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Transformation of photoinactive to photoactive protochlorophyllide in isolated prolamellar bodies of wheat ( Triticum aestivum ) exposed to low pH and ATP
Author(s) -
Grevby Cecilia,
Ryberg Margareta,
Sundqvist Christer
Publication year - 1987
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1987.tb06125.x
Subject(s) - protochlorophyllide , oxidoreductase , pigment , chemistry , darkness , fluorescence , sodium dodecyl sulfate , enzyme , biochemistry , chlorophyll , biology , botany , organic chemistry , optics , physics
Isolated prolamellar bodies from the etioplasts of dark‐grown wheat ( Triticum aestivum L. cv. Walde, Weibull) contain the enzyme NADPH‐protochlorophyllide oxidoreductase. The organisation of this enzyme in a pigment‐protein complex results in fluorescence emission maxima at 633 and 657 nm. Isolated prolamellar bodies stored in darkness for 24 or 48 h at 4°C (pH 7.2) in the presence of NADPH showed a fluorescence emission ratio 657/633 nm around 4 at −196°C. With acidic conditions this fluorescence ratio increased, with an optimum at pH 5.5. Such an increase was even more pronounced in the presence of ATP and NADPH with ratios up to 8, but was completely blocked when the sulfhydryl inhibitor, dithiobis‐nitrobenzoic acid, was added. As shown by sodium dodecyl sulfate polyacrylamide gel electrophoresis the amount of NADPH‐protochlorophyllide oxidoreductase in the prolamellar bodies did not change during storage for 24 or 48 h. The total amount of protochlorophyllide measured in acetone extracts did not change significantly during storage for 48 h. The values were similar for storage at pH 7.2 and 5.5, but at lower pH (around 5) the pigment content decreased to a third. The most plausible explanation for the increase in fluorescence ratio is that low pH and ATP give rise to a change in conformation, which results in transformation of the short wavelength (633 nm) fluorescing protochlorophyllide to the long wavelength (657 nm) fluorescing form.