Abstract
Intracellular chloroplast positioning is an important process to optimize photosynthesis. The actin cytoskeleton has been suggested to participate in the chloroplast positioning. However, the manner of participation has not yet been elucidated. To verify our hypothesis that chloroplasts are anchored to the cortical cytoplasm by actin filaments, from spinach mesophyll protoplasts, we prepared plasma-membrane (PM) ghosts in which the cytoplasmic side of PM was exposed. Treatment with latrunculin B or Ca2+ induced fragmentation of actin filaments and detachment of chloroplasts from the PM ghosts. A calmodulin antagonist W7 antagonized the effects of Ca2+. From these results, we assumed participation of villin, an actin-binding protein exhibiting the Ca2+- calmodulin dependent actin-depolymerizing activity. We detected two kinds of villin-like proteins in spinach leaves. Both proteins were localized in the vicinity of chloroplasts on PM ghosts. In addition, different localization of these proteins in mesophyll cells was suggested
