RECONSTRUCTIONS OF THE GRANA-FRETWORK SYSTEM OF A CHLOROPLAST

The grana-fretwork system was reconstructed from serial sections representing 0.5 μm slice, in profile view, from the midregion of a chloroplast of Nicotiana tabacum. Reconstructions show grana in multiple strata. The fretwork integrates the grana in all three dimensions. Large grana are visualized as complex structures consisting of two or more eccentrically stacked solids that vary in height and diameter. The close spacing and overlapping positions of grana in the plastid explain why phase microscopy cannot be used to demonstrate adequately the numerous strata of grana within a chloroplast. The grana are not far enough apart to allow for successful optical sectioning of a plastid in face view. In profile view no distinct grana can be resolved because the grana-fretwork system has the aspect of a “honeycomb.” Thus, observations with a light microscope are not adequate to determine the arrangement of grana in a chloroplast, and the recently-proposed model showing all grana of a plastid to be arranged in a single spiral ribbon must be rejected as incompatible with properties of real plastids.     

SUBSTRUCTURE OF CHLOROPLAST LAMELLAE

(1) Chloroplast lamellae, like many other membranes, are composed of 90-A subunits. (2) The way in which the 90-A units associate with one another determines the quantasome structures of the membrane. There appear to be four 90-A subunits per quantasome in the most highly organized arrays. In at least some cases, the way in which the subunits bind one to another is under environmental control. (3) Extraction experiments are consistent with a model in which the membrane lipid surrounds the protein framework of the membrane.     

CHLOROPLAST PIGMENTS OF CHLOROMONADOPHYCEAE

The chloroplast pigments of 2 species of Chloro-monadophyceae have been examined. Both Gonyo-stomum semen and Vacuolaria virescens possessed only one chlorophyll, chlorophyll a. Gonyostomum contained 4 carotenoids, but not fucoxanthin and peridinin. Vacuolaria also possessed 4 carotenoids which have been identified as β-carotene and the 3 xanthophylls commonly found in the Xanthophyceae (as represented by Tribonema aequale). These are antheraxanthin, lutein monoepoxide, and an hydroxy lutein monoepoxide-like xanthophyll. The taxonomic significance of these findings, the first for the Chloromonadophyceae, is discussed.     

DIFFERENTIATION OF THE CHLOROPLAST OF ANTHOCEROS

It has been demonstrated that the following changes accompany differentiation in the plastid of the liverwort Anthoceros eckloni. The inner membrane of the plastid folds to give rise to small vesicles which grow and may fuse to form thylakoids, i.e. flat bags. The thylakoids may "pair" to produce the doublets (thick membranes) of the grana. The doublets may be produced also by the invagination of a thylakoid. In both cases, the doublets are produced only where outside-to-outside contact of thylakoid membranes occurs, which supports the thesis that the thylakoid membranes are polarized. The thylakoids also fold outwards, anastomose, and may fuse. This results in a complicated membrane system, for which an interpretation becomes very difficult. The starch is produced in the matrix, and the pyrenoid bodies are interpreted as specialized regions of the matrix. Younger plastids have grana, but the mature plastid has so many doublets that distinct grana cannot be recognized. This interpretation of the changes which occur during the differentiation of the plastid differs radically from those of Menke (1961) and Manton (1962) who studied this same genus, but is compatible with findings in algae and angiosperms.     

A CYTOCHEMICAL DESCRIPTION OF THE MULTIPLICATION OF MENGOVIRUS IN L-929 CELLS

A correlation of cytochemical changes with virus production has been studied in L cells infected with Mengovirus. After a latent period of about 2 hours, virus was produced rapidly, reaching maximum titers of up to 12,000 particles per cell in 6 to 8 hours. The earliest cytological change was in the nucleus and consisted of a slight condensation of chromatin. There is no evidence, however, for the multiplication of either the viral RNA or protein in the nucleus. RNA, of high molecular weight, accumulated in the perinuclear area of the cytoplasm and was later found in inclusions. The perinuclear RNA was digestible with RNase and may be located in or on ribosomes. The inclusion RNA was resistant to RNase but could be removed by pepsin or potassium permanganate; it is probably in completed virus particles. Viral antigen was first observed in a perinuclear location and later in the above-mentioned inclusions. Although the viral protein contains appreciable amounts of arginine and lysine, it is not a basic protein of the histone type. Phase-contrast microscopy of living cells clearly demonstrated the role of the inclusions in release of virus from infected cells. A comparison is made between these cytological changes in Mengo-infected cells and those which have been found by other workers in polio-infected cells. There are many very similar changes.     

