Pollen morphology and localization of Ni in some Ni-hyperaccumulator taxa of <i>Alyssum</i> L. (Brassicaceae)

Pollen morphology of seven Alyssum L. taxa growing on serpentine soils in different places in the European Mediterranean macrobioclimate territory were studied, described and compared. Cluster analysis was performed to show similarity between species and their populations. The shape of the pollen grains varies among the species and among the grains within the same anther. The pollen grains are 3-colpate, prolate, with long and narrow colpi reaching the poles. The ornamentation of the exine varies from micro-reticulate to reticulate between the species. Pollen sterility/fertility was also calculated. The highest percentage of sterile pollen (73.76%) was calculated for Alyssum murale subsp. murale and the lowest (9.54%) for A. bertolonii subsp. bertolonii. All species are representatives of sect. Odontarrhena (C.A. Meyer) Koch well known as Ni-hyperaccumulators. Nickel and other elements present in pollen and stamen were studied by inductively coupled plasma-mass spectrometry. The stamen parts of all species were micromorphologically analyzed by scanning electron microscopy coupled to an energy-dispersive X-ray probe. Accumulation of Ni was detected in the stamens of all studied species and rarely in the pollen grains. The distribution patterns of Ni were similar among the species examined.本研究针对欧洲地中海大气候区不同地域蛇纹岩土中生长的7个庭荠属（Alyssum L.）类群的花粉形态开展了研究、描述与比较分析。通过聚类分析揭示了各物种及其种群间的相似性关系。花粉粒形态在物种间以及同一花药内的不同花粉粒间均存在差异。供试花粉粒均为3沟型、长球形，具狭长且延伸至两极的萌发沟。不同物种的花粉外壁纹饰从微网状至网状不等。本研究同时统计了花粉育性与不育性占比：不育花粉占比最高的为Alyssum murale subsp. murale（73.76%），最低的为A. bertolonii subsp. bertolonii（9.54%）。所有供试物种均隶属于齿丝庭荠组（sect. Odontarrhena (C.A. Meyer) Koch），该组类群作为镍超富集植物广为人知。本研究采用电感耦合等离子体质谱法（inductively coupled plasma-mass spectrometry）对花粉与雄蕊中的镍及其他元素进行了检测；同时通过扫描电子显微镜（scanning electron microscopy）-能量色散X射线探针（energy-dispersive X-ray probe）联用技术，对所有供试物种的雄蕊开展了微观形态学分析。结果显示，所有供试物种的雄蕊中均检测到镍富集现象，而花粉粒中镍富集现象较为罕见。供试物种间的镍分布模式较为相似。