Cell communication in pollen allelopathy analyzed with laser-scanning confocal microscopy

The contacts between the intact pollen grains of 6 allelopathically active medicinal plants and weeds (Knautia arvensis, Artemisia absinthium, Artemisia vulgaris, Hypericum perforatum, Plantago major and Solidago virgaurea) were studied using the fluorescent microspores by laser-scanning confocal microscopy (LSCM). The pollens of Knautia arvensis or Plantago major were chosen as pollen-acceptors in the model microspore mixtures, while pollens of other species were considered as pollen-donors (of allelochemicals released in excretions). Red-fluorescing excretions from pollens of Artemisia absinthium or Solidago virgaurea accumulated on the green-fluorescing surface of Knautia arvensis. In pollen mixture of Knautia-Artemisia, the germination of Knautia pollens was completely inhibited, whereas the pollen development of Artemisia was decreased up to 33% than control. On the contrary in pollen mixture of Knautia-Solidago, the germination of Knautia pollens was increased to 209% of control, and LSCM-images showed the red-fluorescing excretions from Solidago pollen on Knautia pollen tubes. In model system of indifferent (both germinated like in control) spp., pollens from Plantago major (acceptor) and Hypericum perforatum (donor), red-fluorescing pigment hypericin was released from the pollen-donor, only it coloured the surface of pollen-acceptor. LSCM images may be useful to analyse the natural events, which occur inside and on the surface of contacting foreign pollens.