Comparison of high-light effects with and without methyl viologen indicate barley chlorina mutants exhibit contrasting sensitivities depending on the specific nature of the chlorina mutation: Comparison of wild-type, chlorophyll b-less clo f2 and light-sensitive, xhlorophyllb-deficient clo f104 mutants

This study compared the response to methyl viologen (MV)-induced photooxidation in wild-type barley (wt), and both its chlorina f104-nuclear gene mutant (that restricts Chl a and b synthesis) and its f2-nuclear gene mutant (that inhibits all Chl b synthesis). Without MV, the f2 mutant showed the highest sensitivity to high light, with Fv/Fm being reduced by 80% after 80 min of irradiation. There was little difference in response to high light without MV between f104 and wt. After vacuum infiltration with 100 μM MV and exposure to high light, f104 exhibited the highest sensitivity while f2 was the most tolerant to the photooxidation effects. 77K fluorescence spectral analysis indicated that PSII of f104 was especially damaged, as evidenced by the appearance of a new Chl a emission band around 700 nm at the expense of the F685 and F695 bands from the PSII core-inner antenna. With MV, chlorophyll degraded more rapidly in f104 than in either f2 or wt. During MV treatment, zeaxanthin content increased significantly during the initial period of exposure (0-20 min) in all strains, but decreased sharply in f104 after longer exposure time (20-80 min). β-Carotene, on a chlorophyll basis, was not much changed under high light without MV, but with MV it decreased significantly, mostly in f104, intermediately in f2 and least in wt. We conclude that the light-sensitive chlorosis phenotype of f104 is exacerbated by MV-induced photooxidation