Immunolocalization of actin in root statocytes of Lens culinaris L.

Lentil root statocytes show a strict structural polarity of their organelle s with respect to the g vector. These cells are involved in the perception of gravity and are responsible for the orientation of the root, Actin filam ents take part in the positioning of their organelles and could also be inv olved in the transduction of the gravitropic signal. A pre-embedding immuno gold silver technique was carried out with a monoclonal antibody in order t o study the distribution of actin cytoskeleton in the statocytes at the ele ctron microscopic level. Some areas were never labelled (cell wall, vacuole , nucleoplasm, mitochondria, starch grains of the amyloplasts) or very slig htly labelled (stroma of the amyloplasts), The labelling was scattered in t he cytoplasm always close to, or on the nuclear and amyloplast envelopes an d the tonoplast, Associations of 2 to 6 dots in file were observed, but the se short files were not oriented in one preferential direction. They corres ponded to a maximum distance of 0.9 mu m This work demonstrated that each s tatocyte organelle was enmeshed in an actin web of short filaments arranged in different ways. The images obtained by rhodamine-phalloidin staining we re in accordance with those of immunogold labelling. The diffuse fluorescen ce of the cytoplasm could be explained by the fact that the meshes of the w eb should be narrow. The vicinity of actin and of the amyloplasts envelope could account for the movement of these organelles that was observed in spa tial microgravity.