double fertilization process

Biol. Each made the discovery independently of the other. Updates? ARABIDOPSIS DEHISCENCE ZONE POLYGALACTURONASE1 (ADPG1), ADPG2, and QUARTET2 are polygalacturonases required for cell separation during reproductive development in Arabidopsis. doi: 10.1126/science.1243005, Crawford, B. C. W., Ditta, G., and Yanofsky, M. F. (2007). The degeneration of the 2nd synergid cell thus leads to the stop of attractant secretion and ultimately prevents polyspermy. In theorchidsand in some other plants with minute seeds that contain no reserve materials, endosperm formation is completely suppressed. The division of the basal cell gives rise to the suspensor, which eventually makes connection with the maternal tissue. doi: 10.1007/s00709-007-0269-4, Lush, W., Grieser, F., and Wolters-Arts, M. (1998). Peptide isolation, cDNA cloning, and differential expression in leaves and methyl jasmonate-treated cells. Due to the limitations of the light microscope, there were many unanswered questions regarding the process of double fertilization. The cotyledons nurture the developing embryo in these plants. Disorganization of F-actin cytoskeleton precedes vacuolar disruption in pollen tubes during the in vivo self-incompatibility response in Nicotiana alata. Bot. Dev. doi: 10.1006/bbrc.1997.6514, Capron, A., Gourgues, M., Neiva, L. S., Faure, J. Science 287, 321324. (2011). J. Integr. doi: 10.1104/pp.110.161927, Cheung, A, Y., Wang, H., and Wu, H. M. (1995). Activation of the cell cycle might also represent a key mechanism for the activation and progression of seed development. Following the initial fertilization event, the second sperm nucleus is diverted to fertilize an additional egg nucleus found in the egg cytoplasm. A pollen tube growth stimulatory glycoprotein is deglycosylated by pollen tubes and displays a glycosylation gradient in the flower. Passive & Active Absorption of Water in Plants, ScienceFusion Matter and Energy: Online Textbook Help, NY Regents Exam - Living Environment: Test Prep & Practice, Introduction to Biology: Certificate Program, High School Biology: Homework Help Resource, UExcel Earth Science: Study Guide & Test Prep, DSST Principles of Physical Science: Study Guide & Test Prep, Principles of Physical Science: Certificate Program, Create an account to start this course today. The central cell is important for triple fusion, one of the events in the double fertilization process. Double fertilization | Definition, Angiosperm, Results In, Diagram Only one of the four resulting megaspores survives. Gamete fusion is required to block multiple pollen tubes from entering an Arabidopsis ovule. In most other seed plants, this second 'ventral canal nucleus' is normally found to be functionally useless. Double fertilization has a couple of advantages. Synergid cell death in Arabidopsis is triggered following direct interaction with the pollen tube. Seed Growth. Female control of male gamete delivery during fertilization in Arabidopsis thaliana. Recently, it was shown that the pollen tube is repelled by the filiform apparatus and instead grows along the cell wall of the synergid cells until it reaches a certain point after the filiform apparatus where its growth is arrested and burst occurs explosively (Leshem et al., 2013). The tip of the pollen tube then enters the ovary and penetrates through the micropyle opening in the ovule. Double fertilization forms a diploid zygote and triploid endosperm, while triple fusion forms only the endosperm. The fertilized central cell forms the endosperm while the fertilized egg cell, the zygote, will form the actual embryo and suspensor. Cell 82, 395403. 17, 11011108. Sign up to highlight and take notes. Angiosperms are divided into two big groups based on morphological traits, including the embryo and seed. - Uses, Types, Examples & Side Effects, What Is an NSAID? A calcium dialog mediated by the FERONIA signal transduction pathway controls plant sperm delivery. This and the above findings using pathenogenetic species imply that the paternal genome plays an essential role during early seed development and that sperm cell factors are also required to activate central cell development (Aw et al., 2010). The generative cell moves through this tube while it divides once by mitosis, producing two haploid cells (two sperms). The pollen tube grows on the septum surface toward the funiculus, the tissue connecting the ovule with the septum (Figures 1BD; Supplemental Movies 1, 2). Science 330, 968971. - Uses & Side Effects, What Is Nicotine? FER acts as a cell surface regulator for RAC/ROP GTPases. Little is known about the activation of gametes and thus seed development immediately after fertilization. doi: 10.1126/science.1195211, Kim, S., Mollet, J.