Substratum wettability and charge influence the spreading of Dictyostelium amoebae and the formation of ultrathin cytoplasmic lamellae

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Abstract
Amoebae of Dictyostelium discoideum attach and spread on strongly hydrophobic methylated glass and polystyrene as well as the hydrophilic surfaces of clean glass, polylysine adsorbed on glass and acid-treated polystyrene. On polylysine-treated glass, spreading is rapid and the edges of the fully spread cells withdraw, forming a wide 0.1 μm thick lamella, which gives a very dark image in the interference reflection microscope. The optical properties of the lamella have been analysed in detail using finite aperture theory and can be distinguished from dark images generated by a small aqueous cell-substratum separation. The formation of the lamella is discussed in terms of the mechanics of cell movement.