Chromosome analysis and DNA homology in threePicea species,P. mariana,P. rubens,andP. glauca (Pinaceae)

A detailed karyotype analysis was made on the somatic complement ofPicea rubens andP. glauca. B-chromosomes were observed in someP. glauca populations. The karyotypes are generally asymmetrical with most of the chromosomes having median to median-submedian centromeres.Picea glauca chromosomes 2, 3, 7, and 8 have secondary constriction on their short arm and chromosome 10 has a secondary constriction on the long arm. Chromosome 3 was the most easily identifiable, as it has two secondary constrictions located on the short arm. InP. rubens, all the chromosomes but chromosomes 8 and 9 have one to four distinctive secondary constrictions. In general, the diagrammatic comparisons show a high degree of similarity amongP. mariana, P. rubens, andP. glauca. GenomicP. mariana probe strongly hybridized to dots of genomic DNA fromP. rubens andP. glauca indicating that there is a high sequence homology among these three species. The synchronizing agent, hydroxyurea was used at different concentrations to enhance the mitotic index of cell suspensions derived from embryogenic cultures. Hydroxyurea at 1.25 mM increased significantly the mitotic index. An increase of hydroxyurea from 1.25 mM to 5 mM and 10 mM resulted in a steady decrease of mitotic index.     

ACTIVE GROWTH OF THE OCEANIC DINOFLAGELLATE CERATIUM TERES IN THE CARIBBEAN AND SARGASSO SEAS ESTIMATED BY CELL CYCLE ANALYSIS1

The growth rate of an oceanic dinoflagellate, Ceratium teres Kofoid, was investigated in the Sargasso and Caribbean Seas from September 1989 to July 1990 using the cell cycle analysis method. Estimated growth rates ranged from 0.29 to 0.58 day^?1 and were 1.5–7.2 times higher than generally accepted rates for oceanic dinoflagellates. The higher rates in this report were mainly due to an improvement in techniques that determine the duration of a terminal cell cycle phase in situ. The day-to-day variation in growth rates was surprisingly small, but, from long-term measurements, a weak correlation was found among temperature, daily irradiance, and seasonal growth rate. The calculated species-specific primary production ranged from 0.5 to 1.8 mg C·m^?2·day^?1, about 1% of the estimated total production. Ceratium teres may be an important carbon source at the base of the grazing food chain.     

Importance of dormancy and sink strength in sprouting of onions (Allium cepa) during storage

In onion ( Allium cepa L.) postponement of sprouting is necessary to achieve long term storage. We studied the factors determining sprouting during dry storage at 16°C. The period to visible sprouting depends on the length of the dormancy period, if present, and on the growth rate of the sprout. In the three cultivars tested, sprouts were initiated within 2 weeks after harvest indicating the absence of a real dormancy period. Sprout length increased linearly during storage. The mitotic activity of the apex decreased before harvest, was low at the transition from scale to leaf formation, and increased again when the sprout was initiated. From a few weeks before harvest, the initially high fructan content of the scales decreased, leading to a large increase in fructose. The sprout always contained enough carbohydrates for growth (between 50 and 60 mg g⁻¹ dry weight, of which 30% was fructan). The activity of sucrose synthase (EC 2.4.1.13) increased as the sprout grew, indicating an increase in sink strength. Invertase (EC 3.2.1.26) was absent in all bulb organs, during the various developmental stages. Although carbohydrates and enzymes were available for fast sprouting, sprout growth was still linear instead of exponential during dry storage at temperatures favorable for growth (16°C). The relative importance of factors determining sprouting are discussed.     

Spatial relationships between the anterior centriole and the mitotic center during interphase in the amoebae of the myxomycete Physarum polycephalum

