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Suspensors are anatomical structures found in certain fungi and plants.
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Suspensors are anatomical structures found in certain fungi and plants.
In fungi, suspensors are filamentous structural formations having the function of holding a zygospore between two strains of hyphae.[ citation needed ]
In plants, suspensors are found in zygotes in angiosperms, connecting the endosperm to an embryo. Usually in dicots the suspensor cells divide transversally a few times to form a filamentous suspensor of 6-10 cells. The suspensor helps in pushing the embryo into the endosperm. The first cell of the suspensor towards the micropylar end becomes swollen and functions as a haustorium. The haustorium has wall ingrowths similar to those of a transfer cell. The last of the suspensors at the end of the embryo is known as hypophysis. Hypophysis later gives rise to the radicle and root cap. During embryo development in angiosperm seeds, normal development involves asymmetrical division of the unicellular embryo, inducing polarity. The smaller terminal cell divides to become the proembryo while the larger basal cell divides laterally to form the suspensor. The suspensor is analogous to a placental mammalian's umbilical cord.[ citation needed ]
A gametophyte is one of the two alternating multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has one set of chromosomes. The gametophyte is the sexual phase in the life cycle of plants and algae. It develops sex organs that produce gametes, haploid sex cells that participate in fertilization to form a diploid zygote which has a double set of chromosomes. Cell division of the zygote results in a new diploid multicellular organism, the second stage in the life cycle known as the sporophyte. The sporophyte can produce haploid spores by meiosis that on germination produce a new generation of gametophytes.
Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae, commonly called angiosperms. They include all forbs, grasses and grass-like plants, a vast majority of broad-leaved trees, shrubs and vines, and most aquatic plants. The term "angiosperm" is derived from the Greek words ἀγγεῖον / angeion and σπέρμα / sperma ('seed'), meaning that the seeds are enclosed within a fruit. They are by far the most diverse group of land plants with 64 orders, 416 families, approximately 13,000 known genera and 300,000 known species. Angiosperms were formerly called Magnoliophyta.
Sex is the trait that determines whether a sexually reproducing organism produces male or female gametes. A male organism produces small mobile gametes, while a female organism produces larger, non-mobile gametes. An organism that produces both types of gamete is called a hermaphrodite. During sexual reproduction, a male and a female gamete fuse to form a zygote, which develops into an offspring that inherits traits from each parent.
An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm cell. The resulting fusion of these two cells produces a single-celled zygote that undergoes many cell divisions that produce cells known as blastomeres. The blastomeres are arranged as a solid ball that when reaching a certain size, called a morula, takes in fluid to create a cavity called a blastocoel. The structure is then termed a blastula, or a blastocyst in mammals.
In botany, a seed is a plant embryo and food reserve enclosed in a protective outer covering called a seed coat (testa). More generally, the term "seed" means anything that can be sown, which may include seed and husk or tuber. Seeds are the product of the ripened ovule, after the embryo sac is fertilized by sperm from pollen, forming a zygote. The embryo within a seed develops from the zygote and grows within the mother plant to a certain size before growth is halted.
Fertilisation or fertilization, also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. While processes such as insemination or pollination which happen before the fusion of gametes are also sometimes informally referred to as fertilisation, these are technically separate processes. The cycle of fertilisation and development of new individuals is called sexual reproduction. During double fertilisation in angiosperms the haploid male gamete combines with two haploid polar nuclei to form a triploid primary endosperm nucleus by the process of vegetative fertilisation.
In botany, apomixis is asexual development of seed or embryo without fertilization. However, other definitions include replacement of the seed by a plantlet or replacement of the flower by bulbils.
Gametogenesis is a biological process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid gametes. Depending on the biological life cycle of the organism, gametogenesis occurs by meiotic division of diploid gametocytes into various gametes, or by mitosis. For example, plants produce gametes through mitosis in gametophytes. The gametophytes grow from haploid spores after sporic meiosis. The existence of a multicellular, haploid phase in the life cycle between meiosis and gametogenesis is also referred to as alternation of generations.
A coenocyte is a multinucleate cell which can result from multiple nuclear divisions without their accompanying cytokinesis, in contrast to a syncytium, which results from cellular aggregation followed by dissolution of the cell membranes inside the mass. The word syncytium in animal embryology is used to refer to the coenocytic blastoderm of invertebrates. A coenocytic colony is referred to as a coenobium, and most coenobia are composed of a distinct number of cells, often as a multiple of two.
In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. It consists of three parts: the integument, forming its outer layer, the nucellus, and the female gametophyte in its center. The female gametophyte — specifically termed a megagametophyte— is also called the embryo sac in angiosperms. The megagametophyte produces an egg cell for the purpose of fertilization. The ovule is a small structure present in the ovary. It is attached to the placenta by a stalk called a funicle. The funicle provides nourishment to the ovule.
Elaioplasts are one of the three possible forms of leucoplasts, sometimes broadly referred to as such. The main function of elaioplasts are synthesis and storage of fatty acids, terpenes, and other lipids, and they can be found in the embryonic leaves of oilseeds, citrus fruits, as well as the anthers of many flowering plants.
