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The structural organization of transcriptionally active DNA that contains cistrons for precursor molecules of ribosomal RNA is described in positively stained spread preparations from nuclei and nucleoli isolated from the green alga, Acetabularia mediterranea Lmx. These nuclei contain large aggregates of nucleolar subunits in which fibril-covered regions, the putative active cistrons for precursors of ribosomal RNA, alternate with fibril-free intercepts, the "spacers." The length distribution of the different intercepts of this DNA is given, and the pattern is compared with those shown in animal cell systems. The data are discussed in relation to problems of transcription and of amplification of ribosomal RNA genes.

Structures with a lampbruch-chromosome-like morphology are described in the nucleoplasm of primary nuclei of the green alga, Acetabularia mediterranea, by light and electron microscopy in sections of cells fixed in situ and in spread preparations of isolated nuclear components. These chromosomes reveal typical loops (up to 20 micronm long), chromomere-like nodules (1-2 micronm in diameter), and 2-4 micronm large axial globules. Associations of some of these chromosomes with nucleolar structures and with the nuclear envelope are also recognized. The light microscopically identified loops are correlated with distinct fibrillogranular structures observed in the thin sections and with the very long matrix units seen in the spread preparations. The similarity of these structures to the lampbrush chromosomes of various animal cell types, all exclusively stages of meiotic prophase, is discussed as well as the possible relation of the appearance of lampbrush chromosomes to a defined phase of the vegatative growth of this alga.

Cell division in vegetative filaments of the green alga Oedogonium cardiacum is presented as an experimental system. We report on how we have used this system to study the effects of isopropyl N-phenylcarbamate (IPC) on the mitotic apparatus and on the phycoplast, a planar array of cytokinetic microtubules. Polymerization of microtubules was prevented when filaments, synchronized by a light/dark regime and chilled (2 degrees C) while in metaphase or just before phycoplast formation, were exposed to 5.5 x 10(-4) M IPC and then returned to room temperature. Spindles reformed or phycoplasts formed when these filaments were transferred to growth medium free of IPC. However, the orientation of both microtubular systems was disturbed: the mitotic apparatus often contained three poles, frequently forming three daughter nuclei upon karyokinesis; the phycoplast was often stellate rather than planar, and it sometimes was displaced to the side of both daughter nuclei, resulting in a binucleate and an anucleate cell upon cytokinesis. Our results suggest that IPC (a) prevents the assembly of microtubules, (b) increases the number of functional polar bodies, and (c) affects the orientation of microtubules in O. cardiacum. High voltage (1,000 kV) electron microscopy of 0.5-microm thick sections allowed us to visualize the polar structures, which were not discernible in thin sections.

Using a glycerination procedure designed to avoid excessive plasmolysis or disruption of the ectoplasm, microfilaments in bundles at the ectoplasm-endoplasm interface of Nitella internode cell segments were found to bind rabbit heavy meromyosin (HMM) in situ. All HMM arrowheads in a bundle seem to have the same polarity and many lie in register as judged from the electron micrographs; the arrowhead periodicity is approximately 380 . The decorated microfilaments are thus similar to those seen in negatively stained cytoplasmic suspensions of internode cells. In glycerinated material, as well as in suspensions, the microfilaments are closely associated with chloroplasts. The microfilaments lie adjacent to or are attached to the chloroplast envelope. The results provide further evidence that the microfilaments thought to play a role in cytoplasmic streaming in vivo in Nitella consist of actin and suggest that they may be anchored to the chloroplasts.

