紫花含笑（♀）、灰岩含笑（♂）及其杂种F1代花粉萌发试验研究

对紫花含笑(Michelia crassipes)、灰岩含笑(M.calcicola)及其杂种F1代花粉生活力进行了研究,为基于紫花含笑和灰岩含笑杂种F1代的含笑属观赏植物新品种培育与种质创新提供科学数据及研究资料.研究发现,亲本(紫花含笑和灰岩含笑)新鲜花粉萌发率均可达90％以上,杂种F1代花粉萌发率从38％到79％不等,平均为57.7％,低于双亲.亲本及其杂种F1代花粉萌发的最适温度为25℃,温度过高花粉管的伸长受到抑制,并导致花粉管顶端破裂.亲本及多数杂种F1代的新鲜花粉在100 g/L和150 g/L的蔗糖浓度下萌发率都较高;经-20℃贮藏后的花粉对蔗糖浓度的敏感性要高于新鲜花粉.杂种F1代及其亲本的花粉在离体培养中均会出现双萌发管现象.番红染料对液体培养基中的花粉有致死和染色作用,有利于统计杂种F1代及其亲本的花粉萌发率.     

4种杂交杨对土壤水分变化的生态学响应

以田间持水量的100% (T1, 对照)、70% (T2)、50% (T3)和30% (T4)为4个水分处理梯度, 比较研究了4种不同品系的杂交杨(Populus)——15-29 (P. trichocarpa × P. deltoids)、DN-2 (P. deltoids × P. nigra)、DN-14274 (P. deltoids × P. nigra)和R-270 (P. deltoids × P. nigra)在不同水分处理和不同处理阶段对水分亏缺的反应。结果表明, 4种杂交杨品系对水分亏缺较敏感, 都通过关闭气孔、降低叶面积以有效地调节水分的散失, 降低光合速率、蒸腾、水势, 增加水分利用效率, 改变生物量的分配等一系列生理适应机制以及形态策略, 来应对不同程度的水分亏缺, 只是不同品系的适应程度不同。在生物量分配上, R-270主要降低叶干重, 而其它3个品系的叶、茎和根干重全部降低; 随着水分亏缺的加重, 15-29和R-270的根冠比增加, 根部获得更多的同化物分配, 从而有利于水分的吸收, 增加其抗旱性。DN-2的碳同位素组成δ¹³与水分利用效率呈显著正相关(r= 0.631, p<0.01)。而R-270的δ¹³与水分利用效率呈负相关, 但不显著, 只有在处理T4下呈显著负相关(r= -0.732, p<0.01), 表明土壤水分影响了碳同位素的分馏, 不同品系相反的结果表明同位素分馏的遗传变异。与T3和T4相比, T1和T2处理的苗木具有较高的生物量、叶面积、光合速率、蒸腾、水势以及气孔导度, 说明4个杂交杨品系在充足或适当的灌溉条件下具有较高的生产力。在T3和T4处理下, 4个品系表现出不同的生存策略, 但生产力均较低, 因此在干旱胁迫下很难形成高生产力。与DN-2和DN-14274相比, 15-29和R-270对水分胁迫表现出更强的适应性反应, 具有较强的抗旱性, 可用作防护林品种。     

Subgenome analysis of two southern hemisphere allotriploid species in Sphagnum (Sphagnaceae)

Sphagnum ×australe s.l. and S. ×falcatulum s.l. are both cryptic species complexes of gametophytically allodiploid and allotriploid cytotypes, with the allodiploid cytotype being one parent of the respective allotriploid cytotype. Phylogenetic analyses of S. ×australe s.l. and S. ×falcatulum s.l. were undertaken using sequences from two plastid loci and cloned sequences from three nuclear loci. Subgenomes from three subgenera were detected in allotriploid S. ×australe. The haploid parent of allotriploid S. ×australe was S. fimbriatum (subg. Acutifolia). One of the two subgenomes contributed by allodiploid S. australe was associated with S. strictum (subg. Rigida); the parental species associated with the other subgenome could not be identified, either at the species level or in terms of subgenus association. It may represent an early diverging lineage of subg. Sphagnum or a previously undetected subgenus. Allotriploid S. ×falcatulum has subgenomes from two subgenera. This study confirms prior findings that S. cuspidatum (subg. Cuspidata) was the haploid parent of allotriploid S. ×falcatulum. One of the two subgenomes contributed by allodiploid S. ×falcatulum was associated with subg. Cuspidata (species unidentified) and the second was associated with subg. Subsecunda (species unidentified). Recurrent allopolyploidy appears to have been associated with the complex evolutionary processes (inter-subgeneric hybridization, interploidal hybridization, double allopolyploidy) which resulted in each of these two allotriploids. The highest level of divergence detected among the subgenomes in each of these Sphagnum allotriploids is comparable to the average genetic divergence reported for angiosperm allopolyploids.     

