The breeding of two polyploid rice lines with the characteristic of polyploid meiosis stability

Polyploidization is a basic feature of plant evolution. Nearly all of the main food, cotton and oil crops are polyploid. When ploidy levels increase, yields double; this phenomenon suggested a new strategy of rice breeding that utilizes wide crosses and polyploidization dual advantages to breed super rice. Because low seed set rates in polyploid rice usually makes it difficult to breed, the selection of Ph-liked gene lines was emphasized. After progenies of indica-japonica were identified and selected, two polyploid lines, PMeS-1 and PMeS-2 with Polyploid Meiosis Stability (PMeS) genes were bred. The procedure included seven steps: selecting parents, crossing or multiple crossing, back-crossing, doubling chromosomes, identifying the polyploid, and choosing plants with high seed set rates that can breed themselves into stable lines. The characteristics of PMeS were determined by observing meiotic behaviors and by cross-identification of seed sets. PMeS-1 and PMeS-2, (japonica rice), have several characteristics different from other polyploid rice lines, including a higher rate of seed set (more than 65%, increasing to more than 70% in their F1 offspring); and stable meiotic behaviors (pairing with bivalents and quarivalents nearly without over-quarivalent in prophase, nearly without lagging chromosomes in metaphase and without micronuclei in anaphase and telophase). The latter was obviously different from control polyploid line Dure-4X, which displayed abnormal meiotic behaviors including a higher rate of multivalents, univalents and trivalents in prophase, lagging chromosomes in metaphase and micronuclei in anaphase and telophase. There were also three differences of the breeding method between PMeS lines and normal diploid lines: chromosomes doubling, polyploidism identifying and higher seed set testing. The selection of PMeS lines is the first step in polyploid rice breeding; their use will advance the progress of polyploid rice breeding, which will in turn offer a new way to breed super rice. Supported by the National Natural Science Foundation of China (Grant Nos. 39970447, 30240090, 30471063 and 30650002), the High Technology Research and Development Program of China (Grant No. SZ-01-02-02), the Chenguang Youth Science and Technology Project of Wuhan City (Grant No. 20045006071-31), and the Educational Commission of Hubei Province of China (Grant No. 2004D004)     

Unusual cytological patterns of microsporogenesis in Brachiaria decumbens: abnormalities in spindle and defective cytokinesis causing precocious cellularization

Cytogenetic studies carried out in the tetraploid accession BRA001068 of Brachiaria decumbens, also known as cv. Basilisk, revealed an unusual pattern of microsporogenesis. The spindle in metaphase I and anaphase I became heavily stained with propionic carmine. In telophase I, the interzonal microtubules continued to be intensely stained, and during the phragmoplast formation the fibers were pushed to the cell wall, persisting until prophase II, even after cytokinesis. Due to its tetraploid condition, the accession presented many cells with precocious chromosome migration to the poles in metaphase I and laggards in anaphase I that gave rise to micronuclei in telophase I. While in other polyploid accessions of Brachiaria micronuclei remained in this condition until the second cytokinesis, the micronuclei in this accession organized their own spindle in the second division. In several microsporocytes, the micronuclei with their minispindle were divided further into microcytes by additional cytokinesis. Some curious planes of cytokinesis were found in some cells, with partitioning of cytoplasm into cells of irregular shape. The result consisted of a high frequency of abnormal products of meiosis. Quadrivalents were observed in diakinesis at low frequency, which suggests a segmental allotetraploid and the inability of both genomes to co-ordinate their activities, leading to multiple spindle and precocious cellularization. In spite of abnormal meiotic products reducing pollen fertility, seed production was normal. Enough normal pollen was available to fertilize the central-cell nucleus of the embryo sac and produce normal endosperm in this pseudogamous aposporous apomictic accession.     

Genome duplication effects on pollen development and the interrelated physiological substances in tetraploid rice with polyploid meiosis stability

The breeding of polyploid rice made no breakthrough for a long time because of low seed set. The discovery and application of polyploid meiosis stability (PMeS) material played a pivotal role in solving this problem. Our results indicated that genome duplication led to different outcomes in different rice cultivars in terms of pollen fertility, viability, and the accumulation of important physiological substances such as free proline and endogenous hormones. Pollen from the PMeS HN2026-4X lines showed a high fertility and viability similar to those of HN2026-2X (4X indicates tetraploid while 2X indicates the diploid), whereas both rates decreased dramatically in Balilla-4X. The results of pollen microstructure and ultrastructure investigations suggested that the pollen development pattern in HN2026-4X appeared normal at all stages, but a lot of changes were discovered in Balilla-4X. Stable meiosis, timely tapetum degradation, and normal mitochondria development were critical factors insuring the high frequency pollen fertility of PMeS rice. The free proline content increased markedly in HN2026-4X as compared to HN2026-2X, but it was decreased for Balilla-4X. Genome duplication effects on regulating endogenous hormones accumulation in pollen were evident, resulting in the clear difference between PMeS HN2026-4X and Balilla-4X. The accumulation of IAA, ZR, and GA in mature pollen distinguished HN2026-4X from Balilla-4X, which was linked to normal pollen development. In particular, the excessive accumulation of ABA at the meiosis stage may be correlated to disorganized meiosis in Balilla-4X. All the results provided unequivocal evidence that genome duplication played specific roles in the normal pollen development of PMeS HN2026-4X.     

