Pollen-pistil interaction in Mauritia flexuosa: structural and cytological aspects provide insight into the reproductive success of a dioecious palm with supra-annual flowering in a semiarid environment.

The success of pollen-pistil interaction in Mauritia flexuosa (buriti), a palm adapted to the humid ecosystems, 'veredas', within the Cerrado, is influenced by intrinsic and environmental factors. Its supra-annual flowering, dioecy, and adverse climate conditions pose challenges for fertilization, therefore information on floral biology is essential. This study aimed to ascertain stigma receptivity, and elucidate structural, cytochemical, and ultrastructural aspects of the pollen-pistil relationship. Flowers were analysed at intervals post-anthesis (hpa) and post-pollination (hpp). A stigma receptivity test was performed using HO solution. Pistil samples were processed for anatomical, histochemical, and electron microscopy evaluation. The stigma is wet and papillate type, with subepidermis containing sclerenchyma connected to vascular bundles. Stigma receptivity lasts around 36 hpa. The pollen tube penetrates the papilla at 2 hpp and develops in the symplast, towards the stylar canal. The papillae have loose cell walls that facilitate the secretion and contain a rich population of organelles, including large peroxisomes. Fertilization occurs 24 hpp, and during this period the stigma surface is free of pathogens. The vascular connection to the pistil surface favours the germination of pollen grains. The pistil has a strong protective system until fertilization occurs. The symplastic growth of the pollen tube in the stigma and the efficient secretory apparatus of the pistil contribute to rapid fertilization. These structural characteristics and secretion dynamics enhance reproduction of buriti, even with supra-annual flowering and in semiarid conditions.