Warning: this is a very niche question related to mycology + microscopy
I understand that clamp connections are the connections between hyphal cells, and that they have something to do with the way that cells replecate - the nucleus divides, half of it gets sent over this little shoot that becomes the clamp connection, and gets transferred to the cell before it (I doubt I remembered that correctly). But I’d like to know what importance (if any) they serve in identification? Do all cells in a mushroom have these connections?
I found a rarer species, Cortinarius acutus, and while I was looking under the microscope, this question came about. I thought I’d photograph what I thought to be clamp connections in the lamellae tissue. Are these examples of clamp connections?
Clamps can be a diagnostic feature to distinguish some species of fungi, as some species have clamps on all septa (cell connections), while others only have them on some or none at all, or only in certain tissues.
Most basidiomycete fungi have clamps to some degree, but they can also be completely absent or really hard to see without a high-end microscope.
The septum in the first photo looks like it is clamped, while I cannot find any clamps in the second photo (doesn’t mean they aren’t there, could just be a wrong angle). When microscoping fungi it’s good to take your time and ideally look at several preparations to get a feel for the different features in your specimen.
Here are illustrations from two of my books of different types of clamp connections:
It’s been a while since I looked at this for botany class (we now focus mostly on plants since there’s a separate mycology course) but from I remember clamp connections have something to do with how certain fungi (mostly basidiomycetes) orchestrate nuclear and cell division. Several things are at play here:
When two hyphae of different mating types (say + and -) meet, their cells fuse and form a dikaryon: cells with two nuclei in them, one + and the other -. This is somewhat similar to egg and sperm fusing (most fungi don’t have gametes in the traditional sense) and a precursor to eventual nuclear fusion = fertilization and zygote formation. However, that doesn’t happen until much later in the fungal life cycle (inside the fruiting bodies, aka mushrooms). Until then, the dikaryon cells will divide and produce hyphae with two nuclei per cell. For this to work for eventual fertilization utilizing the two mating types, each daughter cell will need again one + and one - nucleus after division.
In fungal mitosis, the nuclear envelope doesn’t break down but instead the spindle forms inside each nucleus, separating the chromosomes, and eventually each nucleus splits into two nuclei. So after a round of nuclear division, the dikaryon cells become tetrakaryon with four nuclei. Because of the way the cells are elongated in the hyphae, one of the nuclei will be closer to the tip, the other closer to the fusion site. Let’s say the cell is oriented with the + nucleus near the tip and - nucleus near the base. After nuclear division the four nuclei are now oriented from the tip as +, +, -, -. Simply splitting the cell in two now would separate this into one cell with +,+ and another with -,- nuclei. That would not result in cross-fertilization between mating types when nuclei eventually fuse into a zygote, but instead inbreeding for each one.
So the clamp connections exist to shuffle the daughter nuclei during division into a +, -, +, - order and ensure both cells after cell division end up with +, - nuclei again. This diagram shows what’s going on, using black and white nuclei to indicate the two mating types:
Thanks for the explanations everyone, very much appreciated. I’m still definitely new to fungi microscopy, so I have quite a bit to learn when it comes to “what am I actually looking at?” and “why is that there?”. Very fun. Mushlove :)
So at the end of that diagram there, the tip of the hyphae continues growing until its long enough to where it needs to make a new cell (rinse and repeat)?
Essentially, yes - until it grows into a fruiting body and makes basidia. At that point the nuclei fuse into a diploid zygote, meiosis occurs, and haploid spores are formed.
