A comparative cytogenetic study of the rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) autotetraploid restorers and hybrids

We studied pollen fertility, seed set and cytogenetic characteristics of restorer lines and F1 hybrids of autotetraploid rice. T4002, T4063, T461A × T4002 and T461A × T4063 showed significantly higher pollen fertility and seed set than T4132 and T461A × T4132. Meiotic pairing configurations of T4002, T4063, T4132, T461A × T4002, T461A × T4063 and T461A × T4132 were 0.05 I + 19.96 II (9.89 rod + 10.07 ring) + 0.01 III + 2.00 IV, 0.11 I + 19.17 II (8.90 rod + 10.37 ring) + 0.09 III + 2.26 IV + 0.01 VI, 1.34 I + 9.46 II (4.50 rod + 4.96 ring) + 0.80 III + 6.02 IV + 0.09 VI + 0.09 VIII, 0.02 I + 14.36 II (6.44 rod + 7.91 ring) + 0.01 III + 4.80 IV + 0.01 VIII, 0.06 I + 17.67 II (11.01 rod + 6.67 ring) + 0.06 III + 3.10 IV + 0.01 VI and 1.11 I + 11.31 II (5.80 rod + 5.51 ring) + 0.41 III + 5.63 IV + 0.03 VI + 0.03 VIII, respectively. Configuration 16 II + 4 IV and 12 II + 6 IV occurred in the highest frequency among the autotetraploid restorers and hybrids. Meiotic chromosome behaviors were less abnormal in the tetraploids with high seed set than those with low seed set. The hybrids had fewer frequencies of bivalents, univalents, trivalents and multivalents than the restorers, but higher frequency of quatrivalents than the restorers at MI. The frequency of univalents at MI had the most impact on pollen fertility and seed set, i.e., pollen fertility decreased with the increase of univalents. The secondary impact factors were trivalents and multivalents, and bivalents and quatrivalents had no effect on pollen fertility and seed set. The correlative relationship between pollen fertility and cytogenetic behaviors could be utilized to improve seed set in autotetraploidy breeding.     

Cytological studies on meiosis and male gametophyte development in autotetraploid cucumber

With improved staining and chromosome preparation techniques, meiosis of pollen mother cells (PMCs) and male gametophyte development in autotetraploid cucumber (Cucumis sativus L.) was studied to understand the correlation between chromosomes behaviour and fertility. Various chromosome configurations, e.g. multivalent, quadrivalents, trivalents, bivalents and univalents were observed in most PMCs at metaphase I. Lagging chromosomes were frequently observed at anaphase in both meiotic divisions. In addition, chromosomes segregations were not synchronous and equal in some PMCs during anaphase II and telophase II. Dyads, triads, tetrads with micronuclei and polyads were observed at tetrad stage, and the frequencies of normal tetrad with four microcytes were only 55.4 %. The frequency of abnormal behaviour in each stage of meiosis was counted, and the average value was 37.2 %. The normal meiotic process could be accomplished to form the microspore tetrads via simultaneous cytokinesis. Most microspores could develop into fertile gametophytes with 2 cells and 3 germ pores through the following stages: single-nucleus early stage, single-nucleus late stage and 2-celled stage. The frequency of abnormalities was low during the process of male gametophyte development. The germination rate of pollen grains was 46.9 %. These results suggested that abnormal meiosis in PMCs was the reason for low pollen fertility in the autotetraploid cucumber.     

同源四倍体水稻恢复系TP-4和D明恢63与保持系D46B的细胞遗传学比较

以高结实率的同源四倍体水稻恢复系TP-4和D明恢63及优良保持系D46B为材料进行细胞遗传学研究。所有四倍体材料的染色体组成均为2n = 48, 这与有丝分裂的结果一致。恢复系TP-4和D明恢63及保持系D46B的中期Ⅰ单价体和三价体的比例都很低, 配对染色体的比率在99%以上, 具有优良的细胞学特征。恢复系TP-4和D明恢63在中期Ⅰ四价体频率分别为2.00/PMC和2.26/PMC, 而保持系D46B在中期Ⅰ四价体频率为6.00/PMC, 极显著地高于恢复系品系因而具有更好的染色体配对性质; 后期Ⅰ保持系D46B的染色体滞后频率为10.62%, 远低于恢复系材料TP-4的19.44%和D明恢63的23.14%, 接近二倍体对照明恢63的7.30%水平; 末期Ⅰ保持系D46B具有比恢复系更低频率的微核数而末期ⅡD46B的正常四分小孢子比率不但高于恢复系品系甚至高于二倍体对照。相关分析表明后期Ⅰ染色体滞后细胞比率同末期Ⅰ异常细胞比率呈极显著的正相关, 推测后期Ⅰ染色体分离和末期Ⅰ微核形成可能是由相同的显性单基因或主效基因控制。     

