Studies on the Morphology, Ontogeny and Embryology of the Flowers of Hedycarya Arborea J.R. et G. Forst. (Subfamily Monimioideae) and Laurelia Novae-Zelandiae A. Cunn. (Subfamily Atherospermoideae) of the Family Monimiaceae

<p>The inflorescences, flowers and the vascularization of floral parts of Hedycarya arborea and Laurelia novae-zelandiae were described and comparisons made with other members of the family in an attempt to determine the basic types of inflorescences, flowers and floral vascularization in the family. The vegetative, inflorescence and floral meristems of the two genera were compared. It was concluded that the vegetative apices of both had the tunica-corpus configuration typical of many other woody Ranales and other orders. The inflorescence apices were quite similar to the vegetative ones. The young floral apices are in a state of transition from a tunica-corpus to a mantle-core configuration and older floral apices had the mantle-core configuration, which is typical of the floral apices of many woody Ranales. Unusual features of the floral apices of Hedycarya and Laurelia were the lack of a pronounced rib meristem and the occurrence of relatively frequent divisions within vacuolate cells of the core. The ontogeny of the stamens of Hedycarya and Laurelia was described and comparisons were made. In both genera the micro-sporangium developed in a similar fashions: in Hedycarya 5-6 wall layers are formed inside the epidermis; in Laurelia there are 3-5 layers. Both genera had a typically thickened endothecium and a tapetum of the secretory type in which the tapetal cells become binucleate during the first meiotic division of the pollen mother cells. In Hedycarya the meiotic divisions of the pollen mother cells are of the successive type in which walls form by means of centrifugal cell plates Pollen grains remain in permanent tetrads in this genus. In Laurelia wall formation at the end of meiosis is of a modified simultaneous type, which may not have been hitherto described in the literature. Pollen grains are not in permanent tetrads. When the first division occurs in each microspore in Hedycarya, all four cells of a tetrad are at the same stage of division and the generative cell is cut off towards the distal face of the grain. Each microspore is in the two celled condition when shed. It was deduced that the generative cell is cut off against what represents a radial wall of the grain (with reference to the tetrad stage) in Laurelia. Pollen is shed in either the two or three celled condition. Comparisons were made with the development of microsporangia and male gametophytes in other woody Ranales. A study was made of the ontogeny, structure and function of the staminal appendages of Laurelia. It was found that the appendages function as nectaries, the nectar being predominantly sucrose. After a discussion of the various theories as to the morphological nature of the staminal appendages of the Laurales, it was concluded that they are morphologically staminodes. The carpels of Hedycarya and Laurelia have a basically similar ontogeny in which, as in the Lauraceae, the terminal stigmatic region develops from a solid terminal meristem in contrast to many woody Ranales in which the stigma-consists of crests which surround the external part of the cleft of the carpel. The ovules of Hedycarya and Laurelia resemble those of most other woody Ranales in being bitegmic, crassinucellate and anatropous with a monosporic 8-nucleate embryo sac of the Polygonum type. Both linear and T-shaped megaspore tetrads were found in the two genera. Laurelia has pseudocarps which develop after anthesis and enclose plumose achenes, but in Hedycarya the fruits are drupes. It was concluded that Laurelia and Hedycarya belong to two subfamilies which have been separated from each other for a long time and have undergone considerable evolution in different directions. It was also concluded that the Monimiaceae are closely related to the Lauraceae.</p>

Studies on the Morphology, Ontogeny and Embryology of the Flowers of Hedycarya Arborea J.R. et G. Forst. (Subfamily Monimioideae) and Laurelia Novae-Zelandiae A. Cunn. (Subfamily Atherospermoideae) of the Family Monimiaceae

