CELL WALL FORMATION IN PEDIASTRUM BIRADIATUM AS REVEALED BY THE ELECTRON MICROSCOPE

Moner, J. G. (U. Massachusetts, Amherst), and G. B. Chapman. Cell wall formation in Pediastrum biradiatum as revealed by the electron microscope. Amer. Jour. Bot. 50(10): 992–998. Illus. 1963.-An electron microscopic study of cell wall development in P. birudiatum is described. Micrographs were taken of thin sections of cells from several stages involved in the transformation of the motile zoospore into the 4-pronged adult cell type during asexual reproduction. The cell wall begins as a thin membrane which does not change noticeably during the transformation of the zoospore to the adult cell type. In a subsequent period of not more than 6 hr, a definitive cell wall arises accompanied or followed shortly by the appearance of a globular network on the underside of the cell wall proper. During all of the developmental stages osmiophilic globuli are found in the cytoplasm, frequently at the cell surface. Similar, though smaller, globuli are found in the chloroplasts of Pediastrum and other plants, indicating that these bodies may have a plastid origin. It is suggested that whole osmiophilic globuli, or parts thereof, may be transferred to the cell wall proper, giving rise, ultimately, to the globular network.     

SOME ASPECTS OF THE STRUCTURAL ORGANIZATION OF THE MYOFIBRIL AS REVEALED BY ANTIBODY-STAINING METHODS

From observations of fluorescent antibody staining and antibody staining in electron microscopy, evidence is presented for the following: (a) Direct contact of the actin and myosin filaments occurs at all stages of contraction. This results in inhibition of antibody staining of the H-meromyosin portion of the myosin molecule in the region of overlap of the thin and thick filaments. (b) Small structural changes occur in the thick filaments during contraction. This leads to exposure of antigenic sites of the L-meromyosin portion of the myosin molecule. The accessibility of these antigenic sites is dependent upon the sarcomere length. (c) The M line is composed of a protein which is weakly bound to the center of the thick filament and is not actin, myosin, or tropomyosin. (d) Tropomyosin as well as actin is present in the I band. (e) If actin or tropomyosin is present in the Z line, it is masked and unavailable for staining with antibody.     

The nucleolonema of plant and animal cells: a comparison

Depending on the author and the animal or plant origin of the material under study, the term "nucleolonema" is used in different contexts and thus indicates nucleolar ultrastructures that are different. In this paper, we attempt to clarify this state of affairs and to propose a definition for the plant cell nucleolonema.     

CELL FORM AND SURFACE PATTERNS IN CHROOMONAS and CRYPTOMONAS CELLS (CRYPTOPHYTA) AS REVEALED BY SCANNING ELECTRON MICROSCOPY1

Fifteen freshwater cryptomonad species were freeze-dried and examined with the scanning electron microscope. Surveys of cell surfaces revealed four general cell types. Chroomonas type cells lack a furrow but possess a shallow vestibular depression where the flagella are inserted. The presence of a gullet could not be detected. Cryptomonas spp. displayed three morphological types, all lacking gullets. The first type of Cryptomonas has a simple, shallow furrow with ridges that apparently can close to form a raphe but an oval opening or stoma remains at the posterior end and an opening from the vestibulum is formed at the anterior end. The second Cryptomonas type consists of a complex furrow with furrow ridges and folds that extend almost two-thirds of the cell length. A sloma is present in the central region of the closed furrow. The folds apparently can separate thereby exposing the underlying furrow. The third type of Cryptomonas possesses a simple, non-closing furrow. At the anterior end there is a vestibular ligule which extends from the dorsalleft side of the cell and covers the region of the vestibulum where the contractile vacuole discharges.     

CELL SHAPE AND WALL PATTERN IN RELATION TO CYTOPLASMIC ORGANIZATION IN PEDIASTRUM SIMPLEX

P. simplex is a single-pronged, fenestrated species of Pediastrum. Comparison is made in regard to cell differentiation and structure with P. boryanum, a 2-pronged, unfenestrated species, with emphasis on the origin of cell wall pattern and the regulation of cell shape. The characteristic wall pattern is initiated with the deposition of plaques of wall material of the outer wall layer when zoospores have assembled in the colony. The pattern is postulated to be templated in the plasma membrane. The inner, thicker wall layer is fibrillar and deposited from vesicles derived from the golgi apparatus. In P. simplex 2–4 dictyosomes are present in contrast to the single dictyosome of P. boryanum. The dictyosomes lie at the concave inner face of the nucleus. Blebs of its ribosome-free outer membrane are contributed to the forming face of the golgi apparatus. Parallel microtubules underlie the plasma membrane in the aggregating zoospores and disappear after the initiation of wall formation. The possible role of microtubules and other organelles in the determination of cell shape in Pediastrum is discussed.     