A mutation in the spindle checkpoint arresting meiosis II in Brachiaria ruziziensis.

Cytological characterization of BRA005568 accession of Brachiaria ruziziensis (2n = 2x = 18) showed a totally unexpected high frequency of abnormal meiotic products, from triads to hexads, and also tetrads with micro nuclei or microcytes. Meiosis I had a low frequency of abnormalities, mainly related to the chiasma terminalization process. In meiosis II, however, frequency of abnormalities increased exceptionally. Early prophase II was normal with the chromosome set enclosed by the nuclear envelope. However, in late prophase II, owing to the breakdown of the nuclear envelope, the chromosomes were scattered in the cytoplasm. Some chromosomes did not reach the metaphase II plate and remained scattered. The behavior of sister cells was inconsistent. While in one cell the chromosomes were totally aligned at the metaphase II plate, in the other they could be found completely scattered, leading to an asynchronous cell division. Cells with scattered chromosomes were unable to progress in meiosis. Thus, anaphase II failed to occur and sister chromatids were not released. Cells with non-aligned chromosomes in the metaphase II plate did not receive the "go ahead" sign to initiate anaphase II. Consequently, the scattered chromosomes produced telophase II nuclei of different sizes in situ. The asynchronous behavior led to the formation of a wide range of meiotic products. Results suggest that the present accession contains a mutation affecting the spindle checkpoint that arrests the second meiotic division.     

DNA damage response during mouse oocyte maturation

Because low levels of DNA double strand breaks (DSBs) appear not to activate the ATM-mediated prophase I checkpoint in full-grown oocytes, there may exist mechanisms to protect chromosome integrity during meiotic maturation. Using live imaging we demonstrate that low levels of DSBs induced by the radiomimetic drug Neocarzinostatin (NCS) increase the incidence of chromosome fragments and lagging chromosomes but do not lead to APC/C activation and anaphase onset delay. The number of DSBs, represented by γH2AX foci, significantly decreases between prophase I and metaphase II in both control and NCS-treated oocytes. Transient treatment with NCS increases >2-fold the number of DSBs in prophase I oocytes, but less than 30% of these oocytes enter anaphase with segregation errors. MRE11, but not ATM, is essential to detect DSBs in prophase I and is involved in H2AX phosphorylation during metaphase I. Inhibiting MRE11 by mirin during meiotic maturation results in anaphase bridges and also increases the number of γH2AX foci in metaphase II. Compromised DNA integrity in mirin-treated oocytes indicates a role for MRE11 in chromosome integrity during meiotic maturation.     

小麦ph1b突变体与小黑麦杂交的细胞遗传学研究

本文利用普通小麦品系"中国春"(对照)、中国春ph1b突变体分别与八倍体小黑麦、六倍体小黑麦杂交,杂种F1的减数分裂前期Ⅰ染色体行为表现异常,中期Ⅰ出现较多的单价体、棒状二价体和多价体,在后期和末期出现落后染色体、染色体片断和微核。原因是ph1b基因的存在造成染色体联会机制紊乱,致使一些部分同源染色体配对并发生互换,有可能在以后的世代产生染色体易位与基因重组。     

禾谷镰孢菌Fusarium graminearum Schwabe分生孢子萌发过程中的核相变化及有丝分裂过程观察

通过Giemsa染色观察禾谷镰孢菌Fusarium graminearum分生孢子萌发过程中的核相变化及有丝分裂过程。观察表明,分生孢子细胞为单核,细胞核在分生孢子细胞内分裂后进入芽管,在芽管内进行多次分裂,使芽管内细胞核数目不断变化。禾谷镰孢菌有丝分裂过程可以分为4个时期,前期染色体逐渐浓缩变短,中期染色体清晰可见,后期染色单体发生分离并向相反的两极移动,末期形成新的子核。有丝分裂过程中染色体的分离同步或不同步,不同步分离中的滞后染色体形成后期桥的现象更为普遍。     

