VARIATION OF NUCLEAR DNA CONTENT IN HELIANTHUS ANNUUS (ASTERACEAE)

Nuclear 2C DNA content was determined by laser flow cytometry for 13 diploid (2n = 34) lines (cultivated varieties and inbred lines) of Helianthus annuus. Mean DNA amount of second leaf nuclei varied from 6.01 to 7.95 pg (32%) among lines. Mean DNA content varied up to 19% within lines. Variability in mean DNA content exceeding 27% and 48% was detected among leaves from different nodes of plants of the open-pollinated variety, Californicus, and the inbred line, RHA 299, respectively. The root tip and shoot tip nuclei of H. annuus have been reported to consist of a mixture of aneuploid (17 to 33 chromosomes) and diploid (34 chromosomes) cells, a condition called aneusomaty. Chromosome counts of root tips and an analysis of the distribution of DNA content of large numbers of nuclei from leaves indicate that aneusomaty either does not occur, or is not common, among the lines investigated. The intraspecific, intraline, and intraplant variation in DNA content in H. annuus support the concept that a sizable portion of a plant genome is unstable and subject to rapid changes in DNA amount.     

THE NUCLEAR DNA CONTENT OF DEVELOPING BARLEY ALEURONE CELLS

The nuclear DNA content of developing barley aleurone cells was examined by Feulgen cytophotometry using the Cytophotometric Data Conversion (CYDAC) system. At no time in their development did aleurone cells exhibit a single peak corresponding to the triploid (3N) amount of DNA. Although considerable heterogeneity was observed at every stage of development, the mean nuclear DNA content approximately doubled from the earliest to the most mature stage.     

THE NUCLEAR DNA CONTENT OF LARGE VENTRAL SPINAL NEURONS

Abstract— A nuclear fraction has been obtained from large spinal neurons previously isolated from bovine ventral spinal cord in bulk suspensions. The fraction contained an average of 5.3 ± 0.9 pg DNA/nucleus, indicating a high incidence of diploid nuclei. This conclusion was confirmed by distribution analysis of DNA in propidium iodide-stained nuclei examined by flow microfluorometry. That technique showed that at least 90% of the nuclei from large spinal neurons are diploid. Mixed, mostly non-neuronal nuclei derived from many types of cells in the ventral spinal cord contained an average of 5.9 ± 0.6 pg DNA/nucleus, 19% of which possibly possess more than diploid amounts of DNA. The uniform DNA content in nuclei of large spinal neurons and most other types of cells in the ventral spinal cord contrasts sharply with a wide variation (av 26-fold) in the nuclear volumes of the same cells.     

NUCLEAR DNA CONTENT IN POPULATIONS OF PINUS RIGIDA

Five populations of Pinus rigida growing in contrasting ecological situations ranging from North Carolina (35°53'N latitude) to Quebec (45°06'N latitude) showed no significant variation in amounts of nuclear DNA with respect to germinating seedlings. Nuclear volume of dormant nuclei also showed no significant variation between and within populations, a finding that is consistent with the concept that the basic 2C DNA value of Pinus rigida is uniform under all habitats. This finding is in contrast to numerous reports for other coniferous species.     

VARIATION WITHIN FRENCH BEAN VARIETIES

The internal variability of several varieties and strains of French bean is investigated, confining attention to the single character, seed weight. Out of eleven strains examined only two appeared to be homogeneous for seed weight, whilst two were obviously heterogeneous even by superficial examination of the seed.
A comparison of the distribution of seed weights in five strains of Canadian Wonder showed that each strain contains at least two or three lines out of the minimal estimate of four shared between them.
The natural out-crossing of fourteen varieties, including those analysed for seed weight, is compared. There are indications that varieties vary in their out-crossing propensities. No indication was found of the causes of the high frequencies of out-crossing occasionally encountered.
The possible sources of intra-varietal variation are briefly surveyed.     

