NON-IDENTICAL MECHANISMS OF MITOTIC ARREST BY RESPIRATORY INHIBITORS IN PEA ROOT TIPS AND SEA URCHIN EGGS

The adenosine triphosphate (ATP) content of pea root tips is about 0.40 mmole/kg fresh weight. The effects of partial and complete anaerobiosis, and of carbon monoxide and hydrogen cyanide, on the ATP level are described. The ATP content was shown to correspond closely to the oxygen uptake under these conditions. However, there was no relation between the ATP level and the rate of mitosis, a situation which is in contrast with that in sea urchin eggs. In anaerobic conditions, mitoses in pea root tips could continue at a reduced rate, even though the ATP content had fallen to 1.5 per cent of the normal value in air The ATP level in anaerobic conditions corresponded closely to the expected rate of ATP regeneration from known anaerobic sources of energy. Calculations show that even this severely restricted supply of energy would be more than adequate to drive the anaphase chromosome movements, so it is suggested that the concept of a mitotic energy reservoir is superfluous in root tips. No evidence could be found for the involvement during mitosis in sea urchin eggs of a non-respiratory ferrous complex such as occurs in pea root tips. Hence the dilemma remains, that whereas mitoses in both sea urchin eggs and pea root tips are arrested by respiratory inhibitors, yet the biochemical mechanisms of the arrest in the two types of cell are totally distinct.     

CREATINE KINASE FROM BRAIN: KINETIC ASPECTS

Abstract— Creatine kinase derived from rabbit brain has been re-examined with respect to its kinetic features. The enzyme from brain has lower Michaelis constants for both ADP and creatine phosphate than does the enzyme from rabbit muscle. Substrate inhibition by excess creatine phosphate occurs at a concentration approximating that found in the tissue. The enzyme from muscle is less sensitive to substrate inhibition.
The crude mitochondrial fraction from rat brain was centrifuged in a sucrose density gradient and the distribution of enzymatic activities among the subfractions was determined. The distribution of creatine kinase resembled that of two glycolytic enzymes; no evidence for a mitochondrial localization was found.     

CELL CLASSIFICATION AND KINETIC ASPECTS OF NORMOBLASTIC AND MEGALOBLASTIC ERYTHROPOIESIS

Mitotic indices and ³H-thymidine flash labelling indices have been determined in a total of 6000 erythroid cells from patients with megaloblastic anaemia (vitamin B₁₂ deficiency) and 4000 erythroid cells from patients with increased, normoblastic erythropoiesis. In the anaemic states there is a lack of mitoses in the more mature erythroid compartments relative to the number of mitoses in the early erythroid precursors; this must reflect skipped division and/or cell death in the later precursors. In order to further locate the deficit of mitoses, erythropoietic cells were subdivided in a way which aimed at stratifying them according to cell generations. It appears that there are four consecutive generations of recognizable proliferating red cell precursors. Balance considerations of mitotic figures suggest that in stressed normopoiesis all cells which enter generation III divide, whereas only about one-half of cells leaving generation III divide again in generation IV. In megaloblastic erythropoiesis it appears that only about one of three cells which leave generation III divide in generation IV. The data suggest that in megaloblastic anaemia, skipped division and/or cell death to a large extent take place in generation IV or at the transition from III to IV. In normoblastic erythropoiesis, the ratio labelled cells/mitotic cells is rather independent of cell maturation. In contrast, this ratio varies considerably in megaloblastic erythropoiesis, from 25:1 in early forms to 4-5:1 in late forms. As an explanation of the lack of mitoses, relative to cells in DNA-synthesis, in the early stages and the relative surplus of mitoses in the late stages it is proposed that cell cycle and cytological boundaries do not coincide in all cells. The present observations can be accounted for if a significant fraction of cells change their morphology (from basophilia to polychromasia) between their DNA-synthesis phase and the subsequent mitosis. It cannot be decided whether in addition there is a death function between DNA-synthesis and mitosis in the large basophilic megaloblasts, megaloblastic system could absorb a direct entry from the large basophilic cells amounting to perhaps about one-half of the flux through the S-pool of the large basophilic cells without being more dominated by very large cells than is actually the case; still, in large measure this will depend on the time from entry into the polychromatic pool until the subsequent mitosis or possible cell death. The alternative is a significant death function between S-phase and mitosis at the level of the large basophilic E1-E2 cells (generation I + II).     

