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49 pages, 18874 KiB

Open AccessEditor’s ChoiceArticle

Morphological and Ultrastructural Features of Selected Epidendroideae Pollen Dispersal Units and New Insights into Their Chemical Nature

by Carola Purgina, Silvia Ulrich, Martina Weber and Friðgeir Grímsson

Plants 2024, 13(8), 1114; https://doi.org/10.3390/plants13081114 - 16 Apr 2024

Cited by 2 | Viewed by 1954

Abstract

Orchidaceae display enormous diversity in their flower morphology, which is particularly evident in their pollen dispersal units (pollinia, pollinaria). The packaging of pollen by elastoviscin leads to a great diversity of these morphologically and structurally complex pollen units. Despite being one of the most diverse angiosperm families, the available palynological data on orchids remain limited and sometimes contradicting. This study provides new insights into the pollen morphology and ultrastructure of five orchid species from the subfamily Epidendroideae, using combined light, scanning electron, and transmission electron microscopy. The aim was to compare the morphology and ultrastructure of pollen dispersal units and to elucidate the chemical nature of the pollen wall layers and of elastoviscin. Our combined light and electron microscopy investigation demonstrated the presence of six tetrad types even within a single pollinium, which is unique for orchids. The application of different staining methods confirmed the assumed lipidic nature of elastoviscin and the differences in its contrast and ultrastructure suggest a mixture of sticky materials with dissimilar chemical compositions. This study affirmed that sporopollenin is mostly restricted to the outer pollen grains of peripheral tetrads in compact and sectile pollinia, while inner tetrads exhibit highly reduced non-sporopollenin pollen walls. Full article

(This article belongs to the Section Plant Cell Biology)

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12 pages, 3455 KiB

Open AccessFeature PaperArticle

Pollination in Epidendrum densiflorum Hook. (Orchidaceae: Laeliinae): Fraudulent Trap-Flowers, Self-Incompatibility, and a Possible New Type of Mimicry

by Rodrigo Santtanna Silveira, Rodrigo Bustos Singer and Viviane Gianluppi Ferro

Plants 2023, 12(3), 679; https://doi.org/10.3390/plants12030679 - 3 Feb 2023

Cited by 6 | Viewed by 3638

Abstract

The pollination and the breeding system of Epidendrum densiflorum (Orchidaceae: Laeliinae) were studied through fieldwork and controlled pollinations in cultivated plants. Pollination is exclusively promoted by males of diurnal Lepidoptera: five species of Arctiinae and four of Ithomiinae were recorded as pollinators. These male insects are known to obtain alkaloids (through the nectar) in flowers of Asteraceae and Boraginaceae. However, the flowers of E. densiflorum are nectarless, despite presenting a cuniculus (a likely nectariferous cavity). Pollinators insert their proboscides into the flowers and remove or deposit the pollinaria while searching for nectar. The floral tube is very narrow, and insects struggle for up to 75 min to get rid of the flowers. Plants are pollinator-dependent and nearly fully self-incompatible. Pollinarium removal, pollination, and fruiting success (2.85%) were very low; facts that are consistent with the patterns globally observed in deceptive (rewardless) orchids. Nilsson’s male efficiency factor (0.245) was also low, indicating pollen loss in the system. Based on our field observations, we suggest that the fragrance of E. densiflorum likely mimics these plants that are normally used as a source of alkaloids by male Lepidoptera, a hypothesis that we intend to test in the future. Full article

(This article belongs to the Special Issue Floral Secretory Tissue: Nectaries and Osmophores)

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10 pages, 9015 KiB

Open AccessArticle

Pollinaria Reconfiguration Mechanism of Widespread Euro-Mediterranean Orchids: The Effects of Increasing Air Temperature

by Micaela Lanzino, Anna Maria Palermo and Giuseppe Pellegrino

Plants 2022, 11(10), 1327; https://doi.org/10.3390/plants11101327 - 17 May 2022

Cited by 1 | Viewed by 2930

Abstract

Orchids are fascinating for many reasons: their reproductive strategies, their pollination systems and the various morphological adaptations they have evolved, including the presence of pollen grains agglomerated into two masses, called pollinia, which form a structure known as a pollinarium. After withdrawal from a flower, the pollinarium undergoes a bending movement such that the pollen masses become correctly orientated to strike the stigma. We evaluated the duration of pollinator visits to inflorescences and the effects of temperature on pollinaria reconfiguration in eight orchid species in order to analyze the effects of increasing air temperature on the changes in bending time, and thus on geitonogamy levels. The impact of temperature on insect behavior was not assessed because our priority was to understand the effects of temperature on the process of pollinaria reconfiguration. All the examined species showed natural reconfiguration times that were 1.7–3.0 times longer than the pollinator residency times. A higher temperature showed a reduction in bending time regardless of the species tested. However, the bending time was never shorter than the residence time of the insects on the flower. Our data showed that high temperatures had a limited effect on the pollinarium reconfiguration time, thus indicating that high temperatures had a limited effect on folding compared to the effect that it had on the viability of the pollen. Full article

(This article belongs to the Special Issue Orchid Research: From Genomics to Diversity Conservation)

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