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

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 microscop y. Initial development was normal in both mesophyll cell (MC) and bundle sh eath cell (BSC) chloroplasts. Starch, which was abundant in BSC chloroplast s of wild type maize, did not accumulate in the mutant. As tissue aging pro gressed, both plastid types exhibited symptoms typical of photooxidative in jury. Injury, seen as chloroplast swelling, lipid accumulation and envelope disruption, appeared sooner in BSC chloroplasts than in MC chloroplasts. C hloroplasts in guard cells possessed starch granules and only showed ultras tructural injury after the starch granules disappeared. Stomata developed n ormally in the hcf103-114 mutant. The results are discussed in terms of the known roles of plastoquinone in chloroplast metabolism. (C) 1998 Elsevier Science B.V. All rights reserved.