Association between chemical and genetic variation in Calophyllum inophyllum, a medicinally important tree of the Western Ghats of India

Intersubspecific autotetraploid rice hybrids have high heterosis in both vegetative and reproductive growth, but low seed set hinders commercial utilization of autotetraploid rice. Autotetraploid rice hybrids with high and low pollen fertility were used in the present study to compare microtubule distribution patterns and chromosome behavior during pollen mother cell (PMC) meiosis, using indirect immunofluorescence laser scanning confocal microscopy. Microtubule distribution patterns of autotetraploid hybrids were similar to diploid rice, but many different kinds of abnormalities were found in the hybrid with low pollen fertility and seed set. Abnormal microtubule organization including structurally distorted microtubules at pachytene, loosely knitted perinuclear microtubules at diakinesis during prophase?I, and abnormal spindles, viz. multipoles, loss of spindle pole focus, abnormal size of spindles, and so on, were found at metaphase?I and metaphase?II. Some cells developed into triad with no formation of tetrad. Abnormal chromosome behaviors included high percentage of multivalents, chromosome lagging, chromosome bridges, and micronuclei. All these abnormalities were found more frequently in low-fertile hybrid than in high-fertile hybrid. These results suggest that abnormal microtubule distribution pattern is an important factor which affects pollen fertility and percentage seed set in autotetraploid rice, and may also have a close relationship with chromosome behavior.     

Cytogenetic studies on <Emphasis Type="Italic">Metasequoia glyptostroboides</Emphasis>, a living fossil species

The chromosome morphology and meiotic pairing behavior in the pollen mother cells (PMCs) of Metasequoia glyptostroboides were investigated. The results showed that: (1) The chromosome number of the PMCs was 2n=22. (2) The PMCs developed in the successive manner, and the nucleoids in the dynamic development were similar to those of the other gymnosperms. (3) At prophase, most of the chromosomes were unable to be identified distinctively because the chromosomes were long and tangled together. The chromosome segments were paired non-synchronously. At pachytene, the interstitial or terminal regions of some bivalents did not form synapsis and the paired chromosomes showed difference in sizes, indicating that there were structure differences between the homologous chromosomes. (4) At diakinesis, the ring bivalents showed complicated configurations due to the differences in location and number of chiasmata. In addition, there were cross-linked bivalents. (5) At metaphase I, the chromosome configuration of each cell was 8.2II ⁰ + 1.1II + 1.3II ⁺ + 0.8I. Most of the chromosomes were ring bivalents, but some were cross-linked bivalents, rod bivalents, or univalents. (6) 15\% PMCs at anaphase I and 22\% PMCs at anaphase II presented chromosome bridges, chromosome fragments, micronuclei, and lagging chromosomes. Twenty seven percent microspores finally moved into one to three micronuclei. Twenty five percent pollens were abortive. The results indicated that the observed individual of M. glyptostroboideswas probably a parpcentric inversion heterozygote, and there were structural and behavioral differences between the homologous chromosomes. The chromosomal aberration of M. glyptostroboidesmay play an important role in the evolution of this relict species, which is known as a living fossil. Further evidence is needed to test whether the differences between homologous chromosomes were due to hybridization.     

Mitotic and meiotic irregularities in somatic hybrids of Lycopersicon esculentum and Solanum tuberosum.

