30nm染色质纤维是这一过程中能分辨的最细的形态单位。     

LASER MICROSCOPE IRRADIATION OF PHYSARUM POLYCEPHALUM: DYNAMIC AND ULTRASTRUCTURAL EFFECTS

Streaming plasmodia of Physarum polycephalum were irradiated with a microscope-mounted ruby laser and the resulting changes were recorded by cinemicrography or streak photographs. Some lesions were processed for electron microscopy. By varying the incident energy, three levels of response were detected. Two transient responses, a gelation briefly blocking streams and a more severe gelation with contraction, changed movement patterns but not organelle ultrastructure. At higher energies, a permanently coagulated lesion was rapidly segregated from normal and transiently altered cytoplasm by formation of new membranes. Within the coagulum, pigment granules were destroyed, membranes were disrupted, and cytoplasm was flocculent. Nuclei and mitochondria were compact in the center and swollen in a peripheral space left by contraction of the coagulum. These changes are probably caused by heat produced by the interaction between the laser beam and the pigment granules of the plasmodium. Many of the changes seem to be secondary responses that follow the primary capture of energy during irradiation.     

THE CHANGING PATTERN OF BIREFRINGENCE IN PLASMODIA OF THE SLIME MOLD, PHYSARUM POLYCEPHALUM

Plasmodia of the acellular slime mold, Physarum polycephalum, reveal a complex and changing pattern of birefringence when examined with a sensitive polarizing microscope. Positively birefringent fibrils are found throughout the ectoplasmic region of the plasmodium. In the larger strands they may be oriented parallel to the strand axis, or arranged circularly or spirally along the periphery of endoplasmic channels. Some fibrils exist for only a few minutes, others for a longer period. Some, particularly the circular fibrils, undergo changes in birefringence as they undergo cyclic deformations. In the ramifying strand region and the advancing margin there is a tendency for fibrils of various sizes to become organized into mutually orthogonal arrays. In some plasmodia the channel wall material immediately adjacent to the endoplasm has been found to be birefringent. The sign of endoplasmic birefringence is negative, and its magnitude is apparently constant over the streaming cycle. The pattern of plasmodial birefringence and its changes during the shuttle streaming cycle of Physarum are considered in the light of several models designed to explain either cytoplasmic streaming alone or the entire gamut of plasmodial motions. The results of this and other recent physical studies suggest that both streaming and the various other motions of the plasmodium may very likely be explained in terms of coordinated contractions taking place in the fibrils which are rendered visible in polarized light.     

多头绒泡菌有丝分裂后细胞核重建过程的形态学研究

以进行自然同步核内有丝分裂的多头绒泡菌(Physarum polycephalum)原生质团为材料,应用常规制片和整体银染后制片的电镜技术研究了有丝分裂后细胞核的形态构建过程。形成新核仁的前体物质在有丝分裂中期时散在染色体区域的周围,末期时与染色体组一起到达两极。子细胞核刚形成时核仁物质与染色质混合,以后核仁物质相互汇合并同染色质逐渐分开,最后形成一个大核仁。染色质在有丝分裂后期开始解集缩,到两极后在新形成的子核中进一步松解。染色质在充分松解后又开始集缩活动,形成一些集缩比较紧密的染色质小块。随着细胞核的进一步发育在核膜和核仁之间形成许多大小不等,形状不规则的染色质团块。     

肌动蛋白是多头绒泡菌细胞核骨架和染色体骨架的组成成分

自多头绒泡菌(Physarum polycephalum Schw.)的原质团中分离细胞核和染色体,分别经DNaseⅠ消化和2 mol/L NaCl抽提后制备成细胞核骨架和染色体骨架。以抗肌动蛋白的抗体作一抗、FITC标记的羊抗兔IgG抗体作二抗进行的间接免疫荧光实验结果显示,细胞核骨架和染色体骨架都分别与抗体呈阳性反应。间接免疫斑点印迹实验结果进一步证实,细胞核骨架和染色体骨架的蛋白质成分中存在与肌动蛋白抗体呈阳性显色反应的抗原。以抗肌动蛋白的抗体作一抗、金颗粒标记的蛋白A作二抗的间接免疫电镜实验结果表明,在实验组间期细胞核的核仁、集缩染色质和核基质以及中期染色体上都有很多金颗粒分布。上述结果证明,肌动蛋白是多头绒泡菌细胞核和染色体及其骨架的组成成分。