AUTORADIOGRAPHIC STUDIES OF NUCLEIC ACIDS AND PROTEINS DURING MEIOSIS IN LILIUM LONGIFLORUM

Taylor , J. Herbert (Columbia U., New York, N. Y.) Autoradiographic studies of nucleic acids and proteins during meiosis in Lilium longiflorum. Amer. Jour. Bot. 46(7): 477–484. Illus. 1959.—A study was made of the incorporation of glycine-C¹⁴, orotic acid-C¹⁴ and cytidine-H³ into nucleic acids and proteins of sporogenous and tapetal cells of lily anthers preceding and during meiosis. Methods for differential extraction of nucleic acids from tissue sections, which had been frozen, dehydrated by alcohol-substitution, and fixed in hot alcohol, were tested by chromatographic analysis of extracts. Both acid and enzyme hydrolysis were shown to be useful for quantitative or, at least, semi-quantitative work. DNA synthesis was shown to occur only during premeiotic interphase in sporogenous cells, but at two intervals in tapetal nuclei, once when the microsporocytes are in zygotene and again during pachytene. Each time the synthetic period was followed by a normal mitosis. Accumulation of RNA in microsporocytes occurred at stages up to late leptotene. After this period, labeled RNA accumulated almost exclusively in their nuclei and at a slower rate than in earlier stages. DNA synthesis, as measured by incorporation of glycine-C¹⁴ and orotic acid-C¹⁴, gave the same results and confirm earlier results with inorganic phosphate-P³². For RNA, glycine-C¹⁴ and orotic acid-C¹⁴ gave different results. When glycine-C¹⁴ was the source of label, incorporation of C¹⁴ in RNA stopped during DNA synthesis in sporogenous cells. Glycine-C¹⁴ was not utilized to a significant extent at any time by tapetal cells for RNA synthesis, but extensively for DNA and protein synthesis. Orotic acid-C¹⁴ was incorporated into RNA of both tapetum and sporogenous cells at various periods in development apparently including the interval of DNA synthesis. Protein synthesis as measured by incorporation of glycine is relatively rapid during premeiotic interphase and leptotene. It continues during the remainder of prophase, but at a much reduced rate. In tapetal cells the rate is rapid in the nuclei during periods of DNA synthesis, but even faster in both cytoplasm and nucleus after divisions are completed and the microsporocytes are in late prophase and division stages. This period of synthesis is perhaps necessary for the postmeiotic functioning of tapetum when it appears to secrete the wall materials for the microspores.     

Microsporogenesis and tapetal development in fertile and cytoplasmic male-sterile sugar beet (Beta vulgaris L.)

Summary The development of sporogenous and tapetal cells in the anthers of male-fertile and cytoplasmic male-sterile sugar beet (Beta vulgaris L.) plants was studied using light and transmission electron microscopy. In general, male-sterile anthers showed a much greater variability in developmental pattern than male-fertile anthers. The earliest deviation from normal anther development was observed to occur in sterile anthers at meiotic early prophase: there was a degeneration or irregular proliferation of the tapetal cells. Other early aberrant events were the occurrence of numerous small vesicles in the microspore mother cells (MMC) and a disorganized chromatin condensation. Deviations that occurred in sterile anthers at later developmental stages included: (1) less distinct inner structures in the mitochondria of both MMC and tapetal cells from middle prophase onwards. (2) dilated ER and nuclear membranes at MMC prophase, in some cases associated with the formation of protein bodies. (3) breakdown of cell walls in MMCs and tapetal cells at late meiotic prophase. (4) no massive increase in tapetal ER at the tetrad stage. (5) a general dissolution of membranes, first in the MMC, then in the tapetum. (6) abortion of microspores and the occurrence of a plasmodial tapetum in anthers reaching the microspore stage. (7) no distinct degeneration of tapetal cells after microspore formation. Thus, it seems that the factors that lead to abortive microsporogenesis are structurally expressed at widely different times during anther development. Aberrant patterns are not restricted to the tetrad stage but occur at early prophase.     