DROUGHT STRESS RESPONSES OF MICROSERIS SPECIES DIFFERING IN NUCLEAR DNA CONTENT

Anatomical and physiological responses to drought stress were compared in two Microseris species differing in DNA content and originating from contrasting habitats relative to water availability (M. bigelovii, DNA = 2.6 pg nucleus^–1, more xeric; M. laciniata, DNA = 6.8 pg nucleus^–1, mesic). Leaf mesophyll cell volume was positively correlated with DNA content and negatively correlated with tissue elasticity, i.e., low ϵ̄ and thin cell walls. Drought stress increased leaf tissue elasticity (lower ϵ̄, thinner cell walls). Cell volume, cell wall thickness, cell number, and leaf area were decreased most by drought stress in M. laciniata. Osmotic adjustment with a 20% increase in total solutes (mostly amino acids) after stress was observed in both species, but their estimated contribution to the change in osmotic potential was larger in M. bigelovii. These findings indicate that the Microseris species studied respond to low water availability by maintaining turgor with 1) small cell volumes, 2) elastic tissues (low ϵ̄, thin cell walls), and 3) osmotic adjustment. Both enhanced tissue elasticity and small cell volume appear to be inherent characteristics in M. bigelovii and drought-induced responses in M. laciniata. These data are compatible with the hypothesis that natural selection may influence DNA content through differential sensitivity of cell growth to environmental stress.     

VARIATION IN STRUCTURE AMONG FRUITS OF MALOIDEAE (ROSACEAE)

Fruits of Rosaceae subfamily Maloideae are known as pomes, a fruit type unique to the Maloideae. Using light microscopy we examined the pomes of 173 species, broadly representing the taxonomic diversity of the subfamily. Significant variation occurs among pomes in retention, orientation, and texture of calyx lobes on the distal end of the fruit; density and distribution of sclereids in the flesh; heterogeneity among flesh parenchyma cells; carpel number and number of ovules per carpel; degree of connation among the carpels and adnation between ovary and hypanthium; and texture of the core. Phenetic clustering closely links congeneric fruits. Sorbus is a notable exception; fruits of the compound-leaved species form a cluster unrelated to fruits of the simple-leaved species. Fruits of Malus are also heteromorphic. Division of the Maloideae into two tribes, Crataegeae and Sorbeae, based largely on texture of the core is not substantiated. We hypothesize that the ancestral pome had five carpels, minimal connation of carpels, minimal adnation of ovaries to the hypanthium, two ovules per carpel, and a leathery core. Various adaptations for frugivore dispersal of the seeds partially explain trends in pome evolution.     

NATURE OF THE PLANT COMMUNITY. V. VARIATION WITHIN THE TRUE PRAIRIE COMMUNITY-TYPE

Mc Millan , C. (U. Texas, Austin.) Nature of the plant community. V. Variation within the true prairie community-type. Amer. Jour. Bot. 46(6): 418–424. Illus. 1959.—Population samples of grass species were transplanted to Lincoln, Nebraska, from two grassland communities within the general distribution of the true prairie community-type. These represented extensive grassland areas near Watertown, South Dakota, and Manhattan, Kansas. True prairie relicts near Colorado Springs, Colorado and in the Black Hills of southwestern South Dakota were also studied in the transplant garden. Only in one species, Stipa spartea Trin., were the transplanted populations essentially similar in behavior. In 8 of the species, Koeleria cristata (L.) Pers., Bouteloua gracilis (H.B.K.) Lag., B. curtipendula (Michx.) Torr., Schizachyrium scoparium Nash, Andropogon gerardi Vitman, Panicum virgatum L., Sorghastrum nutans (L.) Nash, and Sporobolus heterolepis (A. Gray) A. Gray, the Manhattan populations were the latest flowering. In Elymus canadensis L., the Manhattan population was the earliest flowering. The abstraction of two communities into a true prairie type of community with other communities of similar species-populations is a convenient method for discussing distributional phenomena. However, extreme caution must be used in generalizing about characteristics other than distributional. If the 10 species in the present study were designated by letters, the Watertown and Manhattan communities could be compared ecologically as a b' c d e f g h i j and a b c' d' e' f' g' h' i' j'. The use of taxonomic relationship in vegetational studies is convenient for the reduction of sample size, but the vital aspect of studying variation within the species is in the determination of harmony between vegetation and its habitat. The relict communities are in adjustment with their habitats and represent the results of natural selection in favoring early-flowering variants within a number of different species. The key to distribution of the true prairie vegetation, widespread or relict, lies in the harmony between a habitat variable and a vegetation variable. Through natural selection, each stand of true prairie may be fundamentally different from any other stand.     