Chromosome numbers were determined in metaphase complements of root-tip meristems of 107 tomato (+) potato somatic hybrids, obtained from five different combinations of parental genotypes. Of these hybrids 79% were aneuploid, lacking one or two chromosomes in most cases. All four hybrids that were studied at mitotic anaphase of root tips showed laggards and bridges, the three aneuploids in a higher frequency than the single euploid. Hybrid K2H2-1C, which showed the highest percentage of aberrant anaphases, possessed 46 chromosomes. Fluorescence in situ hybridization with total genomic DNA showed that this hybrid contained 23 tomato, 22 potato, and 1 recombinant chromosome consisting of a tomato chromosome arm and a potato chromosome arm. The potato parent of K2H2-1C was aneusomatic in its root tips with a high frequency of monosomic and trisomic cells and a relatively high frequency of cells with one fragment or telosome. Meiotic analyses of three tomato (+) potato somatic hybrids revealed laggards, which occurred most frequently in the triploid hybrids, and bridges, which were frequently present in pollen mother cells (PMCs) at anaphase I of hypotetraploid K2H2-1C. We observed putative trivalents in PMCs at diakinesis and metaphase I of eutriploid A7-82A and quadrivalents in part of the PMCs of hypotetraploid K2H2-1C, suggesting that homoeologous recombination between tomato and potato chromosomes occurred in these hybrids. All three hybrids showed a high percentage of first division restitution, giving rise to unreduced gametes. However, shortly after the tetrad stage all microspores completely degenerated, resulting in exclusively sterile pollen.     

Cytogenetic studies on microsporogenesis and male gametophyte development in autotriploid cucumber (Cucumis sativus L.): implication for fertility and production of trisomics

To understand the correlation between chromosomes behavior and fertility in autotriploid cucumber (Cucumis sativus L.), microsporogenesis in pollen mother cells (PMCs) and male gametophyte development were studied using improved staining and chromosome preparation techniques. Meanwhile, for more efficient selection of trisomics from the progeny of autotriploid-diploid crosses, fertilization rates of ovules from reciprocal crosses were counted to observe the transfer rate of gametes in the autotriploid cucumber. Variable chromosome configurations, e.g. multivalents, quadrivalents, trivalents, bivalents and univalents were observed in the most PMCs of the autotriploids at metaphase I. Chromosome lagging and bridges at anaphase in both meiotic divisions resulted from irregular chromosome separation and asynchronization was frequently observed as well, which led to formation of micronuclei and inviable gametes. The frequency of normal PMCs in autotriploids at the stage of tetrad was only 40.6%. Among those normal microspores, most of them (91.2%) could develop into normal gametophytes with 2 cells and 3 germ pores. Stainability and germination rate of pollen grains were only 18.8 and 13.5%, respectively. However, chromosomes separated to form gametes with 8 chromosomes at anaphase I, suggesting a possible method for the production of primary trisomics from the progeny of autotriploid-diploid crosses. Fruit set of 3n × 2n and 2n × 3n were 80 and 70%, respectively. It obtained an average of 6.2 plump seeds per fruit in 3n × 2n, while 4.9 in 2n × 3n crosses. Transfer rates of gametes through the gastrula or the pollen in autotriploids were 13.4 and 10.4%, respectively. Some aneuploid gametes (n + 1 = 8, n + 2 = 9) also have capability of setting seed and sexual reproduction besides normal gametes containing whole chromosome sets (n = 7, 2n = 14). Further, some primary trisomic plants were selected from the progeny of autotriploid-diploid crosses. Based on the results obtained we suggest that abnormal meiosis in PMCs was the cytogenetic reason for low fertility of autotriploid cucumber pollen. 3n × 2n cross was more efficient for selecting primary trisomic plants in cucumber.     

Cytogenetic and molecular characterization of intergeneric hybrids between Brassica napus and Orychophragmus violaceus.

Twenty-two intergeneric hybrids from a cross between Brassica napus (AACC, 2n = 38) cultivar Oro and the ornamental crucifer Orychophragmus violaceus (OO, 2n = 24) were produced without embryo rescue. The plants were classified into three groups based on morphological and cytological observations and RAPD banding patterns. Plants of Group I had morphological traits of both parents and 2n = 29 chromosomes. In these plants, 62.1% of the pollen mother cells (PMCs) had the pairing configuration 1 III + 9 II + 8 I; the remaining PMCs had 10 II + 9 I. The plants possessed 97.6-98.8% B. napus specific and 9.2-11.7% O. violaceus specific RAPD fragments. Plants of Group II exhibited novel morphological traits and possessed 2n = 35, 36, or 37 chromosomes. Plants of Group III were morphologically similar to B. napus and possessed 2n = 19, 37, 38, or 39 chromosomes. Plants of Group II and Group III had 94.1-99.4% B. napus specific RAPD fragments and no O. violaceus specific RAPD fragments. Chromosome fragments were observed in PMCs of most of the F1 plants in all groups. Based on the cytological results and RAPD analysis, it is suggested that genome doubling and chromosome elimination occurred in the intergeneric hybrids of B. napus x O. violaceus.     