THE CYTOLOGY OF POLLEN ABORTION IN C-CYTOPLASMIC MALE-STERILE CORN ANTHERS

Anther development of the C-cytoplasmic male-sterile (cms C) and the normal cytoplasm version (N) in the W182BN corn inbred was studied by light and electron microscopy. Deviation from normal pollen development was first observed in the tapetal cells at the tetrad stage of development. Two types of tapetal abnormalities were observed in plants with C cytoplasm. The first behaved like the N anther until the tetrad stage, when numerous small vacuoles appeared in the tapetal cells. Inner and radial tapetal cell walls broke down normally, but irregular Ubisch body deposition was observed, and exine development was inhibited and delayed. The tapetum and microspores disintegrated at the intermediate microspore stage. The second type of tapetum was highly vacuolated at the early tetrad stage, with dense inner and radial cell walls that remained intact and enlarged when the tetrads aborted. No organellar abnormalities, such as the mitochondrial changes observed in cms T, were observed in C anthers.     

白菜核雄性不育花药超微结构的研究

对白菜核雄性不育两用系的可育与不育花药进行了超微结构的比较观察。结果显示不育花药的造孢细胞核仁靠边分布:包裹小孢子母细胞的胼胝质厚薄不均匀,不完整等早期异常现象。减数分裂后,四分体细胞中常有多个细胞核。从四分体释放出的小孢子外壁的孢粉素物质不均匀沉积．呈不连续的单层异常结构。最后小孢子通过细胞质收缩方式败育。在可育花药中,绒毡层细胞在小孢子发育后期已显示出退化迹象,同时在细胞中开始积累脂类物质。但在同时期的不育花药中, 绒毡层细胞没有显示出退化的迹象,也不合成脂类物质。从时间上看,败育花药中小孢子母细胞及小孢子的异常在先,绒毡层细胞的异常在后。本研究揭示了白菜核雄性不育花药的超微结构特征, 对我们以前的光学显微镜观察结果予以补充和修正。     

Invasive tapetum and tricelled pollen inAmbrosia trifida (Asteraceae,tribeHeliantheae)

Staminate flowers of giant ragweed,Ambrosia trifida L. (Asteraceae, tribeHeliantheae, subtribeAmbrosiinae) were processed into resin and sectioned 1–2 µm thick. The invasive (amoeboid) anther tapetum remains parietal until microspores are released from tetrads, then it swells and invades the locule, merging gradually into a single protoplast that flows among the microspores. After the tapetal membrane ruptures at late microspore stage, tapetal debris fills the locule, then disappears as pollen matures. Pollen becomes tricelled before anthesis. The two sperm cell nuclei are slender and wormlike. The present report supports the two generalizations that invasive tapetum and tricelled pollen are attributes of theAsteraceae.     

Sporoderm in Populus and Salix

Four phenomena were observed in a study of Populus tremula and P. tremula f. gigas microspores from before microspore mitosis through mature pollen which may have general significance in the ontogeny of pollen grains: 1) The exine and orbicules (Ubisch bodies) were covered by membranes. 2) The exine and the tapetal surfaces where orbicules form were covered by a polysaccharide (PAS positive) coat until after microspore mitosis; subsequently the tapetum became plasmodial. 3) Material having the staining characteristics of the nexine 2 (endexine in the sense of Fægri) accumulated on membranes in microspores in the space between the exine and the plasma membrane. That material was almost completely gone from the wall in mature pollen. The membranes on which material had accumulated migrated through the exine. Following passage through the exine these membranes were seen as empty fusiform vesicles in micrographs of anthers prepared by commonly used methods. 4) At about microspore mitosis when the cellulosic intine begins to form, microtubules about 240 A in diameter occurred near the plasma membrane and generally parallel with it. Positive acid phosphatase reactions in tapetal cells together with the morphology of orbicules and other tapetal organelles suggest that the wall of orbicules, which is like the pollen exine, may form as a residual product of a lysosome system.

Sections of mature Salix humilis pollen were compared with Populus.     

Microsporogenesis in male sterile Rosmarinus officinalis L. (Lamiaceae), an ultrastructural study

Within an extensive reproductive biology program on Rosmarinus officinalis a study of microsporogenesis in male sterile plants has been carried out. Two events, related to the two types of male sterile flowers found in this species (MS; Male sterile and INT; Intermediate male sterile flowers), are described. The first event is characterized by the early appearance of necrotic areas in the anther tissues during the final differentiation phases of the MS flowers, before meiosis takes place. Initially, these necrotic areas are small, later on they enlarge affecting the sporogenous tissue and tapetum. All the anthers in which necrosis has begun finally become aborted and lack pollen grains. The second event is manifested in the anthers of the INT flowers. Previous to the release of the microspores from the callosic envelope, vacuolisation of the tapetal cells takes place. The tapetum does not properly carry out its secretory function. It accumulates some substances in vacuoles and starch granules in plastids. The microspores degenerate in the vacuolate stage. In the epidermal and endothecial cells modifications are observed which may be related to the carbohydrate metabolism. Indehiscent, whitish anthers containing inviable microspores result. We have not found significant differences between the mitochondria in the anthers of the fertile flowers and MS or INT flowers. But we suggest, for both events, a metabolic failure, possibly controlled by cytoplasmic genes as the origin of male sterility. Paracrystalline material has been detected in microspore nuclei of developing INT anthers, though it does not seem to be related to the expression of male sterility.     

