Croceous glands in Polygala adenophora (Polygalaceae): structure, histochemical, and functional aspects

Abstract

ABSTRACT Croceous glands are visible structures defined by their rounded shape and yellowish color. They have great taxonomic importance, being used to delimit the Timutua section, one of the 14 sections of the subgenera Polygala, genera Polygala, the most representative of the family Polygalaceae, with about 120 species recorded in Brazil. However, detailed information about the nature of croceous glands is still missing. Thus, this study aimed to characterize the origin, structure, and function of the croceous glands in the floral structures, fruits, leaf blades, and stems of Polygala adenophora. Samples of P. adenophora at different developmental stages (flower buds, fully developed flowers and fruits), as well as stems, and leaves collected from the 1st, 3rd, 6th, and 9th nodes were obtained from a coastal area in Pará state, Brazil. The samples were fixed in FAA50 or buffered neutral formalin and submitted to light microscopy and scanning electron microscopy. Histochemical tests were carried out for lipophilic and hydrophilic compounds. Our results showed that the croceous glands are secretory cavities and ducts of schizolysigenous origin, present since the beginning of the development of vegetative and reproductive organs. The cavities and ducts produce a lipophilic compound consisting of essential oils and lipids. We hypothesize that this exudate possibly has a protective function, acting against pathogen and herbivore attacks.