-C., Dong, J., Zhang, K., Park, S.-Y., and Lord, E. M. (2003). The Supplementary Material for this article can be found online at: http://www.frontiersin.org/journal/10.3389/fpls.2014.00452/abstract, Alandete-Saez, M., Ron, M., and McCormick, S. (2008). This category only includes cookies that ensures basic functionalities and security features of the website. Developmental and evolutionary hypotheses for the origin of double Mol. In vitro fertilization (IVF) is a treatment for infertility or genetic problems. Pollen tube attraction by the synergid cell. Double Fertilization in Angiosperms - Vedantu The signaling events involved in this recognition process still await their discovery. I feel like its a lifeline. The central cell surrounds the egg apparatus. Central cell-derived peptides regulate early embryo patterning in flowering plants. GCS1/HAP2 is another factor required for gamete interaction in Arabidopsis. 48, 5472. Since two fertilization events coincide, it is called double fertilization. Identification of the pollen self-incompatibility determinant in Papaver rhoeas. Attractive and repulsive interactions between female and male gametophytes in Arabidopsis pollen tube guidance. 3 antipodal cells, 2 polar central cells, 2 synergids & 1 egg cell. At the upper end of the megagametophyte are three antipodal cells. They include four basic parts: To unlock this lesson you must be a Study.com Member. As the embryo and cotyledons enlarge, they become crowded inside the developing seed and are forced to bend. doi: 10.1111/j.1744-7909.2009.00847.x, Keywords: pollen tube, ovule, gamete interaction, cell fusion, signaling, fertilization, polyspermy, Citation: Bleckmann A, Alter S and Dresselhaus T (2014) The beginning of a seed: regulatory mechanisms of double fertilization. (2001). In maize pollen tube arrival is associated with the secretion of defensin-like ZmES proteins, inducing pollen tube burst by activating the K+ -channel Zea mays 1 (KZM1) in the pollen tube membrane (Amien et al., 2010). After pollen germination, the vegetative cell forms a tube and grows by tip-based-growth mechanism along papillae cells of the stigma into the style toward the transmitting tract. Chen, Y.-H., Li, H.-J., Shi, D.-Q., Yuan, L., Liu, J., Sreenivasan, R., et al. The mature embryo sac. Relatively high calcium is localized in synergid cells of wheat ovaries. [10] The additional fertilization product in Ephedra does not nourish the primary embryo, as the female gametophyte is responsible for nutrient provision. U.S.A. 98, 1284312847. In angiosperms, unlike gymnosperms, the endosperm is formed: Which of the following is necessary for a pollen grain to germinate? The origin of double fertilization in flowering plants: looking into Conserved molecular components for pollen tube reception and fungal invasion. In Zea mays, EGG APPARATUS1 (ZmEA1), a small hydrophobic precursor protein of 94 aa was reported as an egg apparatus-specific protein required for micropylar pollen tube guidance (Mrton et al., 2005, 2012). Science 307, 573576. HAP2/GCS1 and tetraspanins at the surface of gametes may be involved in mediating membrane fusion. Before double fertilization can occur, pollination must take place. 11, 4959. A species-specific cluster of defensin-like genes encodes diffusible pollen tube attractants in Arabidopsis. Development 127, 45114518. Double Fertilization in Plants: Process with Diagram | StudySmarter Succeeding the penetration of the mature female gametophyte by the pollen tube, female cytoplasm and free nuclei move to surround the pollen tube. Plant Physiol. MAA3 (MAGATAMA3) helicase gene is required for female gametophyte development and pollen tube guidance in Arabidopsis thaliana. Recently, de novo expression of closely related MYB transcription factors and other genes were reported to be induced during pollen tube growth through the style regulating themselves a number of downstream genes. Plant Sci. Explore the definition of reproductive structures in. After fertilization these different tissues form the seed coat. In angiosperms, one sperm fertilizes the egg to form the 2 n zygote, and the other sperm fertilizes the central cell to form the 3 n endosperm. doi: 10.1093/mp/sst050, Okuda, S., Tsutsui, H., Shiina, K., Sprunck, S., Takeuchi, H., Yui, R., et al. The zygote splits to form the upper cell (terminal cell) and the lower cell (basal cell). For