Ultrastructure of the tapetal cell wall in the stamenless-2 mutant of tomato (Lycopersicon esculentum): correlation between structure and male-sterility

Summary In the stamenless-2 (sl-2) mutant of tomato (Lycopersicon esculentum Mill.), the breakdown in microsporogenesis corresponded with various abnormalities in the ultrastructure of the tapetal cell wall. In some mutant anthers, the inner tangential wall was excessively loosened allowing the passage of tapetal cell wall material and cytoplasmic contents into the anther locule. This presumably altered the osmoticum of the locule and resulted in plasmolysis of the microspores. Membranous fragments commonly observed in the normal tapetal cell wall, and presumed to have a role in transfer of materials from the tapetum to microspores, were absent from thesl-2 mutant. This was associated with reduced transfer of materials, such as lipids, to the developing pollen grains. In addition, a lining of sporopollenin-like deposits that coated the inner tangential wall of the normal tapetum, was discontinuous in the mutant. In mutant anthers where the tapetal cell wall did not loosen, the transfer of all materials was restricted and this resulted in the collapse of sporogenous material.     

白菜细胞核雄性不育花药的细胞化学观察

对一种由一对隐性基因控制的白菜细胞核雄性不育和可育株的花药进行了细胞学和组织化学研究。种子播种后,有1/4植株为不育株,其余的为可育株。通过对不育株和可育株花药发育的细胞学观察,确认不育花粉的败育发生在小孢子发育时期。用组织化学的方法研究了可育株和不育株花药发育过程中的多糖和脂类的分布动态,发现在减数分裂前,可育花药和不育花药的药隔细胞中都储藏了大量的淀粉粒。二者的差异仅是不育花药的绒毡层细胞液泡化明显。在减数分裂后的小孢子发育时期,可育花药的绒毡层细胞具有将药隔细胞中的淀粉粒多糖吸收并转化成脂类的功能,小孢子及以后的二胞花粉中也积累了大量的脂类储藏物质在不育花药中,虽然减数分裂后药隔细胞中的淀粉粒也都消失,但绒毡层细胞中的脂类物质相比很少,同时绒毡层细胞显示了明显的多糖反应,表明不育花药的绒毡层细胞将糖类转化为脂类的功能受阻。在小孢子的表面有些脂类物质,但在细胞质中却没有脂类积累。这一结果暗示在该种白菜细胞核雄性不育株中,由于花药绒毡层细胞转换多糖为脂类的功能失常,导致了小孢子的败育。     

POLLEN PORE DEVELOPMENT AND ITS SPATIAL ORIENTATION DURING MICROSPOROGENESIS IN THE GRASS SORGHUM BICOLOR

The spatial relationships observed during microsporogenesis and pollen development in Sorghum bicolor indicate that a strong polarization exists in the anther locule and within individual microspores and pollen grains. During all developmental stages, each sporogenous cell and its derivatives lie continuously adjacent to the tapetum. The microspores and pollen grains form depressions in the tapetal orbicular wall. When the single pore of each microspore is initiated, as a gap in the primexine, it too lies adjacent to the tapetum and remains tightly appressed there until pollen maturity. A sequence of polar phenomena in microspores and pollen grains centers on an axis through the pore and perpendicular to the tapetal surface. These events include migrations of the microspore and vegetative nuclei, initial placement of the generative cell opposite the pore and its later migration, and a polar engorgement process whereby the pore end of the pollen grain (adjacent to the tapetum) fills with starch grains first. The tapetal cytoplasm completely degenerates at precisely the time of pollen engorgement, and its degradation products are believed to be available for pollen uptake at this time. The continuous association of the sporogenous cells or their cellular derivatives and their pores with the tapetum is thought to play an indispensible role in pollen development in sorghum and probably in all other grasses as well. The consistent position of the pore adjacent to the tapetum should be considered another common feature of microsporogenesis in the Gramineae. The characteristic exine pattern forms over the operculum and annulus of the pore, but the lamellae, which underlie the annulus, form a highly modified multilayered nexine. Membrane-like cores are observed in these lamellae and are believed to be involved in the initiation of sporopollenin deposition, but they are obliterated by pollen maturity. Neither the cores nor the lamellae are found in other parts of the pore or in the nonapertured wall.     