MORPHOLOGICAL AND FUNCTIONAL ASPECTS OF AN INSECT EPIDERMAL GLAND

The sternal gland of primitive termites of the genus Zootermopsis (Z. nevadensis or Z. angusticollus) (Hagen) seems more organized than that of higher termites, in being comprised of three cell layers. It is also studded with about 200 campaniform sensilla. Below the meshwork cuticle of the gland lies a layer of columnar epithelial cells whose apical surfaces form a brush border, and whose basal surfaces are sculptured into a basketwork into which the second layer fits. Below the brush border are small microtubule-associated pits and coated vesicles. No channels can be seen either within or, except for the sensilla, between the cells. The second cell layer probably secretes the trail-following pheromone. Numerous electron-lucent droplets and large channels containing lipid micelles are found in the cytoplasm here, but the channels cannot be traced out of the secretory layer. The third layer consists of large pyriform cells. The campaniform sensilla are composed of three cells: the sensory cell proper whose dendrite carries a modified 9 + 0 sensory process, an accessory supporting cell that secretes an electron-opaque sheath, and an enveloping cell. At the cell borders of the sensillum, regions of septate and tight junction appear. There are also septate junctions between columnar cells and possibly tight junctions between columnar and secretory cells that would open an intracellular and molecular pathway to the endocuticle. The campaniform sensilla may be part of a feedback control system that determines the amount of pheromone deposited during trail laying.     

CELL ARREST IN Gl AND G2 OF THE MITOTIC CYCLE OF VICIA FABA ROOT MERISTEMS

Experiments were performed with cultured excised primary root tips of Vicia faba ‘Longpod’ to determine: (1) the proportion of meristematic cells arrested in Gl and in G2 during carbohydrate starvation, and to determine if the proportion is fixed or can be varied experimentally; (2) the effect of increased starvation on the ability of arrested cells in Gl and G2 to initiate DNA synthesis and mitosis, respectively, when exogenous sucrose was supplied; and (3) whether puromycin, cycloheximide, or actinomycin D prevented the initiation of DNA synthesis and the onset of mitosis. Microspectrophotometry of nuclear DNA and autoradiographic measurements of incorporated ³H-thymidine showed that 72 hr of starvation immediately after excision produced tissue with more than 70 % of the cells arrested in G2 and less than 30 % in Gl. If cultured for three days and then starved for 72 hr, the tissue had nearly equal numbers of cells arrested in Gl and G2. As the duration of starvation increased, the time required to initiate DNA synthesis and to divide when carbohydrate was replenished also increased. Inhibition of protein synthesis by puromycin and cycloheximide prevented the initiation of DNA synthesis and mitosis, but actinomycin D, an inhibitor of RNA synthesis, did not prevent division of cells from G2 nor DNA synthesis by cells from Gl. The experiments demonstrated that the mitotic cycle of Vicia has two major controls, one in Gl and another in G2, and that other factors determine how many cells are affected by either of these cycle controls.     

SOME STRUCTURAL AND FUNCTIONAL ASPECTS OF THE MITOTIC APPARATUS IN SEA URCHIN EMBRYOS

The mitotic figures in dividing cells of sea urchin embryos, from first division to the onset of cilia formation, were studied with regard to the filament system and its relation to kinetochores, chromosomes, and poles, as well as to fixation conditions which would best preserve these structures. With regard to fixation, variations in the salt concentration and pH of the fixative indicated that an extraction effect on the chromosomes noted in earlier work was probably due to a combination of neutral pH and salt concentration equivalent to sea water. The presence of the 15 mµ filaments depended on the presence of either of two stabilizing conditions: pH 6.1 or presence of the salts of sea water, presumably the divalent cations of Ca and Mg. Kinetochores and centrioles were unaffected by the fixative variations. The 15 mµ filaments, reported earlier in the central spindle, are also found in great numbers in the asters of early cleavage divisions. However, with successive divisions and reduction in cell size, the aster disappears at about the 32 to 64 cell stage, and the 15 mµ filaments are entirely associated with the central spindle. This disappearance of the aster suggests that it may be, in fact, merely a specialization of large cells for cytokinesis.     