FLOW-CYTOMETRIC ANALYSES OF NUCLEAR DNA CONTENT IN FOUR FAMILIES OF NEOTROPICAL BATS

Flow-cytometric analyses of 29 species of microchiropteran bats representing four families and 20 genera revealed that bats possess only 79% (5.43 pg) of the DNA content of a “typical” mammal (e.g., Mus musculus strain C57BL; 7 pg). Chiroptera, the second largest order of mammals, is thus an exception to the prevailing view that mammals possess a minimum nuclear DNA content of 7 pg. Limitations on cell size resulting from a high metabolic rate may have constrained evolution of DNA content and could explain why the extensive heterochromatic additions that are common in some groups of mammals are absent in bats. Chromosomes of bats have been well studied; detailed chromosomal banding data are available for nearly all the species used in this investigation. However, no significant correlations were found between DNA content and karyotypic characteristics such as 2n, fundamental number, and rate or pattern of chromosomal evolution.     

膀胱肿瘤DNA含量、核形态学特点与AgNORs计数的研究

应用图像分析技术对４３例膀胱肿瘤细胞ＤＮＡ含量和核形态参数进行了定量测定,同时进行核仁组成区（ＡｇＮＯＲｓ）计数研究,结果表明：肿瘤细胞的ＤＮＡ含量及干系水平与组织学分级基本一致,ＤＮＡ含量及干系水平越高,则恶性程度越高,ＤＮＡ含量与核面积及核最短直径的变化里正相关性,与ＡｇＮＯＲｓ的计数无明显相关性。这三项检测方法对肿瘤生物学行为判断均有重要的参考价值。     

油桐尺蠖核多角体病毒的基因型变异

本文用AvaⅡ、BamHⅠ、EcoRⅠ和HindⅢ四种限制性内切酶对油桐尺蠖核多角体病毒(Buzvra suppressaria Nuclear PolyhedrosisVirus)DNA作酶解图谱分析,比较了湖北、湖南、四川三个分离株的基因组。三者图谱基本相似,但少数片段略有不同。亚克分子片段的存在表明野生的油桐尺蠖核多角体病毒有基因型变异,包含着数个基因型变种。     

武汉东湖磷含量的变动及其分布

本文总结了武汉东湖水体中磷含量（均以PO4计算）的周年逐月季节和年际变动及其分布上的差异（1973－1985年）。按面积加权法计算总磷的平均含量为0．244毫克／升（1983－1985年）,总溶解磷和溶解活性磷的平均含量分别为0．121毫克／升和0．051毫克／升（1981－1984年）,总磷和总溶解磷周年中出现两次高峰含量,即春季（3－5月）和夏末秋初（8－9月）。低含量出现在水温最低的冬季（12－2月）,周年中溶解活性磷高峰含量出现在冬末春初（1－3月）,低含量多数出现在春天夏初（5－7月）。东湖水体中磷含量平面分布有明显的差异,而垂直分布表层和底层差异小,各种形态磷的组成中颗粒磷所占比较最大（1983－1984年平均值）,平均占总磷63．4％,溶解非活性磷所占比较最小,平均占总磷12．0％。     

INTERSPECIFIC COMPETITIVE INTERACTIONS AND THE MAINTENANCE OF GENOTYPIC VARIATION WITHIN TWO PERENNIAL GRASSES

Theoretical models predict that natural selection acting through competitive interactions should lead to increased divergence in resource use and to more equal competitive abilities among different genotypes. The consequent overcompensatory interactions and similar competitive abilities will favor maintenance of genotypic diversity. In field experiments we found that naturally co-occurring genotypes of two perennial grasses, Danthonia spicata and Anthoxanthum odoratum, differed in interspecific competitive performance. The competitive performance of a given genotype often depended on the genotypic identity of the competing species, especially in Danthonia spicata. Both overcompensatory and undercompensatory interactions were found, but neither was prevalent for both species. These data indicate that interactions between species are complex and have an important genetic component. The results from this experiment are compatible with a competitive explanation for the maintenance of genetic variation, but the persistence of weakly competitive genotypes cannot be explained.     

