Effect of high temperature on meiosis in Lolium: Nucleolar inactivation

Examining the Effects of Temperature on Recombination in Wheat

Meiotic recombination plays a crucial role in the generation of new varieties. The effectiveness of recombination is limited by the distribution of crossover events, which in wheat and many other crops is skewed toward the distal regions of the chromosomes. Whole-genome sequencing of wheat has revealed that there are numerous important genes in the pericentromeric regions, which are inaccessible to manipulation due to the lack of crossover events. Studies in barley have shown that the distribution of recombination events can be shifted toward the centromeres by increasing temperature during meiosis. Here we present an analysis of the effects of temperature on the distribution and frequency of recombination events in wheat. Our data show that although increased temperature during meiosis does cause an inward shift in recombination distribution for some chromosomes, its overall utility is limited, with many genes remaining highly linked.

The effect of B-chromosomes of rye on the chromosome association in F1 hybrids Triticum aestivum x Secale cereale in the absence of chromosomes 5B or 5D

T. aestivum var. 'Chinese Spring' (monosomic 5B and 5D, respectively) was crossed with S. cereale (with and without B-chromosomes). The resulting nullisomic 5B hybrids exhibited a high degree of chromosome association both at 20°C and 10°C. The presence of B-chromosomes reduced association slightly whether 5B was present or not.In nullisomic 5D hybrids B-chromosomes of rye raise chromosome association at 20°C when compared to hybrids with 5D, with as well as without, B's. At 10°C, due to the absence of the Ltp gene on 5D, chromosome association in nullisomic 5D hybrids is low, and no effects of rye B-chromosomes is detectable.The hypothesis that B-chromosomes of rye carry (an) asynaptic gene(s) decreasing effective pairing, and (an) independent post-synaptic gene(s) increasing chiasma frequency on effective pairing sites, is presented.

GENOTYPIC INTERACTION FOR CHIASMA FORMATION AT LOW TEMPERATURE IN THE HYBRID BETWEEN TRITICUM AESTIVUM 'CHINESE SPRING' AND AEGILOPS SPELTOIDES DEFICIENT FOR CHROMOSOME 5D

In F1 plants from crosses between Triticum aestivum var. 'Chinese Spring' monosomic 5D and Aegilops speltoides Tausch. var. aucheri (Boiss) it was found that at a temperature of 12 °C the presence of chromosome 5D is necessary to maintain the level of homoeologous pairing and chiasma formation observed under greenhouse conditions. Some genotypes of Ae. speltoides, however, were more efficient than others in compensating for the absence of chromosome 5D. The differences in compensating ability indicate the existence of several alleles in Ae. speltoides that counteract the low-temperature pairing system on chromosome 5D. An analogous system of alleles previously reported in Ae. speltoides that suppresses the chromosome 5B diploidising system of wheat was substantiated by the present study. The results indicate, however, that the two systems are independent.

THE EFFECT OF TEMPERATURE ON MEIOSIS AND POLLEN DEVELOPMENT IN WHEAT AND RYE

The durations of meiosis and pollen development were estimated in Petkus Spring rye and Chinese Spring wheat grown at 15, 20 and 25 °C. Over the range 15-25 °C, meiotic duration and pollen maturation time decreased with increasing temperature and the ratio between the durations of these stages at 25 °C and at 15 °C (Q10) indicated that the temperature responses of meiotic and pollen development were similar in both species. Both within and between species meiosis and pollen maturation had constant relative durations at each temperature. The effect of low temperature on the duration of meiosis and pollen development was similar in Holdfast, an extreme type of winter wheat, as in Chinese Spring. The relevance of these results to hybrid cereal breeding are mentioned. In plants grown at 25 °C, abnormal meiotic and pollen development resulting in male sterility was seen in some anthers. The cause of male sterility appeared to be thickening of tapetal cell walls concurrent with abnormal late meiotic development in PMC's.

MORPHOLOGY OF THE PACHYTENE CHROMOSOMES IN PRUNUS PERSICA

Morphology of the pachytene chromosomes was studied in three genotypes of Prunus persica (L.) Batsch. Each of the eight bivalents has been identified by its distinctive morphological features such as length, position of the centromere, and distributional pattern of the heterochromatic chromomeres. On the basis of total length the chromosomes were numbered from one to eight, the last being the shortest of the complement. In all bivalents the heterochromatin is clustered around the centromere. The chromosomes of the three clones are alike. A heterochromatic knob is present in the distal part of the shorter arm of chromosome five from 'Raritan Rose'. This knob was not present in the other two genotypes studied.Two pairs of chromosomes participate in the organization of a single nucleolus. At pachytene and later stages of prophase, small nucleoli-like bodies associated with or close to the bivalents were frequently observed.

Cytological investigation of Triticale

A cytological investigation of 15 different 56-chromosome Triticale and 16 Triticale with 42 chromosomes was carried out. 4 were primary Triticale and 12 were secondary Triticale. Chromosome pairing was not disturbed; 21 and 28 bivalents were found in the hexaploids and octoploids, respectively. Meiotic irregularities were established, however, in all the Triticale studied; in octoploids the frequency of the irregularities was 22-88% and in hexaploids it was 12-87%.In metaphase and anaphase asynchronous separation of chromosomes was noted. Incompatibility between wheat and rye genomes and the inactivation of single loci of rye chromosomes are suggested as the main causes of the irregularities in meiosis.Mitotic disturbances were found in all the amphidiploids. The frequency of anomalies in mitosis was considerably lower than in meiosis: in octoploids they made up 5%-11% and in hexaploids 6.2%-15.2%. In all the amphidiploids studied chimera plants were found containing pollen mother cells with different chromosome numbers. The chromosome number in the aneuploid cells varied from 8-48 in hexaploids and from 8-62 in octoploids. Octoploid Triticale had 29.4%-72.9% aneuploid pollen mother cells, while hexaploid Triticale had 5-2%-55-7%.

RNA and protein in nucleolar structures of dragonfly oocytes

Dragonfly and damselfly oocytes regularly contain two nucleolus like bodies of different sizes, a primary nucleolus and a secondary nucleolus. The primary nucleolus stains more deeply with RNA stains than with an arginine stain; the seconidary nuicleolus stains conzversely. The primary nulcleolus incorporates uridine under all conditions tested; the secondary, only after precautions have been taken to preserve soluble RNA. Both inicorporate lysine.