Pavement cell chloroplast behaviour and interactions with other organelles in Arabidopsis thaliana

Abstract

Chloroplasts are a characteristic feature of green plants. Mesophyll cells possess the majority of chloroplasts and it is widely believed that with the exception of guard cells, the epidermal layer in most higher plants does not contain chloroplasts. However, recent observations on Arabidopsis have shown a population of chloroplasts in pavement cells that are smaller than mesophyll chloroplasts and have a high stroma to grana ratio. Here using stable transgenic lines expressing fluorescent proteins targeted to the plastid stroma, plasma membrane, endoplasmic reticulum, tonoplast, nucleus, mitochondria, peroxisomes, F-actin and microtubules we characterize the spatiotemporal relationships between the pavement cell chloroplasts (PCC) and their subcellular environment. Observations on the PCC suggest a source-sink relationship between the epidermal and the mesophyll layers and the Arabidopsis mutants glabra2 (gl2) and immutans (im) underscore their developmental plasticity. Our findings lay down the foundation for further investigations aimed at understanding the precise role and contributions of PCC in plant interactions with the environment.