Emissive europium complexes that stain the cell walls of healthy plant cells, pollen tubes and roots

The cell-staining behaviour of a set of five emissive europium complexes has been studied in Nicotiana tabacum BY-2 cells and pollen tubes, Nicotiana benthamiana plant leaves and in the root hairs of the wild-type plant Arabidopsis thaliana (Columbia). The cell walls were stained selectively, notably in the tobacco BY-2 cells, by the complex [EuL¹] that contains one azathiaxanthone chromophore. Internalisation only occurred in cells that had been deliberately permeabilised or were dying. No uptake was observed within healthy plant leaves. In root hairs, the cell wall was strongly stained as well as the mitochondria, revealed by time-lapsed microscopy that showed the tumbling of the mitochondria in the living tissue, confirmed by co-localisation studies. In pollen tubes, the cell wall was also stained; rapid bursting of the pollen tip occurred following incubation with [Eu.L¹], triggered by excitation with 405 nm laser light. Such behaviour is consistent with local perturbation of cell wall permeability and integrity, associated with the reactivity of the chromophore triplet excited state.