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

Abstract

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.

GUN4-Porphyrin Complexes Bind the ChlH/GUN5 Subunit of Mg-Chelatase and Promote Chlorophyll Biosynthesis inArabidopsis

“…Mutants that are impaired in their ability to synthesize chlorophyll were previously reported to exhibit more severe chlorophyll deficiencies after fluence rates were increased (Falbel et al, 1996). To test whether these F191A-and R211A-expressing lines exhibit light-sensitive phenotypes similar to other chlorophylldeficient mutants, we transferred them to a higher fluence rate.…”

“…In bright light, deficiencies in chlorophyll, chlorophyll binding proteins, and grana thylakoids are enhanced relative to the wild type (Allen et al, 1988;Falbel et al, 1996). Mutant alleles that attenuate Mgchelatase activity were proposed to enhance sensitivity to highintensity light at least in part by causing PPIX to overaccumulate.…”

“…oxygen ( 1 O 2 ) in illuminated chloroplast membranes (Falbel and Staehelin, 1994;Falbel et al, 1996). Differential production of ROS from the light reactions of photosynthesis (Niyogi, 1999;Li et al, 2009) in these mutants might also contribute to their light sensitivities.…”

LCAA, a Novel Factor Required for Magnesium Protoporphyrin Monomethylester Cyclase Accumulation and Feedback Control of Aminolevulinic Acid Biosynthesis in Tobacco

“…Besides defects in the cpSRP system, modest reductions of chlorophyll synthesis also specifically impair LHC protein accumulation (Falbel and Staehelin, 1994;Falbel et al, 1996;Tottey et al, 2003;. Plants ensure the assembly of sufficient amounts of core complexes of PSII and PSI by preferentially incorporating chlorophyll a into their reaction centers.…”

“…WT, Wild type. (Falbel and Staehelin, 1994;Falbel et al, 1996;Tottey et al, 2003): chlorophyllide a oxygenase, which catalyzes the highly regulated step of chlorophyll(ide) a-to-chlorophyll (ide) b conversion, has a relatively low affinity for chlorophyll(ide) a. In consequence, chlorophyll b synthesis becomes more active when chlorophyll a-binding sites of the reaction center proteins are saturated.…”