Optical Multichannel Analysis of Protochlorophyllide Phototransformation in Detergent-Solubilized Etioplast Membranes of Wheat

Extracts of wheat etioplast membranes obtained after treatment with 7 mᴍ n-octyl-β-ᴅ-glucopyranoside (OG), n-dodecyl-β-ᴅ-maltoside (DM) or Triton X-100 contained the three spectral forms of Pchlide (the photoactive Pchlide638 and Pchlide650 and the inactive Pchlide630) in various relative amounts . The OG extract had a Pchlide composition close to that of the intact membranes whereas the DM extract was enriched in Pchlide638 and the Triton extract was enriched in Pchlide630. Measurements of the kinetics of phototransformation and of timeresolved absorbance spectra during phototransformation in continuous light shows that the inactive Pchlide630 is in fact slowly transformed to Chlide, especially in the Triton extract where this form is more abundant. Addition of NADPH favours the phototransformation of Pchlide630 and the slow regeneration of Pchlide638 and Pchlide650 from Pchlide630 in darkness after illumination. No such regeneration was however observed in the Triton extract. NADPH had only slight effects on the Chlide shift towards shorter wavelengths after phototransformation in solubilized membranes.