The plastid DNA of maize seedlings is subjected to increasing damage as the seedlings develop.  The DNA damage is due to oxidative environments created by photo-oxidative reactions and photosynthetic/ respiratory electron transfer.  Some DNA molecules are repaired but DNA with unrepaired damage is apparently degraded to non-functional fragments.
DNA repair proteins are encoded by the cells nuclear genome and then translocated to plastids where they maintain genome stability/ integrity by repairing the plastids DNA.  For example, in chloroplasts of the moss Physcomitrella patens, a protein employed in DNA mismatch repair (Msh1) interacts with proteins employed in recombinational repair (RecA and RecG) to maintain plastid genome stability.