萝卜与甘蓝属间杂种基因组原位杂交分析

用基因组原位杂交方法（Genomic in situ hybridization, 简称GISH）研究了萝卜( Raphanus sativus,2n=18,RR)和甘蓝（Brassica oleracea , 2n=18, CC）属间杂种F1减数分裂过程。结果表明杂种体细胞染色体组成为RC,2n=18,但花粉母细胞有三种不同类型：1. RC,2n=18, 终变期染色体平均配对构型为14.87Ⅰ+1.20Ⅱ+0.04Ⅲ+0.06Ⅳ, 染色体配对主要发生在萝卜和甘蓝染色体之间, 后期Ⅰ9条萝卜染色体主要以5/4和6/3的分离比移向两极, 所形成配子的染色体数目和组成均不平衡,配子败育; 2. RRCC,4n=36, 终变期染色体形成18个二价体,后期Ⅰ染色体均衡分离,形成RC不减数配子;3. RRCC缺体,4n=30－34, 少数萝卜染色体丢失,形成的配子具有全套的甘蓝染色体和部分萝卜染色体。     

东乡野生稻与栽培稻正反交种间杂种F1的雄配子发生与发育

该文以东乡野生稻与栽培稻(美国光壳稻P1003)的正反交种间杂种F₁(正交为光壳稻P1003×东乡野生稻; 反交为东乡野生稻×光壳稻P1003)为试材, 研究其各个减数分裂时期的染色体行为特征、染色体交换重组及雄配子发育特点。结果表明: 正反交杂种F₁花粉母细胞细胞核减数分裂的同步性较高, 细胞质为连续型胞质分裂类型。在细胞核分裂的过程中, 核仁在前期I到中期I逐渐消失。染色体在前期I到中期I逐渐收缩, 变得更加清晰可见。在终变期和中期I, 90.54%以上的花粉母细胞能形成12个二价体(含少数棒状二价体和8字型二价体), 部分花粉母细胞(正交9.46%, 反交7.65%)出现少量的单价体、三价体和四价体。后期I观察到1.27%–1.35%的花粉母细胞含有1至数条落后染色体。最终有92.6%–94.8%的小孢子能发育成形态正常、染色能力强的成熟花粉粒。另外, 在正交杂种F₁的粗线期中存在2个核仁, 而反交杂种F₁及其双亲的粗线期只有1个核仁。这些研究结果可为作物品种改良、种质资源创新以及种间亲缘关系研究提供细胞学证据。     

Chromosome pairing in triploid intergeneric hybrids ofFestuca pratensis withLolium multiflorum, revealed by GISH

Genomic in situ hybridisation (GISH) was used to reveal chromosome pairing in two partly fertile, triploid (2n = 3x = 21) hybrids obtained by crossing the diploid (2n = 2x = 14) Festuca pratensis Huds. (designated FpFp), used as a female parent, with the autotetraploid (2n = 4x = 28) Lolium multiflorum Lam. (designated LmLmLmLm), used as a male parent. The pattern of chromosome pairing calculated on the basis of the mean values of chromosome configurations identified in all 100 PMCs analysed, was: 0.71I Lm + 2.24I Fp + 2.18II Lm/Lm + 0.54II Lm/Fp + 4.18III Lm/Lm/Fp. A relatively high number of Lm/Lm bivalents and Fp univalents, and a low number of Lm/Fp bivalents and Lm univalents indicated that the pairing was preferential between L. multiflorum chromosomes. Other observations regarding chromosome pairing within the Lm/Lm/Fp trivalents also confirmed this preferential pairing in the analysed triploids, as the Fp chromosome was not randomly located in the chain- and frying-pan-shaped trivalents. The similarities and differences in chromosome pairing at metaphase I and the level of preferential pairing between Lolium chromosomes in the different triploid Lolium-Festuca hybrids are discussed.     

