Soil bacterium DNA was isolated by minor modifications of previously described methods. After purification on hydroxyapatite and precipitation with cetylpyridinium bromide, the DNA was sheared in a French press to give fragments with an average molecular mass of 420,000 daltons. After repeated hydroxyapatite purification and precipitation with cetylpyridinium bromide, high-pressure liquid chromatography analysis showed the presence of 2.1% RNA or less, whereas 5-methylcytosine made up 2.9% of the total deoxycytidine content. No other unusual bases could be detected. The hyperchromicity was 31 to 36%, and the melting curve in 1 X SSC (0.15 M NaCl plus 0.015 M sodium citrate) corresponded to 58.3 mol% G+C. High-pressure liquid chromatography analysis of two DNA samples gave 58.6 and 60.8 mol% G+C. The heterogeneity of the DNA was determined by reassociation of single-stranded DNA, measured spectrophotometrically. Owing to the high complexity of the DNA, the reassociation had to be carried out in 6 X SSC with 30% dimethyl sulfoxide added. Cuvettes with a 1-mm light path were used, and the A275 was read. DNA concentrations as high as 950 micrograms ml-1 could be used, and the reassociation rate of Escherichia coli DNA was increased about 4.3-fold compared with standard conditions. C0t1/2 values were determined relative to that for E. coli DNA, whereas calf thymus DNA was reassociated for comparison. Our results show that the major part of DNA isolated from the bacterial fraction of soil is very heterogeneous, with a C0t1/2 about 4,600, corresponding to about 4,000 completely different genomes of standard soil bacteria.(ABSTRACT TRUNCATED AT 250 WORDS) Images

High diversity in DNA of soil bacteria.

Cultivated peanut (Arachis hypogaea) is an allotetraploid with closely related subgenomes of a total size of ∼2.7 Gb. This makes the assembly of chromosomal pseudomolecules very challenging. As a foundation to understanding the genome of cultivated peanut, we report the genome sequences of its diploid ancestors (Arachis duranensis and Arachis ipaensis). We show that these genomes are similar to cultivated peanut's A and B subgenomes and use them to identify candidate disease resistance genes, to guide tetraploid transcript assemblies and to detect genetic exchange between cultivated peanut's subgenomes. On the basis of remarkably high DNA identity of the A. ipaensis genome and the B subgenome of cultivated peanut and biogeographic evidence, we conclude that A. ipaensis may be a direct descendant of the same population that contributed the B subgenome to cultivated peanut.

/pdf/the-genome-sequences-of-arachis-duranensis-and-arachis-220f9uc21x.pdf

The genome sequences of Arachis duranensis and Arachis ipaensis, the diploid ancestors of cultivated peanut.

Mutants of Arabidopsis thaliana deficient in gibberellin synthesis (ga1-3 and ga1-6), and a gibberellin-insensitive mutant (gai) were compared to the wild-type (WT) Landsberg erecta line for flowering time and leaf number when grown in either short days (SD) or continuous light (CL). The ga1-3 mutant, which is severely defective in ent-kaurene synthesis because it lacks most of the GA1 gene, never flowered in SD unless treated with exogenous gibberellin. After a prolonged period of vegetative growth, this mutant eventually underwent senescence without having produced flower buds. The gai mutant and the “leaky” ga1-6 mutant did flower in SD, but took somewhat longer than WT. All the mutants flowered readily in CL, although the ga1-3 mutant showed some delay. Unlike WT and ga1-3, the gai mutant failed to respond to gibberellin treatment by accelerating flowering in SD. A cold treatment promoted flowering in the WT and gai, but failed to induce flowering in ga1-3. From these results, it appears that gibberellin normally plays a role in initiating flowering of Arabidopsis.

Gibberellin Is Required for Flowering in Arabidopsis thaliana under Short Days.

All else being equal, polyploids are expected to have larger C-values (amount of DNA in the unreplicated gametic nucleus) than their diploid progenitors, increasing in direct proportion with ploidy. This expectation is observed in some polyploid series, especially those newly formed, but there are examples suggesting that C-values in particular polyploids are less than expected. The availability of the Angiosperm DNA C-values database (http:// www.rbgkew.org.uk/cvavhomepage.html) has allowed this question to be addressed across a broad range of angiosperms and has revealed striking results deviating from expectation: (i) mean 1C DNA amount did not increase in direct proportion with ploidy, and (ii) mean DNA amount per basic genome (calculated by dividing the 2C value by ploidy) tended to decrease with increasing ploidy. These results suggest that loss of DNA following polyploid formation, or genome downsizing, may be a widespread phenomenon of considerable biological significance. Recent advances in our understanding of the molecular events that take place following polyploid formation together with new data on how DNA amounts can both increase and decrease provide some insights into how genome downsizing may take place. The nature of the evolutionary forces that may be driving DNA loss are also discussed.