example magatama (maa) mutants show defects in central cell maturation; both haploid nuclei are smaller and often fail to fuse. While synergid cells are essential for pollen tube attraction, burst and sperm cell release (see below), the function of antipodal cells is so far unknown. (a) In the first stage of development, the terminal cell divides, forming a globular pro-embryo. GCS1/HAP2 is a conserved protein and has been identified in genomes of all major eukaryotic taxa except fungi. A transcript encoding the Interleukin-1 Receptor-Associated Kinase (IRAK)/Pelle-like kinase gene SHORT SUSPENSOR (SSP), which was shown to be delivered by sperm cells, becomes translated in the zygote and acts in the YODA (YDA) MAPK pathway during zygote elongation (Bayer et al., 2009). Process of Fertilization in Plants - CBSE Tuts Nature 342, 955957. The connection between Ca2+cyto and D-serine by GLR channels in growing pollen tubes was already described above. In gymnosperms, pollination involves pollen transfer from the male cone to the female cone. The female gametophyte (embryo sac) is produced in the ovule enclosed by the ovary. Plant Reprod. doi: 10.1007/s00497-013-0221-z, Wu, H. M., Wang, H., and Cheung, A. Y. The male gametophytes, or microgametophytes, that participate in double fertilization are contained within pollen grains. 101, 712. 62, 16211631. Fertilization Mechanisms in Flowering Plants - PMC They surround the pistil, which represents the female flower organ. Pollen tube burst depends on the presence and activation of FER-, LER-, NTA-, and VDD-dependent signaling cascades culminating in the death of the receptive synergid cell (indicated by diffusing red color). [2], Evidence of double fertilization in Gnetales, which are non-flowering seed plants, has been reported. AtEXO70A1, a member of a family of putative exocyst subunits specifically expanded in land plants, is important for polar growth and plant development. The conserved plant sterility gene HAP2 functions after attachment of fusogenic membranes in Chlamydomonas and Plasmodium gametes. Angiosperms possess different strategies to recognize self from alien pollen and evolved independent self-incompatibility (SI) mechanisms to prevent self-fertilization. The terminal cell also divides, giving rise to a globular-shaped proembryo (Figure 2a). During pollen tube growth the tip needs to modulate the surrounding cell wall of stylar cells enabling its penetration through the extra-cellular space, most likely by interaction with extensin-like proteins and arabinogalactan proteins as well as the secretion of cell wall softening enzymes and inhibitors such as polygalacturonases and pectin methylesterase inhibitors (Cosgrove et al., 1997; Grobe et al., 1999; Stratford et al., 2001; Ogawa et al., 2009; Nguema-Ona et al., 2012; Woriedh et al., 2013). doi: 10.1126/science.1244454, Higashiyama, T., Kuroiwa, H., Kawano, S., and Kuroiwa, T. (1998). Article was last reviewed on Thursday, February 2, 2023, Your email address will not be published. doi: 10.1016/j.pbi.2011.09.003, Kaji, K., Oda, S., Shikano, T., Ohnuki, T., Uematsu, Y., Sakagami, J., et al. Did you have an idea for improving this content? The nutrients are transferred from the endosperm to the growing cotyledons and the mature seed does not have an endosperm anymore. Proc. Although the mutant cdka;1 central cell showed mitotic divisions upon egg cell fertilization, it appeared mostly unfertilized, and endosperm proliferation and thereby seed development stopped after a certain time point. doi: 10.1042/BST0380631, Le Naour, F., Rubinstein, E., Jasmin, C., Prenant, M., and Boucheix, C. (2000). Female components, which are directly involved in gamete fusion are so far unknown in higher plants. Arabidopsis Book 9:e0155. With very few exceptions (e.g., thedandelion), development of the ovule into a seed is dependent uponfertilization, which in turn follows pollination. (2009). Failed fertilization occurs in 5-10% of IVF cycles and 2-3% of ICSI cycles, resulting in heavy financial and psychological burdens on patients . The Chlamydomonas Fus1 protein is present on the mating type plus fusion organelle and required for a critical membrane adhesion event during fusion with minus gametes. 24, 170175. Double fertilization occurs only in angiosperms (flowering plants) inside the female structures in the flower. ANXUR1 and 2, sister genes to FERONIA/SIRENE, are male factors for coordinated fertilization. In contrast, parthenogenetic egg cells do not arrest and initiate cell division without fertilization. It develops from the primary endosperm cell during double fertilization. Calcium and reactive oxygen species rule the waves of signaling. 