Antheridiogens are a class of chemicals secreted by

fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes except t ...

gametophyte A gametophyte () is one of the two alternation of generations, alternating multicellular organism, multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has on ...

s that have "been shown to influence production of male

gametangia A gametangium (plural: gametangia) is an organ or cell in which gametes are produced that is found in many multicellular protists, algae, fungi, and the gametophytes of plants. In contrast to gametogenesis in animals, a gametangium is a haploid st ...

and thus mating systems in a large number of terrestrial fern species". Antheridiogens are only observed in

homosporous In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, ...

fern species, as all gametophytes are potentially bisexual (have the ability to produce both

archegonia An archegonium (pl: archegonia), from the ancient Greek ''ἀρχή'' ("beginning") and ''γόνος'' ("offspring"), is a multicellular structure or organ of the gametophyte phase of certain plants, producing and containing the ovum or female ga ...

and

antheridia An antheridium is a haploid structure or organ producing and containing male gametes (called ''antherozoids'' or sperm). The plural form is antheridia, and a structure containing one or more antheridia is called an androecium. Androecium is also t ...

Background

The first study regarding antheridiogen was published by Walter Döpp in 1950. In this article, he explains the discovery of a molecule, which he titled "A-substanz", that caused premature formation of antheridia when agar media was reused after cultivation of ''

Pteridium aquilinum ''Pteridium aquilinum'' (bracken, brake or common bracken), also known as eagle fern, is a species of fern occurring in temperate and subtropical regions in both hemispheres. Originally native to Eurasia and North America, the extreme lightness o ...

.'' A majority of the studies regarding antheridiogen were done by two researchers, Ulrich Näf and H. Schraudolf.

Sex-determination pathway

The way in which antheridiogen determines sex in ferns is a "spatiotemporally split gibberellin synthesis pathway".

Gibberellin Gibberellins (GAs) are plant hormones that regulate various developmental processes, including stem elongation, germination, dormancy, flowering, flower development, and leaf and fruit senescence. GAs are one of the longest-known classes of p ...

is a group of

hormone A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are required ...

s that control plant processes. In the first step of this process, gametophytes, or

prothalli A prothallus, or prothallium, (from Latin ''pro'' = forwards and Greek ''θαλλος'' (''thallos'') = twig) is usually the gametophyte stage in the life of a fern or other pteridophyte. Occasionally the term is also used to describe the young ...

, express gibberellin (GA) specific genes, which produces a GA intermediate molecule that is then secreted into the external environment. In the second step, antheridiogens are taken up by neighboring gametophytes in the colony and undergoes a series of molecular changes that allow it to finally induce or suppress formation of antheridia or archegonia. This helps regulate the sex ratio of the colony. The timing with which antheridiogen affects the gender of growing gametophytes is still under study. One theory states that "the spores that germinate first develop as hermaphrodites and secrete antheridiogen, while those that germinate later or develop more slowly become male under the influence of the secreted antheridiogen". Depending on the ratio of males to hermaphrodites, either outcrossing or inbreeding is selected for by the population. Studies performed on ''

Ceratopteris richardii ''Ceratopteris richardii'' is a fern species belonging to the genus ''Ceratopteris'', one of only two genera of the subfamily Parkerioideae of the family Pteridaceae. It is one of several genera of ferns adapted to an aquatic existence. ''C. ri ...

'' have proven that a growing gametophyte is only able to respond to its own antheridiogen for a brief period of time in very early stages of growth, and that if exposure is removed, undifferentiated cells can revert from male to hermaphrodite. The reversibility of male expression proves that levels of antheridiogen must be maintained in order to keep male expression from disappearing. Antheridiogen has also been shown to allow spores that are grown in complete darkness to grow. Spores that are buried underground, if reached by antheridiogen, can form gametophytes that reach the surface. Or, they form a small amount of antheridia, and the sperm produced can reach the female gametophytes above ground. The way in which the sex of each individual is determined is a form of

environmental sex determination Environmental sex determination is the establishment of sex by a non-genetic cue, such as nutrient availability, experienced within a discrete period after fertilization. Environmental factors which often influence sex determination during develop ...

(ESD). In contrast to

chromosomal A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

sex determination, sex determination through ESD is extremely flexible, allowing for sex changes throughout the individual's life in response to colony or environmental changes. One study performed on the fern species ''

Woodwardia radicans ''Woodwardia radicans'', the chain fern, European chain fern or rooting chainfern, is a species of fern in the family Blechnaceae, mainly found in Macaronesia and southwestern Europe, but is also found in southern Italy and Crete. Growing to tal ...

'' found that sex expression of mature gametophytes is dependent on stress conditions. In good conditions, gametophytes reached sexual maturity at a larger size and became females and then bisexuals, whereas in stressful conditions, gametophytes reached sexual maturity at a smaller size and became males.

Connections

The idea of an antheridiogen is very similar to that of

pheromone A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...

s, which exist in some mammals. Although mammalian sex determination is decided by chromosomes, chemicals called pheromones are released, detected by the olfactory system, and can control social behaviors and hormone levels. The presence of human pheromones remains a long-contested topic, as there have not been any studies that completely prove the existence of pheromones or of a possible pathway of detection.

References

{{reflist Plant reproduction Chemical substances Ferns