Functional aspects of floral nectar secretion of Ananas ananassoides, an ornithophilous bromeliad from the Brazilian savanna

STALHL, JM; NEPI, M; GALETTO, L; GUIMARAES, E; RODRIGUES MACHADO, S

ANNALS OF BOTANY

OXFORD UNIV PRESS

Lugar: Oxford; Año: 2012 vol. 109 p. 1243 - 1252

0305-7364

Background and Aims Several members of Bromeliaceae show adaptations for hummingbird pollination in theNeotropics; however, the relationships between floral structure, nectar production, pollination and pollinatorsare poorly understood. The main goal of this study was to analyse the functional aspects of nectar secretionrelated to interaction with pollinators by evaluating floral biology, cellular and sub-cellular anatomy ofthe septal nectary and nectar composition of Ananas ananassoides, including an experimental approach tonectar dynamics.? Methods Observations on floral anthesis and visitors were conducted in a population of A. ananassoides in theBrazilian savanna. Nectary samples were processed using standard methods for light and transmission electronmicroscopy. The main metabolites in nectary tissue were detected via histochemistry. Sugar composition wasanalysed by high-performance liquid chromatography (HPLC). The accumulated nectar was determined frombagged flowers (?unvisited?), and floral response to repeated nectar removal was evaluated in an experimentaldesign simulating multiple visits by pollinators to the same flowers (?visited?) over the course of anthesis.? Key Results The hummingbirds Hylocharis chrysura and Thalurania glaucopiswere the most frequent pollinators.The interlocular septal nectary, composed of three lenticular canals, extends from the ovary base to the style base. Itconsists of a secretory epithelium and nectary parenchyma rich in starch grains, which are hydrolysed during nectarsecretion. The median volume of nectar in recently opened ?unvisited? flowers was 27.0 mL, with a mean (sucrosedominated)sugar concentration of 30.5 %. Anthesis lasts approx. 11 h, and nectar secretion begins before sunrise.In ?visited? flowers (experimentally emptied every hour) the nectar total production per flower was significantlyhigher than in the ?unvisited? flowers (control) in terms of volume (t ¼ 4.94, P ¼ 0.0001) and mass of sugar(t ¼ 2.95, P ¼ 0.007), and the concentration was significantly lower (t ¼ 8.04, P ¼ 0.0001).?Conclusions The data suggest that the total production of floral nectar in A. ananassoides is linked to thepollinators? activity and that the rapid renewal of nectar is related to the nectary morphological features.