8, e25682. It cannot be explained by mechanical breakdown due to an invading pollen tube. Dev. Ann. Pollen germination (1) and fertilization (2). Curr. doi: 10.1016/j.devcel.2013.04.001, Watanabe, M., Suwabe, K., and Suzuki, G. (2012). EC1 leads to the relocalization of HAP2/GCS1 from the endomembrane system to the sperm cell plasma membrane and thus activates sperm cells enabling them to fuse with the female gametes (Sprunck et al., 2012). 40.5D: Double Fertilization in Plants - Biology LibreTexts doi: 10.1016/0092-8674(95)90428-X, Wu, J., Wang, S., Gu, Y., Zhang, S., Publicover, S. J., and Franklin-Tong, V. E. (2011). 42, 358363. Curr. 26, 159179. Have all your study materials in one place. Egg cell-secreted EC1 triggers sperm cell activation during double fertilization. They develop within the microsporangia, or pollen sacs, of the anthers on the stamens. Thus, after the double fertilization, the ovule develops into a seed that contains an embryo and the endosperm, surrounded by the integuments that become the seed coat. Acta 1833, 15731581. Stop procrastinating with our study reminders. Recently, two pollen-expressed mitogen-activated protein kinases (MAPKs), MPK3 and MPK6, were identified in Arabidopsis, which are part of the ovular guidance network. Up to now the final processes of fertilization seem to involve partly conserved proteins even from lower to higher eukaryotes. Pollen tube entry into the synergid cell of Arabidopsis is observed at a site distinct from the filiform apparatus. a triploid endosperm, through the fusion of another sperm cell with the two polar nuclei of the female gametophyte. The growth direction of the pollen tube is regulated by the formation of different gradients including water, -amino butyric acid (GABA), calcium and other small molecules such as D-serine. doi: 10.1016/j.cub.2013.04.043, Liu, Y., Misamore, M. J., and Snell, W. J. After successful double fertilization further signaling events are activated to prevent polyspermy. Flowers are the reproductive structures of angiosperms. The presence of a calmodulin-binding domain in NTA supports the idea of a Ca2+-dependent signaling network, which is activated upon pollen tube arrival. doi: 10.1105/tpc.108.063768, Okuda, S., Suzuki, T., Kanaoka, M. M., Mori, H., Sasaki, N., and Higashiyama, T. (2013). Biol. The triploid cell grows into the endosperm and will nourish the developing embryo. 22, 10901094. Sex. It is controversial whether this requires active transport or is solely based on cytoplasmic flow associated with burst of both pollen tube and receptive synergid cell and/or the architecture of the egg apparatus. Collaborative non-self recognition system in S-RNase-based self-incompatibility. Double fertilization happens when pollen is deposited from the anther (male) to the flowers stigma (female). Pollen grains are transported to the female part of another flower through pollination. Is HAP2-GCS1 an ancestral gamete fusogen? Fusion of sperm cell (male gamete) with egg cell (female gamete) to form a diploid zygote. myb97/101/120 triple mutants exhibited uncontrolled growth and failed to discharge their sperm cells after entering the embryo sac (Liang et al., 2013). The process involves the fusion of one female gamete or egg cell (megagametophyte, or the embryo sac) with two male gametes (sperm cells). Section snippets The phylogenetic distribution of double fertilization. 118, 733741. Its extended growth inside the female flower tissue is regulated by many different guidance, attraction and support mechanisms. 23, 12091214. doi: 10.4161/psb.25682, Van Ex, F., Jacob, Y., and Martienssen, R. A. A perfect summary so you can easily remember everything. The germination of the pollen tube requires water, oxygen, and certain chemical signals. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. Aneuploidy Definition & Disorders | What is Aneuploidy? 