Morphology, anatomy and histochemistry of anther and pollen grain of Passifloraceae in the Rio Grande do Sul State, Brazil

Abstract

This study aims to expand the knowledge about the external and internal morphology of the anther and pollen grain of thirteen species of Passiflora L. (subgenera Astrophea, Decaloba and Passiflora) occurring in Rio Grande do Sul and Santa Catarina, under light and scanning electron microscopy, contributing with morphological characteristics to the taxonomic and systematic analysis of the group. The species of Passiflora have tetrasporangiated anthers with a longitudinal dehiscence, showing different sizes and vascularization patterns. The anthers exhibit persistent epidermis,with a smooth to striated cuticle, elongated to short estomial cells, lignified endothecium with different thicknesses, collapsed middle layers, conspicuous tapetal membrane and small orbicules. The pollen grains present lipophilic substances on the sporoderm, starch grains and PAS-positive vegetative cell. The intine is tri-stratified (pectic, pectic-protein and pectocellulosic layers). The exine is differentiated in ectexine and endexine. Three structural patterns of the sporoderm were found: type 1, with thick intine, warty ectexine internally, absence of compact basal layer, mixed nexin 1 with immersed columella (subgenus Passiflora); type 2, with thin intine, internally smooth endexine, compact basal layer of ectexine (subgenres Astrophea and Decaloba); type 3, with thin intine, internally smooth endexine, no basal layer, mixed and granular nexin 1 (P. suberosa - Decaloba). Some features found in this study deserve attention for their phylogenetic potential, as the size and vascular patterns of the anthers, the presence of elongated stomial cells, endothecium thickening types, patterns of the exine reticulum (amplitude and presence of bacilli) and sporoderm structure.