XVI International Botanical Congess

CryoSEM and X-ray microanalysis of Pelvetia compressa receptacles cryofixed during potentiation and gamete expulsion were used to investigate whether osmomechanical forces mediate gamete release. Oogonia were compressed as they moved through the paraphysis-occluded pore. Receptacles exhibited a range of patterns of K distribution between and including 2 extremes: 1) Inside most cells except mature gametangia and epidermis, and 2) Extracellular, in the extensive ECM. Such variability was observed also as a continuous wave along a single receptacle, suggesting a dynamic event. The longitudinal pattern of Cl efflux is similar to K efflux and both quickly became undetectable in the medulla due to diffusion and/or swelling of the ECM. These results indicate that the cells accumulate and discharge large quantities of K and Cl into the ECM.