Ultrastructural changes during nectar secretion from extrafloral nectaries of Pithecellobium dulce Benth

The structural changes in the secretory cells are important to understand the ontogeny and nectar secretion process from the nectaries. In this study, we investigated the ultrastructural changes during different developmental/secretion stages of extrafloral nectaries (EFNs) of Pithecellobium dulce. The dense cytoplasm with active biosynthesis mechanisms such as ribosomes, mitochondria, large nucleus, and plastids with accumulated starch grains characterized the pre-secretion stage of young nectariferous cells. During the secretory phase, the cytoplasm showed distinct changes associated with endomembrane transport such as the predominant occurrence of Golgi, secretory vesicles, and ER resulting in the subsequent appearance of secretions in the intercellular and subcuticular spaces. Cell wall loosening following the dissolution of middle lamellae leading to the formation of subcuticular spaces was evident during advanced stages of nectar secretion. The characteristic cytoplasmic and apoplastic changes associated with cell death were noticed during the post-secretory stages. The structural evidence from the present study suggests the occurrence of two modes of secretion (merocrine and holocrine) during the early and late stages of secretion in the EFNs of P. dulce.

Automated summary

This study investigated the ultrastructural changes during different developmental/secretion stages of extrafloral nectaries (EFNs) of Pithecellobium dulce. The cytoplasm of young nectariferous cells during the pre-secretion stage was dense and characterized by active biosynthesis mechanisms. The secretory phase showed distinct changes in cytoplasm associated with endomembrane transport and the subsequent appearance of secretions in intercellular and subcuticular spaces. Advanced stages of nectar secretion revealed cell wall loosening and the formation of subcuticular spaces. The structural evidence suggests the occurrence of two modes of secretion (merocrine and holocrine) in the EFNs of P. dulce.