Juan Orellana

Nucleolar organizer activity in wheat, rye and derivatives analyzed by a silver-staining procedure

Nucleolar activity was analyzed in wheat (Triticum sp.), rye (Secale cereale) and several types of wheat-rye derivatives using a modified, highly reproducible, silver staining procedure (Lacadena et al. 1984). A comparative analysis of the nucleolar organizer regions (NORs) of somatic metaphase chromosomes was made by phase contrast, C-banding, and silver staining. The frequency distribution of the number of nucleoli visualized at interphase by silver staining was also used to infer the activity of NORs. The results agree quite well with data from in situ hybridization reported by other authors. The behavior of euploid, ditelosomic and nulli-tetrasomic plants of common wheat showed the relative nucleolar activity of the four organizer chromosomes to be: 6B > 1B > 5D > 1A. — Several types of wheat-rye derivatives were analyzed: interspecific hybrid, triticale, addition and substitution lines, and plants with the genome constitutions, AABBDR, ABDR + 5D, ABRR, and ABRRR. In all cases the nucleolar organizer chromosome 1R of rye was suppressed by the presence of wheat chromosomes.

Nucleolar activity and competition (Amphiplasty) in the genus Aegilops

SummaryNucleolar activity and competition (amphiplasty) has been analysed in diploid, tetraploid and hexaploid species of Aegilops using a highly reproducible silver-staining procedure. A comparative analysis of somatic metaphase chromosomes by phase contrast, C-banding and Ag-staining was made to analyse the activity of the nucleolar organiser regions (NORs). With the exception of Ae. crassa 4x, amphiplasty occurs in all the tetraploid and hexaploid species analysed. The U genome from Ae. umbellulata suppresses completely the NOR activity of the genomes M° (Ae. ovata), Sv (Ae. variabilis), D (Ae. juvenalis) and C (Ae. triuncialis) and that of one pair of the nucleolar organiser chromosomes of the genomes Mc (Ae. columnaris), Mb (Ae. biuncialis), Mj (Ae. juvenalis) and Mt (Ae. triaristata 6×). The nucleolar activity of the D genome is completely suppressed by the genomes U (Ae. umbellulata), C (Ae. cylindrica) and Mv (Ae. ventricosa).

Metaphase I bonds, crossing-over frequency, and genetic length of specific chromosome arms of rye

Using a Giemsa C-banding procedure three chromosome pairs (3, 6 and 7) have been identified in meiosis of the F1 of a cross between two rye inbred lines. Two of these chromosome pairs (3 and 7) were heterozygous for a prominent telomeric heterochromatic band. The comparison between the frequencies of the different meiotic configurations at metaphase I, anaphase I and metaphase II presented by these two chromosome pairs has allowed the estimation of the chiasma frequency and the genetic length of the chromosome arms 3 short and 7 long.

Interactions between wheat, rye and Aegilops ventricosa chromosomes on homologous and homoeologous pairing

Different wheat-rye, Ae. ventricosa-rye and wheat-ventricosa-rye genome combinations were analysed at meiosis. In all cases it was possible to estimate the frequencies of the different types of homologous and homoeologous pairing, by using a C-banding technique. Rye homologous pairing decreased in the presence of wheat and Ae. ventricosa genomes with respect to that observed in diploid rye. However, the frequencies of all types of homoeologous pairing were very constant in all hybrids analysed and independent of the number of genomes which were present in the hybrids.

Meiotic behaviour of chromosomes 1R, 2R and 5R in autotetraploid rye

The meiotic behaviour of chromosomes 1R, 2R and 5R was studied in C-banded preparations of autotetraploid rye. Analysis of pairing and chiasma formation was based on metaphase I configurations, using the model designed by Sybenga, with slight modifications. Frequencies of two modes of pairing (one quadrivalent or two bivalents) differed from those expected for random pairing. Although preferential pairing for some arm pairs of chromosome 2R was detected, this did not seem to be the cause of the increased bivalent pairing. This increase was attributed to either the spatial separation of the four homologous chromosomes in some premeiotic cells into two groups of two, or a correction of the synaptonemal complex, or both. The number of chiasmate associations showed variation between chromosomes and between arms within the same chromosome. It was closely related to arm length, but different after quadrivalent and bivalent pairing. This is suggested to be a consequence of partner exchange interfering with pairing and, consequently, with chiasma formation, and a different chiasma distribution after quadrivalent pairing. Variation between chromosomes in the frequencies of alternate and adjacent co-orientation in metaphase I quadrivalents without interstitial chiasmata suggests that the relative positions of the centromeres in the quadrivalent influence their co-orientation.