GROWTH AND MITOTIC ACTIVITY OF LUNG COLONIES DERIVED FROM MOUSE TERATOCARCINOMAS

This study dealt with the mitotic activity of lung colonies in the process of differentiation of mouse teratocarcinoma cells injected in vivo . The results showed that three stages were identifiable in respect to the mitotic activity: 1) a lag stage for a few days after injection, 2) a stage during which maximum mitotic activity is observed for several days following the first stage and 3) a third stage displaying a decrease in mitotic activity. There is a correspondence between these three steps in mitotic activity and differentiation in lung colonies previously identified by histological observations.     

云南盘鮈不同地理居群的形态变异及分化

将采自中国元江、南盘江和金沙江水系的233尾云南盘鮈和短鳔盘鮈鱼类标本,按采集点地理位置就近的原则归类分为11个组,共测量了21个框架结构性状和22个常规性状。应用多变量形态度量学方法比较云南盘鮈各地理居群间的形态差异;并期望补充云南盘鮈与短鳔盘鮈的形态学鉴别特征。主成分分析结果表明,全部标本聚集在一起没有分离。差异系数分析结果表明,金沙江组内、元江组内及短鳔盘鮈与各水系间标本的差异系数均达不到亚种水平。南盘江组内,仅组7(罗平八大河)和组8(广南大里塘)标本的"腹鳍起点-背鳍起点距/体长"的差异系数大于1.28,但仅凭一个性状不足以用来区分云南盘鮈的不同地理居群;组7(罗平八大河)和组6(罗平多依河)标本的"腹鳍起点-背鳍起点距/体长"这一比例性状的差异系数大于1.28,但这一比例性状亦没有与其他性状构成一定的性状组合,不足以用来从形态上区分云南盘鮈与短鳔盘鮈。这就说明并不是所有的类群,或在不同水系分布的同一物种均会发生分化;另外,利用形态度量学未能找到进一步区分云南盘鮈与短鳔盘鮈的形态学证据,今后需要从分子生物学等方面寻找二者间新的分类学证据。     

一种从琼脂糖凝胶中回收DNA片段的简单电洗脱装置

我们设计了一种简单电洗脱装置,从琼脂糖胶中回收ＤＮＡ。该装置由两个带旋盖的小管、两块透析膜和一个凝胶屏障组成。在电场作用下,ＤＮＡ从凝胶中迁移出来,通过凝胶屏障进入由凝胶屏障和透析膜组成的回收小仓。用微量吸样器收集ＤＮＡ,乙醇沉淀和清洗。该法ＤＮＡ的回收率约８５％;回收的ＤＮＡ可用于基因工程常规实验。     

MORPHOLOGICAL AND MOLECULAR CHARACTERIZATION OF PLANKTONIC CYANOBACTERIA FROM BELGIUM AND LUXEMBOURG1

For the first time in Belgium and Luxembourg, the diversity and taxonomy of 95 cyanobacterial strains isolated from freshwater blooms were assessed by the comparison of phenotypes and partial 16S rRNA gene sequences. The results showed the high diversity of nanoplanktonic, picoplanktonic, and benthic–periphytic cyanobacteria accompanying the main bloom‐forming taxa. Indeed, besides 15 morphotypes of bloom‐forming taxa, seven non‐bloom‐forming planktonic morphotypes and 11 morphotypes from benthic–periphytic taxa were isolated in culture from the plankton samples of 35 water bodies. The bloom‐forming strains belonged to the genera Microcystis, Woronichinia, Planktothrix, Anabaena, and Aphanizomenon, whereas the other strains isolated from the same samples were assigned to the nanoplanktonic Aphanocapsa, Aphanothece, Snowella, and Pseudanabaena; to the picoplanktonic Cyanobium; and to the benthic–periphytic Geitlerinema, Komvophoron, Leptolyngbya, Lyngbya, Phormidium, Calothrix, Nostoc, and Trichormus. The results supported both the polyphyletism of genera such as Aphanocapsa, Aphanothece, Leptolyngbya, Geitlerinema, Anabaena, and Aphanizomenon as well as the validity of genera such as Microcystis, Planktothrix, and Pseudanabaena with gas vesicles and cells constricted at the cross wall. The results obtained showed the close relationship between Snowella and Woronichinia for which very few sequences exist. The first sequence of Komvophoron appeared poorly related to other available cyanobacterial sequences. Although in a few cases a good agreement existed between phenotypic and genotypic features, there was generally a discrepancy. Strains with identical morphotypes show small differences in the 16S rRNA sequences, which might be related to the different chemical properties of their habitats. The results showed the importance of the polyphasic approach in order to improve the taxonomy of cyanobacteria.     

