Photoinduced formation of pheophytin/chlorophyll-containing complexes during the greening of plant leaves

Abstract

Illumination of etiolated maize leaves with low-intensity light produces a chlorophyll/pheophytin-containing complex. The complex contains two native chlorophyll forms Chl 671/668 and Chl 675/668 as well as pheophytin Pheo 679/675 (with chlorophyll/pheophytin ratio of 2/1). The complex is formed in the course of two successive reactions: reaction of protochlorophyllide Pchlde 655/650 photoreduction resulted in chlorophyllide Chlde 684/676 formation, and the subsequent dark reaction of Chlde 684/676 involving Mg substitution by H2 in pigment chromophore and pigment esterification by phytol. Out data show that the reaction leading to chlorophyll/pheophytin-containing complex formation is not destructive. The reaction is in fact biosynthetic, and is competitive with the known reactions of biosynthesis of the bulk of chlorophyll molecules. The relationship between chlorophyll and pheophytin biosynthesis reactions is controlled by temperature, light intensity and exposure duration.The native complex containing pheophytin a and chlorophyll a is supposed to be a direct precursor of the PS II reaction centre in plant leaves.

Light-regulated pigment interconversion in pheophytin/chlorophyll-containing complexes formed during plant leaves greening

“…Regardless of the degree of Pchlide 655/650 phototransformation, the ratio of Pheo and Chl concentrations remained constant under continuous lowintensity illumination (Ignatov and Litvin 1994). This observation seemed to be at variance with the data on the fast transformation of Pheo into Chl, observed in experiments with alteration of light and dark periods (see above).…”

“…From these data it may be concluded that Pheo formed from Chlide 684/676 during further dark reactions is transformed into chlorophyll. It was previously shown that the intermediates as well as products of dark transformation of Chlide 684/676 are esterified (Ignatov and Litvin 1994).…”

Normal-phase HPLC Separation of Possible Biosynthetic Intermediates of Pheophytin a and Chlorophyll a′

“…20,21 However, the Pheo a/Chl a ratio, which they estimated from the fluorescence excitation spectra, was as high as 50%, which is far from the value obtained here (about 0.47%). Such a discrepancy might, at least partially, be due to a difference in the illumination conditions.…”

“…In our experiments, PChlide accumulated in the dark was almost completely photo-reduced to Chlide a by illumination (data not shown), but only 5 to 30% of PChlide was photo-reduced in the experiments of Ignatov and Litvin. 20 Under greening conditions where the amounts of Chl(ide) a are limited, Pheo a might be preferentially accumulated. Further experiments are required to clarify the discrepancy between the two experiments.…”

Pigment Biosynthesis: Chlorophylls, Heme, and Carotenoids

“…It is generally assumed that the pheophytin a associated with PS II reaction centers is formed by the spontaneous loss of the during insertion of chlorophyll a into the reaction center complex. However, recent studies in higher plants (Litvin et al, 1993;Ignatov and Litvin, 1994) suggest that pheophytin a formation may proceed directly from minor, long-wavelength chlorophyll precursors (e.g., the chlorophyllide precursor, P650).…”