Chloroplast biogenesis during the early stage of leaf development in rice

In rice, the developmental process in leaf formation can be divided into 7 stages (stages P0 to P6). We investigated chloroplast biogenesis and physiological changes in the developing leaves at the stage P4, during which leaf blade elongation and establishment of basic leaf blade structure occur. Chlorophyll content was negligible in the leaves early in the P4 stage and increased rapidly as they enters the late P4 phase. Chlorophyll fluorescence ratio (Fv/Fm) also increased markedly and the final value was comparable with that of mature leaves. Gene expression analysis showed that during the P4 stage, chloroplasts in the leaf cell undergo all three steps of differentiation: (i) plastid division and DNA replication (ii) establishment of plastid genetic system (iii) activation of photosynthetic apparatus. These observations suggest that the P4 is key in the development of a leaf, during which leaf rapidly differentiated both morphologically and physiologically, and that the P4 leaf is suitable for investigation of physiological relationships between chloroplast and leaf development.