Data from: The Arabidopsis arc5 and arc6 mutations differentially affect plastid morphology in pavement and guard cells in the leaf epidermis

Chloroplasts, or photosynthetic plastids, multiply by binary fission, forming a homogeneous population in plant cells. In Arabidopsis thaliana, the division apparatus (or division ring) of mesophyll chloroplasts includes an inner envelope transmembrane protein ARC6, a cytoplasmic dynamin-related protein ARC5 (DRP5B), and members of the FtsZ1 and FtsZ2 families of proteins, which co-assemble in the stromal mid-plastid division ring (FtsZ ring). FtsZ ring placement is controlled by several proteins, including a stromal factor MinE (AtMinE1). During leaf mesophyll development, ARC6 and AtMinE1 are necessary for FtsZ ring formation and thus plastid division initiation, while ARC5 is essential for a later stage of plastid division. Here, we examined plastid morphology in leaf epidermal pavement cells (PCs) and stomatal guard cells (GCs) in the arc5 and arc6 mutants using stroma-targeted fluorescent proteins. The arc5 PC plastids were generally a bit larger than those of the wild type, but most had normal shapes and were division-competent, unlike mutant mesophyll chloroplasts. The arc6 PC plastids were heterogeneous in size and shape, including the formation of giant and mini-plastids, plastids with highly developed stromules, and grape-like plastid clusters, which varied on a cell-by-cell basis. Moreover, unique plastid phenotypes for stomatal GCs were observed in both mutants. The arc5 GCs rarely lacked chlorophyll-bearing plastids (chloroplasts), while they accumulated minute chlorophyll-less plastids, whereas most GCs developed wild type-like chloroplasts. The arc6 GCs produced large chloroplasts and/or chlorophyll-less plastids, as previously observed, but unexpectedly, their chloroplasts/plastids exhibited marked morphological variations. We quantitatively analyzed plastid morphology and partitioning in paired GCs from wild-type, arc5, arc6, and atminE1 plants. Collectively, our results support the notion that ARC5 is dispensable in the process of equal division of epidermal plastids, and indicate that dysfunctions in ARC5 and ARC6 differentially affect plastid replication among mesophyll cells, PCs, and GCs within a single leaf.叶绿体（chloroplast），即光合质体（photosynthetic plastid），通过二分裂方式增殖，在植物细胞中形成均一的质体群体。在模式植物拟南芥（Arabidopsis thaliana）中，叶肉叶绿体的分裂装置包含内膜跨膜蛋白ARC6、细胞质动力蛋白相关蛋白ARC5（DRP5B）以及FtsZ1和FtsZ2家族蛋白成员，这些蛋白共同组装形成质体基质中部的FtsZ环（FtsZ ring）。FtsZ环的定位受多种蛋白调控，其中包括基质因子MinE（AtMinE1）。在叶肉发育过程中，ARC6与AtMinE1是FtsZ环形成以及质体分裂起始所必需的，而ARC5则是质体分裂后期阶段的关键因子。本研究借助基质靶向荧光蛋白，对arc5与arc6突变体的叶表皮铺层细胞（pavement cells, PCs）以及气孔保卫细胞（guard cells, GCs）中的质体形态进行了观察分析。结果显示，arc5突变体的铺层细胞质体整体略大于野生型，但与突变体叶肉叶绿体不同，其大多数质体形态正常且具备分裂能力；arc6突变体的铺层细胞质体则呈现大小与形态的异质性，包含巨型质体、微型质体、具有高度发达质体小管的质体以及葡萄状质体簇，且不同细胞间的表型存在差异。此外，两个突变体的气孔保卫细胞均呈现独特的质体表型：arc5突变体的保卫细胞极少缺乏含叶绿素的质体（叶绿体），但会积累微小的无叶绿素质体，而大多数保卫细胞发育出类似野生型的叶绿体；arc6突变体的保卫细胞如先前研究所示，会产生大型叶绿体和/或无叶绿素质体，但令人意外的是，其叶绿体/质体呈现出显著的形态变异。本研究还对野生型、arc5、arc6以及atminE1植株的成对保卫细胞中的质体形态与分配进行了定量分析。综合来看，本研究结果证实ARC5对于表皮质体的均等分裂并非必需，同时表明ARC5与ARC6的功能缺失会在单张叶片的叶肉细胞、铺层细胞与保卫细胞之间对质体复制产生差异性影响。