Amoebae of the Myxomycete Physarum polycephalum in the interphase state typically contain only one proflagellar apparatus in which the anterior kinetosome (anterior centriole) is attached to the microtubule organizing center 1 (mtoc 1). We built strains possessing more than one mtoc 1 and a variable number of anterior centrioles to allow the appearance of new structures. In 8% of the amoebae of these strains, the 1:1 attachment between the anterior centriole and the mtoc 1 is not always respected. In nine cases studied using tridimensional reconstructions from ultrastructural thin sections, the pattern of attachment was more complex. A mtoc 1 could be linked to several anterior centrioles, and/or reciprocally an anterior centriole could be linked to several mtoc 1. In one case, an anterior centriole was not linked to a mtoc 1 and in three cases, a single centriole exhibited anterior and posterior characteristics. These observations suggest that (1) each pair of centrioles constitutes a morphological and physiological entity that is distinct from the mitotic center (mtoc 1); (2) the attachment of the anterior centriole to the mtoc 1 occurs at the end of each mitosis; (3) there is an inductory process during the morphogenesis of the link between the anterior centriole and the mtoc 1; (4) the anterior characteristics of a centriole can be present in the absence of the link with the mtoc 1; (5) the anterior and posterior characteristics of a centriole are not exclusive of each other, ruling out the existence of a lineage corresponding to the anterior centriole and a lineage corresponding to the posterior centriole; and (6) the differences between anterior and posterior centrioles result from a maturation process.     

Effect of CO2 on short-term human lymphocyte culture in vitro

Summary There was no significant difference in the mitotic indices of the cultures maintained at different CO₂ concentrations, i.e. 0%, 5% and 10%. However, considerable variation was recorded among different individuals. Supported by National Cancer Institute Contract No. 1 CP 43251.     

Laser microirradiation of kinetochores in mitotic PtK2 cells

Irradiation of the kinetochore region of PtK₂ chromosomes by laser light of 532 nm was used to study the function of the kinetochore region in chromosome movement and to create artificial micronuclei in cells. When the sister kinetochores of a chromosome were irradiated at prometaphase, the affected chromosome detached from the spindle and exhibited no further directed movements for the duration of mitosis. The chromatids of the chromosome remained attached to one another until anaphase, at which point they separated. No poleward movement of the chromatids was observed, and at telophase they passively moved to one of the daughter cells and were enclosed in a micronucleus. The daughter cell containing the micronucleus was then isolated by micromanipulation and followed through subsequent mitoses. At the next mitosis, two chromosomes, each with two chromatids, condensed in the micronucleus. These chromosomes did not attach to the spindle and showed chromatid separation, but no poleward movements at anaphase. They were again enclosed in micronuclei at telophase. The third generation mitosis was similar to the second. Occasionally, both the irradiation-produced and naturally occurring micronuclei exhibited no chromosome condensation at mitosis. Feulgenstained monolayers of PtK₂ cells with naturally occurring micronuclei showed that some micronuclei stain positive for DNA and others do not. This finding raises questions about the fate of chromosomes in a micronucleus.     

Chromatin structure during the prereplicative phases in the life cycle of mammalian cells

The object of this study was to determine the kinetics of chromosome decondensation during the G₁ period of the HeLa cell cycle. HeLa cells synchronized in the G₁ period following the reversal of mitotic block were fused with Colcemid-arrested mitotic HeLa cells at 1.5, 3, 5, and 7 h after the reversal of N₂O block. The resulting prematurely condensed chromosomes (PCC) were classified into six categories depending on the degree of their condensation. The frequency of occurrence of each category was plotted as a function of time after mitosis. The results of this study indicate that the process of chromosome decondensation, initiated during the telophase of mitosis continues throughout the G₁ period without any interruption, thus the chromatin reaches an ultimate state of decondensation by the end of G₁ period, when DNA synthesis is initiated.     

Mitotic cycle time and DNA content in annual and perennialMicroseridinae (Compositae,Cichoriaceae)

Within eight annual and perennialMicroseridinae species studied, the duration of the mitotic cycle is positively correlated with the nuclear DNA content, cycle time (hrs) = 7.3 + 0.32 × pg DNA/nucleus. Within the generaAgoseris andMicroseris, the annuals have lower DNA contents and more rapid mitotic cycle times than do the perennials. This relationship is predicted by the nucleotypic theory ofBennett. Annual species ofPyrrhopappus have relatively high DNA contents and a proportionately longer mitotic cycle time, but contrary to that expected by the nucleotypic theory as originally proposed have the fastest growth rate and shortest generation time observed in theMicroseridinae. This rapid developmental rate is discussed, nucleotypically, however, by analyzing relationships between DNA content, mitotic cycle time, and cell size.