Development of ultrastructural damage to chloroplasts in a plastoquinone-deficient mutant of maize

Abstract

The ultrastructure of a recently discovered mutant of maize (mutant hcf103-114) that is completely lacking plastoquinone (Cook, W.B., Miles, D., 1992. Nuclear mutations affecting plastoquinone accumulation in maize. Photosyn. Res. 31, 99–111) was investigated. This mutant fails to green and dies at an early age. Tissues along a developmental gradient (from base to tip of a maize leaf) were fixed and prepared for examination via electron microscopy. Initial development was normal in both mesophyll cell (MC) and bundle sheath cell (BSC) chloroplasts. Starch, which was abundant in BSC chloroplasts of wild type maize, did not accumulate in the mutant. As tissue aging progressed, both plastid types exhibited symptoms typical of photooxidative injury. Injury, seen as chloroplast swelling, lipid accumulation and envelope disruption, appeared sooner in BSC chloroplasts than in MC chloroplasts. Chloroplasts in guard cells possessed starch granules and only showed ultrastructural injury after the starch granules disappeared. Stomata developed normally in the hcf103-114 mutant. The results are discussed in terms of the known roles of plastoquinone in chloroplast metabolism.