A comparison of mutation induction in diploid and tetraploid rice

Summary A comparative assessment of the frequency and spectrum of chlorophyll mutations in the M ₂ and M ₃ of three diploids and one tetraploid of rice after X-irradiation was made. As well as a linear relationship of the frequency of mutations with the dose of mutagen, a saturation effect was also evident. Among the three diploids, the maximum frequency of mutations was observed in T. N. 1, followed by G. E. B. 24 and A. S. D. 8. The diploid of G. E. B. 24 showed a higher frequency of mutations than the tetraploid when measured on the M₁ plant basis only. The diploids showed a higher rate of mutations in the M ₂ than in the M₃.There was no relationship between the frequency of different types of chlorophyll mutations and the dose of X-rays. Albina, occurred in greater proportion than the other types of mutations in the diploids as well as in the tetraploid. The diploid showed a wider spectrum in the M ₂, whereas the tetraploid recorded the maximum types of mutations in the M ₃. Striking differences in the spectrum and the relative frequency of each type were observed among the three diploids and also between the diploid G. E. B. 24 and its tetraploid.The frequency and spectrum of induced mutations in the diploid and autotetraploid provided an insight into the genetic behaviour of the diploid and autotetraploid of G. E. B. 24, indicating that the genetics of diploidisation of the existing diploid rice may give evidence on the nature of the evolutionary pathway.     

RFLP variation in diploid and tetraploid alfalfa

Summary Alfalfa (Medicago sativa L.) is a major forage crop throughout the world. Although alfalfa has many desirable traits, continued breeding is required to incorporate pest resistances and other traits. We conducted this study to determine the amount of restriction fragment length polymorphism (RFLP) variability present within and between diploid and tetraploid alfalfa populations, and whether or not this variability is sufficient for construction of an RFLP map. Diploid plants from M. sativa ssp. falcata, ssp. coerulea, and ssp. sativa and tetraploid spp. sativa cultivars Apollo, Florida 77, and Spredor 2 were included. A total of 19 cDNA clones was probed onto genomic Southern blots containing DNA digested by EcoRI, HindIII, or BamHI. Phylogenetic trees were produced, based on parsimony analysis of shared restriction fragments. Evidence for extensive gene duplication was found; most probes detected complex patterns of restriction fragments. Large amounts of variation are present within all diploid subspecies. M. sativa ssp. falcata plants formed clusters distinct from ssp. sativa or ssp. coerulea plants, which were not distinctly clustered. Some M. sativa ssp. falcata plants were more similar to the other groups than to other plants within ssp. falcata. Variation among tetraploid cultivars showed that Florida 77 and Apollo had more similarities than either showed with Spredor 2. All three cultivars showed large within-population variation, with Apollo being the most diverse and Spredor 2 the least. Based on these results, development of an RFLP map at the diploid level appears possible. Also, differentiation of cultivars, particularly ones of divergent origin, seems possible based on RFLP patterns.     

Desynapsis in diploid and tetraploid clones of ryegrass

Desynapsis is described in diploid and tetraploid plants of perennial ryegrass. The plants were derived by repeated cloning of a single mixoploid (2n=14 and 28) detected among colchicine-treated seedlings. The diploid and tetraploid clones varied in degree of desynapsis, chiasma number, and fertility. The variation among the clones was probably environmental. The progeny of the mixoploid parent included dipoids, tetraploids, and an aneuploid. One diploid and the aneuploid were desynaptic and originated perhaps by selfing. Apparently a single recessive gene determined desynapsis. The role of synaptic genes in controlling the chemical structure and function of nucleoprotein macromolecules is discussed.     

Isozyme gene duplication in diploid and tetraploid potatoes

Summary Isozyme techniques allow the study of gene redundancy in different ploidy levels of potato (Solanum tuberosum). In tetraploid potatoes all isozyme loci are duplicated. No sign of structural or regulatory divergence was found, as is expected due to their tetrasomic inheritance patterns. In addition to this genetic redundancy, produced by a relatively recent polyploidization event, some additional redundancy was found for at least three enzymes even in diploid groups and species. These older duplicate genes show structural and regulatory divergence, indicating they appeared by a separate polyploidization event far in the past. Their common origin is still recognizable by both their expression in the same subcellular compartment and by the dimerizing ability of the isozymes they encode. To account for the present chromosome number x = 12 of the Solanaceae family, the most frequently found among the species, a hypothetical polyploidization event is proposed.     