Effects of diazepam (Valium) on photosynthesis, chlorophyll/photosynthesis ratios, respiration, uptake of rubidium ions, and ultrastructure of Scenedesmus obliquus synchronized by a light-dark regimen of 14:10 hrs were determined. 80 and 160 muM diazepam, added to the nutrient medium at the start of the light-dark change (i.e., start of the cell cycle) gradually reduced rates of photosynthesis, below the initial rates from the beginning of the experiment. Contents of chlorophyll, however, remained nearly unaffected. Consequently, the diazepam-treated cells had a higher chlorophyll/photosynthesis ratio--also with regard to respiration in order to calculate the gross photosynthesis. The occurrence of photorespiration cannot be assumed. The net influx of rubidium was slightly reduced by 100 muM diazepam 0.5 and 2.0 hrs after the start of the cell cycle and was strongly inhibited after 5 to 14 hrs. 80 and 160 muM diazepam caused separation of thylakoids, formation of giant mitochondria and enlargement of vacuoles.

p-Hydroxycinnamic acid was found to be located within the plastids of the green alga Dunaliella marina. Thylakoid fractions desintegrated by ultrasonic treatment were capable of converting L-phenylalanine into o- and p-hydroxycinnamic acids; the hydroxylation reaction was increased by addition of NADPH. Hydroxycinnamic acids produced when [3-14C]cinnamate was incubated with varying amounts of [4'-3H]L-phenylalanine exhibited a 3H/14C ratio 10-150 times higher than that of the cinnamic acid reisolated from the incubation mixture. The lack of equilibration between cinnamate formed from L-phenylalanine and cinnamate added to the solution supports the hypothesis that cinnamate as an intermediate in hydroxycinnamate formation remains bound to the membrane enzyme complex. A model of membrane-bound multienzyme complexes is proposed for the conversion of aromatic amino acids into phenols.

The streaming endoplasm of characean cells has been shown to contain previously unreported endoplasmic filaments along which bending waves are observed under the light microscope using special techniques. The bending waves are similar to those propagated along sperm tails causing propulsion of sperm. In Nitella there is reason to believe that nearly all of the filaments are anchored in the cortex and that their beating propels the endoplasm in which they are suspended. This hypothesis is supported by calculations in which typical and average wave parameters have been inserted into the classical hydrodynamic equations derived for sperm tail bending waves. These calculations come within an order of magnitude of predicting the velocity of streaming and they show that waves of the character described, propagated along an estimated 52 m of endoplasmic filaments per cell, must generate a total motive force per cell within less than an order of magnitude of the forces measured experimentally by others. If we assume that undulating filaments produce the force driving the endoplasm, then the method described for measuring the motive force could lead to a lower than actual value for the motive force, since both centrifugation and vacuolar perfusion would reverse the orientation of some filaments. Observations of the initiation of particle translation in association with the filaments suggest that particle transport and wave propagation, which occur at the same velocity, may both be dependent on the same process. The possibility that some form of contractility provides the motive force for filament flection and particle transport is discussed.

The buoyant density in CsCl of ribosomes from chloroplasts of the green alga Chlorella pyrenoidosa and two species of higher plants, Pisum sativum and Chenopodium album, has been studied. From the relative protein content it was calculated that 70S ribosomes from chloroplasts are much smaller than 80S cytoplasmic ribosomes (3.0-3.1 X 10(6) and 4.0 X 10(6) daltons) and slightly larger than 70S ribosomes from bacteria (E. coli 2.5 X 10(6) daltons). Chloroplast ribosomes from pea seedlings were analyzed by two-dimensional polyacrylamide gel electrophoresis. They appear to contain 71 proteins. This indicates that chloroplast ribosomes contain a larger number of proteins than do the ribosomes from E. coli and other species of Enterobacteriaceae. Further study will permit a probable evaluation of the validity of Mereschkowsky's hypothesis that the photosynthetic plastids of eukaryotic plant cells are the evolutionary descendants of endosymbiotic blue-green algae.

The development of the rhizoid cells of the green alga Ulva mutabilis was investigated at the ultrastructural level paying special attention to the mechanism of attachment of the plant. Cytochemical data concerning the initial settling of the early zygote are also given. On the basis of histochemical staining and enzyme treatment it is concluded that the adhesive material secreted by the rhizoid cells is chemically different from that secreted by the zygote during the initial settling of the alga.

