SPECIFIC REPRODUCTIVE HORMONES 373 



10. SPECIFIC REPRODUCTIVE HORMONES 



Hormones — endogenous chemical substances which influence or de- 

 termine reproductive processes — have been unequivocally demon- 

 strated in certain of the Oomycetes, notably Achlya spp., by J. R. Raper, 

 who reviewed the entire field in 1952 (236). 



Certain strains of Achlya bisexualis and A. ambisexualis are "heter- 

 othallic," i.e., the male and female sex organs — antheridia and oogonia, 

 respectively — are borne on different thalli. This type of heterothallism 

 is perhaps more clearly described as haplodioecism. When thalli of 

 opposite sex are in the same medium, the development of the sex or- 

 gans is under hormonal control. The hormones whose existence and 

 action must be inferred from convincing physiological and morpho- 

 genetic evidence are summarized in Table 1. It is apparent that the 



Table l.The Sexual Hormones of Achlya Spp. 



Hormone Produced by Action 



A, A 2 Female vegetative plant Induces antheridial hyphae on male 



plant 

 A 1 Male vegetative plant Augments A and A 2 



A 3 Male vegetative plant Depresses action of A and A 2 



B Antheridial hyphae Induces oogonial initials on female plant 



C Oogonial initials (a) Induces antheridial hyphae to grow 



along a concentration gradient toward 

 the oogonium; (b) induces the forma- 

 tion and delimitation of the antherid- 

 ium in the male plant 

 D Antheridia Induces (a) delimitation of the oogonium 



and (b) differentiation of oospheres 



* From Raper (236). 



entire sequence of events leading up to fertilization is under specific 

 and sequential hormonal control. The hormones are produced in ex- 

 tremely small amounts, so small that only a start has been made toward 

 chemical fractionation (237). Biological activities indicate that the 

 battery of hormones produced by A. bisexualis is not fully identical 

 with that of A. ambisexualis (234). 



Others of the Saprolegniacae — Thraustotheca clavata and the "homo- 

 thallic" Achlya americana — are governed in reproduction by similar 

 but not identical hormone systems (235, 236). Preliminary evidence 

 of a hormonal system in Sapromyces reinschii has also been obtained 

 (30). 