Cytological evidence for chromosome elimination in wheat x Imperata cylindrica hybrids

Haploid induction of wheat by crossing with Imperata cylindrica pollen is an efficient method for doubled haploid breeding. We investigated the process of wheat haploid formation after crossing with I. cylindrica. Our cytological observations of zygotes showed the successful fertilization of parental gametes. Wheat haploids were formed by complete elimination of I. cylindrica chromosomes. Missegregation of I. cylindrica chromosomes was observed in the first cell division of zygote. At metaphase I. cylindrica chromosomes did not congress onto the equatorial plate. The sister chromosomes did not move toward the poles during anaphase, though their cohesion was released normally. I. cylindrica chromosomes were still in the cytoplasm at telophase and eliminated from daughter nuclei. After two-celled stage, we could find no I. cylindrica chromosome in the nuclei but micronuclei containing I. cylindrica chromatin in the cytoplasm. These observations indicate that I. cylindrica chromosomes are completely eliminated from nuclei in the first cell division probably due to lack of functional kinetochores.     

CELL DIVISION IN SPIROGYRA. I. MITOSIS

Dividing cells of Spirogyra sp. were examined with both the light and electron microscopes. By preprophase many of the typical transverse wall micro-tubules disappeared while others were seen in the thickened cytoplasmic strands. Microtubules appeared in the polar cytoplasm at prophase and by prometaphase they penetrated the nucleus. They were attached to chromosomes at metaphase and early anaphase, and formed a sheath surrounding the spindle during anaphase; they were seen in the interzonal strands and cytoplasmic strands at telophase. The interphase nucleolus, containing 2 distinct zones and chromatinlike material, fragmented at prophase; at metaphase and anaphase nucleolar material coated the chromosomes, obscuring them by late anaphase. The chromosomes condensed in the nucleoplasm at prophase, moving into the nucleolus at prometaphase. The nuclear envelope was finally disrupted at anaphase during spindle elongation; at telophase membrane profiles coated the reforming nuclei. During anaphase and early telophase the interzonal region contained vacuoles, a few micro-tubules, and sometimes eliminated n ucleolar material; most small organelles, including swollen endoplasmic reticulum and tubular membranes, were concentrated in the polar cytoplasm. Quantitative and qualitative cytological observations strongly suggest movement of intact wall rnicrotubules to the spindle at preprophase and then back again at telophase.     

MITOSIS IN THE ALGA VACUOLARIA VIRESCENS

Details of mitosis in the chloromonadophycean alga Vacuolaria virescens Cienk. have been studied with the light microscope. The chromosomes are relatively large (up to μ in length at metaphase) and so mitotic stages are readily distinguishable. Chromosomes can be recognized in interphase nuclei as fine strands of chromatin. Contraction of these chromosomes marks the beginning of mitosis and continues progressively until the transition from metaphase to anaphase. Disintegration of nucleoli is complete by late prophase and nucleolar reformation begins in telophase. Some chromosomes exhibit less densely stained regions; centromeres are also present as indicated by their differential staining and by the behavior of chromosomes at metaphase and anaphase. At anaphase progeny chromosomes move apart parallel to the division axis of the nucleus. As anaphase progresses the chromosomes fuse at the polar surface of the progeny chromosome groups. This process continues in telophase and the chromosome groups become more spherical. By the end of telophase nucleolar reformation has begun and the chromosomes have relaxed to their interphase condition.     

Nuclear and microtubular cycles in heterophasic multinuclearTriticum root-tip cells induced by caffeine

Summary Nuclear and microtubular cycles were studied in large heterophasic multinuclear cells induced in root tips ofTriticum turgidum by caffeine treatment. Multinuclear cells and cells with polyploid nuclei exhibited various configurations of multiple and complex preprophase microtubule (Mt) bands (PPBs), including helical ones. The developmental stages of PPBs in some heterophasic cells did not comply with the cell cycle stages of the associated nuclei, a fact indicating that these events are not directly controlled by the associated nuclei. The heterophasic cells exhibited asynchronous nuclei at different stages of mitosis. In cells displaying prophase and interphase nuclei, the prophase spindle was either absent or developed around both of them or developed around the prophase nuclei earlier than around the interphase ones. During prometaphase-metaphase of the advanced nuclei the lagging interphase nuclei were induced to form prematurely condensed chromosomes (PCCs) along with spindle formation around them. These observations suggest that the mitotic transition in heterophasic cells is delayed but is ultimately achieved due to the effect of the advanced nuclei, which induces a premature mitotic entry of the lagging nuclei. Although kinetochore Mt bundles were found associated with PCCs, their metaphase and anaphase spindles were abnormal resulting in abnormal or abortive anaphases. In some heterophasic cells, metaphase-anaphase transition did not take place simultaneously in different chromosome groups, signifying that the cells do not exit from the mitotic state after anaphase initiation of the advanced nuclei. Asynchronous pace of mitosis of different chromosome groups was also observed during anaphase and telophase. Implications of these observations in understanding plant cell cycle regulation are discussed.Abbreviations cdk cyclin dependent kinase - Mt microtubule - PCC prematurely condensed chromosome - PPB preprophase band     

