The antheridiogen response in C. A single spore always develops as a hermaphrodite when grown in the absence of A CE. The hermaphrodite consists of a single sheet of cells with a distinct multicellular meristem that forms a meristem notch and multiple archegonia that develop adjacent to the meristem notch, which are highlighted in the SEM boxed area of the hermaphrodite.
The male lacks a meristem and almost all cells differentiate as antheridia. The SEM shows six antheridia, each having a ring cell and a cap cell that pops open to release sperm. When a male gametophyte is transferred to media lacking A CE , some cells divide and begin to form a hermaphroditic prothallus. Typical of other ferns, a C. The lateral meristem not only confers indeterminate growth to the gametophyte, but its formation coincides with a loss in ability to respond to A CE as well as the secretion of A CE.
Archegonia invariably initiate close to the meristem notch of the hermaphrodite, well after the lateral meristem is well developed. While the hermaphroditic program of expression cannot be reversed, the male program of expression is reversible. Cells of the male gametophyte prothallus, when transferred to media lacking A CE , will divide to ultimately form one or more new hermaphroditic prothalli Figure 2E.
Antheridiogen thus serves multiple functions in male gametophyte development: it represses divisions of the prothallus that establish the lateral meristem; it promotes the rapid differentiation of antheridia; it represses its own biosynthesis; and it serves to maintain in the gametophyte an ability to respond to itself. All of the antheridiogens that have been structurally characterized from ferns are gibberellins GAs Yamane et al.
Although the structure of ACE is unknown, GA biosynthetic inhibitors reduce the proportion of males in a population of C. Most recent studies aimed at understanding how antheridiogen determines the sex of the gametophyte have focused on two species of homosporous ferns: C. Ceratopteris richardii is a semi-tropical, annual species and is useful as a genetic system for many reasons.
Large numbers of single-celled, haploid spores typically 10 6 can be mutagenized and mutants identified within 2 weeks after mutagenesis. Gametophytes can be dissected and regrown, making it possible to simultaneously self-fertilize and out-cross a single mutant gametophyte. Because C. Over 70 mutants affecting sex determination have been characterized, most falling into three major phenotypic groups: the hermaphroditic her mutants, which are hermaphroditic in the presence or absence of A CE , the transformer tra mutants, which are male in the presence or absence of A CE , and the feminization fem mutants, which are female in the presence or absence of A CE and produce no antheridia.
Through test of epistasis i. This pathway reveals that there are two major regulators of sex: TRA , which is necessary for lateral meristem and archegonia development female traits , and FEM , which is necessary for antheridia development the male trait. TRA promotes the development of a gametophyte with female traits and represses the development of antheridia by repressing the FEM gene that promotes male development. What is remarkable about this pathway is that it is inherently flexible, which is consistent with what is understood about sex determination in this species by A CE.
Figure 3. The SD pathway in C. T bars represent repressive events whereas arrows indicate activating events. While this model explains how male and female gametophyte identities are determined, it does not explain the hermaphrodite.
One possibility is that in certain cells of the hermaphrodite, the activities of FEM and TRA are reversed, allowing FEM to be expressed in cells that will eventually differentiate as antheridia. Testing this and other possibilities will require the cloning of the sex-determining genes and assessing their temporal and spatial patterns of expression in the developing hermaphrodite. The sex-determining pathway in C.
Based on the similarities between the GA signaling pathway in angiosperms and the sex determination pathway in C. Lygodium japonicum is another homosporous fern species with an antheridiogen response.
This species has the distinct advantage of having its antheridiogens structurally well characterized. Two different GAs have been identified as antheridiogens in this species, including GA 9 methyl ester Yamane et al. GA 73 methyl ester is the most active antheridiogen and is able to induce antheridia formation at the incredibly low concentration of 10 —15 M. To test the hypothesis that antheridiogen is synthesized through the GA biosynthetic pathway, L.
Their expression patterns revealed that all but GA30ox were more highly expressed in older gametophytes that secrete antheridiogen, consistent with the expectation that antheridiogen biosynthesis genes are up-regulated in gametophytes that secrete it.