Genome downsizing in polyploid plants

The KNOTTED-1 (KN1) locus of maize is defined by dominant mutations that affect leaf cell fates. Transposon tagging led to the isolation of the gene and the discovery that KN1 encodes a homeo domain. Immunolocalization studies showed that in wild-type maize plants, KN1 protein is present in nuclei of apical meristems and immature shoot axes but is down-regulated as lateral organs, such as leaves, are initiated. The protein is not immunohistochemically detectable in wild-type leaves at any stage. In developing leaves of plants carrying the dominant Kn1 mutation, temporally and spatially restricted ectopic expression of KN1 causes the mutant phenotype. To better understand the function of KN1 in plant development, we sought to determine the phenotype of plants in which KN1 was constitutively expressed. We find that tobacco plants transformed with the KN1 cDNA driven by the CaMV 35S promoter have a dramatically altered phenotype. The phenotypes are variable and depend on the level of KN1 protein. Plants expressing moderate levels of KN1 are reduced in stature with rumpled or lobed leaves. Plants with relatively high levels of KN1 lack apical dominance and are severely dwarfed in overall height and leaf size. Small shoots originate from the surface of these diminutive leaves. On the basis of phenotypes in maize and tobacco, we propose that the KN1 homeo box gene plays a role in determining cell fate. The consequences of KN1 overexpression appear to depend on the concentration of KN1 and the timing of its expression during organogenesis.

/pdf/overexpression-of-the-maize-homeo-box-gene-knotted-1-causes-3bz5cltqmd.pdf

Overexpression of the maize homeo box gene, KNOTTED-1, causes a switch from determinate to indeterminate cell fates.

Botanical Microtechnique and Cytochemistry

Nuclear DNA contents of a conventionally inbred flue-cured tobacco (Nicotiana tabacum L.) cultivar. 'Coker 139,' and two selected, doubled haploid (dihaploid) lines developed from it by anther culture and colchicine chromosome doubling were compared. The dihaploid lines had previously been shown to be lower yielding and agronomically inferior to the parental cultivar. Nuclei of leaf and root cells of the dihaploids possessed significantly higher amounts of DNA than the parental cultivar, although chromosome numbers (2n = 48) had not changed. Mean nuclear DNA content of the dihaploid lines was 10.62 pg, while nuclei of the parental cultivar contained 9.32 pg. The anther-culture process and (or) the nature of vegetative nuclei of pollen grains from which haploid plants originate have been suggested as possible contributing factors to higher DNA values. An average 12% increase in heterochromatin (condensed chromatin) in dihaploids, and significant differences in thermal denaturation of parental and dihaploid...

Evaluation of nuclear DNA content and heterochromatin changes in anther-derived dihaploids of tobacco (Nicotiana tabacum) cv. Coker 139

Requirement of an internal standard for microspectrophotometric measurements of dna

The base composition of peanut (var. NC-17) DNA determined from thermal denaturation profiles showed an average guanine plus cystosine content of 34% which was in close approximation to 36% guanine plus cytosine calculated from the buoyant density. Buoyant density also indicated the absence of satellite DNA. The genome size, 2.0 x 10(9) base pairs, as determined by reassociation kinetics of the single copy DNA was close to the genome size determined by cytophotometry, 2.1 x 10(9) base pairs. Peanut DNA averaging 450 to 600 base pairs long, reassociated in phosphate buffer and fractionated by hydroxylapatite, indicated a DNA genome composition of 36% nonrepetitive or single copy DNA; reassociation in formamide and followed by optical methods indicated the repetitive DNA possesses highly repeated, intermediately repeated and rarely repeated components of DNA with DNA sequences repeated on the average about 38,000, 6,700, and 200 times each. Different criteria of reassociation in formamide revealed further subdivisions of these four separate components of DNA. The DNA of above mentioned NC-17 variety compared to Florigiant variety showed no differences in thermal denaturation profiles, buoyant density, or in genome size.

Reassociation Kinetics and Cytophotometric Characterization of Peanut (Arachis hypogaea L.) DNA.

A B S T R A C T Quantitative changes in DNA, histone, RNA, and total protein have been measured in meristematic cells during floral evocation.2 A single 22-hr, long-day exposure induced twomonth-old vegetative plants of Sinapis alba to flower. Periodic collections of shoot apices were made and stained with Schiff's reagent (DNA), azur B (RNA), alkaline fast green (histone), and naphthol yellow S (total protein). The two-wavelength method was used for DNA and histone measurements and the one-wavelength, two-area procedure was chosen for RNA and total protein determinations. The DNA and histone amounts per cell decreased to a minimum value 34 hr after treatment, and most of the nuclei shifted from 4C to 2C values. DNA and histone quantities paralleled each other from 34-46 hr, after which time the histone values continued to increase and the DNA values decreased. The RNA values increased rapidly after treatment as did the total protein quantities, after a slight decrease at 34 hr concurrent with the 4C to 2C cell population shift. The significance of these events is discussed in relation to the changes which were previously described in the shoot apex of

https://www.jstor.org/stable/info/2441143

Jerome P. Miksche

Papers

Botanical Microtechnique and Cytochemistry

Evaluation of nuclear DNA content and heterochromatin changes in anther-derived dihaploids of tobacco (Nicotiana tabacum) cv. Coker 139

Requirement of an internal standard for microspectrophotometric measurements of dna

Reassociation Kinetics and Cytophotometric Characterization of Peanut (Arachis hypogaea L.) DNA.

Quantitative study of nucleic acids and proteins in the shoot apex of sinapis alba during transition from the vegetative to the reproductive condition