Process Of Pollen Tube Growth Research Articles

The Role of Calcium/Calcium-Dependent Protein Kinases Signal Pathway in Pollen Tube Growth.

Pollen tube (PT) growth as a key step for successful fertilization is essential for angiosperm survival and especially vital for grain yield in cereals. The process of PT growth is regulated by many complex and delicate signaling pathways. Among them, the calcium/calcium-dependent protein kinases (Ca2+/CPKs) signal pathway has become one research focus, as Ca2+ ion is a well-known essential signal molecule for PT growth, which can be instantly sensed and transduced by CPKs to control myriad biological processes. In this review, we summarize the recent progress in understanding the Ca2+/CPKs signal pathway governing PT growth. We also discuss how this pathway regulates PT growth and how reactive oxygen species (ROS) and cyclic nucleotide are integrated by Ca2+ signaling networks.

Pollination, Fertilization, and Embryo Development in Southern China Fresh-eating Jujube

To explore the reasons for seed abortion in southern China fresh-eating jujube, improve its reproductive biology, and provide a theoretical basis for the crossbreeding of jujube, we carried out self-pollination and cross-pollination experiments with Ziziphus jujuba Mill. ‘Zhongqiusucui’ as the female parent. We observed the process of pollen tube growth in pistil and embryo development by fluorescence microscopy and paraffin section methods. The results show there were self- and cross-incompatibilities during pollination and fertilization, and there were no significant differences in pollen germination and pollen tube growth between self-pollination and cross-pollination. It took at least 4 hours for pollen and stigma to recognize each other, 6 hours for pollen to germinate on the stigma, and 12 hours for the pollen tube to penetrate the mastoid cells of the stigma. After 48 hours of pollination, the pollen tube reached one third of the style. The pollen tube remained stagnant 72 to 120 hours after pollination, and remained at one third of the stylar canal. Simultaneously, the pollen tubes on the stigma twisted and interacted with each other, and expanded into a spherical shape. A few pollen tubes reached the ovary and completed fertilization. However, some early globular embryos degenerated before forming into globular embryos and resulted in the formation of empty embryo sacs, which leads to seed abortion. In conclusion, the poor pollination and fertilization, and the blocked development of the embryo resulted in seed abortion in Z. jujuba ‘Zhongqiusucui’.

Pollination, Fertilization, and Embryo Development in Southern China Fresh-eating Jujube

To explore the reasons for seed abortion in southern China fresh-eating jujube, improve its reproductive biology, and provide a theoretical basis for the crossbreeding of jujube, we carried out self-pollination and cross-pollination experiments with Ziziphus jujuba Mill. ‘Zhongqiusucui’ as the female parent. We observed the process of pollen tube growth in pistil and embryo development by fluorescence microscopy and paraffin section methods. The results show there were self- and cross-incompatibilities during pollination and fertilization, and there were no significant differences in pollen germination and pollen tube growth between self-pollination and cross-pollination. It took at least 4 hours for pollen and stigma to recognize each other, 6 hours for pollen to germinate on the stigma, and 12 hours for the pollen tube to penetrate the mastoid cells of the stigma. After 48 hours of pollination, the pollen tube reached one third of the style. The pollen tube remained stagnant 72 to 120 hours after pollination, and remained at one third of the stylar canal. Simultaneously, the pollen tubes on the stigma twisted and interacted with each other, and expanded into a spherical shape. A few pollen tubes reached the ovary and completed fertilization. However, some early globular embryos degenerated before forming into globular embryos and resulted in the formation of empty embryo sacs, which leads to seed abortion. In conclusion, the poor pollination and fertilization, and the blocked development of the embryo resulted in seed abortion in Z. jujuba ‘Zhongqiusucui’.

Friend or foe: Signaling mechanisms during double fertilization in flowering seed plants.

Since the first description of double fertilization 120 years ago, the processes of pollen tube growth and guidance, sperm cell release inside the receptive synergid cell, as well as fusion of two sperm cells to the female gametes (egg and central cell) have been well documented in many flowering plants. Especially microscopic techniques, including live cell imaging, were used to visualize these processes. Molecular as well as genetic methods were applied to identify key players involved. However, compared to the first 11 decades since its discovery, the past decade has seen a tremendous advancement in our understanding of the molecular mechanisms regulating angiosperm fertilization. Whole signaling networks were elucidated including secreted ligands, corresponding receptors, intracellular interaction partners, and further downstream signaling events involved in the cross-talk between pollen tubes and their cargo with female reproductive cells. Biochemical and structural biological approaches are now increasingly contributing to our understanding of the different signaling processes required to distinguish between compatible and incompatible interaction partners. Here, we review the current knowledge about signaling mechanisms during above processes with a focus on the model plants Arabidopsis thaliana and Zea mays (maize). The analogy that many of the identified "reproductive signaling mechanisms" also act partly or fully in defense responses and/or cell death is also discussed.