<p>The inflorescences, flowers and the vascularization of floral parts of Hedycarya arborea and Laurelia novae-zelandiae were described and comparisons made with other members of the family in an attempt to determine the basic types of inflorescences, flowers and floral vascularization in the family. The vegetative, inflorescence and floral meristems of the two genera were compared. It was concluded that the vegetative apices of both had the tunica-corpus configuration typical of many other woody Ranales and other orders. The inflorescence apices were quite similar to the vegetative ones. The young floral apices are in a state of transition from a tunica-corpus to a mantle-core configuration and older floral apices had the mantle-core configuration, which is typical of the floral apices of many woody Ranales. Unusual features of the floral apices of Hedycarya and Laurelia were the lack of a pronounced rib meristem and the occurrence of relatively frequent divisions within vacuolate cells of the core. The ontogeny of the stamens of Hedycarya and Laurelia was described and comparisons were made. In both genera the micro-sporangium developed in a similar fashions: in Hedycarya 5-6 wall layers are formed inside the epidermis; in Laurelia there are 3-5 layers. Both genera had a typically thickened endothecium and a tapetum of the secretory type in which the tapetal cells become binucleate during the first meiotic division of the pollen mother cells. In Hedycarya the meiotic divisions of the pollen mother cells are of the successive type in which walls form by means of centrifugal cell plates Pollen grains remain in permanent tetrads in this genus. In Laurelia wall formation at the end of meiosis is of a modified simultaneous type, which may not have been hitherto described in the literature. Pollen grains are not in permanent tetrads. When the first division occurs in each microspore in Hedycarya, all four cells of a tetrad are at the same stage of division and the generative cell is cut off towards the distal face of the grain. Each microspore is in the two celled condition when shed. It was deduced that the generative cell is cut off against what represents a radial wall of the grain (with reference to the tetrad stage) in Laurelia. Pollen is shed in either the two or three celled condition. Comparisons were made with the development of microsporangia and male gametophytes in other woody Ranales. A study was made of the ontogeny, structure and function of the staminal appendages of Laurelia. It was found that the appendages function as nectaries, the nectar being predominantly sucrose. After a discussion of the various theories as to the morphological nature of the staminal appendages of the Laurales, it was concluded that they are morphologically staminodes. The carpels of Hedycarya and Laurelia have a basically similar ontogeny in which, as in the Lauraceae, the terminal stigmatic region develops from a solid terminal meristem in contrast to many woody Ranales in which the stigma-consists of crests which surround the external part of the cleft of the carpel. The ovules of Hedycarya and Laurelia resemble those of most other woody Ranales in being bitegmic, crassinucellate and anatropous with a monosporic 8-nucleate embryo sac of the Polygonum type. Both linear and T-shaped megaspore tetrads were found in the two genera. Laurelia has pseudocarps which develop after anthesis and enclose plumose achenes, but in Hedycarya the fruits are drupes. It was concluded that Laurelia and Hedycarya belong to two subfamilies which have been separated from each other for a long time and have undergone considerable evolution in different directions. It was also concluded that the Monimiaceae are closely related to the Lauraceae.</p>

The Culture and Correlative Electron Microscopy of Pollen Mother Cells in Meiosis: Development of Techniques and Some Observations on Selected Topics

<p>Reliable techniques for the living cell culture and correlative light and electron microscopy (EM) of meiotic pollen mother cells (PMCs) of Iris spuria, Allium triquetrum and Tradescantia flumenensis are described in detail. Living PMCs were successfully cultured in a slide chamber on agar/sucrose medium. Cells were covered with an inert oil to prevent their dehydration, and some cells were cultured from metaphase I to tetrad cell formation over a 20 hour period. Other PMCs were fixed with glutaraldehyde and flat embedded using a modification of the agar sandwich technique of Mole-Bajer and Bajer (1968). This technique was developed to permit the preselection of PMCs at known meiotic stages, for subsequent EM examination. Serial thin sections were cut at known planes of section; and 3-D reconstructions of MT distribution, and MT counts from transverse sections were completed. It was also possible to examine sections of an Iris anaphase I PMC which had been previously studied in life. Anaphase I and II chromosome velocities were analysed in the three species. Mean velocities were approximately 0.5 mu m/min with some variation from cell to cell and between sister half-spindles. In Allium anaphase I there was also variation in chromosome velocity within the half-spindle; and this variation was found not to be related to chromosome position on the metaphase I plate. Spindle elongation was zero in Allium anaphase I and in Iris anaphase II, but was detectable in Allium anaphase II (40%) and in "Iris anaphase I (l5%). The extent of spindle elongation in Tradescantia could not be determined. The kinetochore region in the first meiotic division consisted of two closely appressed, but structurally (and functionally) distinct, sister kinetochores. At meiosis II, the two sister kinetochores were separate from each other and faced opposite poles. The kinetochore arrangement probably changes from side-by-side (meiosis I) to back-to-back (meiosis II) during chromosome recondensation at prophase II in these cells. Bundles of non-kinetochore microtubules (nkMTs) span the interzone between sister chromosome units at metaphase I and II and anaphase II. Bundles of kinetochore MTs (kMTs) do not increase in divergence at any stage of meiosis studied; there was little interaction between nkMTs and kMTs, and MT-MT cross bridges were rare. These observations are not consistent with models of chromosome movement based on MT sliding or zipping. No relationship was found between nkMT distribution and spindle elongation, and the several different nkMT distributions which have been reported for other cell types may be variations on a structural theme. Spindle endoplasmic reticulum (ER) in meiosis II was found to be derived largely from invaginations and evaginations of the nuclear envelope. Growth of existing spindle ER was proposed to account for the doubling in the amount of ER observed between interphase and prometaphase II. Randomly oriented elements of ER, in early prometaphase II spindles may become passively aligned along the interpolar axis and then actively transported polewards at later stages of prometaphase II and metaphase II. Suggestions for future research are offered.</p>