GA3ox expression showed the opposite pattern of expression; i. To explore this further, the same authors assayed the effects of prohexadione, a GA3ox inhibitor, on antheridia formation in the presence of GA 4 which has an OH group at the C3 position or GA 9 methyl ester which lacks the OH group at C3 ; both GA 9 and GA 4 induce antheridia formation by themselves. Whereas prohexadione plus GA 9 methyl ester inhibited antheridia formation, prohexadione plus GA 4 did not, demonstrating that C3 hydroxylation of antheridiogen is essential for inducing antheridia formation.
In another series of experiments, the authors found that GA 9 methyl ester was converted to GA 9 in young gametophytes. Based on these and other results, a model was proposed whereby antheridiogen GA 9 methyl ester is synthesized via a GA biosynthetic pathway and secreted by older gametophytes. When it is taken up by younger gametophytes, the methyl ester is removed by a possible methyl esterase then hydroxylated at the C3 position by GA3ox to GA 4 , where it is perceived and transduced by the GA signaling pathway in young gametophyte.
Because GA 9 methyl ester is more hydrophobic and more efficiently taken up by gametophytes than GA 9 , splitting the GA biosynthetic pathway between young and older gametophytes was proposed to enhance the sensitivity of young gametophytes to the secreted antheridiogen by their neighbors and, at the same time, promote the activation of male traits once inside the young gametophyte Tanaka et al.
In addition to characterizing antheridiogen biosynthesis in L. They found that a L. Appears in. Fern propagation In this activity, students learn how to propagate ferns. Add to favourites. Go to full glossary Add 0 items to collection. Download 0 items.
Twitter Pinterest Facebook Instagram. Email Us. See our newsletters here. Would you like to take a short survey? Within the sporangia are spore producing cells called sporogenous cells. These cells undergo meiosis to form haploid spores. The spores on most ferns are the same size and perform the same function.
Therefore ferns are known as homosporous plants. The sporangia are usually in clusters known as sori, found on the underside of the fern leaves.
Some ferns have a covering over the sporangia known as an indusium. When the spores are mature, they are released from the sporangia. If a spore lands on a suitable site, it will germinate and grow via mitosis into a mature gametophyte plant. A gametophyte is the plant that produces gametes.
The fern gametophyte is a small approximately 5 mm , bisexual, heart-shaped plant called a prothallus. The prothallus is haploid, since it grew from a spore which had been formed by meiosis. It does not have any vascular tissue and uses small rhizoids to anchor it to the ground. On the underside of the prothallus the sex organs form.
The female structure, called an archegonium, contains a single egg. The male structure, the antheridium, contains many flagellated sperm. The sperm are released from the antheridium and swim through a thin film of water to a nearby archegonium to fertilize the egg.
Since the antheridium and archegonium are on the same prothallus the fern has several strategies to prevent self-fertilization. These strategies will be discussed later in this paper. Once fertilization of the egg has occurred, a diploid zygote has been created. As the zygote grows into an embryo it remains attached to the prothallus. The embryonic plant depends upon the prothallus for water and nutrients. As the embryo grows and develops into a mature diploid plant the prothallus dies.
This mature plant is called the sporophyte generation since it produces spores. The sporophyte plant is the one most commonly recognized as a fern. In a sense, this is true, but the tiny plantlets that emerge from spores are genetically different from adult ferns.
Note that sperm and egg may be produced on the same gametophyte, so a fern may self-fertilize. Advantages of self-fertilization are that fewer spores are wasted, no external gamete carrier is required, and organisms adapted to their environment can maintain their traits.
The advantage of cross-fertilization , when it occurs, is that new traits may be introduced into the species. The fern "life cycle" refers to sexual reproduction. However, ferns use asexual methods to reproduce, too. Actively scan device characteristics for identification. Use precise geolocation data. Select personalised content. Create a personalised content profile. Measure ad performance. Select basic ads. Create a personalised ads profile. Select personalised ads. Apply market research to generate audience insights.
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