Dynamics of nuclear phase changes during pollen tube growth by using in vitro culture in Petunia

In flowering plants, pollen germinates to deliver sperm cells to the egg and central cells during double fertilization. In a bicellular pollen species, sperm cells are formed as the pollen tube grows. However, the process of pollen tube growth is difficult to observe as it proceeds in inside the pistil. Here, an in vitro liquid pollen culture system was applied to pollen of Petunia cultivars to analyze the nuclear phase transitions during pollen tube growth by microscopy and flow cytometry. The pollen germination frequencies for eight Petunia cultivars were initially evaluated. Among them, the cultivar ‘Chiffon’ showed the highest pollen germination frequency and was used for further analysis. Fluorescence microscopy revealed that pollen had two nuclei just after germination, indicating the generative and vegetative cells. Twelve hours after pollen germination, three nuclei were observed in the cultures, suggesting that nuclei indicated two sperm cells and one vegetative cell had developed and the generative cells had divided in vitro. Flow cytometry successfully detected nuclear phase changes during pollen tube growth, and the analysis suggested male germ unit formation, which develops from the connection between the generative and vegetative cells, or between the two sperm cells and the vegetative cell. These results show that the pollen grains could germinate in vitro and generative cells could divide to form sperm cells under these culture conditions. This in vitro liquid pollen culture system will shed light on physiological events regulated in pollen tubes.

The pollen tube journey in the pistil and imaging the in vivo process by two-photon microscopy

The process of pollen germination and tube growth in the pistil involves a series of cell-cell interactions, some facilitating fertilization while others prohibiting pollen tube access to the female gametophyte, either because of incompatibility or as a result of mechanisms to avert polyspermy and to ensure reproductive success. Understanding pollen tube growth and guidance to the female gametophyte has long been a pursuit among plant biologists, and observations indicate that diverse strategies may be adopted by different plant species. Recent studies in Arabidopsis, maize, and Torenia fournieri suggest that low molecular weight secretory molecules probably play major roles in the short-range attraction of pollen tubes to the female gametophyte. The process of pollen tube growth in the pistil occurs beneath several cell layers so much of the information that conveys the intimate partnership between penetrating pollen tubes and the female tissues has come from fixed samples and observations of in vitro pollen tube growth responses to female factors. A unique glimpse of the in vivo pollen germination and tube growth process is provided here by intra-vital two-photon excitation (TPE) microscopy of pollinated Arabidopsis pistils that remained on intact plants. Further discoveries of critical factors of male or female origins and how they control the pollen tube growth and fertilization process will broaden our understanding of the common themes and diverse strategies that plants have evolved to ensure reproductive success. The advancement of imaging technology to monitor pollination and fertilization and the development of probes to monitor various aspects of the pollen tube growth process, including pollen intracellular dynamics, will allow us to superimpose details obtained from studying pollen tube growth in culture conditions to interpret and understand the in vivo events.

Ion transporters involved in pollen germination and pollen tube tip-growth

Pollen germination (PG) and pollen tube growth (PTG) play crucial roles in sexual reproduction of flowering plants by sending sperm cells to the ovule. These two processes are regarded as ideal model system for the study of cell signaling and cell polarized growth. It has been considered for a long time that ion transports across the pollen tube membranes are essential for pollen tube navigation and growth. Previous transcriptome analyses for Arabidopsis have shown that the transcripts related to cellular transport are correspondingly overrepresented during the process of pollen tube growth. Here, we showed that 459 transporter genes expressed during PG and PTG in Arabidopsis. In addition, the gene expression profiles of ion (including Ca2+, H+, K+, Cl-) channels and transporters were further analyzed. This analysis provides novel information for the potential candidate genes involving in ion fluxes across the pollen tube membranes and in regulation of pollen tube tip growth.

