Pollen grains contain numerous hydrolytic enzymes, many of which are released upon contact with the stigma. Rejón et al. carry out for the first time a systematic functional classification of esterases in pollen grains from a plant with a wet stigma, Olea europaea. They find that olive pollen esterases can be classified into four functional groups: carboxylesterases, acetylesterases, cholinesterases and esterases/lipases. The cellular localization of esterase activity indicates that the intine is a storage site for esterolytic enzymes in olive pollen. From inhibition assays they conclude that these esterases are likely to be involved in pollen germination, and pollen tube growth and penetration of the stigma.