Call degradation in diploid and tetraploid green toads

According to the 'environmental selection' hypothesis, the physical characteristics of environments influence the evolution of long-range acoustic signals by favouring those properties that decrease sound attenuation and distortion with distance. Different environments could favour different acoustic properties and therefore contribute to the intra- and interspecific variation of calls. In the present paper, we investigate whether this hypothesis could explain the differences between the advertisement calls of three taxa of central-Asian green toads: lowland diploids, highland tetraploids and lowland tetraploids. The pattern of propagation of 12 natural calls (four for each taxon) was analysed in nine localities of Kyrgyzstan and Kazakstan. We broadcast the calls and recorded them along a trasect at distances of 2, 4, 8, 16, and 32 m from the speaker, to estimate sound attenuation and propagation. Attenuation was quantified from the oscillogram (by directly calculating the SPL of calls) and from the power spectrum (by measuring the relative amplitude of the fundamental frequency) , whereas degradation was estimated by cross-correlating spectrograms of the same call at different distances. Results show that: (1) the pattern of sound propagation significantly differs among localities in relation to the different vegetation and environmental noise; (2) in most localities, call attenuation and degradation differ significantly among the three taxa ; (3) such differences are not consistent to those expected under the hypothesis of environmental selection: independent of altitude, lowland tetraploid calls fare worse than both diploid and highland tetraploid calls, whereas diploid and highland tetraploid calls show different patterns of propagation in a few localities only.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 78 , 11–26.     

Correspondence of trichome mutations in diploid and tetraploid cottons

Quantitative variation for leaf trichome number is observed within and among Gossypium species, varying from glabrous to densely pubescent phenotypes. Moreover, economically important cotton lint fibers are modified trichomes. Earlier studies have mapped quantitative trait loci (QTLs) affecting leaf pubescence in Gossypium using allotetraploids. In this study, we mapped genes responsible for leaf trichome density in a diploid A genome cross. We were able to map 3 QTLs affecting leaf pubescence based on trichome counts obtained from young leaves (YL) and mature leaves (ML). When the F(2) progeny were classified as pubescent versus glabrous, their ratio did not deviate significantly from a 3:1 model, suggesting that glabrousness is inherited in a simple Mendelian fashion. The glabrous mutation mapped to linkage group A3 at the position of major QTL YL1 and ML1 and appeared orthologous to the t1 locus of the allotetraploids. Interestingly, a fiber mutation, sma-4(ha), observed in the same F(2) population cosegregated with the glabrous marker, which indicates either close linkage or common genetic control of lint fiber and leaf trichomes. Studies of A genome diploids may help to clarify the genetic control of trichomes and fiber in both diploid and tetraploid cottons.     

Triploid and tetraploid hybrids from diploid x tetraploid crosses in Grindella (compositae)

Crosses between the diploids G. oxylepis var. eligulata Steyermark (Mexico) and G. havardii Steyermark (New Mexico) and the tetraploid G. aphanactis Rydb. (New Mexico) were made. With G. aphanactis as the pistillate parent and G. havardii as the pollen parent a triploid hybrid was obtained in which the maximum meiotic configuration observed was 6m. The plant was 10 % fertile. Two triploid hybrid plants were also obtained when G. aphanactis was used as the pistillate parent and G. oxylepis var. eligulata was the pollen parent. One plant was about 20 % fertile and the other had a maximum configuration of 3_II + 4_III. The reciprocal cross produced a tetraploid which had a maximum configuration of 6_II + 3_IV and was 8 % fertile. The tetraploid plant undoubtedly resulted from the union of an unreduced gamete from the 2n parent and a normally reduced gamete from the tetraploid. Morphology of the hybrids was usually intermediate when compared with the parental species, although some characters in the triploids were those of the diploid parent. Chromosome end arrangements of the respective genomes and putative pairing relationships are presented and phylogenetic implications are discussed. It is concluded that G. aphanactis is more closely related to G. havardii than to G. oxylepis var. eligulata.     

