Chloroplast and Nuclear Transcripts for Plastid Proteins in <i>Arabidopsis thaliana</i>: Tissue Distribution in Mature Plants and During Seedling Development and Embryogenesis

Abstract

Abstract We have investigated the distribution of transcripts for chloroplast proteins involved in photosynthesis and carbon assimilation in Arabidopsis thaliana . The probes that were used for assessment of transcripts represent the chloroplast genes psbA (encoding the D1 protein of photosystem II) and rbcL (for the large subunit of RubisCO) as well as the nuclear rbcS gene family for the RubisCO small subunit. With any of these probes we find a tissue‐specific distribution of transcripts in mature plants, with the highest concentration in rosette leaves and almost undetectable amounts in roots. The transcripts detected by each of these probes reveal similar spatial distribution and temporal kinetics during seedling development, with maximal levels around 70 h after sowing. They each show higher levels under light‐grown as compared to dark‐grown conditions, indicating a coarse control that ensures roughly coordinated levels throughout plastid differentiation. Embryonic transcripts are present in much higher concentration within the ground meristem and protoderm than in the procambium, which seems to reflect the different degree of determination towards the subsequent function in photosynthesis. Transcripts were detected in all characteristic stages throughout embryogenesis including the (non‐green) proembryo stage, suggesting that chlorophyll accumulation is not essential for expression of these genes at the RNA level. Both processes, hence, appear to be triggered by earlier molecular events that remain to be characterized.