高温对小麦叶绿体核糖体和叶绿体蛋白质生物合成的影响

本实验用蔗糖密度梯度离心分离小麦叶片的核糖体,用 SDS-聚丙烯酰胺凝胶电泳分离叶绿体蛋白质。对在高温和常温条件下生长的小麦分析比较表明:在34℃高温下,小麦叶片能正常地形成细胞质的80S 核糖体,而影响了叶绿体的70S 核糖体的形成,从而使由叶绿体基因组控制的蛋白质的生物合成受阻。由 SDS-凝胶电泳分析表明:高温处理的小麦,其叶绿体蛋白质的电泳条带少于常温下生长的小麦。在这些消失的多肽中,主要是叶绿体基因组的翻译产物,如二磷酸核酮糖羧化酶大亚基。由于叶绿体内这些具有光合生理功能的蛋白质的合成受阻,从而导致小麦叶片光合强度的降低。     

THE CHLOROPLAST STRUCTURE OF IOJAP MAIZE

The ultrastructure of the plastids from the genetically caused but maternally transmitted mutant iojap of maize was studied at four stages of development. The plastids of green and potentially green tissue were normal at all stages studied. The plastids of the white tissue were aberrant at all stages studied and lacked the normal grana-fretwork system as well as a normal prolamellar body. DNA-like fibrils were present in aberrant plastids, but ribosomes were absent. This indicates that chloroplast ribosomes are important in chloroplast membrane formation. Aberrant plastids fail to develop normally and are not a degeneration of normal plastids. Aberrant and normal plastids occur in single cells in green tissue, but only aberrant plastids have been found in white tissue.     

A CYTOCHEMICAL STUDY OF CYTOPLASMIC BASIC PROTEINS IN THE ASCIDIAN OOCYTE

The cytoplasm of young oocytes of the ascidians contains high concentrations of proteins which are stainable with alkaline fast green at pH 8.1 and above. These proteins cannot be stained even with acid dyes at low pH unless RNA is removed. Deamination and formalin blockage of amino groups is incapable of destroying the net positive charge on these protein molecules in the presence of RNA, but these treatments destroy the charge if RNA is removed. It is therefore concluded that basic proteins and RNA exist as a nucleoprotein complex in the ribosomes of these young oocytes. The detectable RNA of the mature oocytes and unfertilized eggs shows no evidence of being associated with basic proteins.     

白菜细胞核雄性不育花药的细胞化学观察

对一种由一对隐性基因控制的白菜细胞核雄性不育和可育株的花药进行了细胞学和组织化学研究。种子播种后,有1/4植株为不育株,其余的为可育株。通过对不育株和可育株花药发育的细胞学观察,确认不育花粉的败育发生在小孢子发育时期。用组织化学的方法研究了可育株和不育株花药发育过程中的多糖和脂类的分布动态,发现在减数分裂前,可育花药和不育花药的药隔细胞中都储藏了大量的淀粉粒。二者的差异仅是不育花药的绒毡层细胞液泡化明显。在减数分裂后的小孢子发育时期,可育花药的绒毡层细胞具有将药隔细胞中的淀粉粒多糖吸收并转化成脂类的功能,小孢子及以后的二胞花粉中也积累了大量的脂类储藏物质在不育花药中,虽然减数分裂后药隔细胞中的淀粉粒也都消失,但绒毡层细胞中的脂类物质相比很少,同时绒毡层细胞显示了明显的多糖反应,表明不育花药的绒毡层细胞将糖类转化为脂类的功能受阻。在小孢子的表面有些脂类物质,但在细胞质中却没有脂类积累。这一结果暗示在该种白菜细胞核雄性不育株中,由于花药绒毡层细胞转换多糖为脂类的功能失常,导致了小孢子的败育。     

THE MOLECULAR ORGANIZATION OF CHLOROPLAST MEMBRANES

The presence of subunits in chloroplast membranes is suggested by polarization, fluorescence, and X-ray studies. Subunits (quantasomes) may be observed in the electron microscope on dried shadowed membranes and in replicas of membranes produced by the freeze-etching technique. Regular subunits are also observed with the electron microscope in thin sections of chloroplast membranes. Chemical considerations suggest that many membranes are composed of lipoprotein subunits. Thin sections reveal two types of chloroplast membranes, the fret membranes composed of one layer of subunits, and the partitions composed of two layers of subunits. Chloroplast membranes consist of about 45% protein and 55% lipid. Some 80% of the lipids are the highly surfactant glycolipids. In this paper the subunits are visualized as assymetric lipoproteins, probably having a protein core surrounded by components determined by the nature and environment of the membrane. Since the stroma, fret channels, and loculi contain aqueous materials, it is further postulated that the membranes bordering these spaces bind the highly surfactant glycolipids. The region between the two rows of subunits in the partition appears to be highly hydrophobic, rich in chlorophyll, and low in glycolipids. Some chlorophyll also may occur within the subunits both in the partitions and in the fret membranes. Since four subunits appear to comprise a quantasome, at least two types of forces, inter- and intra-quantasome forces, bind the subunits together in sheets. Chloroplast membranes thus differ from a “unit membrane” in two important respects: (1) they must be an aggregate of globular subunits, and (2) the lipoprotein subunits consist of a protein matrix which binds the chlorophylls and lipids by hydrophobic association with their hydrocarbon moieties.