19, R19R20. The megagametophyte, which is usually haploid, originates from the (usually diploid) megaspore mother cell, also called the megasporocyte. (2013b). The pollen tube is guided by the chemicals secreted by the synergids present in the embryo sac; it enters the ovule sac through the micropyle. Grobe, K., Becker, W. M., Schlaak, M., and Petersen, A. The ECM provides essential nutrients as well as components for an accelerated, extended and guided pollen tube growth (Palanivelu and Preuss, 2006). In Arabidopsis the conserved tetraspanin family consists of 17 members. This interaction is a dynamic process. Arabinogalactan proteins in root and pollen-tube cells: distribution and functional aspects. . (2008). doi: 10.2307/2439772, Brownfield, L., Hafidh, S., Borg, M., Sidorova, A., Mori, T., and Twell, D. (2009). Can. SI is best understood in Brassicaceae, which use a surface-localized S-locus receptor kinase (SRK) in papilla cells (Takasaki et al., 2000) and a pollen coat localized cysteine-rich protein (SP11/SCR) (Schopfer, 1999; Shiba et al., 2001) to distinguish self from alien pollen. Thus, in gymnosperms, if fertilization does not occur, the resources used for the growth of the female gametophyte might be wasted. Commun. (1999). HALF FILLED promotes reproductive tract development and fertilization efficiency in Arabidopsis thaliana. Ethylene signaling is required for synergid degeneration and the establishment of a pollen tube block. Semi-in vitro fertilization experiments revealed an oscillation of Ca2+cyto levels in growing pollen tubes depending on their distance from an unfertilized ovule and especially from the synergid cells (Shi et al., 2009; Iwano et al., 2012). It is well conceivable that sperm cells deliver factors, which activate female gametes after fusion. While TET11 and especially TET12 are located at the surface of sperm cells and reach high concentrations in the membrane region connecting both sperm cells, TET9 appears at the surface of female gametophyte cells including the egg and central cell (Boavida et al., 2013). Science 293, 14801483. Chemocyanin, a small basic protein from the lily stigma, induces pollen tube chemotropism. doi: 10.1007/s00299-009-0725-z, Shiba, H., Takayama, S., Iwano, M., Shimosato, H., Funato, M., Nakagawa, T., et al. It fuses with the egg cell to form the zygote. Plant Physiol. Plant Cell Rep. 28, 12531264. 55, 406414. Subsequently, both sperm cells arrive at the gamete fusion site and fertilize the egg and central cell (Hamamura et al., 2011). A major challenge for the near future is to understand fertilization mechanisms also in crop plants, especially in the grasses, which represent the most economically important plant family. doi: 10.1126/science.1201101. 108, 739747. It harbors the female gametes (egg and central cell) and is surrounded by the nucellus tissue as well as the inner and outer integuments. In angiosperms, one sperm fertilizes the egg to form the 2n zygote, and the other sperm fertilizes the central cell to form the 3n endosperm. doi: 10.1016/j.bbamcr.2012.10.009, Steinhorst, L., and Kudla, J. Explosive discharge of pollen tube contents in Torenia fournieri. Report a problem. Double fertilization| Sexual reproduction in flowering plants | Biology It contains, for example, a high Ca2+ concentration, which is known to play a key role during the regulation of pollen tube growth (Brewbaker and Kwack, 1963; Chaubal and Reger, 1990; Iwano et al., 2004; Michard et al., 2011) and also seems to trigger pollen tube burst afterwards (see below). doi: 10.1093/aob/mcr111, Kasahara, R. D., Maruyama, D., Hamamura, Y., Sakakibara, T., Twell, D., and Higashiyama, T. (2012). Ferris, P. J., Woessner, J. P., and Goodenough, U. W. (1996). Introduction The process of double fertilization is a unique biological process in which one sperm fuses with the egg to produce the embryo while the second fuses with the central cell to form the endosperm, a nutritive tissue needed for growth of the succeeding . 5:452. doi: 10.3389/fpls.2014.00452. All rights reserved. Nat. In Arabidopsis this process was shown to be tightly regulated and usually only a single pollen tube exits the transmitting tract in proximity of an unfertilized ovule. Get unlimited access to over 88,000 lessons. Double fertilisation is significant because it involves the use of both the male gametes produced by a pollen grain. doi: 10.1104/pp.122.1.11, Higashiyama, T., Yabe, S., Sasaki, N., Nishimura, Y., Miyagishima, S, Kuroiwa, H., et al. Double fertilization in angiosperms is a process where a zygote and endosperm are formed in plants that have fruits and flowers. Of the two sperm cells, one sperm fertilizes the egg cell, forming a diploid zygote; the other sperm fuses with the two polar nuclei, forming a triploid cell that develops into the endosperm. doi: 10.1371/journal.pbio.1001449, Uebler, S., Dresselhaus, T., and Mrton, M.