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Fig. 8.1 The Divinyl (
DV
)-
Monovinyl (
MV
) Pchlide
a
pool
8.1.1 Chemical Heterogeneity of the Pchlide a Pool
Biosynthetic Heterogeneity of the Pchlide
a
Chromophore.
When more powerful fluorescence spectroscopic techniques were used to
reinvestigate the chemical structure of the Pchlide
a
of green plants, it was
discovered that it was chemically heterogeneous and consisted of DV and
monovinyl (MV) components (Fig.
8.1
) (Belanger and Rebeiz
1980a
). The chemi-
cal structure of the Pchlide
a
pool was ascertained by chemical derivatization
coupled to fluorescence spectroscopy, as well as by NMR and field desorption
mass spectroscopy (Belanger and Rebeiz
1980b
; Wu and Rebeiz
1984
). The
conversion of DV and MV Pchlide a to DV and MV Chlide
a
respectively was
demonstrated by Dugan and Rebeiz (
1982
).
In discussing Pchlide
a
biosynthetic heterogeneity distinctions will be made
between (a) etiolated and green plants, (b) between biosynthesis during the dark
and light phases of the photoperiod in green plants, and (c) between DDV-LDV-
LDDV and DMV-LDV-LDMV plant species. As will be discussed in Chap.
14
,
DDV-LDV-LDDV plant species such as cucumber accumulate mainly DV Pchlide
a
in darkness and in the light. In the light, Chl biosynthesis proceeds mainly via
regenerated DV Pchlide
a
. On the other hand, DMV-LDV-LDMV plant species such
as corn wheat and barley accumulate mainly MV Pchlide
a
in darkness. In the light,
some DV Pchlide
a
is formed, but Chl biosynthesis proceeds mainly via regenerated
MV Pchlide
a
(Abd-El-Mageed et al.
1997
).
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