15N isotope dilution to quantify dinitrogen (N2) fixation associated with Canadian and Brazilian wheat

1983 ◽  
Vol 61 (6) ◽  
pp. 1667-1671 ◽  
Author(s):  
R. J. Rennie ◽  
J. R. deFreitas ◽  
A. P. Ruschel ◽  
P. V. Vose
Keyword(s):  
Isotope Dilution ◽  
Chromosome Pair ◽  
Azospirillum Brasilense ◽  
Triticum Aestivum L ◽  
Dilution Technique ◽  
15N Isotope ◽  
Wheat Varieties ◽  
Single Chromosome ◽  
Total Plant ◽  
High Degree

Putative dinitrogen (N2) fixation associated with wheat (Triticum aestivum L. emend. Thell) has been studied using acetylene reduction and nonisotopic N-balance techniques. Absolute proof of N2 fixation using 15N2 (gas) or 15N isotope dilution procedures has not been reported. This paper presents the first use of the 15N isotope dilution technique to determine in wheat the percent plant N derived from associated N2 fixation. Although inoculation with either Bacillus polymyxa (C-11-25) or Azospirillum brasilense (ATCC 29145) resulted in no significant increase in total plant N in nine Canadian and one Brazilian wheat varieties, isotopic N data showed that N2 fixation did occur. The amounts of plant N derived from atmosphere, fertilizer, and soil varied. A high degree of plant–bacterial specificity existed. In several instances, the substitution of a single chromosome pair in the wheat regulated the amount of N2 fixed. The agreement between this 15N isotope experiment and two previous nonisotopic experiments suggests that the trait supporting N2 fixation in wheat may be consistently expressed in the varietal lines.

scholarly journals Chromosome Banding in Amphibia. XXXII. The Genus Xenopus (Anura, Pipidae)

2015 ◽  
Vol 145 (3-4) ◽  
pp. 201-217 ◽  
Author(s):  
Michael Schmid ◽  
Claus Steinlein
Keyword(s):  
Chromosome Pair ◽  
Repetitive Sequences ◽  
5S Rdna ◽  
Mitotic Chromosomes ◽  
Banding Patterns ◽  
Single Chromosome ◽  
Replication Banding ◽  
Rdna Sequences ◽  
High Degree ◽  
Replication Bands

Mitotic chromosomes of 16 species of the frog genus Xenopus were prepared from kidney and lung cell cultures. In the chromosomes of 7 species, high-resolution replication banding patterns could be induced by treating the cultures with 5-bromodeoxyuridine (BrdU) and deoxythymidine (dT) in succession, and in 6 of these species the BrdU/dT-banded chromosomes could be arranged into karyotypes. In the 3 species of the clade with 2n = 20 and 4n = 40 chromosomes (X. tropicalis, X. epitropicalis, X. new tetraploid 1), as well as in the 3 species with 4n = 36 chromosomes (X. laevis, X. borealis, X. muelleri), the BrdU/dT-banded karyotypes show a high degree of homoeology, though differences were detected between these groups. Translocations, inversions, insertions or sex-specific replication bands were not observed. Minor replication asynchronies found between chromosomes probably involve heterochromatic regions. BrdU/dT replication banding of Xenopus chromosomes provides the landmarks necessary for the exact physical mapping of genes and repetitive sequences. FISH with an X. laevis 5S rDNA probe detected multiple hybridization sites at or near the long-arm telomeric regions in most chromosomes of X. laevis and X. borealis, whereas in X. muelleri, the 5S rDNA sequences are located exclusively at the long-arm telomeres of a single chromosome pair. Staining with the AT base pair-specific fluorochrome quinacrine mustard revealed brightly fluorescing heterochromatic regions in the majority of X. borealis chromosomes which are absent in other Xenopus species.

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