用ERIC—PCR法研究番茄根际细菌群落结构变化

采用单一碳源回收菌群的方法和ERIC—PCR方法相结合,检测番茄(Lycopersicon escu-lentum Mill．)根际接种转基因微生物E4(Enterobacteria cloacae)后的根际微生物的群落结构和多样性的变化。结果表明：采用单一碳源回收菌群和ERIC—PCR相结合的方法,可以准确、直观和清楚地检测到E4释放到环境中后对根际微生物的群落结构和种群数量的影响。这种单一碳源培养法与ERIC—PCR相结合的方法,将有可能成为一种研究环境微生物群落结构变化的常用方法。     

用ERIC-PCR法研究番茄根际细菌群落结构变化*

采用单一碳源回收菌群的方法和ERIC PCR方法相结合 ,检测番茄 (Lycopersiconescu lentumMill )根际接种转基因微生物E4 (Enterobacteriacloacae)后的根际微生物的群落结构和多样性的变化。结果表明 :采用单一碳源回收菌群和ERIC PCR相结合的方法 ,可以准确、直观和清楚地检测到E4释放到环境中后对根际微生物的群落结构和种群数量的影响。这种单一碳源培养法与ERIC PCR相结合的方法 ,将有可能成为一种研究环境微生物群落结构     

THE MICROCRYSTALLINE STRUCTURE OF CELLULOSE IN CELL WALLS OF COTTON, RAMIE, AND JUTE FIBERS AS REVEALED BY NEGATIVE STAINING OF SECTIONS

With a new technique of negative staining of sections, it has been possible to observe directly, in ultrathin sections under the electron microscope, the original microcrystalline and microfibrillar structure of cellulose as it occurs in living cells. This method has advantages over the study of isolated fibers used so far by others, in that the original arrangement of microfibrils is better preserved, and their collapse into larger fibrillar units is prevented. With this method, the cell walls of ramie, jute, and cotton fibers have been studied. The size (diameter, 25 to 40 A) and the longitudinal periodicity observed in the single microfibrils and the orientation and spatial arrangement of the microcrystallite within the microfibrils are found to correspond with the latest models derived by others from data obtained by indirect methods such as X-ray diffraction. The microfibril size of about 35 A, found by measuring these structures in sections, agrees with the latest conclusions reached by others in recent work with isolated fibrils.     

NUCLEOLAR AND NUCLEAR RNA SYNTHESIS DURING THE CELL LIFE CYCLE IN MONKEY AND PIG KIDNEY CELLS IN VITRO

The incorporation of 5-³H-uridine and 5-³H-cytidine into nucleolar and nonnucleolar RNA in the nucleus of monkey and pig kidney cells was measured in vitro during the cell life cycle. Time-lapse cinematographic records were made of cells during asynchronous exponential proliferation, in order to identify the temporal position of individual cells in relation to the preceding mitosis. Immediately following cinematography, cells were labeled with uridine-³H and cytidine-³H for a short period, fixed, and analyzed by radioautography. Since the data permit correlation of the rate of RNA labeling with the position of a cell within the cycle, curves could be constructed describing the rate of RNA synthesis over the average cell cycle. RNA synthesis was absent in early telophase, and rose very abruptly in rate in late telophase and in very early G₁ in both the nucleus and the reconstituting nucleolus. Thereafter, through the G₁ and S periods the rate of nuclear RNA synthesis rose gradually. When we used a 10-min pulse, there was no detectable change in the rate for nucleolar RNA labeling in monkey kidney cells during G₁ or S. When we used a 30-min labeling time, the rate of nucleolar RNA labeling rose gradually in pig kidney cells. With increasing time after mitosis, the data became more variable, which may, in part, be related to the variation in generation times for individual cells.     

银鲴自然群体线粒体DNA的遗传分化

运用２１种限制性内切酶对银鲴自然群体进行了ｍｔＤＮＡ的限制性片断长度多态性（ＲＦＬＰ）分析。发现银鲴自然群体存在丰富的ｍｔＤＮＡ多态性,从４个群体３９个个体中,共检测到１２种单倍型,对这一现象的成成因进行了探讨。依据单倍型和群体的系统发育关系,结合地理分布的资料,对其现今分布区相互间的历史联系及其对银鲴起源和分化的影响进行了分析。     

百合生殖细胞分裂过程中微管分布的显微荧光观察

用抗微管蛋白抗体和荧光标记技术,观察了百合生殖细胞经有丝分裂形成精细胞过程中微管的变化。生殖细胞在分裂的前期,存在于核外围以及细胞两端胞质内的微管大都以微管束的形式沿细胞长轴方向平行排列。在靠近核的部位,有些微管有时会斜向排列。分裂进入中期后,染色体集中排列在赤道面。在染色体周围可以见到有多束与细胞长轴平行排列着的微管,但这些微管束是在分裂中期时新形成的或是在前期已存在,尚难以断定。这些微管束有一个特点,就是当它们延伸至赤道板部位时,在每一条微管束上都有一个无荧光的小圆区;这个小圆区可能代表着丝粒的位置。细胞分裂进入后期,姊妹染色单体分别向两极移动形成两组染色体。在它们之间近赤道板位置出现了一个具有强烈荧光的区域,显示在这一部位,微管相当浓密。从这一强烈荧光区向两极分别伸出多条微管束。因此,在这一强烈荧光区内可能有多个微管束重叠。到细胞分裂末期,在这一强烈的荧光区的中央出现了一条横向的无荧光区。这一区域有可能为胞质完成分裂后新形成的细胞板所在的部位。