Conjugation in Zygnemataceae:

Algae have sex too! (at least some of them)

Amongst the Zygnemaceae, the process of conjugation consists of the joining together of the contents of two haploid cells from (usually) different filaments.

A: Conjugation in Spirogyra : these filaments were already conjugating when sampled (in early April) and show the typical results of scalariform ('ladderlike') conjugation

 

Two filaments lie parallel, and outgrowths from each filament grow towards each other, then fuse to form a conjugation tube.
The cell in the centre of the lower filament is forming conjugation tubes with two other cells: only one of these will fuse successfully, allowing the contents of one cell to transfer to the other.

The dark oval shapes are diploid zygospores, formed after nuclear fusion between the two haploid cells. They form in only one of the two filaments.  

Sometimes more than two filaments take part in conjugation: see this 'menage a trois'  

Note that the centre filament has no zygospores: it appears to have donated all the contents of participating cells to the other filaments. See also the two cells in the upper filament which have not succeeded in conjugating: their tubes have not fused with the cell they contacted, as a cell from another filament got there first.

The zygospores are green when seen in dark-ground illumination:

Sometimes conjugation occurs between cells in the same filament:
lateral conjugation.

 

This set of pictures of Mougeotia   shows the early stages of the process: unfortunately they did not go on to complete the process in captivity.

Progressive development of geniculations ('knee bends') associated with lateral conjugation: this may be Mougeotia geniculata. The cell diameter is 32µm.


     


These two pictures show the short rhizoid-like branches which grow out from one filament to make contact with another (not always successfully):

 

Sometimes the side branches reach several cells in length:


Cell contents change their appearance: the chloroplast contracts and becomes more dense, contracting away from the other organelles

 

A general view of the filaments:



The organelle which appears to have subunits is a pyrenoid
(starch storage body)



The bulge in the cell wall grows until it develops into a tube:
when the end opens the spore escapes:

   

[snaps]

John Kinross