Pollen wall and stigma surface in the marine angiosperms Thalassia and Thalassodendron

Abstract

The pollen wall and stigma surface of two tropical sea-grasses, Thalassia hemprichii and Thalassodendron ciliatum, have been investigated by electron microscopy and optical cytochemistry. In the spherical inaperturate pollen of Thalassia the exine consists of free bacula with a rudimentary foot layer and endexine. Non-specific esterase activity has been detected in the intine. The enzyme seems to be introduced into the layer at the vacuolate stage when evaginations extend from the spore cytoplasm. The stigma in Thalassia is papillate and the papillae are covered by a pellicle in which esterase activity has been detected. The implications of exterase in the pollen wall and stigma surface in post-pollination behaviour in Thalassia are discussed with reference to terrestrial species. The exine of the filamentous pollen of Thalassodendron is unstructured and unornamented and gives a negative reaction for esterase. The stigma in Thalassodendron bears irregular ridges and hollows and does not have a pellicle.