多辐溲疏群体同工酶变异的数量分析

研究了四川南川金佛山特产的多辐溲疏不同海拔和生境的５个群体的４１个个体叶片过氧化物酶,过氧化氢酶,酯酶,淀粉酶,柠檬酸脱氢酶及谷氨酸脱氢酶同工酶谱带位置上的变异式样,来自同一群体的不同个体在谱带上表现出极大的相似性,而来源于不同群体的个体却表现出明显的趋异性,显示出酶谱带位置与群体生长的生境有显著的相关性,一定的群体具有某些特有的酶谱带,空间隔离限制了群体间个体的相互基因交流,在进化中那些适应新的     

LIFE-HISTORY VARIATION WITHIN A POPULATION OF THE COLONIAL ASCIDIAN BOTRYLLUS SCHLOSSERI. I. THE GENETIC AND ENVIRONMENTAL CONTROL OF SEASONAL VARIATION

Many empirical analyses of life-history tactics are based on the assumption that demographic variation ought to be greatest among populations or species living in different environments. However, in a single population of the sessile colonial sea squirt Botryllus schlosseri, there are two discrete life-history morphs. Semelparous colonies are characterized by a) death immediately following the production of a single clutch, b) early age at first reproduction, c) rapid growth to first reproduction, and d) high reproductive effort. In contrast, iteroparous colonies a) produce at least three clutches before dying, b) postpone sexual reproduction until they are nearly twice the age of semelparous colonies, c) grow at about half the rate of semelparous colonies, and d) invest roughly 75% less in reproductive effort than semelparous colonies. Semelparous colonies numerically dominate the population through midsummer; later in the summer, iteroparous colonies are most numerous. Field and laboratory common-garden experiments, along with breeding studies, indicate that the demographic differences between the morphs are genetically determined. Consequently, the seasonal switch from dominance by semelparous colonies to dominance by iteroparous colonies may be an evolved response to a seasonally changing environment. On theoretical grounds, temporal variation in selection is thought to play a relatively unimportant role in maintaining genetic polymorphism; nonetheless, the seasonally recurrent life-history polymorphism shown in this study indicates that temporal variation in selection can lead to the maintenance of genetic polymorphism for traits strongly affecting fitness.     

PHENOTYPIC VARIATION WITHIN “INDIVIDUAL” LICHEN THALLI

“Individual” large diam lichen thalli of Umbilicaria vellea (L.) Ach. and U. mammulata (Ach.) Tuck. are not uniform in physiological activity or enzymatic phenotype. Horizontal variation in net photosynthetic rates and dark respiration rates was found, but this was independent of the mass of the photosynthesizing or respiring tissues. In addition, sublethal temperature pretreatments reduced the net photosynthetic and respiratory rates of some areas of the thallus, but increased others. Assays of isoenzyme phenotypes showed that all large diam thalli are extensively polymorphic while young, small diam thalli are mainly monomorphic. Taken together, the results say that the concept of the “individual” may be inappropriate for these organisms.     

SOME OBSERVATIONS ON DNA CONTENT AND CELL AND NUCLEAR VOLUME GROWTH IN THE DEVELOPING XYLEM CELLS OF CERTAIN HIGHER PLANTS

List , Albert , Jr . (Douglass Coll., Rutgers U., New Brunswick, N. J.) Some observations on DNA content and cell and nuclear volume growth in the developing xylem cells of certain higher plants. Amer. Jour. Bot. 50(4): 320–329. Illus. 1963.—The developing metaxylem cells of Acorus calamus roots undergo an over-all growth in cell and nuclear volume that may be expressed roughly as a constant ratio of relative growth rates. Within this over-all growth picture, however, there is a periodicity of both nuclear and cell volume growth. Other plants such as Peltandra, Eleocharis, and Dennstaedtia undergo a similar volume growth. Marsilea tracheary elements have an increase in nuclear number per cell by simultaneous divisions. Arisaema metaxylem nuclei go through a series of DNA doublings correlated with nuclear volume doubling and cell volume increase, at least up to the 16- or 32-ploid level. The cells display some tendency to fall into size classes, expressing a pulsation in growth. A fluctuating alternation or stepwise growth of cell and nucleus appears to describe the data more suitably than the allometric growth equation. In Zea, the cell and nuclear volumes for metaxylem cells fit a fluctuating envelope better than the straight line, and there is again the probability that cell volumes fall into size classes related to nuclear volume class. The DNA content of the nuclei was determined to fall into a frequency distribution having peaks at the 4-, 8-, 16-, and 32-ploid equivalent, agreeing with an earlier report for diploid maize. DNA content was highly correlated with nuclear volume in the over-all growth of the metaxylem cells.