Sexual Plant Reproduction最新文献

Egg development in Pteridium aquilinum var. latiusculum was studied using ultrastructural and cytochemical methods to examine structural features influencing fertilization in leptosporangiate ferns. Ultrastructural observations indicate a separation cavity is first formed above the egg during oogenesis with a pore region persistently connecting the egg and the ventral canal cell. The egg envelope is formed by deposition of amorphous materials in the separation cavity on the outer surface of plasmalemma. The egg envelope was not formed across the pore region; instead, a fertilization pore was formed. During oogenesis, the egg nucleus produced extensive evaginations containing osmiophilic bodies. Cytochemical experiments revealed that the egg envelope displays strong periodic acid-Schiff reaction indicative of polysaccharides, with negligible Sudan black B staining for lipids, suggesting that the egg envelope is composed principally of polysaccharides, and not lipids. The present manuscript provides new insights into egg structure and development of Pteridium, including discovery and characterization of the fertilization pore and observations on the chemical nature of the egg envelope, thus contributing to the understanding of the cytological mechanism of the sexual reproduction of ferns.

Sexual reproduction is essential for the propagation of higher plants. From an agronomical point of view, this is a particularly key process because fertilization guarantees fruit formation in most cultivated fruit species. In the olive, however, in spite of its agricultural importance, little attention has been paid to the study of sexual reproduction. In order to investigate the cellular and molecular mechanisms that regulate pollen-pistil interactions in the olive during the progamic phase, it is essential to first have a good knowledge of the reproductive structures involved in such interactions. This study characterizes the anatomical and ultrastructural changes in the olive pistil, beginning from the young pistil developing within the bud until the time of petal loss and visible stigma senescence. We have correlated changes in the pistil with a series of defined floral developmental stages and determined that olive pistil structures cannot be considered completely mature and ready to be pollinated and fertilized until the onset of anthesis. Our results clearly show histological and ultrastructural variation during the diverse flowering events. We discuss whether the changes observed might influence or result from pollen-pistil interactions during the progamic phase.

We isolated protoplasts from male and female gametophytes of a strictly dioecious strain of the coenocytic marine green alga Bryopsis plumosa. The protoplasts successfully developed into macrothalli. These in turn produced swimming cells, which appeared similar to biflagellated gametes even when the mixed protoplasts were comprised of protoplasm from male and female gametophytes. We found that swimming cell sizes depended on the male/female protoplasm ratio; macrothalli successfully produced swimming cells with male/female protoplasm ratios of 10:0; 9:1; 7:3; 5:5; 1:9; and 0:10. In male/female protoplasm ratios ranging from equal to strongly female biased (5:5; 3:7; 1:9), swimming cells exhibited normal behaviors of gametes and resultant zygotes, displaying positive and negative phototaxis, respectively. Negatively phototactic swimming cells were quadriflagellated and had two nuclei, apparently as a result of fusion, but never developed into microthalli. Thus, these swimming cells might lack functionality essential for normal gametes. Our findings suggested that natural monoecy observed in this genus did not originate from hybridization of protoplasm between the sexes.

Agave tequilana is a monocarpic perennial species that flowers after 5-8 years of vegetative growth signaling the end of the plant's life cycle. When fertilization is unsuccessful, vegetative bulbils are induced on the umbels of the inflorescence near the bracteoles from newly formed meristems. Although the regulation of inflorescence and flower development has been described in detail for monocarpic annuals and polycarpic species, little is known at the molecular level for these processes in monocarpic perennials, and few studies have been carried out on bulbils. Histological samples revealed the early induction of umbel meristems soon after the initiation of the vegetative to inflorescence transition in A. tequilana. To identify candidate genes involved in the regulation of floral induction, a search for MADS-box transcription factor ESTs was conducted using an A. tequilana transcriptome database. Seven different MIKC MADS genes classified into 6 different types were identified based on previously characterized A. thaliana and O. sativa MADS genes and sequences from non-grass monocotyledons. Quantitative real-time PCR analysis of the seven candidate MADS genes in vegetative, inflorescence, bulbil and floral tissues uncovered novel patterns of expression for some of the genes in comparison with orthologous genes characterized in other species. In situ hybridization studies using two different genes showed expression in specific tissues of vegetative meristems and floral buds. Distinct MADS gene regulatory patterns in A. tequilana may be related to the specific reproductive strategies employed by this species.

Zygospore formation in different strains of the Closterium peracerosum-strigosum-littorale complex was examined in this unicellular isogamous charophycean alga to shed light on gametic mating strains in this taxon, which is believed to share a close phylogenetic relationship with land plants. Zygospores typically form as a result of conjugation between mating-type plus (mt(+)) and mating-type minus (mt(-)) cells during sexual reproduction in the heterothallic strain, similar to Chlamydomonas. However, within clonal cells, zygospores are formed within homothallic strains, and the majority of these zygospores originate as a result of conjugation of two recently divided sister gametangial cells derived from one vegetative cell. In this study, we analyzed conjugation of homothallic cells in the presence of phylogenetically closely related heterothallic cells to characterize the reproductive function of homothallic sister gametangial cells. The relative ratio of non-sister zygospores to sister zygospores increased in the presence of heterothallic mt(+) cells, compared with that in the homothallic strain alone and in a coculture with mt(-) cells. Heterothallic cells were surface labeled with calcofluor white, permitting fusions with homothallic cells to be identified and confirming the formation of hybrid zygospores between the homothallic cells and heterothallic mt(+) cells. These results show that at least some of the homothallic gametangial cells possess heterothallic mt(-)-like characters. This finding supports speculation that division of one vegetative cell into two sister gametangial cells is a segregative process capable of producing complementary mating types.