COMPARISON OF MITOTIC PHENOMENA AND EFFECTS INDUCED BY HYPERTONIC SOLUTIONS IN HELA CELLS

Interphase HeLa cells exposed to solutions that are 1.6 x isotonic manifest a series of morphological transformations, several of which grossly resemble those which occur when untreated cells enter prophase. These include chromosome condensation with preferential localization at the nuclear envelope and nucleolus, ruffling of the nuclear envelope, and polyribosome breakdown. The nucleolus loses its fibrous component and appears diffusely granular. At 2.8 x isotonicity the nuclear envelope is selectively dispersed although other membranes show morphological alterations also. The characteristic transitions of the lysosomes, Golgi complex, and microtubules seen in normal mitosis do not occur during hypertonic treatment. All the changes induced with hypertonic solutions are rapidly reversible, and the nucleus particularly goes through a recovery phase which bears some similarity to that of the telophase nucleus. The prophase-like condensation of the chromatin following exposure of the intact cell to hypertonic medium cannot be reproduced on an ultrastructural level in the isolated nucleus with any known variation in salt concentration, suggesting significant modifications of the nuclear contents during isolation. In addition to these morphological responses, hypertonic solutions also markedly and reversibly depress macromolecular synthesis. The polyribosome disaggregation that results from exposure to hypertonic solutions may be partially prevented by prior exposure to elevated Mg⁺⁺ concentrations; this same ion is also partially effective in preventing the polyribosome breakdown which normally occurs as cells enter mitosis.     

DETERMINATION OF NUMBER AND MITOTIC ACTIVITY OF SHOOT APICAL INITIAL CELLS BY ANALYSIS OF MERICLINAL CHIMERAS

The dimensions of mericlinal sectors in periclinal chimeras resulting from replacement-displacement phenomena have been used to determine the number of shoot apical initial cells and their mitotic activity. Narrow sectors were always short, extending an average of less than three nodes. All long sectors were wide, involving 1/3 or 1/2 of the circumference of the stem. These observations define the origin of all primary growth as from 1–3 apical initial cells in each of the apical layers. The sectors reveal a surprising stability of cellular position at the center of growth, with a specific initial cell maintaining its position during formation of over 100 nodes. During vigorous vegetative growth of Ligustrum ovalifolium the initials themselves divide only about once in 12 days during the formation of three nodes. The mitotic index of the initials in privet shoot apices is 1.4, and this rate of division is sufficient for them to be the ultimate source of all cells composing the shoot.     

大蒜根尖细胞有丝分裂同步化诱导与中期染色体分离

本研究以大蒜（Ａｌｌｉｕｍｓａｔｉｖｕｍ）根尖为材料,用ＨＵ－ＡＰＭ双阻断法对细胞有丝分裂中期同步化和前,后,末期部分同步化作了探讨。表明在１．２５ｍｍｏｌ／ＬＨＵ,４μｍｏｌ／ＡＰＭ处理可使细胞有丝分裂中期指数（Ｍｅｔ．Ｉ）达３５％,１８ｈｒ的ＨＵ单独处理可检测到２７％的前期分裂细胞,ＨＵ对后,末期的部分同步化也有明显作用,约有１７％的后,末期细胞被检测,用Ｓｃｈｕｂｅｒｔ介绍的方法,分离出中期     

