PLANT PHYSIOLOGY , Vol 104, Issue 2 639-648, Copyright © 1994 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
Characterization of a Family of Chlorophyll-Deficient Wheat (Triticum) and Barley (Hordeum vulgare) Mutants with Defects in the Magnesium-Insertion Step of Chlorophyll Biosynthesis
T. G. Falbel and L. A. Staehelin
Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309
During thylakoid membrane biogenesis, chlorophyll (Chl) biosynthesis and
the accumulation of Chl-binding proteins are tightly linked,
light-regulated processes. We have investigated the consequences faced by
mutant plants with defects in Chl biosynthesis by studying a series of five
homeologous allelic chlorina mutants in wheat (Triticum) and one
phenotypically related barley (Hordeum vulgare) mutant that express the
same pleiotropic mutant phenotype but to different extents. These mutants
accumulate Chl at different rates, with the most severely affected plants
having the slowest rate of Chl accumulation. Analysis of precursor pools in
the Chl synthesis pathway indicates they have a partial block in Chl
synthesis and accumulate protoporphyrin IX (Proto), the last porphyrin
compound common to both heme and Chl synthesis. The affected plants with
the most severe phenotypes accumulate the most Proto. Chloroplasts isolated
from these mutants exhibit a lower activity of the enzyme Mg-chelatase,
which catalyzes the first committed step in Chl synthesis. The most
severely affected plants exhibit the greatest reduction in Mg-chelatase
activity. Heme levels and protoporphyrinogen oxidase activity were the same
for mutant and wild-type plants. We suggest that a block in Mg-chelatase
activity in these mutants could account for the other traits of their
pleiotropic phenotype previously described in the literature.
