PLANT PHYSIOLOGY , Vol 112, Issue 2 821-832, Copyright © 1996 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Severity of Mutant Phenotype in a Series of Chlorophyll-Deficient Wheat Mutants Depends on Light Intensity and the Severity of the Block in Chlorophyll Synthesis
T. G. Falbel, J. B. Meehl and L. A. Staehelin
Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, Colorado 80309
Analyses of a series of allelic chlorina mutants of wheat (Triticum
aestivum L.), which have partial blocks in chlorophyll (Chl) synthesis and,
therefore, a limited Chl supply, reinforce the principle that Chl is
required for the stable accumulation of Chl-binding proteins and that only
reaction centers accumulate when the supply of Chl is severely limited.
Depending on the rate of Chl accumulation (determined by the severity of
the mutation) and on the rate of turnover of Chl and its precursors
(determined by the environment in which the plant is grown), the mutants
each reach an equilibrium of Chl synthesis and degradation. Together these
mutants generate a spectrum of phenotypes. Under the harshest conditions
(high illumination), plants with moderate blocks in Chl synthesis have
membranes with very little Chl and Chl-proteins and membrane stacks
resembling the thylakoids of the lethal xantha mutants of barley grown at
low to medium light intensities (which have more severe blocks). In
contrast, when grown under low-light conditions the same plants with
moderate blocks have thylakoids resembling those of the wild type. The wide
range of phenotypes of Chl b-deficient mutants has historically produced
more confusion than enlightenment, but incomparable growth conditions can
now explain the discrepancies reported in the literature.
