title: Profiling and functional classification of esterases in olive (Olea europaea) pollen during germination.
abstract: OBJECTIVE
  A pollen grain contains a number of esterases, many of which are released upon contact with the stigma surface. However, the identity and function of most of these esterases remain unknown. In this work, esterases from olive pollen during its germination were identifided and functionally characterized.
  
  
  METHODS
  The esterolytic capacity of olive (Olea europaea) pollen was examined using in vitro and in-gel enzymatic assays with different enzyme substrates. The functional analysis of pollen esterases was achieved by inhibition assays by using specific inhibitors. The cellular localization of esterase activities was performed using histochemical methods.
  
  
  RESULTS
  Olive pollen showed high levels of non-specific esterase activity, which remained steady after hydration and germination. Up to 20 esterolytic bands were identified on polyacrylamide gels. All the inhibitors decreased pollen germinability, but only diisopropyl fluorophosphate (DIFP) hampered pollen tube growth. Non-specific esterase activity is localized on the surface of oil bodies (OBs) and small vesicles, in the pollen intine and in the callose layer of the pollen tube wall. Acetylcholinesterase (AChE) activity was mostly observed in the apertures, exine and pollen coat, and attached to the pollen tube wall surface and to small cytoplasmic vesicles.
  
  
  CONCLUSIONS
  In this work, for the first time a systematic functional characterization of esterase enzymes in pollen from a plant species with wet stigma has been carried out. Olive pollen esterases belong to four different functional groups: carboxylesterases, acetylesterases, AChEs and lipases. The cellular localization of esterase activity indicates that the intine is a putative storage site for esterolytic enzymes in olive pollen. Based on inhibition assays and cellular localization of enzymatic activities, it can be concluded that these enzymes are likely to be involved in pollen germination, and pollen tube growth and penetration of the stigma.
authors.affiliation: Department of Biochemistry, Cell and Molecular Biology of Plants, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas (CSIC), Granada, Spain.
authors.forename: Juan D
authors.initials: JD
authors.lastname: Rejón
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Zienkiewicz
authors.forename: María Isabel
authors.initials: MI
authors.lastname: Rodríguez-García
authors.forename: Antonio J
authors.initials: AJ
authors.lastname: Castro
mesh_terms: D004791:Enzyme Inhibitors / Q000494:pharmacology; D004950:Esterases / Q000037:antagonists & inhibitors / Q000145:classification* / Q000302:isolation & purification / Q000378:metabolism; D018525:Germination / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D008970:Molecular Weight; D031658:Olea / Q000201:enzymology* / Q000502:physiology / Q000648:ultrastructure; D010940:Plant Proteins / Q000145:classification / Q000378:metabolism; D011058:Pollen / Q000201:enzymology* / Q000502:physiology / Q000648:ultrastructure; D013696:Temperature; D013997:Time Factors
chemical_list: D004791:Enzyme Inhibitors; D010940:Plant Proteins; D004950:Esterases