Sexual Sporulation in the Oomycota
- Overview of the life cycle of fungi in the Oomycota:
- SEXUAL SPORULATION involves the formation of specialised reproductive structures (ANTHERIDIA and OOGONIA) in which MEIOSIS results in the fomation of HAPLOID NUCLEI (GAMETES).
- The FUSION of compatible gametes is a preliminary to the formation of DIPLOID OOSPORES, which upon germination return us to the DIPLOID SOMATIC PHASE
- Formation of oogonia and antheridia:
- OOGONIA are usually SPHERICAL and their entire contents differentiate into UNINUCLEATE HAPLOID OOSPHERES.
- In contrast, ANTHERIDIA are ELONGATE, MULTINUCLEATE structures which originate either:
- In HETEROTHALLIC SPECIES each colony produces both oogonia and antheridia, but the oogonia can be fertilized only by antheridia from another colony - i.e. self-fertilization is impossible in heterothallic species due to incompatibility.
- One or more antheridia may become attached to the oogonium.
- The antheridia branch to form FERTILIZATION TUBES, sending one into each oosphere within the oogonium.
- One nucleus from the antheridium passes through each fertilization tube into an oosphere where it fuses with the oosphere nucleus to form a DIPLOID ZYGOTE.
- Each fertilized oosphere now develops a THICK WALL and becomes converted into an OOSPORE.
- After a period of dormancy the oospore germinates and the resulting germ-tube eventually gives rise to a DIPLOID MYCELIUM.