Mode of pollen tube growth in pistils ofTicodendron incognitum(Ticodendraceae, Fagales) and the evolution of chalazogamy

Ticodendron incognitum is the sole species of the Ticodendraceae, which was established as a new family in the Fagales less than 20 years ago. Considering the diverse modes of pollen tube growth observed in other Fagales, we investigated the growth of pollen tubes in the pistil of Ticodendron. At the time of pollination, T. incognitum had four immature ovules in a bilocular ovary, thus exhibiting delayed fertilization, as in other Fagales. During the period when fertilization was delayed, pollen tube growth in the pistil was intermittent, consisting of five steps associated with development of the ovules and embryo sacs. Four cessation sites occurred: in the style, in the tissue of the upper part of the ovary, inside and outside of the funicle and at the chalaza. A single pollen tube eventually reaches a mature embryo sac through the chalaza in one of the four ovules. While both delayed fertilization and intermittent pollen tube growth play a role in male and female gametophyte selection, as in other Fagales, the five-step process of pollen tube growth through the chalaza (i.e. chalazogamy) is characteristic of lineages of the Casuarinaceae, Ticodendraceae and Betulaceae (the latter with the loss of one step). © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 157, 621–631.

The Dynamic Pollen Tube Cytoskeleton: Live Cell Studies Using Actin-Binding and Microtubule-Binding Reporter Proteins

Pollen tubes elongate within the pistil to transport sperm cells to the embryo sac for fertilization. Growth occurs exclusively at the tube apex, rendering pollen tube elongation a most dramatic polar cell growth process. A hallmark pollen tube feature is its cytoskeleton, which comprises elaborately organized and dynamic actin microfilaments and microtubules. Pollen tube growth is dependent on the actin cytoskeleton; its organization and regulation have been examined extensively by various approaches, including fluorescent protein labeled actin-binding proteins in live cell studies. Using the previously described GFP-NtADF1 and GFP-LlADF1, and a new actin reporter protein NtPLIM2b-GFP, we re-affirm that the predominant actin structures in elongating tobacco and lily pollen tubes are long, streaming actin cables along the pollen tube shank, and a subapical structure comprising shorter actin cables. The subapical collection of actin microfilaments undergoes dynamic changes, giving rise to the appearance of structures that range from basket- or funnel-shaped, mesh-like to a subtle ring. NtPLIM2b-GFP is used in combination with a guanine nucleotide exchange factor for the Rho GTPases, AtROP-GEF1, to illustrate the use of these actin reporter proteins to explore the linkage between the polar cell growth process and its actin cytoskeleton. Contrary to the actin cytoskeleton, microtubules appear not to play a direct role in supporting the polar cell growth process in angiosperm pollen tubes. Using a microtubule reporter protein based on the microtubule end-binding protein from Arabidopsis AtEB1, GFP-AtEB1, we show that the extensive microtubule network in elongating pollen tubes displays varying degrees of dynamics. These reporter proteins provide versatile tools to explore the functional connection between major structural and signaling components of the polar pollen tube growth process.

Structural and Signaling Networks for the Polar Cell Growth Machinery in Pollen Tubes

Pollen tubes elongate within the pistil to transport sperms to the female gametophytes for fertilization. Pollen tubes grow at their tips through a rapid and polarized cell growth process. This tip growth process is supported by an elaborate and dynamic actin cytoskeleton and a highly active membrane trafficking system that together provide the driving force and secretory activities needed for growth. A polarized cytoplasm with an abundance of vesicles and tip-focused Ca(2+) and H(+) concentration gradients are important for the polar cell growth process. Apical membrane-located Rho GTPases regulate Ca(2+) concentration and actin dynamics in the cytoplasm and are crucial for maintaining pollen tube polarity. Pollen tube growth is marked by periods of rapid and slow growth phases. Activities that regulate and support this tip growth process also show oscillatory fluctuations. How these activities correlate with the rapid, polar, and oscillatory pollen tube growth process is discussed.

Regulation of pollen tube growth by Rac-like GTPases.

