Department of Biological Sciences, Graduate School of Science, Osaka University, Machikaneyama 1-1, Toyonaka, Osaka 560-0043, Japan.
Plant Cell Physiol. 2011 Nov;52(11):1973-82. doi: 10.1093/pcp/pcr130. Epub 2011 Sep 24.
Chloroplasts are actively anchored at the appropriate intracellular regions to maintain advantageous distribution patterns under specific environmental conditions. Redistribution of chloroplasts is accompanied by their de-anchoring and re-anchoring, respectively, from and to the cortical cytoplasm. In spinach mesophyll cells, high-intensity blue light and Ca(2+) treatment induced the disappearance of the meshwork-like array of actin filaments surrounding chloroplasts, which was suppressed by a calmodulin antagonist. Regulatory mechanisms of chloroplast anchoring were investigated using plasma membrane (PM) ghosts, on which the cortical cytoplasm underlying the PM was exposed. Addition of an actin-depolymerizing reagent or > 1 µM Ca(2+) induced detachment of a substantial number of chloroplasts from the PM ghosts concomitant with disordered actin organization. Calmodulin antagonists and anti-calmodulin antibodies negated the effects of Ca(2+). In addition, Ca(2+)-induced detachment of chloroplasts was no longer evident on the calmodulin-depleted PM ghosts. We propose that chloroplasts are anchored onto the cortical cytoplasm through interaction with the actin cytoskeleton, and that Ca(2+)-calmodulin-sensitized de-anchoring of chloroplasts is a critical early step in chloroplast redistribution induced by environmental stimuli.
叶绿体被主动锚定在适当的细胞内区域，以在特定环境条件下保持有利的分布模式。叶绿体的再分配伴随着它们分别从质膜下皮层和到质膜下皮层的去锚定和再锚定。在菠菜叶肉细胞中，高强度蓝光和 Ca(2+)处理诱导围绕叶绿体的网格状肌动蛋白丝阵列消失，这一过程被钙调蛋白拮抗剂抑制。使用质膜（PM）鬼来研究叶绿体锚定的调节机制，在 PM 下的质膜下皮层被暴露。添加肌动蛋白解聚试剂或 >1 µM Ca(2+) 会诱导大量叶绿体从 PM 鬼上脱离，同时肌动蛋白组织紊乱。钙调蛋白拮抗剂和抗钙调蛋白抗体否定了 Ca(2+)的作用。此外，在钙调蛋白耗尽的 PM 鬼上，Ca(2+)诱导的叶绿体脱离不再明显。我们提出，叶绿体通过与肌动蛋白细胞骨架的相互作用而锚定在质膜下皮层上，并且 Ca(2+)-钙调蛋白敏感的叶绿体去锚定是环境刺激诱导叶绿体再分配的关键早期步骤。
