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Chlide a to Chl a was only partial (38 %) while higher amounts of added Mg 2+
were inhibitory (Daniell and Rebeiz 1984 ). This in turn suggested that something
was still amiss from the used incubation medium.
Effect of Exogenous Geranylgeraniol Pyrophosphate and Phytol
on the Conversion of Chlorophyllide a to Chlorophyll a
Etiochloroplasts were isolated from kinetin and GA-pretreated cotyledons and were
incubated in the fortified incubation medium in the absence (control) or presence of
granylgranyl pyropohosphate (GGDP) or phytol. The addition of the isoprenoid
alcohols did not seriously depress the Pchlide accumulation capabilities of the
plastids. On the contrary, a 52-fold excess of added phytol (50
10 3 mM) with
10 3 mM) significantly enhanced
the rates of Chlide a mobilization by the added isoprenoid alcohols. In the presence
of a 344-fold excess of GGPP (0.33 mM) or 5.2-fold excess of phytol (0.005 mM)
to endogenous Chlide a (0.96
respect to the endogenous Chlide a pool (0.96
10 3 mM), the Chlide a pool was depleted by
92.4 and 89.3 %, respectively, and its level at the end of incubation was similar
to the levels of endogenous Chlide a encountered in plastids freshly isolated
from greening tissues. The bulk of the Chlide a that disappeared was converted
to Chl a (Daniell and Rebeiz 1984 ). Some of it also appeared to be converted to
Chlide b (Daniell and Rebeiz 1984 ).
The joint requirement of ATP, Mg 2+ and phytol for achieving high rates of
conversion of Chlide a to Chl a in organello is described in Daniell and
Rebeiz ( 1984 )
Etiochloroplasts were isolated from kinetin and GA-pretreated cotyledons and were
incubated in the fortified incubation medium in the absence (control) or presence of
GGPP or phytol. the observed enhancement of Chlide a mobilization by the added
isoprenoid alcohols. In the presence of a 344-fold excess of GGPP (0.33 mM) or
5.2-fold excess of phytol (0.005 mM) to endogenous Chlide a (0.96
10 3 mM),
the Chlide a pool was depleted by 92.4 and 89.3 %, respectively, and its level at the
end of incubation was similar to the levels of endogenous Chlide a encountered in
plastids freshly isolated from greening tissues. The bulk of the Chlide a that
disappeared was converted to Chl a. Some of it also appeared to be converted
either to Chlide b (Daniell and Rebeiz 1984 ).
References
Abd-El-Mageed HA, El Sahhar KF, Robertson KR et al (1997) Chloroplast biogenesis 77.
Two novel monovinyl and divinyl light-dark greening groups of plants and their relationship
to the chlorophyll a biosynthetic heterogeneity of green plants. Photochem Photobiol 66:89-96
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