SYNTHETIC HYBRIDS OF NEW WORLD AND OLD WORLD AGROPYRONS. I. TETRAPLOID AGROPYRON SPICATUM × DIPLOID AGROPYRON CRISTATUM

Four interspecific hybrids of tetraploid A. spicatum × diploid A. cristatum ‘Fairway’ were obtained by controlled pollinations of emasculated and unemasculated spikes of A. spicatum. Most vegetative and spike characteristics of the hybrids were intermediate between those of the parent species. Tetraploid A. spicatum behaved cytologically as an autotetraploid, with mean chromosome associations of 0.09 I, 7.95 II, 0.03 III, and 2.98 IV being observed in 103 cells interpreted. The diploid A. cristatum was cytologically regular and formed 7 bivalents in 160 of 163 cells examined. Meiosis in the triploid hybrids was highly irregular, and these plants were completely sterile. Chromosomes of A. spicatum and A. cristatum differed sufficiently in size so that they could be distinguished in the hybrids. Seven bivalents and 7 univalents were formed in 90.5% of 262 cells interpreted at metaphase I. Mean chromosome associations of 6.87 I, 6.98 II, and 0.05 III were observed in the hybrids. Most chromosome pairing was due to autosyndesis of A. spicatum chromosomes, but A. cristatum chromosomes occasionally paired among themselves and with A. spicatum chromosomes. Tetraploid A. spicatum was considered to be an autotetraploid. On the basis of cytological evidence, A. cristatum, A. spicatum, and their interspecific hybrids were represented by genome formulae of AA, BBBB, and ABB, respectively.     

Allelic interaction of F1 pollen sterility loci and abnormal chromosome behaviour caused pollen sterility in intersubspecific autotetraploid rice hybrids

The intersubspecific hybrids of autotetraploid rice has many features that increase rice yield, but lower seed set is a major hindrance in its utilization. Pollen sterility is one of the most important factors which cause intersubspecific hybrid sterility. The hybrids with greater variation in seed set were used to study how the F(1) pollen sterile loci (S-a, S-b, and S-c) interact with each other and how abnormal chromosome behaviour and allelic interaction of F(1) sterility loci affect pollen fertility and seed set of intersubspecific autotetraploid rice hybrids. The results showed that interaction between pollen sterility loci have significant effects on the pollen fertility of autotetraploid hybrids, and pollen fertility further decreased with an increase in the allelic interaction of F(1) pollen sterility loci. Abnormal ultra-structure and microtubule distribution patterns during pollen mother cell (PMC) meiosis were found in the hybrids with low pollen fertility in interphase and leptotene, suggesting that the effect-time of pollen sterility loci interaction was very early. There were highly significant differences in the number of quadrivalents and bivalents, and in chromosome configuration among all the hybrids, and quadrivalents decreased with an increase in the seed set of autotetraploid hybrids. Many different kinds of chromosomal abnormalities, such as chromosome straggling, chromosome lagging, asynchrony of chromosome disjunction, and tri-fission were found during the various developmental stages of PMC meiosis. All these abnormalities were significantly higher in sterile hybrids than in fertile hybrids, suggesting that pollen sterility gene interactions tend to increase the chromosomal abnormalities which cause the partial abortion of male gametes and leads to the decline in the seed set of the autotetraploid rice hybrids.     

Cytogenetic studies in Cyclamen persicum, C. graecum (Primulaceae) and their hybrids

Haploids, diploids and tetraploids of Cyclamen persicum (2n=x=24, 2x=48 and 4x=96), C. graecum (2n=84) and their interspecific hybrids (2n=45, 3x=66, 4x=90) were analyzed cytologically. The mean chromosome association per PMC at diakinesis or at metaphase I in meiosis was 23.29–23.39 I + 0.31–0.36 II in C. persicum (x), 0.17–0.23 I + 23.88–23.92 II in C. persicum (2x), 0.52–1.18 I + 46.39–46.78 II + 0.03–0.09 III + 0.41–0.48IV in C. persicum (4x) and 0.40–0.46I + 41.34–41.63 II + 0.02 III + 0.07–0.21IV in C. graecum. The mean chromosome association per PMC at diakinesis or at metaphase I was 0.47–0.62 I + 44.69–44.76 II in the hybrid (2n=90) of C. persicum (4x) × C. graecum, 38.48–42.50 I + 1.27–3.26 II in microspore-derived plants (2n=45) from the hybrid (2n=90) by anther culture and 26.22–26.67 I + 19.67–19.89 II in the hybrid (2n=66) of C. persicum (2x) × C. graecum. The results indicate that C. graecum is an autotetraploid, the hybrid (2n=4x=90) is an amphidiploid, the microspore-derived plant (2n=45) is a polyhaploid and the hybrid (2n=3x=66) is a sesquidiploid. Based on studies of meiosis, the ploidy levels and the origin of C. graecum and C. persicum are discussed in comparison with several species in the genus Cyclamen.     

