Abstract
Although mesophyll chloroplasts have generally been used for studies on plastid replication, recent studies have suggested that there is tissue-dependent regulation of plastid replication, and that stromule formation may be involved in this process. Here, we report the detailed morphology of immature chloroplasts and their stromules in the leaf epidermis, the intraplastidic localization of chloroplast division regulators AtMinE1 and AtFtsZ1-1, and their associations with plastid replication and development in Arabidopsis. Using a functional AtMinE1-YFP fusion, we demonstrate that AtMinE1 concentrates at the constricting plane of the dividing plastids, and simultaneously diffuses throughout the stroma, in the epidermis of leaves and petals. We also show that the localization of AtMinE1-YFP is highly dependent on its expression level. In the knockdown atminE1 mutant expressing the plastid-targeted CFP, the size of epidermal chloroplasts varied widely, and chloroplasts emanated many stromules. Further examination of plastid morphology and visualization of AtFtsZ1-1 showed that stromule fission mediated by the FtsZ1 ring contributed to plastid heterogeneity in the atminE1 epidermis.
