The NCS2 mutant
mitochondria exert a pleiotropic effect upon chloroplast structure and
function
--D. Roussell, K. Newton, T. Troyan,
G. Bullerjahn, D. Miles, M. Lauer, and S. Pallardy
As previously reported (Thompson and Newton,
MNL 1987), both the mitochondria and chloroplasts in the pale-green sectors
on NCS2 leaves are structurally abnormal. Electron micrographs of cells
from mutant sectors show reduced inner membranes (cristae) in mitochondria
and reduced thylakoids and grana stacking in chloroplasts. Our initial
hypothesis to explain the altered mitochondrion's pleiotropic effect upon
the chloroplast was that photodamage had occurred. Yet, even plants grown
under very low light conditions (4UE) showed evidence of striped sectors
(pale and very pale-green) on the leaves. The chloroplasts have therefore
probably not undergone photodamage, but have instead either developed abnormally
or arrested at some stage of normal development.
Further characterization of these altered
chloroplasts has concentrated on functional assays. Fluorescence induction
kinetic analyses have identified events after PSII, PSI/electron transport,
as abnormal in NCS2 sectors. Thylakoid protein profiles of the PSII complexes
were similar to controls. However, the CP1 protein of the PSI complex was
reduced in chloroplasts from the very pale-green sectors as compared to
the adjacent fully green or normal controls. These results suggest that
the PSI complex is altered in the chloroplasts of the NCS2 sectors. We
have additionally determined that these pale green sectors fix CO2 less
efficiently than adjacent fully green sectors on NCS2 leaves.
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