Presence of Sex Hormones in Achlya | Fungi

In this article we will discuss about the presence of sex hormones in achlya.

It was de Bary (1881) who first reported the presence of sex hormones in dioecious species of Achlya. In 1908, Kaufmann supported the contention of de Bary on the basis of his observations on Saprolegnia hypogyna.

According to Kaufmann, the development of antheridial hyphae is stimulated by certain hormones. Studies conducted by Couch (1924) and Bishop (1957) on Dictyuchus and Sapromyces reinschii and Raper (1954) on Achlya have substantially confirmed the role of hormones in sexual reproduction in fungi.

Therefore the sex hormones may be defined as a diffusible substance playing a specific role in the sexual reproduction that produces it.

Machlis (1972) has classified the sex hormones into the following three types:

(1) Erotactins

(2) Erotropins, and 

(3) Erogens.

Erotactin is a sexual hormone which attracts motile gametes, erotropin is the sex hormone that induces chemotropic growth of sexual structures and erogen is the sex hormone that controls the induction and differentiation of sexual structures.

However, the sex hormone may perform more than one functions, as in Achlya, the hormone that controls development of sexual structures also determines the direction of the sex organs.

Description of some important Sex-Hormones:

Although a large number of sex hormones have been reported, only a few have been chemically characterised and extensively studied. These are – Sirenin, antheridiol and oogoniol, trisporic acid and yeast D factor.

These are briefly described here:

1. Sirenin:

It is a sperm attracting hormone produced by water mould Allomyces, A. macrogynous and A. arbuscula. It is the female gametes which release sirenin to attract the male gametes.

The synthesis of sirenin by female gametes and their function to attract male gametes was demonstrated by Machlis (1958). The empirical formula of sirenin is C₁₅ H ₂₄O₂ and the molecular weight is 236.

It is an oxygenated sesquiterpene and is species specific. Although both D- and L- forms have been isolated, L- form is biologically effective.

2. Antheridiol and Oogoniol:

Raper (1939-1959), on the basis of his classical studies on sex hormones in Achlya, demonstrated the presence of multi hormonal regulatory system in A. ambisexualis and A. bisexualis.

He envisaged the presence of four hormones A, B, C and D but now it has been conclusively proved that only two hormones named as Antherldiol and oogoniol are involved. Hormones A and C are antheridiols and hormones B and D are oogoniols.

Antheridiol is a crystalline compound having empirical formula as C₂₉ H₄₂ O₅ and molecular weight as 470. The hormone was isolated by Mc Morris and Barksdali (1967) and its structure was proposed by Arsenault et al (1969).

Antheridiol:

It is reported to stimulate four types of reactions:

(a) initiation of antheridial hyphae on male plant,

(b) chemotropic stimulation of antheridial hyphae,

(c) stimulation of male hyphae for production of oogoniol and

(d) delimiation of antheridia.

Oogoniol:

The hormone is synthesized by male hyphae of Achlya ambisexualis only in the presence of antheridiol. However, Barksdali et al. (1974) reported that oogoniol is synthesised by some hermaphrodite strains without the stimulus of antheridiol.

Two crystalline compounds, possessing hormone B activity have been isolated from culture filtrates of Achlya heterosexualis by Mc Morris and his coworkers (1975). These have been named oogoniol-1 and oogoniol-2.

Oogoniol is a crystalline steroid with molecular weight as 500. The hormone stimulates the development of oogonium on female hyphae.

3. Trisporic Acid:

Trisporic Acid is a sex hormone which has been isolated from Blakeslea trispora and Mucor mucedo. It has been found to play active role in sexual reproduction of several members of the order Mucorales. Though the concept of sex hormone in mucorales was developed in 1924 by Burgeff, it was only in 1956 that Burgeff could isolate a sex hormone in cell free extract and this sex hormone was named as Trisporic Acid.

It is an unsaturated and oxygenated form of trimethyl cyclo-hexane. Three kinds of trisporic acid have been identified, trisporic acid A, B and C.

Trisporic acid C plays the major role (80%) as a sexhormone, followed with trisporic acid B with 15% activity and trisporic acid A is least active with 1-2% activity. It appears that trisporic acid A does not have the functional group in the acid chain.

Empirical formula of trisporic acid is C₁₈ H₂₆ O₄ and the molecular weight is 306.

The role of sex hormones in Mucor mucedo was studied by Plempel et al. (1957-61). The sex hormone trisporic acid, present in this species is synthesized from B-carotene.

In the heterothallic mycelia, trisporic acid B and C stimulate the development of zygophores. This hormone is synthesized only when the mycelia of (+) and (-) strains grow in a normal continuous diffusable medium.

The hormone trisporic acid synthesized in (-) strain induces the development of progametangium in (-) strains and vice-versa.

The zygophores of (+) and (-) strain are attracted towards each other due to chemotropic response of a volatile substance which also promotes the synthesis of trisporic acid in two opposite mating types.

Fig. 17.9 explains the role of trisporic acid and its collaborative synthesis by the compatible mating types of Mucor mucedo.

It is believed that synthesis of trisporic acid as described for Mucor mucedo takes place in other members of Mucorales as well.

4. Yeast α Factor:

The presence and the involvement of some hormone in the sexual reproduction of Saccharomyces cerevisiae was suggested by Levi in 1950. In this fungus, the haploid cells are of two mating types a and α which conjugate to form diploid cells. In 1956, Levi showed that the α haploid cells produce a diffusible chemical which induces the formation of copulatory process by compatible a cells.

These a cells, due to influence of the chemical substance produced by α cells, stop their growth and reproduction by budding. Instead, these a cells swell in size and form giant cells of various shapes. These giant cells are 30 or more times heavy in dry weight in comparison to normal haploid cells. The α factor acts only on a cells and has no effect on α cells.

The α factor is reported to inhibit DNA replication in the a cells. Duntze (1970 – 1973) isolated the α factor in pure form. It is peptide complexed with copperion and has molecular weight of 1400.