-L. (2013). Seeds are an important part of the human diet. 19, 13271331. Plant Reprod. The gamete fusion process is defective in eggs of Cd9-deficient mice. Misamore, M. J., Gupta, S., and Snell, W. J. 270 lessons A., Vogler, H., Lituiev, D. S., Nestorova, A., and Grossniklaus, U. - Definition, Causes, Symptoms & Treatment, What Are Beta Blockers? doi: 10.1038/ng1694, Ogawa, M., Kay, P., Wilson, S., and Swain, S. M. (2009). Upon pollen tube arrival Ca2+cyto level starts to oscillate in the synergid cells, triggered by the contact of the pollen tube tip with the synergid cell. Species of the Solanaceae, for example, use a pistil-expressed S-RNase, which penetrates the pollen tube (McClure et al., 1989; Luu et al., 2000). You also have the option to opt-out of these cookies. Pathfinding in angiosperm reproduction: pollen tube guidance by pistils ensures successful double fertilization. In mammals, CD9-like membrane spanning proteins of the tetraspanin family are located at the plasma membrane of eggs and were shown to be required for gamete fusion (Kaji et al., 2000; Le Naour et al., 2000; Miyado et al., 2000). The nutritious tissue in gymnosperm is haploid, derived from the female gametophyte haploid tissue. Male-female crosstalk during pollen germination, tube growth and guidance, and double fertilization. 13, 437443. In the pollen tube, the vegetative nucleus and sperm cells move. One sperm fertilizes the egg cell and the other sperm combines with the two polar nuclei of the large central cell of the megagametophyte. Double Fertilisation Process Pollen-Pistil Interaction: The events from pollen deposition on the stigma until the pollen tube enters the ovule are together referred to as pollen-pistil interaction. Accessibility StatementFor more information contact us atinfo@libretexts.org. Double fertilization proceeds from here. Advances in the study of genetic factors and clinical - Springer Plant Cell Physiol. Stop procrastinating with our smart planner features. In Chlamydomonas both GCS1/HAP2 and FUS1 are rapidly degraded after cell fusion, resulting in a fast membrane block to prevent polygamy (Misamore et al., 2003; Liu et al., 2010). Independent control by each female gamete prevents the attraction of multiple pollen tubes. doi: 10.1016/j.cub.2007.05.079, Crawford, B. C. W., and Yanofsky, M. F. (2011). As it travels through the style to reach the embryo sac, the pollen tubes growth is supported by the tissues of the style. Free Ca2+ gradient in growing pollen tubes of Lillium. Analysis of the tip-to-base gradient of CaM in pollen tube pulsant growth using in vivo CaM-GFP system. In ~70% of all angiosperm species including Arabidopsis and maize the embryo sac develops according to the Polygonum type (Drews et al., 1998). The launch of seed development in flowering plants (angiosperms) is initiated by the process of double fertilization: two male gametes (sperm cells) fuse with two female gametes (egg and central cell) to form the precursor cells of the two major seed components, the embryo and endosperm, respectively. Plant Cell 21, 26552671. The gynoecium is the female reproductive part composed of carpels or pistils. doi: 10.1016/S0092-8674(03)00479-3, Palanivelu, R., and Preuss, D. (2006). Guidance in vitro of the pollen tube to the naked embryo sac of Torenia fournieri. The major task of the vegetative cell is to deliver the sperm cells through the maternal tissues of the style and ovary to an unfertilized ovule. Curr. StudySmarter is commited to creating, free, high quality explainations, opening education to all. After the double fertilization in flowering. 263, 3340. Among other components, they secrete LURE peptides, which bind to pollen expressed LIP1/2 receptors thus directing pollen tube growth. Embryos develop elongated structures similar to leaves called cotyledons (sometimes called seed leaves). A cytoplasmic Ca2+ functional assay for identifying and purifying endogenous cell signaling peptides in Arabidopsis seedlings: identification of AtRALF1 peptide. Bot. Plant Reprod. (2001). Another example of central cell-dependent defects in micropylar pollen tube guidance is the transcriptional regulator CENTRAL CELL GUIDANCE (CCG), which is expressed exclusively in the central cell of the female gametophyte (Chen et al., 2007). The next sequence of events varies, depending on the particular species, but in most species, the following events occur. The significance of double fertilization in flowering plants is the increased survival probability of the embryo provided by a highly nutritious tissue (endosperm), and to avoid the waste of resources by forming the endosperm only if the egg is fertilized. A positive signal from the fertilization of the egg cell sets off endosperm proliferation in angiosperm embryogenesis.
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