LIGHT-INDUCED CHLOROPLAST MOVEMENTS IN LEMNA-TRISULCA - IDENTIFICATION OF THE MOTILE SYSTEM

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.