The aquatic carnivorous plant Aldrovanda vesiculosa (Droseraceae) exhibits altered developmental stages in male gametoph
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ORIGINAL ARTICLE
The aquatic carnivorous plant Aldrovanda vesiculosa (Droseraceae) exhibits altered developmental stages in male gametophyte Elisabetta Onelli 1 & Mario Beretta 2 & Alessandra Moscatelli 1 & Marco Caccianiga 1,2 & Michele Pozzi 1 & Nadia Stroppa 1 & Lubomír Adamec 3 Received: 26 May 2020 / Accepted: 31 August 2020 # Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract Aldrovanda vesiculosa (Droseraceae) is a rare aquatic carnivorous plant, distributed in Europe, Asia, Africa, and Australia. Aldrovanda populations can flower prolifically under favourable conditions, but seed set is very limited. We studied the structure of Aldrovanda pollen collected from flowers in different developmental stages (opened and non-opened anthers) from both European and Australian populations to elucidate pollination traits and the basis of poor seed set on the basis of microscopic observation of pollen and anther structure. Microscopic analyses of Aldrovanda pollen showed that this plant has pollen arranged in tetrads like other species in the Droseraceae family. In hydrated pollen, cytoplasmic protrusions originate from pores located along the equatorial wall of monads, and can develop into pollen tubes. Interestingly, pollen development from microspores occurs in open anthers, suggesting a delay of the developmental stages. In addition, pollen development displays altered sperm cell formation and precocious pollen germination. Precocious germination may characterize recalcitrant pollen, which naturally do not undergo dehydration before anthesis and remain partially hydrated, particularly in aquatic and wetland plants. These alterations of male gametophyte development could affect fertilization processes, and be the reason for the low reproductive capability of Aldrovanda observed both in the field and in cultures. Generally, reduced pollen longevity and very quick germination are considered an adaptation to aquatic or wet environments. Keywords Aldrovanda vesiculosa . Pollen development . Pollen structure . Generative cell . Pollination . Anther structure
Introduction Aldrovanda vesiculosa L. (Waterwheel plant, Droseraceae) is a rare and endangered aquatic carnivorous plant exhibiting spectacular, rapid movement of its snapping traps. Aldrovanda grows on a vast range of territories in Europe, Asia, Africa, and Australia and across various climatic zones—from temperate to tropical and subtropical ones— but its recent natural spread includes only around 50 known Handling Editor: Handling Editor: Peter Nick * Lubomír Adamec [email protected] 1
Department of Biosciences, University of Milano, Via Celoria 26, 20133 Milan, Italy
2
“Città Studi” Botanical Garden, Department of Biosciences, University of Milano, Via Celoria 26, 20133 Milan, Italy
3
Institute of Botany of the Czech Academy of Sciences, Dukelská 135, CZ-379 82 Třeboň, Czech Republic
sites worldwide (Cross 2012; Adamec 2018). Plants are perennial, rootless, submerged, and free-floating below the water surface, growing in shallow
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