Population size, self-incompatibility and genetic rescue in diploid and tetraploid races of Rutidosis leptorrhynchoides (Asteraceae)

Self-incompatibility systems function to prevent inbreeding, and work effectively in large, genetically diverse populations. However, a decrease in population size can reduce genetic diversity at the self-incompatibility locus, which leads to a reduction in mate availability and has important demographic implications for small populations. Currently, little is known about the response of self-incompatible polyploid species to a reduction in population size. In Rutidosis leptorrhynchoides there was a significant decrease in the within-population probability of fertilization with a decline in population size for diploid populations and a marginally significant relationship for tetraploid populations, suggesting that in small populations of both chromosome races fertilization success is reduced due to a decrease in self-incompatibility allele (S-allele) diversity. There was no significant difference between the slopes of the fertility-population size relationship for diploid and tetraploid populations which indicates a similar rate of decline in fertilization success with population size for both chromosome races. Fertilization success increased when crosses were undertaken between populations and this was significantly related to population size for diploid and tetraploid populations, indicating that small populations gain the greatest benefit to fertilization success from crossing between populations. For tetraploid populations the benefits of crossing between populations tended to decline more rapidly with increasing population size. These results suggest that for small populations that have reduced fertilization success, genetic rescue by introducing new genetic material from other populations is an important means of ameliorating mate limitation issues associated with reduced S-allele diversity in both diploid and tetraploid races.     

Gene dosage effects in human diploid and tetraploid fibroblasts

The effects of cell ploidy on the biochemical characteristics of cultured cells were compared using human diploid vs tetraploid fibroblasts isolated with a non-selective method. Their DNA replication was compared by thymidine incorporation, and DNA content by Feulgen staining and quantitative analysis. Their RNA and protein content, cell sizes and the specific activities of glucose-6-phosphate dehydrogenase (G-6-PD) and 6-phosphogluconate dehydrogenase (6-PGD) were assayed quantitatively. With the exception of RNA content, all other parameters demonstrated a 2-fold increase reflecting the increase in cell ploidy. These direct gene dosage effects on the genetic material and functional expression of the human genome were in contrast to previous observations in other species and validate the use of human intraspecific euploid hybrids for biochemical and genetic studies.     

Pollen release by diploid and tetraploid sugar-beet plants

Pollen released during three summers at Broom's Barn, Suffolk, by diploid and tetraploid multigerm sugar-beet plants was caught by automatic volumetric spore traps and by glass funnels situated in the crop. Tetraploids produced on average 66% as much pollen as diploids, their pollen grains were larger and they needed drier air to release pollen, the concentration of which increased more slowly early in the day and was particularly small on dull, damp days. Pollen catches from diploids and tetraploids decreased at a similar rate with increasing distance from the pollinators. The germination of fruits harvested from male-sterile plants among the pollinators was consistently less with a tetraploid than with a diploid pollinator, but was not affected by distance of the male-sterile plants from either pollinator.     

Meiotic prophase in diploid and tetraploid strains ofAllomyces macrogynus

Summary Three-dimensional serial section reconstructions of meiotic prophase nuclei ofAllomyces macrogynus (Chytridiomycetes, Blastocladiales) have been carried out. Serial section reconstructions of pachytene nuclei have revealed that the fungus when grown at 23 °C is an autotetraploid and is a diploid when grown at 35 °C for at least 6 months or on a substrate containing para-fluorophenylalanine for 1–2 weeks.Studies of the duplication and migration of the centrioles during the first stages of prophase revealed the existence of four centrioles in the 23 °C strain after centriole duplication and two centrioles in the 35 °C strain after duplication. It is observed that a bivalent attaches to the nuclear envelope at a site where a centriole is situated. It is proposed that the presence of the four centrioles in the 23 °C strain is due to the fact that each bivalent is represented twice in the strain.     

Estimation of preferential pairing in tetraploid x diploid hybridizations

Summary Crosses made between tetraploid and diploid, 2n pollen-producing species directly transfer from one-half to the entire diploid genome from the diploid to the tetraploid level, depending on the mechanism of 2n pollen formation and the amount of crossing-over that occurs. Tetraploid plants that result from tetraploid x diploid hybridizations can be further utilized in a breeding program. It is postulated that preferential pairing between homologous chromosomes derived from the original tetraploid or diploid parent occurs in the tetraploid x diploid hybrid. Depending on the genetic divergence of the species involved, preferential pairing of homologous chromosomes may range from zero to one. Theoretical estimates of the amount of preferential pairing and the standard errors of these estimates are derived for cases where the diploid parent produces 2n gametes by either a first division or a second division restitution mechanism.     

