I think the point, said several times already, has still been missed though. A 50mm macro lens at focusing distance for 1:1 renders a 24mm object as 24mm on film regardless of film size or format. It is 24mm on 135, 120, 4x5 or 8x10 film. The depth of field will be the same too if the aperture is the same as the focal length and subject distance will be the same. Diffraction effects will also be the same at the same aperture. Printing the image to the same scale for the object will yield the same results given equal lens performance.
Things will only change if you decide that rather than 1:1 macro (which is what the OP asked for) you want to fill the piece of film with the image of your object. Then you need 1:1 on 135, ~2:1 (approximately double lifesize) on 120, 4:1 on 4x5 or 8:1 on 8x10 which will require you to change the focal length or subject distance which will change the depth of field and may require different apertures, yielding different diffraction effects. Printing the object to the same object scale will yield different results.
For diffraction you need to see the smallest detail you need to capture. f/22 is surely too small. f/11 would be much better and f/8 might be better still but you may then have too narrow a depth of field for even a seed especially if you go beyond 1:1 which you may need to do for a small seed even on 35mm film.