Abstract
The general variegated plants consist of some layers of white cells containing only abnormal plastids and the other layers of green cells containing only normal chloroplasts. The mixed cells containing both of abnormal plastids and normal chloroplasts have not been thought to exist in variegated knockout mutants for nuclear-encoded chloroplast protein. The existence of mixed cells generally indicates mixing of deficient plastids of genes for plastid-encoded chloroplast protein. Here, we present a variegated Arabidopsis mutant for a nuclear-encoded chloroplast protein, apg5, which has been isolated by using a transposon system based on the Ac/Ds element of maize. The apg5 mutant exhibits pale green cotyledons and variegated true leaves. We found mixed cells containing both of abnormal plastids and normal chloroplasts in apg5 cotyledons by transmission electron microscopy. Furthermore, we observed detailed behavior of abnormal plastids by fluorescence microscopy with apg5 plants expressing YFP-tagged plastids. We discuss about mechanism of formation of mixed cells in knockout mutants for nuclear-encoded protein and functions of the APG5 genes in chloroplast development.
