The Chl a Carboxylic Biosynthetic Routes: Conversion of Chlide a to Chl a - Chlorophyll Biosynthesis and Technological Applications - page 252

Fig. 10.1 The Chl a pool
10.1.1 Chlorophyll a Formation by Esterification
of Chlorophyllide a with Geranylgeraniol
in Etiolated Tissues
In etiolated tissues subjected to a light treatment, formation of Chl a by esterifica-
tion of Chlide a involves a complex set of reactions. Initially, it was observed that
treatment of etiolated bean leaves with 1 min of light followed by dark incubation
resulted in the transient appearance of putative Chlide a -geranylgeraniol (GG) which
was followed by the formation of Chl a -phytol (Ogawa 1975 ). Subsequently etiolated
wheat seedlings treated with herbicides then exposed to light followed by darkness,
resulted in the accumulation of Chl a -GG and Chl a -dihydroxyGG (DHGG) (Rudiger
et al. 1976 ). This was followed by the demonstration of Chlide a esterification
with GG in a cell-free system from maize shoots (Rudiger et al. 1976 ).
Further work dealing with the identification of various esterified Chlide a in
etiolated tissues subjected to a brief light treatment followed by dark incubation,
led to the proposal that during phytylation, Chlide a is first esterified with GG to
yield Chl a -GG, which is reduced stepwise to Chl a -DHGG, to -Chl a-tetrahydroGG
(THGG) and finally to Chl a-hexahydroGG, i.e. Chl a-phytol (Schoch 1978 ).
The above hypothesis was confirmed in cell-free systems from various etiolated
plant tissues. It was demonstrated that in irradiated etioplast-membrane fractions
prepared form oat seedlings, [1- 3 H]-GG and its monophosphate were incorporated
into Chl a only in the presence of exogenous ATP, whereas incorporation of
activated [1- 3 H]-GG pyrophosphate (GG-PP) did not require ATP (Rudiger