<i>OsMAPK6</i> Affects Male Fertility by Reducing Microspore Number and Delaying Tapetum Degradation in <i>Oryza sativa</i> L.

The mitogen-activated protein kinase (MAPK) cascade is important in stress signal transduction and plant development. In the present study, we identified a rice (Oryza sativa L.) mutant with reduced fertility, Oryza sativa mitogen-activated protein kinase 6 (osmapk6), which harbored a mutated MAPK gene. Scanning and transmission electron microscopy, quantitative RT-PCR analysis, TUNEL assays, RNA in situ hybridization, longitudinal and transverse histological sectioning, and map-based cloning were performed to characterize the osmapk6 mutant. The gene OsMAPK6 was expressed throughout the plant but predominantly in the microspore mother cells, tapetal cells, and microspores in the anther sac. Compared with the wild type, the total number of microspores was reduced in the osmapk6 mutant. The formation of microspore mother cells was reduced in the osmapk6 anther sac at an early stage of anther development, which was the primary reason for the decrease in the total number of microspores. Programmed cell death of some tapetal cells was delayed in osmapk6 anthers and affected exine formation in neighboring microspores. These results suggest that OsMAPK6 plays pivotal roles in microspore mother cell formation and tapetal cell degradation.     

CYCLIC INVASION OF TAPETAL CELLS INTO LOCULI DURING MICROSPORE DEVELOPMENT IN NYMPHAEA COLORATA (NYMPHACEAE)

In work with Nymphaea colorata Peter three distinct intervals were recorded during which tapetal cells (protoplasts) protruded into anther locules either as bridges and partitions or as invasive cells between or around tetrads of microspores. Before these intervals and between and after them, tapetal cells, while variable in shape, were noninvasive. Observations were based on sections of over 60 fixed and epoxy-embedded anthers covering the relatively brief interval from the end of meiosis through the vacuolate microspore stage. The progression of development, from early microspore stages through the microspore vacuolate period, is illustrated by transmission electron micrographs showing change in proexine and exine size and complexity. Our results indicate cycles of tapetal cell differentiation and dedifferentiation in this species.     

Nuclear DNA synthesis during the induction of embryogenesis in cultured microspores and pollen of Brassica napus L.

The dynamics of nuclear DNA synthesis were analysed in isolated microspores and pollen of Brassica napus that were induced to form embryos. DNA synthesis was visualized by the immunocytochemical labelling of incorporated Bromodeoxyuridine (BrdU), applied continuously or as a pulse during the first 24 h of culture under embryogenic (32 °C) and non-embryogenic (18 °C) conditions. Total DNA content of the nuclei was determined by microspectrophotometry. At the moment of isolation, microspore nuclei and nuclei of generative cells were at the G1, S or G2 phase. Vegetative nuclei of pollen were always in G1 at the onset of culture. When microspores were cultured at 18 °C, they followed the normal gametophytic development; when cultured at 32 °C, they divided symmetrically and became embryogenic or continued gametophytic development. Because the two nuclei of the symmetrically divided microspores were either both labelled with BrdU or not labelled at all, we concluded that microspores are inducible to form embryos from the G1 until the G2 phase. When bicellular pollen were cultured at 18 °C, they exhibited labelling exclusively in generative nuclei. This is comparable to the gametophytic development that occurs in vivo. Early bicellular pollen cultured at 32 °C, however, also exhibited replication in vegetative nuclei. The majority of vegetative nuclei re-entered the cell cycle after 12 h of culture. Replication in the vegetative cells preceded division of the vegetative cell, a prerequisite for pollen-derived embryogenesis.     

S351┐1西瓜雄性不育的细胞学研究

西瓜Ｓ３５１－１雄性不育材料的细胞学观察表明：与对照的同系可育株相比,败育发生在次级造孢细胞到小孢子母细胞或小孢子四分体阶段,多数不育雄花花药中绒毡层始终未分化,药壁常由７－８层细胞组成,少数不育花药中出现绒毡层徒长现象;次级造孢细胞败育不同步,出现多核及多核仁现象,败育后期,药壁细胞逐渐解体,药室瓦解,花粉囊收缩变形。由此可见：其雄性不育与绒毡层的发育异常有直接联系。     

DNA Synthesis in Microspores in Anther Culture of Wheat (Triticum aestivum L.)