Male gametophyte development leading to the formation of a mature pollen grain is precisely controlled at various levels, including transcriptional, post-transcriptional and post-translational, during its whole progression. Transcriptomic studies exploiting genome-wide microarray technologies revealed the uniqueness of pollen transcriptome and the dynamics of early and late successive global gene expression programs. However, the knowledge of transcription regulation is still very limited. In this study, we focused on the identification of pollen-expressed transcription factor (TF) genes involved in the regulation of male gametophyte development. To achieve this, the reverse genetic approach was used. Seventy-four T-DNA insertion lines were screened, representing 49 genes of 21 TF families active in either early or late pollen development. In the screen, ten phenotype categories were distinguished, affecting various structural or functional aspects, including pollen abortion, presence of inclusions, variable pollen grain size, disrupted cell wall structure, cell cycle defects, and male germ unit organization. Thirteen lines were not confirmed to contain the T-DNA insertion. Among 61 confirmed lines, about half (29 lines) showed strong phenotypic changes (i.e., ≥ 25% aberrant pollen) including four lines that produced a remarkably high proportion (70-100%) of disturbed pollen. However, the remaining 32 lines exhibited mild defects or resembled wild-type appearance. There was no significant bias toward any phenotype category among early and late TF genes, nor, interestingly, within individual TF families. Presented results have a potential to serve as a basal information resource for future research on the importance of respective TFs in male gametophyte development.

To elucidate the functional differences in how Arabidopsis stigmas regulate pollen hydration and germination, we analyzed receptivity of stigmas, epidermal surfaces (leaves, stems of inflorescence bolts, and floral organs), and an abiotic surface (cover glass) for pollen hydration and germination. Using 65% relative humidity (RH), we found that mature pollen grains were able to hydrate and germinate on stigmas at flower developmental stages 9-13, but not on the distal end of pistils at stage 8, epidermal surfaces, or glass. Furthermore, under 100% RH, pollen grains could hydrate on all tested surfaces, but pollen germination was observed only on the young floral organs (stages 9-12) and the stigmas at stages 9-13. The distal ends of pistils at stage 8, the epidermal surfaces, and the cover glass did not support pollen germination even under 100% RH. Our results indicate that pistil factors regulating pollen hydration and germination are synthesized at stage 9 when stigmatic papillar cells begin to develop. Although pistil factors involved in pollen hydration may only be present on the stigma, the factors involved in pollen germination may localize on both the stigma and surfaces of unopened floral organs.

Sexual plant reproduction requires multiple pollen-pistil interactions from the stigma (pollen adhesion, hydration, and germination) to the ovary (fertilization). Understanding the factors that regulate pollen tube growth is critical to understanding the processes essential to sexual reproduction. Many pollen tube growth assays (PTGAs) have shorter and slower pollen tube growth when compared to pollen tube growth through the style. The identification and study of factors that regulate pollen tube growth have been impeded by a lack of an efficient and reproducible PTGA. The objective of this research is to develop a robust assay for Nicotiana tabacum pollen tube growth in an environment that supports sustained and normal growth yet is amenable to testing the effects of specific factors. In this paper, we introduce a novel PTGA, which uses pistils from N. tabacum that lack a mature transmitting tract (TT) due to tissue-specific ablation. The TT-ablated style supports normal pollen tube growth and the hollow structure of the style allows modification of the growth environment by direct injection of test material. This PTGA is robust and allows for rapid and accurate measurement of pollen tube length and pollen tube morphology, supporting pollen tube growth from 20 to 35°C and at pH ranging from 4.8 to 7.6. Use of the ablated style for a PTGA is a novel method for the culture of pollen tubes with sustained growth in vivo while permitting the application of treatments to the growing pollen tubes.

The development of the egg and canal cells in the fern Osmunda japonica Thunb. was studied during oogenesis by transmission electron microscopy. The mature egg possesses no fertilization pore and no typical egg envelope. In addition, an extra wall formed around the canal cells during oogenesis and apparently blocked protoplasmic connections between the egg and the canal cells. The periodic acid Schiff (PAS) reaction revealed that the extra wall was most likely composed of polysaccharides. Maturation of the egg was accompanied by the formation of a separation cavity above the egg and by some changes in the morphology of the nucleus and cytoplasmic organelles. The chromatin of the nucleus becomes condensed and the upper surface of the nucleus becomes closely associated with the plasmalemma. Amyloplasts in the egg cytoplasm were numerous and conspicuous, with most in close proximity to the nucleus. Finally, the cytoplasm on one side of the egg became vesiculated and the overlying plasmalemma was easily disrupted. These cytological features of the egg and the canal cells during oogenesis in O. japonica are markedly different from those of the leptosporangiate ferns and suggest a significant evolutionary divergence in reproductive cellular features between Osmundaceae and leptosporangiate ferns.

Phosphoinositides are important lipids involved in membrane identity, vesicle trafficking, and intracellular signaling. In recent years, phosphoinositides have been shown to play a critical role in polarized secretion in plants, as perturbations of phosphoinositide metabolism, through loss of function mutants, result in defects in root hair elongation and pollen tube growth, where polarized secretion occurs rapidly. In the Brassicaceae, responses of stigmatic papillae to compatible pollen are also thought to involve highly regulated secretory events to facilitate pollen hydration and penetration of the pollen tube through the stigmatic surface. We therefore sought to analyze the female sporophyte fertility of the root hair defective4-1 mutant and the PI 4-kinase β1/β2 double mutant, which differentially affect phosphatidylinositol-4-phosphate (PI4P) levels. Stigmas from both mutants supported slower rates of pollen grain hydration, and the fecundity of these mutants was also diminished as a result of failed pollination events. This study therefore concludes that PI4P is integral to appropriate pistil responses to compatible pollen.