The endosperm is a tissue produced inside the seeds of most of the flowering plants following double fertilization. It is triploid in most species, which may be auxin-driven. It surrounds the embryo and provides nutrition in the form of starch, though it can also contain oils and protein. This can make endosperm a source of nutrition in animal diet. For example, wheat endosperm is ground into flour for bread, while barley endosperm is the main source of sugars for beer production. Other examples of endosperm that forms the bulk of the edible portion are coconut "meat" and coconut "water", and corn. Some plants, such as orchids, lack endosperm in their seeds.
In botany and mycology, a haustorium is a rootlike structure that grows into or around another structure to absorb water or nutrients. For example, in mistletoe or members of the broomrape family, the structure penetrates the host's tissue and draws nutrients from it. In mycology, it refers to the appendage or portion of a parasitic fungus, which performs a similar function. Microscopic haustoria penetrate the host plant's cell wall and siphon nutrients from the space between the cell wall and plasma membrane but do not penetrate the membrane itself. Larger haustoria do this at the tissue level.
Plant embryonic development, also plant embryogenesis is a process that occurs after the fertilization of an ovule to produce a fully developed plant embryo. This is a pertinent stage in the plant life cycle that is followed by dormancy and germination. The zygote produced after fertilization must undergo various cellular divisions and differentiations to become a mature embryo. An end stage embryo has five major components including the shoot apical meristem, hypocotyl, root meristem, root cap, and cotyledons. Unlike the embryonic development in animals, and specifically in humans, plant embryonic development results in an immature form of the plant, lacking most structures like leaves, stems, and reproductive structures. However, both plants and animals including humans, pass through a phylotypic stage that evolved independently and that causes a developmental constraint limiting morphological diversification.
Aleurone is a protein found in protein granules of maturing seeds and tubers. The term also describes one of the two major cell types of the endosperm, the aleurone layer. The aleurone layer is the outermost layer of the endosperm, followed by the inner starchy endosperm. This layer of cells is sometimes referred to as the peripheral endosperm. It lies between the pericarp and the hyaline layer of the endosperm. Unlike the cells of the starchy endosperm, aleurone cells remain alive at maturity. The ploidy of the aleurone is (3n) [as a result of double fertilization].
Double fertilization is a complex fertilization mechanism of flowering plants (angiosperms). This process involves the joining of a female gametophyte with two male gametes (sperm). It begins when a pollen grain adheres to the stigma of the carpel, the female reproductive structure of a flower. The pollen grain then takes in moisture and begins to germinate, forming a pollen tube that extends down toward the ovary through the style. The tip of the pollen tube then enters the ovary and penetrates through the micropyle opening in the ovule. The pollen tube proceeds to release the two sperm in the embryo sac.
Megaspores, also called macrospores, are a type of spore that is present in heterosporous plants. These plants have two spore types, megaspores and microspores. Generally speaking, the megaspore, or large spore, germinates into a female gametophyte, which produces egg cells. These are fertilized by sperm produced by the male gametophyte developing from the microspore. Heterosporous plants include seed plants, water ferns (Salviniales), spikemosses (Selaginellaceae) and quillworts (Isoetaceae).
Megagametogenesis is the process of maturation of the female gametophyte, or megagametophyte, in plants During the process of megagametogenesis, the megaspore, which arises from megasporogenesis, develops into the embryo sac, which is where the female gamete is housed. These megaspores then develop into the haploid female gametophytes. This occurs within the ovule, which is housed inside the ovary.
Nucellar embryony is a form of seed reproduction that occurs in certain plant species, including many citrus varieties. Nucellar embryony is a type of apomixis, where eventually nucellar embryos from the nucellus tissue of the ovule are formed, independent of meiosis and sexual reproduction. During the development of seeds in plants that possess this genetic trait, the nucellus tissue which surrounds the megagametophyte can produce nucellar cells, also termed initial cells. These additional embryos (polyembryony) are genetically identical to the parent plant, rendering them as clones. By contrast, zygotic seedlings are sexually produced and inherit genetic material from both parents. Most angiosperms reproduce sexually through double fertilization. Different from nucellar embryony, double fertilization occurs via the syngamy of sperm and egg cells, producing a triploid endosperm and a diploid zygotic embryo. In nucellar embryony, embryos are formed asexually from the nucellus tissue. Zygotic and nucellar embryos can occur in the same seed (monoembryony), and a zygotic embryo can divide to produce multiple embryos. The nucellar embryonic initial cells form, divide, and expand. Once the zygotic embryo becomes dominant, the initial cells stop dividing and expanding. Following this stage, the zygotic embryo continues to develop and the initial cells continue to develop as well, forming nucellar embryos. The nucellar embryos generally end up outcompeting the zygotic embryo, rending the zygotic embryo dormant. The polyembryonic seed is then formed by the many adventitious embryos within the ovule. The nucellar embryos produced via apomixis inherit its mother's genetics, making them desirable for citrus propagation, research, and breeding.
Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete with a single set of chromosomes combines with another gamete to produce a zygote that develops into an organism composed of cells with two sets of chromosomes (diploid). This is typical in animals, though the number of chromosome sets and how that number changes in sexual reproduction varies, especially among plants, fungi, and other eukaryotes.
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