Onelli Elisabetta, Beretta Mario, Moscatelli Alessandra, Caccianiga Marco, Pozzi Michele, Stroppa Nadia, Adamec Lubomír
Department of Biosciences, University of Milano, Via Celoria 26, 20133, Milan, Italy.
"Città Studi" Botanical Garden, Department of Biosciences, University of Milano, Via Celoria 26, 20133, Milan, Italy.
Protoplasma. 2021 Jan;258(1):71-85. doi: 10.1007/s00709-020-01553-6. Epub 2020 Sep 11.
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.
貉藻（茅膏菜科）是一种稀有的水生食肉植物，分布于欧洲、亚洲、非洲和澳大利亚。貉藻种群在适宜条件下能大量开花，但结实率非常低。我们研究了从欧洲和澳大利亚种群不同发育阶段（开放和未开放花药）的花朵中采集的貉藻花粉结构，通过对花粉和花药结构的显微镜观察来阐明授粉特征以及结实率低的原因。对貉藻花粉的显微镜分析表明，这种植物的花粉像茅膏菜科的其他物种一样以四分体形式排列。在水合花粉中，细胞质突起从位于单核赤道壁上的孔中产生，并能发育成花粉管。有趣的是，小孢子的花粉发育发生在开放的花药中，这表明发育阶段有所延迟。此外，花粉发育显示出精子细胞形成的改变和花粉的早熟萌发。早熟萌发可能是顽拗花粉的特征，这类花粉在花期前自然不会脱水，而是保持部分水合状态，特别是在水生和湿地植物中。雄配子体发育的这些改变可能会影响受精过程，并且是在野外和栽培中观察到的貉藻繁殖能力低的原因。一般来说，花粉寿命缩短和极快萌发被认为是对水生或潮湿环境的一种适应。
