In mesophyll cells of the water plant Lemna trisulca L. chloroplasts r
edistribute in response to blue light. In the present study it is show
n that an actin depolymerizing agent cytochalasin D, a crosslinker of
actin subunits in F-actin m-maleimidobenzoic acid N-hydroxysuccinimide
ester (MBS) as well as N-ethylmaleimide (NEM)-a sulfhydryl group reag
ent, are potent inhibitors of these blue light-induced chloroplast mov
ements in Lemna. Extraction with cold, buffered glycerol solution pres
erves light-induced chloroplast arrangements within cells producing pe
rmeabilized cell models. 'Reactivation' of these cell models by Mg-ATP
results in remarkable movements which can be inhibited by treatment w
ith NEM and cytochalasin D. Immunofluorescence microscopy demonstrates
that a component which is associated with isolated Lemna chloroplasts
cross-reacts with antibodies directed against bovine myosin. These re
sults indicate that a contractile actomyosin system is involved in blu
e light-induced chloroplast movements in Lemna and a putative motor pr
otein, similar to myosin, is associated with the surface of Lemna chlo
roplasts.