Metaphase I bound arms and crossing over frequency in rye

Using a Giemsa C-banding procedure it has been possible to identify at meiosis three chromosome pairs of a local Spanish rye cultivar. Two of these chromosomes (3 and 5) were heterozygous for an interstitial C-band in the long arm and the other (chromosome 7) was heterozygous for a telomeric C-band, also in the long arm. From the frequency of being bound at metaphase I and the frequency of recombined chromatids at anaphase I in the arms considered, estimates of actual chiasma frequencies have been derived. The results have been compared with those obtained in a Fl between two inbred lines. It is concluded that: (i) Although the frequency of bound arms analyzed was similar in all cases, the chiasma frequency was higher in the cultivar than in the Fl plants. Cultivar plants showed a variation in chiasma frequency for the bivalent arms studied which was correlated with the frequency of bound arms per cell, indicating that the estimation for chiasma frequency by means of bound arm frequency has an error that increases with increasing number of bound arms per cell, (ii) Evidence of chiasma terminalization has not been found, (iii) It is suggested that the different rye chromosomes have different chiasma localization patterns, which, in turn, are related with the chiasma frequency.

Analysis of nucleolar activity in Agropyron elongatum, its amphiploid with Triticum aestivum and the chromosome addition lines

SummaryThe nucleolar organizer activity of the Agropyron elongatum, its amphiploid with hexaploid wheat (Triticum aestivum) and the chromosome addition lines is analyzed by the silver-staining procedure. Four Ag-NORs are observed in A. elongatum corresponding to the chromosomes 6E and 7E. In the amphiploid T. aestivum — A. elongatum, eight Ag-NORs are observed which corresponds the wheat chromosomes 1B and 6B and to the elongatum chromosomes 6E and 7E. Thus, there is codominance in the nucleolar organizer activity of the chromosomes of the two species. However, a partial amphiplasty is detected since less than 8 Ag-NORs (7 up to 4) are observed in some metaphase cells; the chromosomes 6E and 7E are occasionally suppressed by wheat chromosomes. This conclusion is confirmed by the behaviour of the addition lines since only in those corresponding to the chromosomes 6E and 7E are the elongatum chromosomes nucleolar active although occasionally they can be suppressed by wheat chromosomes.

Meiotic behaviour of Un, D and R genomes in the amphiploid Aegilops ventricosa -Secale cereale and the parental species

SummaryMeiotic pairing frequencies of the Un and D genomes of Ae. ventricosa and the R of S. cereale could be easily established at metaphase I in Aegilops ventricosa — Secale cereale amphiploid plants as well as in its parental species by using the C-banding technique procedure. The results show a high diminution of chromosome pairing for all genomes in the amphiploid with respect to its parental species probably due to C-heterochromatin content and/or genotypic or cryptic interactions between the three genomes.

Nucleolar organiser activity in Lolium and Festuca. 1. Lolium multiflorum, Festuca arundinacea and Lolium—Festuca Hybrids

Lolium multiflorum, Festuca arundinacea and L. multiflorum-F. arundinacea hybrids were analysed by phase contrast, C-banding and silver-staining methods. Although the number of secondary constrictions detected by phase contrast was always six in L. multiflorum, it was very variable in F. arundinacea (4–12) and Lolium-Festuca hybrids (3–7); in these cases most of the constrictions appeared as euchromatic or c-hetero chromatic material when the C-banding technique was applied. By contrast the number of Ag-NORs was virtually constant in all plant varieties: six interstitial in L. multiflorum, two interstitial and two telomeric in F. arundinacea and three interstitial in the hybrids. These results indicate that not all the secondary constrictions detected by phase contrast are in fact nucleolar organiser regions. In addition a suppression of the nucleolar organisers of F. arundinacea by those of L. multiflorum was detected in the hybrids analysed.

Nucleolar organiser activity in wheat-barley chromosome addition lines

SummaryThe nucleolar organiser activity of cultivated barley, Hordeum vulgare and the wheat-barley chromosome addition lines is analysed by a modified, highly reproducible, silver-staining procedure. Four Ag-NORs are observed in metaphase cells of barley corresponding to chromosomes 5HV and 6HV. Six Ag-NORs are detected in the chromosome addition lines 5HV and 6HV while only four Ag-NORs are observed in the rest of the addition lines analysed (2HV, 3HV, 4HV and 7HV). It is concluded that the nucleolar organiser chromosomes 1B1, 6B1, 5HV and 6HV are active. The chromosome 6HV of barley seems to control the nucleolar activity of its homoeologous 6B of wheat judging from the diminution of the Ag-NOR size of chromosome 6B in the corresponding addition line.