Anthers with mid-unlnucleate microspores were cultured on W5 medium supplemented with 0.5 mg/l kinetin, 2 mg/l 2,4-D and 9% or 3% sucrose. At a series of interval (0, 1, 1.5, 2, 14 days) after cultured, the anthers were labelled with 3H-thymidine (4 MCi/mi) for 24 h, fixed, and then performed autoradiography according to conventional method. Results show that after cultured for 24 h, 3H-thymidine was incorporated into some late-uninucleate microspores (see Plate I, 3), and after for 2.5 days, vegetative nuclei in pollen grains were la- belled (see Plate I, 4). Usually, vegetative nuclei were labelled frequently and generative ones were labelled rarely. Sometimes generative cell which could synthesis DNA might develop suspensor-like structure individually (see Plate I, 13). During early stage of development of a multicellular pollen grain, the DNA synthesis in the cells were synchronized. With pollen development, the synchronism of DNA synthesis was destroyed. When anthers cultured on medium with 3% sucrose, DNA in microspores could be synthesized normally, and the number of labelled microspores was more than that of anthers cultured on medium with 9% sucrose. However, on medium with 3% sucrose, the nuclei in microspores stopped dividing after one or two divisions and the cell wall of them could not be formed and multicellular pollen was not observed. It seems that the absence of multicellular pollen on medium with 3% sucrose was primarily due to the block of cell division and cell wall formation, not due to the interruption of DNA synthesis.     

The HKM gene, which is identical to the MS1 gene of Arabidopsis thaliana, is essential for primexine formation and exine pattern formation

A male-sterile mutant of Arabidopsis thaliana was isolated by T-DNA tagging screening. Using transmission electron microscopy analysis, we revealed that the microspores of this mutant did not have normal thick primexine on the microspore at the tetrad stage. Instead, a moderately electron-dense layer formed around the microspores. Although microspores without normal primexine failed to form a proper reticulate exine pattern at later stages, sporopollenin was deposited and an exine-like hackly structure was observed on the microspores during the microspore stage. Thus, this mutant was named hackly microspore (hkm). It is speculated that the moderately electron-dense layer was primexine, which partially played its role in sporopollenin deposition onto the microspore. Cytological analysis revealed that the tapetum of the hkm mutant was significantly vacuolated, and that vacuolated tapetal cells crushed the microspores, resulting in the absence of pollen grains within the anther at anthesis. Single nucleotide polymorphism analysis demonstrated that the hkm mutation exists within the MS1 gene, which has been reportedly expressed within the tapetum. Our results suggest that the critical process of primexine formation is under sporophytic control .     

Early signs of disruption of wheat anther development associated with the induction of male sterility by meiotic-stage water deficit

 Water deficit during meiosis in microspore mother cells of wheat (Triticum aestivum L.) induces male sterility, which reduces grain yield. In plants stressed during meiosis and then re-watered, division of microspore mother cells seems to proceed normally, but subsequent pollen development is arrested. Stress-affected anthers generally lack starch. We employed light microscopy in conjunction with histochemistry to compare the developmental anatomy of water-stress-affected and normal anthers. The earliest effects of stress, detectable between meiosis and young microspore stages, were the degeneration of meiocytes, loss of orientation of the reproductive cells, and abnormal vacuolization of tapetal cells. Other effects observed during subsequent developmental stages were deposition of starch in the connective tissue where it is normally not present, hypertrophy of the middle layer or endothecial cells, and deposition of sporopollenin-like substances in the anther loculus. The resulting pollen grains lacked both starch and intine. These results suggest that abnormal degeneration of the tapetum in water-stressed anthers coupled with a loss of orientation of the reproductive cells could be part of early events leading to abortion of microspores. Received: 19 July 1996 / Revision accepted: 6 November 1996     

Differences on the microsporogenesis and tapetal development of male fertile and cytoplasmic male sterile pepper (Capsicum annuum L.)

