The histochemistry of carboxylester hydrolases: problems and possibilities

Profiling and functional classification of esterases in olive (Olea europaea) pollen during germination

BACKGROUND AND AIMS

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.

KEY 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.

Epithelial alpha-naphthyl acetate esterases in the green vervet monkey gingiva before and after periodontal surgery and during tooth eruption

To provide enzymatic information on de novo formed junctional (JE) and sulcular epithelium (SE), we performed periodontal surgery on 24 teeth. Ten to 14 days postoperatively, all experimental and 16 control teeth were extracted with adjacent buccal gingiva. In addition, specimens from unerupted and partly erupted teeth containing enamel epithelium (EE) were examined. Fixed cryostat sections were cut in series, stained with HE, or incubated with and without substrate for demonstration of alpha-naphthyl acetate esterase activity and for control purposes, respectively. The distribution and intensity of the alpha-naphthyl acetate esterase activity of newly reformed JE and SE was identical to that of the original JE and SE, i.e. suprabasal and very strong. In contrast, both the oral gingival epithelium (OGE) and the EE displayed a very weak enzyme reaction. These observations indicate that the presence of alpha-naphthyl acetate activity of original and reformed JE and SE is probably site specific and of nondevelopmental origin. Heavy inflammation after healing was associated with enhanced epithelial proliferation of OGE and, in addition, marked esterase activity of these proliferations and corresponding OGE. This points at a possible inflammatory induction of the marked esterase activity seen in JE and SE as well as site-specific, connective tissue influences. Further investigation is needed to elucidate the effect of inflammation on the esterase activity.

Presence of alpha-naphthyl acetate esterase enzymes in dental and oral epithelium of guinea pig embryos

This study examines the distribution of alpha-naphthyl acetate esterase enzymes in reduced enamel epithelium, i.e., post secretory ameloblasts (PSA) and external cells of reduced enamel epithelium (ERE) of continuously growing incisor and molar tooth germs and in the covering oral epithelium (OE). Jaws of guinea pig embryos, 25-50 days of gestation age, were pretreated, frozen, serially cut, and incubated with alpha-naphthyl acetate as substrate and hexazotized pararosaniline as capture agent for demonstration of enzyme activity. In addition, sections were preincubated with various inhibitors of enzyme activity. A strong enzyme reaction, essentially unaffected by pretreatment procedures, was demonstrated in all cells of PSA and ERE, and in suprabasal cells of OE. Preliminary characterization of the alpha-naphthyl acetate esterase enzymes by means of inhibitors suggests a prevailing presence of B-esterase enzymes in both oral and dental epithelia. PSA were selectively stained when 2 x 10(-3) M arsanilic acid was used as inhibitor, ERE were selectively inhibited by 10(-5) M eserine, and cells of OE were selectively stained when 2 x 10(-3) M HgCl2 was used as inhibitor. We therefore conclude that the alpha-naphthyl acetate esterase enzymes in combination with inhibitors may serve as histochemical markers for discrimination of dental and oral epithelium in the guinea pig prior to eruption of teeth.

Ultrastructural cytochemistry of non-specific esterase in murine peritoneal macrophages

Non-specific esterase (NSE) activity was demonstrated in glutaraldehyde-fixed monolayers of murine peritoneal macrophages. Using 2-naphthylthiol acetate (NTA) as substrate and Fast Blue BB as coupling agent a strong osmiophilic reaction product was obtained. The reaction product was observed as electron-dense dots covering cisterns of the rough endoplasmic reticulum, Golgi saccules and vesicles, or as large aggregates in lysosomes. Using alpha-naphthyl butyrate (ANB) as substrate and hexazotized pararosaniline as coupling agent the osmiophilic reaction product was observed extracellularly on the plasma membrane as an electron-dense continuous layer, whereas intracytoplasmic staining of lysosomes was rare. Substitution of the coupling agents in the respective media resulted in a slight reaction with the ANB medium whereas with the NTA medium reaction product was observed only in lysosomal structures. The substrate specificity of the different types of esterases was confirmed after isoelectric focusing on thin-layer polyacrylamide gels. The results indicate that in murine peritoneal macrophages different types on NSE are detected with NTA and ANB, having distinct ultrastructural localizations.