Chloroplast biogenesis 88. Protochlorophyllide b occurs in green but not in etiolated plants.

It has recently been reported that protochlorophyllide (Pchlide) b is an abundant pigment in barley etioplasts but is rather unstable, as it is rapidly converted to Pchlide a by 7-formyl reductase during pigment extraction with conventional 80% acetone (Reinbothe, S., Pollmann, S., and Reinbothe, C. (2003) J. Biol. Chem. 278, 800-806). It has also been claimed that extraction of barley etioplasts with 100% acetone containing 0.1% diethyl pyrocarbonate prevents the conversion of Pchlide b to Pchlide a and leads to the detection of large amounts of Pchlide b in the isolated etioplasts. In this work the extraction protocol of Reinbothe et al. is compared with the more conventional 80% aqueous acetone extraction method. No Pchlide b was detected either in etiolated barley leaves or isolated barley etioplasts irrespective of the extraction protocol. On the other hands, small amounts of Pchlide b were detected in green barley leaves and isolated chloroplasts, extracted either with 80% acetone or 100% acetone containing 0.1% diethyl pyrocarbonate. It is concluded that the proposed occurrence of a light-harvesting POR-Pchlide-a,b complex in etiolated plant tissues is untenable, and its ensuing consequences and implications, for the greening process, are irrelevant.