The Culture and Correlative Electron Microscopy of Pollen Mother Cells in Meiosis: Development of Techniques and Some Observations on Selected Topics

<p>Reliable techniques for the living cell culture and correlative light and electron microscopy (EM) of meiotic pollen mother cells (PMCs) of Iris spuria, Allium triquetrum and Tradescantia flumenensis are described in detail. Living PMCs were successfully cultured in a slide chamber on agar/sucrose medium. Cells were covered with an inert oil to prevent their dehydration, and some cells were cultured from metaphase I to tetrad cell formation over a 20 hour period. Other PMCs were fixed with glutaraldehyde and flat embedded using a modification of the agar sandwich technique of Mole-Bajer and Bajer (1968). This technique was developed to permit the preselection of PMCs at known meiotic stages, for subsequent EM examination. Serial thin sections were cut at known planes of section; and 3-D reconstructions of MT distribution, and MT counts from transverse sections were completed. It was also possible to examine sections of an Iris anaphase I PMC which had been previously studied in life. Anaphase I and II chromosome velocities were analysed in the three species. Mean velocities were approximately 0.5 mu m/min with some variation from cell to cell and between sister half-spindles. In Allium anaphase I there was also variation in chromosome velocity within the half-spindle; and this variation was found not to be related to chromosome position on the metaphase I plate. Spindle elongation was zero in Allium anaphase I and in Iris anaphase II, but was detectable in Allium anaphase II (40%) and in "Iris anaphase I (l5%). The extent of spindle elongation in Tradescantia could not be determined. The kinetochore region in the first meiotic division consisted of two closely appressed, but structurally (and functionally) distinct, sister kinetochores. At meiosis II, the two sister kinetochores were separate from each other and faced opposite poles. The kinetochore arrangement probably changes from side-by-side (meiosis I) to back-to-back (meiosis II) during chromosome recondensation at prophase II in these cells. Bundles of non-kinetochore microtubules (nkMTs) span the interzone between sister chromosome units at metaphase I and II and anaphase II. Bundles of kinetochore MTs (kMTs) do not increase in divergence at any stage of meiosis studied; there was little interaction between nkMTs and kMTs, and MT-MT cross bridges were rare. These observations are not consistent with models of chromosome movement based on MT sliding or zipping. No relationship was found between nkMT distribution and spindle elongation, and the several different nkMT distributions which have been reported for other cell types may be variations on a structural theme. Spindle endoplasmic reticulum (ER) in meiosis II was found to be derived largely from invaginations and evaginations of the nuclear envelope. Growth of existing spindle ER was proposed to account for the doubling in the amount of ER observed between interphase and prometaphase II. Randomly oriented elements of ER, in early prometaphase II spindles may become passively aligned along the interpolar axis and then actively transported polewards at later stages of prometaphase II and metaphase II. Suggestions for future research are offered.</p>

Chromosome behavior during meiosis in pollen mother cells from Saccharum officinarum × Erianthus arundinaceus F1 hybrids