To clarify the time and cause of pollen abortion, differences on the microsporogenesis and tapetum development in the anthers of male fertile maintainer line and cytoplasmic male sterile (CMS) line pepper were studied using transmission electron microscopy. The results showed that CMS line anthers appeared to have much greater variability in developmental pattern than male fertile maintainer line ones. The earliest deviation from normal anther development occurred in CMS line anthers at prophase I was cytomixis in some microspore mother cells (MMCs), and vacuolisation in tapetal cells. Then, MMCs in CMS line anthers developed asynchronously and a small part of ones at the different stage degenerated in advance appearing to have typical morphological features of programmed cell death (PCD). Most MMCs could complete the meiosis, but formed non-tetrahedral tetrad microspores with irregular shape and different size and uncertain number of nuclei, and some degenerated ahead of time as well. Tapetal cells in CMS line anther degenerated during meiosis, and were crushed at the tetrad stage, which paralleled the collapse of pollens. Pollen abortion in CMS line anthers happened by PCD themselves, and the premature PCD of tapetal cells were closely associated with male sterility.     

Changes in calcium and calmodulin levels during microsporogenesis,pollen development and germination in Gasteria verrucosa (Mill.) H. Duval

Summary The distribution of membrane calcium and calmodulin (CaM) has been fluorimetrically determined in the anther of Gasteria verrucosa with particular attention to sporogenous cells, meiocytes, microspores, pollen and stages of pollen germination and tube growth using chlortetracycline (CTC) and fluphenazine (FPZ). CTC and FPZ fluorescence in sporogenous cells is relatively higher than in the adjacent tapetal cells, indicating higher membrane calcium and CaM levels in the former cell type. However, during meiosis there is a significant increase in membrane calcium and CaM levels in the meiocytes compared to that found in the young microspores. CTC and FPZ fluorescence in the sporogenous cells, meiocytes and young microspores is punctate and slightly diffused throughout the cytoplasm. In the microspores of the tetrad and the young released microspores CTC fluorescence (CTCf) is polarized and mainly associated with the area opposite the future colporal region. FPZ fluorescence (FPZf) becomes polarized in the young microspore. Subsequently, there is a shift in the polarity, and most of the CTCf and FPZf in the old microspores and pollen is regionalized towards the colporal region, and the fluorescence is more diffused, indicating a change in the organellar-bound calcium and CaM. This final graded distribution of CTCf is maintained during pollen germination in that the growing pollen tubes invariably show a tip to base membrane-calcium gradient. In the tapetal cells a high level of Ca²⁺ is present during the microspore stage. During the preparation for anthesis the endothecium differentiation is marked by the presence of Ca²⁺. Post-treatment of labelled cells with a Ca²⁺ chelator such as EGTA resulted in a substantial decrease in diffuse and punctate CTCf. Alternatively, treatment of cells with non-ionic detergent Nonidet P-40 resulted in the total elimination of CTCf, suggesting that the observed CTC fluorescence was due to membrane-associated calcium. The cytological specification of CTC as a probe for calcium is discussed. From cytofluorometric measurements and atomic absorption, it became clear that the level of Ca²⁺ in the anther is high during the sporogenous and meiotic phases. An increase in CTCf and FPZf occurred after microspore mitosis. An interaction of Ca²⁺ transport from tapetum to the young pollen is postulated. These findings suggest that the level of Ca²⁺ in the anther during meiosis is generally relatively higher than at the sporogenous or young microspore stage. These findings are discussed in the light of available information on the role of Ca²⁺ and CaM-mediated processes such as cell division, callose synthesis and pollen-tube tip growth.     

白菜核雄性不育花药超微结构的研究

对白菜核雄性不育两用系的可育与不育花药进行了超微结构的比较观察。结果显示不育花药的造孢细胞核仁靠边分布;包裹小孢子母细胞的胼胝质厚薄不均匀,不完整等早期异常现象。减数分裂后．四分体细胞中常有多个细胞核。从四分体释放出的小孢子外壁的孢粉素物质不均匀沉积,呈不连续的单层异常结构。最后小孢子通过细胞质收缩方式败育。在可育花药中．绒毡层细胞在小孢子发育后期已显示出退化迹象,同时在细胞中开始积累脂类物质。但在同时期的不育花药中．绒毡层细胞没有显示出退化的迹象,也不合成脂类物质。从时间上看,败育花药中小孢子母细胞及小孢子的异常在先,绒毡层细胞的异常在后。本研究揭示了白菜核雄性不育花药的超微结构特征．对我们以前的光学显微镜观察结果予以补充和修正。