Analysis of production,early growth and survival ofClarias gariepinus (Burchell),Heterobranchus longifilis (Val.) (Pisces: Clariidae) and their F1 hybrids in ponds

Clarias gariepinus andHeterobranchus longifilis were successfully hybridized to produce reciprocal F₁ progeny during a two-year study.C. gariepinus produced significantly heavier spawn thanH. longifilis during the same period. Fertilized eggs were incubated in aerated static-water in fibre-glass troughs, and hatching rates were not found to be significantly different (P<0.05) between any two of the four catfish groups produced. Eight-day old fry of each group were reared in fertilized nursery ponds, and F₁ hybrids fromH. longifilis maternal parent had the best growth and survival rates at the end of 18 days. The reciprocal cross showed intermediate growth rate between both parents. At harvest, differential growth was less pronounced among both hybrids than among the parents.     

Sen1 Is Recruited to Replication Forks via Ctf4 and Mrc1 and Promotes Genome Stability

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Genomic instability in interspecific cell hybrids III. Repression of Colcemid resistance in hybrids suggests preferential β-tubulin expression

A Colcemid-resistant Chinese hamster line with an altered form of β-tubulin was used in studies of the expression of spindle proteins in interspecific cell hybrids. Eight hybrids between this line, and a Colcemid-sensitive mouse cell line, were studied. The altered hamster β-tubulin was not expressed as an increased resistance to Colcemid in any hybrid. Since the complete hamster chromosome complement was represented among the hybrids, the absence of altered β-tubulin is not due to segregation of the mutant hamster β-tubulin gene. We suggest either that the hamster β-tubulin gene is repressed in hybrids, or that hamster β-tubulin is excluded from the spindle in hybrid cells. We compare these findings with previous reports of the repression of other highly active, moderately repeated constitutive genes in interspecific hybrids.     

Distribution and morphological characters of intermediate forms between the black lemur (Eulemur macaco macaco) and the Sclater's lemur (E. m. flavifrons)

A study of intermediate forms betweenEulemur macaco macaco andE. m. flavifrons was performed on animals in different areas located to the north, south, and east of the known limits of distribution in Maromandia. A large hybridization zone was defined and morphological and dermatoglyphic comparisons were done on the different animals.     

Chromosomal relationships among cultivars of Citrus reticulata Blanco, its hybrids and related species

Karyotypes of 93 individuals belonging to 18 accessions of mandarins, mandarin hybrids and two related species were analysed with the fluorochromes CMA and DAPI, to identify marker chromosomes. The karyotypes revealed highly differentiated banding patterns and could be classified in four groups (I–IV) according to the presence/absence of chromosomes with three bands (type A) or with two bands (one proximal and one terminal, type B, or both terminal, type C). The accessions of group I exhibited the simplest and homozygous karyotypes (lacking chromosome types A, B and C), represented by `Sunki' and `Cleopatra'. Group II (lacking chromosome types A and B) included three accessions of Mediterranean mandarins and `Cravo' mandarin, all of them with very similar and almost completely homozygous karyotypes. All other karyotypes of groups II and III (lacking chromosome type A) were heterozygous for one or more chromosome pairs and most of them seemed to be hybrid derivatives from non-mandarin accessions. Group IV (with chromosome types A and B) was represented only by two heterozygous hybrids (`Murcott' and `King'). The karyotype of most hybrids agrees with one of the possible combinations resulting from chromosome types segregation from their putative ancestor karyotypes, but at least `Orlando' seemed to be a more complex hybrid. Comparing with banding patterns of other Citrus species, those of group I and the Mediterranean mandarins (group II) are the best candidates to represent C. reticulata (sensu Swingle) as a true species.     

The shock of being united and symphiliosis

A common view is that an accidental increase in ploidy contributes to the evolution of neoplastic cells primarily by decreasing the fidelity of mitosis with extra chromosomes and centrosomes. This view implies that how neoplastic cells become polyploid is irrelevant, as it has been widely assumed. If this assumption is correct, then the oncogenic contribution of the pathways to polyploidy and thus their potential as targets for cancer prevention is determined by their incidence in the body. A lesson from plant evolution, in which an accidental increase in ploidy has a prevalent role, suggests that this assumption needs to be reconsidered.