Apomixis and sexuality in diploid and tetraploid accessions of Brachiaria decumbens

 Meiotic and aposporous embryo sacs and the initial steps of parthenogenetic embryogenesis and endosperm formation were investigated in diploid and tetraploid accessions of Brachiaria decumbens in two environments, differing mainly in day length: early summer and late autumn. Both diploid and tetraploid accessions were facultative apomicts. Di(ha)ploids showed a much lower level of apomixis (10% to15%) than tetraploids (80% to 95%). No obligate sexual diploids were found; thus, their occurrence in natural populations is obscure. It is suggested that reproduction in B. decumbens, as in other agamic complexes of the Paniceae tribe, in general, approximates a diploid-tetraploid-(di)haploid reproductive cycle which does not involve triploids. The dihaploids were fertile and survived in nature. Development of the reproductive structures depended on the environment. In autumn, in contrast to early summer, many meiotic and aposporous embryo sacs degenerated during development, leading to a significant reduction in the proportion of parthenogenetic embryos. Whether this effect can be attributed to day length or simply to age remains to be investigated. The ratio of aposporous to sexual embryo sacs was relatively stable over the two seasons. Received: 15 April 1998 / Revision accepted: 13 October 1998     

Ribosomal RNA gene variation in diploid and tetraploid Tolmiea menziesii

Evidence from gross morphology, karyology and flavonoid chemistry suggests that Tolmiea menziesii is one of the clearest examples of autopolyploidy in natural populations. To provide additional data regarding the origin of the tetraploid cytotype of Tolmiea, both the 5S and 18S-25S ribosomal RNA genes were studied at the restriction enzyme level. Using restriction enzymes that cut once per repeat, the lengths of the 5S and 18S-25S ribosomal genes were estimated in diploids and tetraploid plants. There appear to be no consistent differences between diploids and tetraploids for the repeat length of the 18S-25S ribosomal genes. Furthermore, there is no significant repeat length heterogeneity within tetraploid plants for these genes. In addition, no differences in repeat length of the 5S genes were observed among the diploid and tetraploid plants analysed. The homogeneity observed among diploid and tetraploid plants for repeat length of the 5S and 18S-25S ribosomal genes is consistent with the hypothesis that the tetraploid cytotype is of autopolyploid origin.     

Developmental potential of mouse tetraploid cells in diploid <--> tetraploid chimeric embryos

Mouse 2n (lacZ-) <--> 4n (lacZ+) aggregation chimeras were examined 5 or 10 days after uterine transfer to test the potential of 4n cells to contribute to embryonic tissues. Recovered embryos corresponded to embryonic day 7.5 approximately 8.0 and 12.5, respectively. Ten days after transfer, 4n cells were never detected, as reported earlier, in embryonic tissues of chimeras produced by the standard procedure in which one 2n embryo at the8-cell stage is aggregated with a4n embryo at the4-cell stage. However, beta-gal positive cells were present in embryonic tissues, though in a low number, in chimeras produced by a 2n and a 4n embryo at the 4-cell stage. Similar results were obtained when one 2n embryo atthe 8-cell stage was aggregated with two 4n embryos atthe 4-cell stage. beta-gal positive cells were found in the heart, liver, skin and intestinal epithelium. The majority of chimeras 5 days after uterine transfer retained beta-gal positive cells in embryonic tissues. The complete lack of 4n cell contribution to chimeras produced by the standard procedure is therefore attributed to the initial low proportion of 4n cells allocated to epiblast and their severe elimination from embryonic tissues.     

Nucleolar variations during the ontogenesis of diploid and tetraploid cyprinid species

Studying the quantitative characteristics of nucleoli in cells of several cyprinid species ( Cyprinus carpio, Carassius auratus gibelio, Carassius auratus auratus, Aristichthys nobilis, Ctenopharyngodon idella, Hypophthalmichthys molitrix ) has shown a definite programme that controls genetically changes in the nucleolar characteristics during fish ontogenesis. In embryogenesis, the nucleolar activity, which has been estimated from the number and size of nucleoli, decreased; this process was realized dissimilarly in diploid and tetraploid cells. A correlation between the nucleolar characteristics and the body mass of juvenile fish was found. Parameters of the nucleolar activity were closely related to the physiological state of mature organisms and featured tissue specificity, rhythmicity, and high level of heritability.