Thrombopoietin-induced Polyploidization of Bone Marrow Megakaryocytes Is Due to a Unique Regulatory Mechanism in Late Mitosis

Megakaryocytes undergo a unique differentiation program, becoming polyploid through repeated cycles of DNA synthesis without concomitant cell division. However, the mechanism underlying this polyploidization remains totally unknown. It has been postulated that polyploidization is due to a skipping of mitosis after each round of DNA replication. We carried out immunohistochemical studies on mouse bone marrow megakaryocytes during thrombopoietin- induced polyploidization and found that during this process megakaryocytes indeed enter mitosis and progress through normal prophase, prometaphase, metaphase, and up to anaphase A, but not to anaphase B, telophase, or cytokinesis. It was clearly observed that multiple spindle poles were formed as the polyploid megakaryocytes entered mitosis; the nuclear membrane broke down during prophase; the sister chromatids were aligned on a multifaced plate, and the centrosomes were symmetrically located on either side of each face of the plate at metaphase; and a set of sister chromatids moved into the multiple centrosomes during anaphase A. We further noted that the pair of spindle poles in anaphase were located in close proximity to each other, probably because of the lack of outward movement of spindle poles during anaphase B. Thus, the reassembling nuclear envelope may enclose all the sister chromatids in a single nucleus at anaphase and then skip telophase and cytokinesis. These observations clearly indicate that polyploidization of megakaryocytes is not simply due to a skipping of mitosis, and that the megakaryocytes must have a unique regulatory mechanism in anaphase, e.g., factors regulating anaphase such as microtubule motor proteins might be involved in this polyploidization process.     

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.     

The Nucleolus and Parachromatin of the Ascites Tumor Cell

1. A method is described for distinguishing the ribonucleoproteins of the nucleolus and parachromatin of ascitic tumor cells of the mouse. 2. In these cells the transfer of ribonucleoprotein from the nucleus to the cytoplasm can occur in two ways. (a) At the end of prophase the nucleolus separates from the chromosomes and nucleolar fragments are released into the cytoplasm. (b) During prophase the parachromatin is aggregated to form parachromatin bodies which are discharged into the cytoplasm, where they can be detected during metaphase, anaphase, and telophase. 3. A metachromatic form of RNA is demonstrable, and may be synthesized, in close relation to the chromosomes during prophase, metaphase, and anaphase. During telophase the distribution of metachromatic RNA changes, the chromatin loses its metachromasia, and intranuclear metachromatic parachromatin becomes evident.     

A general polyploid model for analyzing gene segregation in outcrossing tetraploid species

Polyploidy has played an important role in higher plant evolution and applied plant breeding. Polyploids are commonly categorized as allopolyploids resulting from the increase of chromosome number through hybridization and subsequent chromosome doubling or autopolyploids due to chromosome doubling of the same genome. Allopolyploids undergo bivalent pairing at meiosis because only homologous chromosomes pair. For autopolyploids, however, all homologous chromosomes can pair at the same time so that multivalents and, therefore, double reductions are formed. In this article, we use a maximum-likelihood method to develop a general polyploid model for estimating gene segregation patterns from molecular markers in a full-sib family derived from an arbitrary polyploid combining meiotic behaviors of both bivalent and multivalent pairings. Two meiotic parameters, one describing the preference of homologous chromosome pairing (expressed as the preferential pairing factor) typical of allopolyploids and the other specifying the degree of double reduction of autopolyploids, are estimated. The type of molecular markers used can be fully informative vs. partially informative or dominant vs. codominant. Simulation studies show that our polyploid model is well suited to estimate the preferential pairing factor and the frequency of double reduction at meiosis, which should help to characterize gene segregation in the progeny of autopolyploids. The implications of this model for linkage mapping, population genetic studies, and polyploid classification are discussed.     