DEVELOPMENTAL ASPECTS OF ROOTS OF PISUM SATIVUM INFLUENCED BY THE G2 FACTOR FROM COTYLEDONS

A G2 Factor present in cotyledons of Pisum sativum influences several developmental events in roots. G2 Factor present in dry seeds (cotyledons and radicles) is transported to roots after germination and promotes cell arrest in G2 in about 35% of all root meristem cells. Present evidence suggests the G2 Factor promotes cell arrest in G2 only in cells that undergo normal cell differentiation (arrest) because the proportion of cells labeled with ³H-TdR after 16 hr does not differ among both seedlings or excised roots in the presence or absence of this substance. In this manner, trigonelline differs from chalones of animal tissues that usually suppress cell proliferation by cell arrest either in G1 or in G2. Experimental results suggest that cortex cells and not cells of vascular tissues in mature root tissues (20–22 mm from the meristem) are influenced by G2 Factor. Other recent publications indicate that the G2 Factor is trigonelline (N-methyl nicotinic acid) and concentrations of synthetic trigonelline from 10⁻⁵ to 10⁻⁷ m are effective in promoting cell arrest in G2 in one of the G2 Factor bioassays.     

A STUDY OF NEWT MITOTIC CHROMOSOMES BY NEGATIVE STAINING

A method is described for bursting single, selected mitotic cells on a fluid surface. Cells from cultures of newt heart tissue were burst on dilute solutions containing potassium and sodium with and without added calcium and also on dilute calcium chloride solution. The material was negatively stained with uranyl acetate or sometimes with ammonium molybdate or sodium phosphotungstate. The bodies of chromatids spread on NaCl/KCl solutions showed many parallel fibers about 150 A in diameter. Loops with a complex nodular structure were observed projecting from the sides and ends of chromatids. In calcium-containing solutions there was evidence of fiber coagulation; the chromatid body was more compact and laterally projecting fibers tended to be pulled out straight. Especially in the absence of calcium the chromosomal fibers had a nodular form and appeared to be composed of irregularly folded fibrillar elements. The question as to whether chromosomal fibers, which range in diameter from about 50 to 300 A, consist of single, folded threads or of two or more adjacent subunits is discussed.     

EVOLUTIONARY ASPECTS OF FRUIT-EATING BY BIRDS

In spite of a considerable literature on fruit-eating, the general evolutionary implications of fruit as a source of food for birds have been neglected. A preliminary attempt is made to explore the evolutionary and ecological consequences of fruit-eating, considered as a mutual interaction between parent plant and dispersal agent. The relationship considered is that obtaining between fleshy fruits and the “legitimate” fruit-eating birds which digest the fleshy part of the fruit and void the seed intact. Evolutionary aspects of seed-eating are also briefly discussed. The “strategies” adopted by fruits for dispersal by birds result in the production of abundant food supplies which are easy of access and exploitable by many species of birds. By contrast, the predation of birds on insects leads to a heterogeneous, sparse and cryptic food supply, to exploit which many different hunting techniques are necessary. Two important evolutionary developments in birds are attributed to these differences in food supply: there tend to be more species in families of insectivorous than of frugivorous birds, and lek behaviour in tropical forest has evolved in predominantly frugivorous birds. The seasonal succession of fruits in temperate latitudes is discussed, and contrasted with the situation in the tropics, using examples from Europe and Trinidad. In general, the succession of ripe fruits in Europe seems to be adapted to the seasonal shifts of the bird populations, and the more nutritious fruits tend to have a more southerly distribution and to ripen later than the more succulent fruits. In the tropics the distinction between nutritious and succulent fruits seems to be largely one of habitat. The constant succession of ripe fruits throughout the year in the tropics probably depends on competition for dispersal by frugivorous birds, which thus ensure the maintenance of their own food supply. This may be regarded as a symbiosis at the level of the ecosystem.     

MORPHOLOGICAL AND BIOCHEMICAL STUDIES OF ISOLATED MITOCHONDRIA FROM FETAL, NEONATAL, AND ADULT LIVER AND FROM NEOPLASTIC TISSUES

A combined morphological and biochemical investigation of mitochondria from developing and rapidly growing tissues ( tumors, fetal, and very early neonatal rat liver) revealed mitochondria which were deficient in respiratory control, showed no valinomycin induced K⁺ accumulation or spontaneous Ca⁺⁺ uptake, and were unable to undergo a swelling-contraction cycle. Electron microscopic examination of fetal and neonatal livers and a mammary tumor revealed mitochondria which differed from controls with respect to matrix density and ability to undergo reversible structural changes. The importance of isolation and assay media in interpretation of results is emphasized.