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Chromosome pairing of standard B chromosomes (Bs) in rye has been studied by synaptonemal complex surface spreading of pollen mother cells containing from one to eight Bs. The main characteristics exhibited by the Bs are: (i) They are often located peripherally in surface spread nuclei and do not show presynaptic alignment. (ii) The period of pairing is delayed relative to that of the A set. (iii) Bs undergo extensive non-homol-ogous pairing at pachytene. (iv) The frequency of trivalents and quadrivalents in plants with 3Bs and 4Bs is about 66% following the expectations on the basis of random pairing among the short and the long arms with a single distal pairing initiation site per arm. Some quadrivalents containing two partner switches were observed, but on the same basis of randomness there was a deficiency of pachytene multivalents in plants with 5–8 Bs. The possible causes of the discrepancy between these observations are discussed. (v) There is a reduction in the frequency of multivalents between pachytene and metaphase I.

In order to elucidate the possible effects of rye B chromosomes (Bs) on synapsis and metaphase-I associations of the A set, a comparative study between pachytene and metaphase-I-cells of rye plants carrying different numbers of Bs (0–8) has been carried out. The number of Bs was found to be positively correlated with the frequency of synaptic irregularities of the A set, i.e. multivalents and foldback pairing, and with the frequency of pachytene interlockings. It is proposed that interlockings are the origin of these irregularities because both appeared in close proximity in many nuclei. Examples of A-B pairing are described. The frequency of synaptic abnormalities seems to be unrelated to the mean of A chromosome-bound arms at metaphase I.

A new feature affecting the transmission rate of rye B chromosomes is described. Progenies of 0B × 2B, 2B × 0B and 2B × 2B crosses were studied, considering both the B chromosome number of the plants crossed and that of their maternal parents. A remarkably large variation within these progenies was observed. The variation found in 0B × 2B crosses was mainly due to the effect of the maternal parent of the males and females involved: pollen grains formed in 2B plants whose maternal parent had 2Bs transmitted B chromosomes at high frequency; 0B plants whose maternal parent had 2B, accepted pollen with Bs at high frequency. Conversely, 2B males and 0B females with 0B maternal parent, formed progeny with B chromosomes at a much lower frequency.A very large variation in B chromosome frequency was also observed in progenies of 2B × 0B crosses although in this case the maternal parent of 2B females does not seem to be the cause of such variation.The observed progenies of 2B x 2B crosses fitted with expectations only when the effect of the maternal parent of the plants used for crosses was considered. The interaction between females having a 2B maternal parent with 2B pollen, and the effect of the male maternal parent was also evident in this case.It seems that 2B chromosomes produce an imprinting in plants, in such a way that all their descendants can be recognised whether they carry Bs or not. The frequency of transmission of B chromosomes is increased through the plants with a 2B maternal parent. A 0B maternal parent causes the transmission frequency to decrease. We believe that these interactions have an important effect at the population level on the maintenance of the polymorphism for B chromosomes.Heredity (1990) 64, 197–204; doi:10.1038/hdy.1990.24

High performance liquid chromatography (HPLC) was applied to study the behavior of a series of 1-hydroxy-imidazole-3-N-oxides (HIO) in solution. Some thermodynamic parameters influencing solute retention were determined from the temperature dependence of the capacity factor (k). A linear relation was derived between k and molecular parameters considering intermolecular association, which was predicted and confirmed. ΔGads values are also highly correlated with connectivity index, molar refractivity and Van der Waals volumes. Retention data for twenty closely related imidazoles were measured and analyzed in relation to hydrophilic parameters.

Twenty ♀ 0B × ♂ 2B crosses were made in which a single male was crossed with four different females, and the character 'mean number of Bs per plant in the progeny' was analysed. The 2B plants used as males and the 0B females belonged either to low or to high transmission rate lines, previously selected. The genetic basis of the difference between the high and low transmission rate lines was statistically tested. The male group (high or low class of the 2B male) has a significant effect on the progeny, while the female group (high or low class of the 0B female) has no significant effect. The genes controlling the transmission rate of B chromosomes affect the proportion of 0B vs. 2B plants in the 0B × 2B cross, but this is not a result of any effect on the nondisjunction mechanism, since the proportion of 1B plants is low in all cases. Structural variants of B chromosomes appeared de novo at a high frequency.Heredity (1995) 74, 518–523; doi:10.1038/hdy.1995.73