Genome relationships in the genus Dasypyrum (Gramineae)

To elucidate the genome relationships in the genus Dasypyrum and the ancestry of tetraploid D. breviaristatum, two cytotypes of D. breviaristatum and D. villosum were reciprocally crossed with one another. Chromosome pairing at the first metaphase of meiosis and fertility were examined in the F1 hybrids and the parental plants. The mean pairing configuration and mean arm pairing frequency in D. villosum-D. breviaristatum (2x) hybrids were 11.12I + 1.44II per cell and 0.107, respectively, and they were almost completely sterile. In D. breviaristatum (4x)-D. breviaristatum (2x) hybrid, up to seven trivalents were formed, and the mean pairing configuration was 3.38I + 3.20II + 3.74III + 0.005IV per cell. The mean arm pairing frequency and relative affinity calculated in that F1 hybrid were 0.915 and 0.641, respectively. Seven bivalents and seven univalents were characteristically formed in D. villosum-D. breviaristatum (4x) hybrids. Based on the present results, we clearly concluded that the genome of diploid D. breviaristatum is distantly related to the genome V of D. villosum, and that these two species have different basic genomes. We, therefore, proposed the symbol Vb for the haploid genome of diploid cytotype of D. breviaristatum. Moreover, we concluded that tetraploid D. breviaristatum is an autotetraploid with doubled sets of the genomes homologous with that of diploid D. breviaristatum, and we proposed the genome constitution VbVb for the haploid genome set of tetraploid cytotype of D. breviaristatum. Furthermore, from the chromosome pairing in the F1 hybrids involving Moroccan and Greek accessions, it was suggested that complicated rearrangements of chromosome structure have occurred in tetraploid D. breviaristatum in its natural populations across the entire distribution area.     

普通小麦与鹅观草属间杂种F1及BC1的分子细胞遗传学、育性和赤霉病抗性研究

通过胚拯救, 成功获得鹅观草Roegneria kamoji (2n=6x=42, SSHHYY)和普通小麦中国春Triticum aesti-vum (2n=6x=42, AABBDD)的正反交属间杂种F1, 并对这些杂种F1及其BC1的形态学、减数分裂配对行为、育性和赤霉病抗性进行研究。结果表明, (鹅观草×中国春)F1和(中国春×鹅观草)F1的形态介于双亲之间。杂种F1花粉母细胞减数分裂中期I染色体构型分别为40.33I + 0.78II + 0.03III和40.40I + 0.79II 。杂种F1高度雄性不育, 用中国春花粉与其回交可获得BC1代种子。(鹅观草×中国春) F1×中国春BC1植株的染色体数目主要分布在55~63之间, 单价体较多, 植株高度不育; (中国春×鹅观草)F1×中国春BC₁植株染色体数目也主要分布在55~63之间, 但其中部分植株拥有整套小麦染色体且能正常配对、分离, 可形成部分可育花粉粒, 能收到少量自交结实种子。在 (鹅观草×中国春)F1中有1株穗型趋向中国春, 其染色体数目为2n=63, 经染色体分子原位杂交(GISH)检测, 含有42条小麦染色体和21条鹅观草染色体。该杂种F1在减数分裂中期I平均每个花粉母细胞有26.40I+18.30II, 但植株高度雄性不育, 用中国春花粉回交能收到BC₁种子。(鹅观草×中国春) F₁ (2n=63)×中国春BC₁的染色体数目主要分布在40~59之间, 其中的外源染色体已经逐渐减少, 虽然该BC₁的穗型已接近中国春, 但仍然高度不育。赤霉病抗性鉴定结果显示, 所有杂种F1及大部分BC₁对赤霉病均表现出较好的抗性。     

Variation in pollen formation and its cytological mechanism in an allotriploid white poplar

Variation in pollen formation and its cytological mechanism in an allotriploid white poplar were investigated by the squashed technique and indirect immunofluorescence. Besides 0.5% stuck pollen grains, this allotriploid produced regularly spherical pollen grains. It was estimated that 90.3% of pollen grains were viable. Diameters of the viable spherical pollen grains ranged from 23.2 to 72.9 μm, with a bimodal frequency distribution. Numerous meiotic abnormalities were found, including highly irregular chromosome pairing, lagging chromosomes and chromosome bridges, micronuclei, and multiple spindles, which indicate highly genetic imbalance of this allotriploid. Some micronuclei triggered minispindle formation in metaphase II and participated in cytokinesis to form microcytes in sporads. Abnormal orientation of metaphase II spindles contributed to production of dyads and triads, which produced unreduced microspores. However, parallel orientation of spindles was not necessary for dyad formation, because an organelle band positioned in the equatorial region prevented the spindles from coalescing. Some microsporocytes exhibited a complete or partial absence of cytokinesis, which resulted in the formation of monads and the increased frequency of dyads and triads. The perspective of this triploid in the polyploid breeding program of white poplar is discussed.     