Cytogenetic studies on two F1 hybrids of autotetraploid rice varieties showing extremely high level of heterosis

Mechanisms of two F1 hybrids (D46A × DTP-4 and D46A × Dminghui63) of autotetraploid rice (2n = 4x = 48) showing extremely high pollen fertility 87.40% and 85.97%, respectively, seed set 82.00% and 79.00%, respectively and extremely high level of heterosis were analyzed cytologically. The chromosome pairing of D46A × DTP-4 and D46A × Dminghui63 was normal at metaphase I(MI), and had almost no I or III, with an average of 0.020I +14.36 II 6.44rod+7.91ring) +0.01III + 4.80 IV + 0.01VIII and 0.06 I + 17.67 II (11.01rod + 6.67ring)] + 0.06 III +3.10IV+0.01VI, respectively. The most frequent chromosome configurations were 10II+7IV and 12II+bIV. The bivalent frequency was less frequent in hybrids than that in restoring parents, and the same results were gained from univalents, trivalent and multivalents. However, the quadrivalent frequency was significantly higher in hybrids than that in restoring parents at MI. The other meiotic phases progressed normally, except for low percentages of PMCs with lagging chromosomes at AI and low percentages of PMCs with micronuclei at telophaseI (TI) and telophaseII (TII). PMCs with lagging chromosomes at AI and PMCs with micronuclei at TI and TII showed negative correlation between pollen fertility and seed set. Above 90% of the PMCs could form normal microspores, which resulted in the production of viable pollen grains, abnormal microspores were observed including penta-fission and hexa-fission. Based on these results we suggest that the two F1 hybrids had better behaviors of chromosome pairing and genetic stability than autotetraploid rice and other autotetraploid plants ever studied.     

Involvement of synaptonemal complex proteins in sex chromosome segregation during marsupial male meiosis

Marsupial sex chromosomes break the rule that recombination during first meiotic prophase is necessary to ensure reductional segregation during first meiotic division. It is widely accepted that in marsupials X and Y chromosomes do not share homologous regions, and during male first meiotic prophase the synaptonemal complex is absent between them. Although these sex chromosomes do not recombine, they segregate reductionally in anaphase I. We have investigated the nature of sex chromosome association in spermatocytes of the marsupial Thylamys elegans, in order to discern the mechanisms involved in ensuring their proper segregation. We focused on the localization of the axial/lateral element protein SCP3 and the cohesin subunit STAG3. Our results show that X and Y chromosomes never appear as univalents in metaphase I, but they remain associated until they orientate and segregate to opposite poles. However, they must not be tied by a chiasma since their separation precedes the release of the sister chromatid cohesion. Instead, we show they are associated by the dense plate, a SCP3-rich structure that is organized during the first meiotic prophase and that is still present at metaphase I. Surprisingly, the dense plate incorporates SCP1, the main protein of the central element of the synaptonemal complex, from diplotene until telophase I. Once sex chromosomes are under spindle tension, they move to opposite poles losing contact with the dense plate and undergoing early segregation. Thus, the segregation of the achiasmatic T. elegans sex chromosomes seems to be ensured by the presence in metaphase I of a synaptonemal complex-derived structure. This feature, unique among vertebrates, indicates that synaptonemal complex elements may play a role in chromosome segregation.     

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。     

A developmental study of constitutive heterochromatin in Microtus agrestis

In the vole, Microtus agrestis, the constitutive heterochromatin is largely restricted to the giant sex chromosomes but varies in its degree of condensation in various cell types. In the cleavage embryos and fibroblasts it formed one or two long and extended heterochromatic fibers, in hepatocytes it formed two large and diffuse masses and in neurons, spermatogonia and oogonia it formed two large and compact masses. The basic patterns of all differentiated cells were essentially unchanged throughout development.—At all stages of development and in cells of all types, mitotic nuclei displayed two large heteropycnotic chromosomes in prophase and persistent condensation in telophase. Apposition and delayed separation of chromatids of the giant chromosomes was also observed in metaphase and anaphase, respectively. During the first meiotic prophase of spermatocytes and oocytes, the giant chromosomes were also heteropycnotic.—The results strongly suggest that constitutive heterochromatin is localized in the same chromosomes throughout development and represents a specific entity.     

秤锤树的核型研究及其减数分裂过程的观察

观察研究了秤锤树有丝分裂和减数分裂的细胞学特征。秤锤树核型为2n=2x=24=4m 7sm(2SAT) 1st,属于较为原始的2A型。有丝分裂间期核为复杂染色中心型,前期出现B染色体,中期染色体中等大小。减数分裂中期具12对正常的二价体,但后期I和后期Ⅱ均有染色体异常现象发生。统计断片、落后染色体和染色体桥出现的比例与花粉粒败育性比例比较一致,表明秤锤树的小孢子在发生和发育过程中较高频率的败育现象可能存存一常的细胞学原因．