Pairing of B isochromosomes in rye was studied by surface spreading of synaptonemal complexes in pollen mother cells from plants containing one small iso-B (iso-BS), one large iso-B (iso-BL), two iso-BL, one iso-Bsplus one standard B (iso-BS+stB), one iso-BSplus two standard Bs (iso-BS+2 stB) and one iso-BLplus two standard Bs (iso-BL+2 stB). The main characteristics of iso-Bs were as follows. (1) Their location in the surface-spread nuclei was peripheral. (2) Their period of pairing relative to that of the A-set was delayed. (3) The commonest pachytene configuration was a symmetrical hairpin loop, although they could also undergo nonhomologous synapsis. (4) Synapsis could start at the chromosome ends, at the putative centromeric region or at both regions more or less simultaneously. (5) The frequency of iso-BLbivalents was only 46 per cent rather than the 66 per cent predicted by the random-end-pairing model. Interchromosomal pairing was frequent in these configurations. (6) In pairing competition situations involving three and four doses of the short arm of the standard B (iso-BS+stB, iso-BS+2 stB), a large predominance of self-synapsed iso-BSunivalents (63 per cent and 80 per cent respectively) was found. On the other hand, there was no apparent pairing preference among four doses of the long arm of the standard B in the iso-BL+2 stB combination. Similarities and differences between the synaptic behaviours of iso-Bs of Crepis capillaris and Secale cereale are discussed.Heredity (1995) 74, 100–107; doi:10.1038/hdy.1995.12

Extensive synaptonemal complex formation was found at prophase I in whole mount spread preparations of a spontaneous haploid rye, Secale cereale, with values of up to 87.8 per cent of the chromosome complement synapsed. Pairing-partner switches were frequent, giving rise to multiple associations in which all or most of the chromosomes were involved. However, the distribution of synaptonemal complex stretches suggests that synapsis does not occur at random. The frequency of multivalents and the mean frequency of bonded arms at metaphase I were 0.03 and 0.39, respectively. Associations between chromosome arms without heterochromatin were more frequent than between the remaining arms. The observation of recombinant chromosomes for telomeric C-bands at anaphase I indicates that metaphase I bonds are true chiasmata. The correspondence between the location of pairing initiation sites and chiasmata indicates that early synapsis could be confined to homologous regions.Heredity (1994) 73, 580–588; doi:10.1038/hdy.1994.165

Selection for plants showing low or high transmission rates of B chromosomes demonstrates the existence of genotypes which affect this character. The results suggest that the gene or genes involved in this control are located in the A chromosomes. It is shown that plants from the low transmission rate class tend to lose ? chromosomes, while plants from the high transmission rate class tend to accumulate Bs. It is therefore concluded that these genotypes can influence the frequency of B chromosomes in different populations.Heredity (1991) 66, 61–65; doi:10.1038/hdy.1991.8

B-chromosomes from an experimental population of the Japanese JNK strain of rye, isogenic for its Bs, have been backcrossed into twelve different inbred lines. The experiment provides a way to study the effects of the Bs against a range of homozygous A-chromosome backgrounds. This publication deals with vigour and fertility: it shows that the rye Bs fit a parasitic model, and that they interact in their effects with the A-chromosome background genotype.

B chromosomes from an experimental population of the Japanese JNK strain of rye, isogenic for its Bs, have been backcrossed into twelve different inbred lines. The experiment is a way of studying the effects of the Bs against a range of different homozygous A chromosome backgrounds. This publication deals with pairing effects of both the As and the Bs, and their interactions, and with pollen mitosis. At meiosis there is a genotypic component to B effects, and they do not appear to act solely through a physical disturbance within the nucleus. In pollen the Bs are always present in more than 50% of the grains regardless of their pairing behaviour during meiosis; this result fits with a ‘parasitic’ model of the activity of rye Bs.

Sulfapyridine is used to test the extended Hildebrand approach for predicting solubility in dioxane-water mixtures. The method provided good agreement with the experimental data. A modification of this method, that directly relates the logarithm of the mole fraction solubility with the solubility parameter of the solvent mixture (δ1) gave results comparable to that of the extended Hildebrand approach. This suggests that the volume fraction of the solvent can be disregarded in the solubility equation. The modified method does not require the knowledge of the ideal solubility of the drug. A single equation based on the solubilities of several sulfonamides is able to accurately calculate the solubility profile of sulfapyridine from 0 to 70% water in dioxane. Beyond 70% water, the extended Hildebrand method or its simplified form provide less errors, but these methods require 12-14 experimental solubilities, whereas the single equation only needs two experimental solubilities.

Electrochemical techniques have attracted much attention in the last decade for oxidative and reductive desulfurization because they require less drastic conditions of temperature and pressure in comparison to other processes that are used for desulfurization. It is known that dibenzothiophene (DBT) can be oxidized progressively to dibenzothiophene sulfoxide (DBTO) and dibenzothiophene sulfone (DBTO2). However, it is interesting to know whether a more complete oxidation of DBTO2is possible by electrochemical treatment in a liquid-liquid two-phase system.