Plant Rac-like GTPases have been classified phylogenetically into two major groups-class I and class II. Several pollen-expressed class I Rac-like GTPases have been shown to be important regulators of polar pollen tube growth. The functional participation by some of the class I and all of the class II Arabidopsis Rac-like GTPases in pollen tube growth remains to be explored. It is shown that at least four members of the Arabidopsis Rac GTPase family are expressed in pollen, including a class II Rac, AtRac7. However, when over-expressed as fusion proteins with GFP, both pollen- and non-pollen-expressed AtRacs interfered with the normal pollen tube tip growth process. These observations suggest that these AtRacs share similar biochemical activities and may integrate into the pollen cellular machinery that regulates the polar tube growth process. Therefore, the functional contribution by individual Rac GTPase to the pollen tube growth process probably depends to a considerable extent on their expression characteristics in pollen. Among the Arabidopsis Racs, GFP-AtRac7 showed association with the cell membrane and Golgi bodies, a pattern distinct from all previously reported localization for other plant Racs. Over-expressing GFP-AtRac7 also induced the broadest spectrum of pollen tube growth defects, including pollen tubes that are bifurcated, with diverted growth trajectory or a ballooned tip. Transgenic plants with multiple copies of the chimeric Lat52-GFP-AtRac7 showed severely reduced seed set, probably many of these defective pollen tubes were arrested, or reduced in their growth rates that they did not arrive at the ovules while they were still receptive for fertilization. These observations substantiate the importance of Rac-like GTPases to sexual reproduction.

Hydroxyproline-rich glycoproteins in plant reproductive tissues: structure, functions and regulation.

The plant reproductive process of pollination involves a series of interactions between the male gametophyte (the pollen grain or pollen tube) and extracellular matrix (ECM) molecules secreted by different cell types along the pollen tube growth pathway in the female organ, the pistil. These interactions are believed to signal and regulate the pollen tube growth process to effect successful delivery of the sperm cells to the ovules where fertilization takes place. Hydroxyproline-rich glycoproteins secreted by plant cells are believed to play a broad range of functions, ranging from providing structural integrity to mediating cell-cell interactions and communication. The pistil and pollen tube ECM is enriched in these highly glycosylated proteins. Our discussions here will focus on a number of these proteins for which most information has been available, from Nicotiana tabacum, its self-incompatible relative N. alata, and Zea mays. In addition, the regulation of the synthesis and glyco-modification of one of these proteins, TTS (transmitting tissue-specific) protein from N. tabacum will be discussed in the light of how differential glycosylation may be used to regulate molecular interactions within the ECM.

Mechanisms of differential pollen donor performance in wild radish, Raphanus sativus (Brassicaceae)

In order to understand the characters on which sexual selection might operate in plants, it is critical to assess the mechanisms by which pollen competition and mate choice occur. To address this issue we measured a number of postpollination characters, ranging from pollen germination and pollen tube growth to final seed paternity, in wild radish. Crosses were performed using four pollen donors on a total of 16 maternal plants (four each from four families). Maternal plants were grown under two watering treatments to evaluate the effects of maternal tissue on the process of mating. The four pollen donors differed significantly in number of seeds sired and differed overall in the mating characters measured. However, it was difficult to associate particular mechanistic characters with ability to sire seeds, perhaps because of interactions among pollen donors within styles or among pollen donors and maternal plants. The process of pollen tube growth and fertilization differed substantially among maternal watering treatments, with many early events occurring more quickly in stressed plants. Seed paternity, however, was somewhat more even among pollen donors used on stressed maternal plants, suggesting that when maternal tissue is more competent, mating is slowed and is more selective.

Il citoscheletro nella crescita del tubetto pollinico

Abstract The cytoskelelon during the pollen tube growth - The process of pollen tube growth is reviewed, with a particular attention to the cytoskeleton of the pollen tube. A relevant emphasis is also given to the role of motor proteins during the translocation of organelles, generative cell and vegetative nucleus.

Influences of pollen tube growth and chromosome elimination in embryo formation by crossing Japanese two-rowed barley with H.bulbosum.

Barley (Hordeum vulgare L.) haploid can be obtained from interspecific hybridization between H. vulgare and H. bulbosum followed by the selective elirnination of H, bulbosum chromosomes. The objective of this study was to investigate the processes of pollen tube growth after pol-lination and chromosome elimination in barley cultivars which showed different efficiency of embryo formation (number of ernbryos obtained / number of florets pollinated) in crossing with diploid H. bulbosum.

Effect of sulphur dioxide on pollen germination and pollen tube growth

Any impairment by a pollutant to the reproductive process in plants, which represents a critical phase in their life-cycle, may have serious implications for their survival. Pollen grains of Cicer arietenum L., Nasturtium indicum L., Petunia alba Juss. and Tradescantia axillaris L. were fumigated with sulphur dioxide under both moist and dry conditions in order to study their germination and tube growth. The sensitivity of moist pollen grains to sulphur dioxide was higher than that of dry pollen grains. The process of pollen tube growth was found to be more sensitive than that of pollen germination.