Production and characterization of intertribal somatic hybrids of Raphanus sativus and Brassica rapa with dye and medicinal plant Isatis indigotica

Intertribal somatic hybrids of Raphanus sativus (2n = 18, RR) and Brassica rapa spp. chinensis (2n = 20, AA) with the dye and medicinal plant Isatis indigotica (2n = 14, I I) were firstly obtained by polyethylene glycol-induced symmetric fusions of mesophyll protoplasts. One mature hybrid with R. sativus established in field had intermediate morphology but was totally sterile. It had the expected chromosome number (2n = 32, RRI I) and parental chromosomes were distinguished by genomic in situ hybridization (GISH) analysis, and these chromosomes were paired as 16 bivalents in pollen mother cells (PMCs) at diakinesis and mainly segregated equally as 16:16 at anaphase I (A I), but the meiotic disturbance in second division was obvious. Five mature hybrids with B. rapa established in field were morphologically intermediate but showed some differences in phenotypic traits and fertility, two were partially fertile. Cytological and GISH investigations revealed that these hybrids had 2n = 48 with AAIIII complement and their PMCs showed normal pairing of 24 bivalents and mainly equal segregation 24:24, but meiotic abnormalities of lagging chromosomes and micronuclei appeared frequently during second divisions. AFLP analysis showed that all of these hybrids had mainly the DNA banding pattern from the addition of two parents plus some alterations. Some hybrids should be used for the genetic improvement of crops and the dye and medicinal plant.     

STERILITY BARRIERS OF SOME ARTIFICIAL F1 ORCHID HYBRIDS: MALE STERILITY. I. MICROSPOROGENESIS AND POLLEN GERMINATION

Microsporogenesis, pollen germination and fertility of males gametes were studied in 24 artificial intergeneric and interspecific F₁ hybrids of orchids. Although parental species had the same chromosome number (2n = 40), microsporogenesis of the hybrids was irregular due to the lack of homology of the chromosomes of the parental species. This led to formation of tetrads of microspores without micronuclei, tetrads with 1–8 micronuclei, triads, dyads with and without micronuclei, and monads. Chromosomes numbers found in haploid microsporocytes ranged from 7 to 40; in micronuclei the chromosome number varied between 1 and 5. In terms of pollen germination, three situations were observed: 1) hybrids whose pollen grains did not germinate in the stigma; 2) hybrids in which the pollen tubes grew down in the style, but did not penetrate into the ovary; 3) hybrids in which the pollen tubes grew down normally through the ovary, reaching the ovules. When the pollen tubes did not penetrate the ovary no fruit was formed. Therefore germination tests carried out in vitro may not indicate pollen fertility, because pollen tube growth in the style of the flower may be insufficient to induce fruit formation or to accomplish fertilization.     

濒危植物巴东木莲花粉母细胞减数分裂观察

对巴东木莲Manglietia patungensis及其近缘种乳源木莲M. yuyuanensis的花粉母细胞减数分裂过程的基本特征进行了比较研究。乳源木莲与巴东木莲的染色体数目和核型相同,但不经任何人为因素诱导,它们之间在减数分裂过程中的染色体行为上有明显差异。(1)巴东木莲减数分裂中期I构型为0.30IV+18.33II+0.15I,与乳源木莲构型19II不同,巴东木莲可能存在同臂内倒位杂合子,染色体结构存在一定的杂合性。(2)后期I和后期II染色体行为异常现象发生频率明显不同。以后期II为例,乳源木莲减数分裂相中有迟滞染色体的细胞占8.8%,迟滞染色体不超过2个;巴东木莲有迟滞染色体等异常现象的细胞占29.2%,迟滞染色体最高达11个,还出现染色体碎裂成断片现象。巴东木莲减数分裂过程中染色体组表现出染色体结构杂合变异和迟滞染色体与染色体的断裂频率很高的异常现象在一定程度上可能影响了雄配子体的发育。