Analysis of highly ordered architecture of actin cytoskeleton in plant cells.

植物绒毛，P-115-ABP和P-135-ABP，含百合花粉粗提物。在Ca^<2+>存在的情况下结合到DNase I亲和柱上，并被EGTA从柱上解离和洗脱。纯化的P-135-ABP在Ca^<2+>存在下加速了g -肌动蛋白的聚合。这些结果表明，在Ca^<2+>存在的情况下，P-135-ABP可以与g -肌动蛋白形成复合物，从而作为肌动蛋白丝聚合的核或种子。此外，P-135-ABP包覆在肌动蛋白丝末端，并在Ca^<2+>存在下切断或解聚丝。P-135-ABP已被证明能将肌动蛋白丝排列成束。因此，像动物绒毛蛋白一样，P-135-ABP以Ca^<2+>依赖的方式对肌动蛋白产生各种影响。根据对P-115-ABP初级结构的分析，推测P-115-ABP也具有与P-135-ABP相似的活性。因此，花粉管中的植物绒毛蛋白负责在柄区捆绑肌动蛋白丝，在柄区存在低浓度的Ca^<2+>，而在顶区参与解聚或切断肌动蛋白丝，在顶区存在相对高浓度的Ca^<2+>。在低分子量g -肌动蛋白结合蛋白profilin的存在下，P-135-ABP没有加速肌动蛋白的聚合。结果表明，在萌发花粉中，g -肌动蛋白几乎与profilin形成复合物，其浓度与肌动蛋白相似。因此，有理由认为植物绒毛蛋白的肌动蛋白成核活性并未在花粉中发挥。绒毛蛋白广泛分布于植物细胞中，如烟草培养细胞BY-2。有趣的是，绒毛蛋白不仅与肌动蛋白丝束共定位，而且与某些被认为是质体的细胞器共定位。因此，植物绒毛蛋白可能是细胞器在细胞中定位的因素之一。

Plant villins, P-115-ABP and P-135-ABP, containing in a crude extract prepared from lily pollen. bound to a DNase I affinity column in the presence of Ca^<2+>, and were dissociated and eluted from the column with EGTA. Purified P-135-ABP accelerated the polymerization of G-actin in the presence of Ca^<2+>. These results indicated that P-135-ABP can form a complex with G-actin in the presence of Ca^<2+> and consequently acts as a nucleus or seed for polymerization of actin filaments. Furthermore, P-135-ABP caped an actin filament end, and severed or depolymerized filaments in the presence of Ca^<2+>. P-135-ABP has been shown to arrange actin filaments into bundles. Hence, like animal villin, P-135-ABP exerts various effects on actin in a Ca^<2+>-dependent manner. Based on an analysis of the primary structure of P-115-ABP, it is assumed that P-115-ABP also has similar activities to those of P-135-ABP. Hence, plant villin in pollen tubes is responsible for bundling actin filaments in shank region, where low concentrations of Ca^<2+> are present, while is involved in depolymerizing or severing actin filaments in apical regions, where relatively high concentrations of Ca^<2+> concentrations are present. In the presence of profilin, a low molecular weight G-actin binding protein, the acceleration of actin polymerization by P-135-ABP was not found. It is indicated that almost of G-actin form complex with profilin present at similar concentration to that of actin in the germinating pollen. Hence, it is reasonable to consider that actin-nucleation activity of plant villin is not exerted in pollen.Villin is widely distributed in plant cells, such as tobacco cultured cells BY-2. Interestingly, villin is co-localized with not only actin-filament bundles, but also certain organelles considered to be plastides. Therefore, it is possible that plant villin is one of factor responsible in the positioning of the organelles in cells.