Background In recent years, sugarcane has attracted increasing attention as an energy crop. Wild resources are widely used to improve the narrow genetic base of sugarcane. However, the infertility of F1 hybrids between Saccharum officinarum (S. officinarum) and Erianthus arundinaceus (E. arundinaceus) has hindered sugarcane breeding efforts. To discover the cause of this infertility, we studied the hybridization process from a cytological perspective. Results We examined the meiotic process of pollen mother cells (PMCs) in three F1 hybrids between S. officinarum and E. arundinaceus. Cytological analysis showed that the male parents, Hainan 92–77 and Hainan 92–105, had normal meiosis. However, the meiosis process in F1 hybrids showed various abnormal phenomena, including lagging chromosomes, micronuclei, uneven segregation, chromosome bridges, and inability to form cell plates. Genomic in situ hybridization (GISH) showed unequal chromatin distribution during cell division. Interestingly, 96.70% of lagging chromosomes were from E. arundinaceus. Furthermore, fluorescence in situ hybridization (FISH) was performed using 45S rDNA and 5S rDNA as probes. Either 45S rDNA or 5S rDNA sites were lost during abnormal meiosis, and results of unequal chromosomal separation were also clearly observed in tetrads. Conclusions Using cytogenetic analysis, a large number of meiotic abnormalities were observed in F1. GISH further confirmed that 96.70% of the lagging chromosomes were from E. arundinaceus. Chromosome loss was found by further investigation of repeat sequences. Our findings provide insight into sugarcane chromosome inheritance to aid innovation and utilization in sugarcane germplasm resources.

Assessment of the roles of SPO11-2 and SPO11-4 in meiosis in rice using CRISPR/Cas9 mutagenesis

In Arabidopsis, chromosomal double-strand breaks at meiosis are presumably catalyzed by two distinct SPO11 transesterases, AtSPO11-1 and AtSPO11-2, together with M-TOPVIB. To clarify the roles of the SPO11 paralogs in rice, we used CRISPR/Cas9 mutagenesis to produce null biallelic mutants in OsSPO11-1, OsSPO11-2, and OsSPO11-4. Similar to Osspo11-1, biallelic mutations in the first exon of OsSPO11-2 led to complete panicle sterility. Conversely, all Osspo11-4 biallelic mutants were fertile. To generate segregating Osspo11-2 mutant lines, we developed a strategy based on dual intron targeting. Similar to Osspo11-1, the pollen mother cells of Osspo11-2 progeny plants showed an absence of bivalent formation at metaphase I, aberrant segregation of homologous chromosomes, and formation of non-viable tetrads. In contrast, the chromosome behavior in Osspo11-4 male meiocytes was indistinguishable from that in the wild type. While similar numbers of OsDMC1 foci were revealed by immunostaining in wild-type and Osspo11-4 prophase pollen mother cells (114 and 101, respectively), a surprisingly high number (85) of foci was observed in the sterile Osspo11-2 mutant, indicative of a divergent function between OsSPO11-1 and OsSPO11-2. This study demonstrates that whereas OsSPO11-1 and OsSPO11-2 are the likely orthologs of AtSPO11-1 and AtSPO11-2, OsSPO11-4 has no major role in wild-type rice meiosis.

Impactul destabilizator al infecțiilor virale asupra microsporogenezei la plantele gazdă

The pathogenicity reactions described in the sensitive genotypes of tomatoes and barley include specifically changes in the processes of meiotic division, with repercussions in the offspring of infected plants. The percentage of aberrant pollen mother cells (PMCs) in the offspring is at the level of control plants, while the percentage of aberrations per PMC and the frequency of meiotic conjugation are significantly higher. The consequences in meiotic division in virus free progenies reflect the destabilizing transgenerational effect of viral infection on microsporogenesis processes.

Cytogenetic characterization of a triploid mulberry (Morus spp.) cultivar Suvarna-2

Mulberry exehibits a high degree of polyploidy ranging from haploidy to docosaploidy and its various species are being cultivated for foliage to practice sericulture and edible fruits. Triploid mulberries for sericulture porpuse and higher polyploids are proved to be superior. The cultivar Suvarna-2 is an improved high leaf yielding triploid in south India. The meiotic behavior of this cultivar has been presented here. Meiosis was highly irregular. Various anomalies such as univalent, bivalents, trivalent, hexavalent, loose association, unequal separation and precocious movement of chromosomes and laggards have been observed in pollen mother cells. These irregularities prevented the formation of viable gamete that leads to pollen sterility.