The processes of mitosis and cytokinesis in the multinucleate green alga Acrosiphonia have been examined in the light and electron microscopes. The course of events in division includes thickening of the chloroplast and migration of numerous nuclei and other cytoplasmic incusions to form a band in which mitosis occurs, while other nuclei in the same cell but not in the band do not divide. Centrioles and microtubules are associated with migrated and dividing nuclei but not with nonmigrated, nondividing nuclei. Cytokinesis is accomplished in the region of the band, by means of an annular furrow which is preceded by a hoop of microtubules. No other microtubules are associated with the furrow. Characteristics of nuclear and cell division in Acrosiphonia are compared with those of other multinucleate cells and with those of other green algae.

The cell wall of Coelastrum is usually composed of three layers. The outermost layer was studied most extensively. It consists of erect tubules which often bear long bristles whose function may be to stabilize the algae in its enviroment. The cell wall can modify its morphology according to the enviroment.

Partially purified cellulase and a cellulase-containing polygalacturonase but notlysozyme extensively degraded the walls of Chlamydomonas reinhardtii and Ulothrix fimbrata and converted intact cells of the algae to spheroplasts. A streptomycete cellulase cochromatographed with the enzyme system releasing glucose from walls of these organisms, and this preparation also converted the algal cells to spheroplasts. The dominant constituent in the walls was carbohydrate, and glucose and small quantities of galacturonic acid but no amino sugars were present in acid hydrolysates of the walls. Glucose accounted for essentially all of the material solobilized by the cellulase preparation. Lysozyme acted on Cylindrospermum sp. walls, and it, but not the otherenzymes, converted some of the Cylindrospermum sp. cells to spheroplasts. Streptomycete enzymes lysing Micrococcus lysodeikticus cochromatographed with the proteins releasing reducing sugars from Cylindrospermum sp. walls, and components in the active fraction converted cells of this alga into spheroplasts. X-ray diffraction revealed that the walls of C. reinhardtii and U. fimbrata but not those of Cylindrospermum sp. contained cellulose. The data suggest that the susceptibility of the first twospecies to microbial degradation in natural ecosystems results from an attack on the cellulose in their walls, and the susceptibility of the third is linked with the microbial production of a lysozyme.

In 1973 one of the present authors described a new method of cytological observation based upon flattening of living cells. This method was tested with several microorganisms as bacteria, fungi and algae. The application of the method allows the clear resolution of cytological structures that are otherwise obscured or can hardly be recognized. In addition cellular motion and development can be followed much better than by usual methods of cell culture. In certain objects (yeasts and fungal hyphae tips) all cellular organelles are forced into one plane of focus and are thus resolved simultaneously even at highest magnification. Different species especially among the yeasts exhibited quite varying intracellular contrast of mitochondria.

The ultrasturcture of the cell nucleus and perinuclear cytoplasm in Acetabularia is quite different in young and old cells. When a nucleus of an old cell was implanted into the cytoplasm of a young cell the nucleus assumed the morphology typical of a young cell within less than 10 days. The cytoplasm of an old cell was able to induce the reverse change in an implanted nucleus from a young cell. This cytoplasmic induction of nuclear ageing appeared to proceed more rapidly than rejuvenation.

A brief description of the effects of gravity on plants, particularly their orientation with reference to its direction, is followed by a presentation of evidence for the operation of specific "gravity sensors", statoliths, subcellular bodies which move or reorient themselves upon reorientation of a plant organ with respect to the direction of the force of gravity. In the singly reacting apical cells of rhizoids of Chara, the statoliths locally regulate the growth of the cell wall simply by blocking or permitting the access of carriers of cell wall material. In multicellular structures (root and stem tips etc.) the statoliths, most likely amyloplasts (starch-containing plastids), must act by creating in the organ a transversal polarity which can be transmitted to the growing region, often several millimetres away. In addition, gravity produces what may be called tonic effects, which quantitatively modify the reaction of the organ to the gravitational stimulation.