Biology Reference
In-Depth Information
The biosynthesis of MV Chlide
b
is highly heterogeneous (
vide infra
). In the
elucidation of this biosynthetic heterogeneity, extensive use was made of kinetic
analysis of precursor-product relationships in vivo. For that purpose, equations
were derived to investigate possible precursor-product relationships in branched
and interconnected pathways (Rebeiz et al.
1988
; Rebeiz
2002
; Tripathy and
Rebeiz
1988
). It was shown that for any two compounds A and B, formed from a
common precursor “P” such as ALA, and having a possible direct precursor-
product relationship between them, for any number of time intervals t1 to t2, an
equation can be derived that describes the relationship between (a) the specific
radioactivity of compound “A”, and the possible radiolabel incorporation from
compound “A” into compound “B”, and (b) the possible net synthesis of compound
“B” from compound “A” (Rebeiz et al.
1988
).
Formation of MV Chlide b from DV Chlide a and MV Chlide
a via Route 4 in Greening DDV-LDV-LDDV Plant Species
Conversion of DV Pchlide
a
to MV Chlide
b
via route 4
i.e.
via DV Chlide
a
, and
MV Chlide
a
, in greening DDV-LDV-LDDV plants is supported by the conversion
of exogenous ALA to MV Chlide
b
and Chl
b
in etiochloroplasts prepared from
etiolated cucumber cotyledons subjected to 4 h of illumination prior to etiochlo-
roplast isolation (Kolossov et al.
1999
). In such systems ALA is converted mainly
to DV Pchlide
a
(Tripathy and Rebeiz
1986
) which is readily convertible to MV
Chlide
a
via DV Chlide
a
(Fig.
13.3
).
Formation of MV Chlide
b
from MV Chlide
a
via Route
14 in Greening DMV-LDV-LDMV Plants
Conversion of MV Chlide
a
to MV Chlide
b
via route 14 in DMV-LDV-LDMV
plants is supported by precursor-product relationships analysis in vivo between MV
Chlide
a
and MV Chl
b
in greening corn seedlings, (Rebeiz et al.
1999
). After 5 h of
greening of etiolated corn seedlings, about 27-36 % of the MV Chl
b
was formed
fromMV Chlide
a.
Under these conditions MV Chlide
a
is formed in turn fromMV
Pchlide
a
(Fig.
13.4
).
Formation of MV Chlide
b
from MV Pchlide
b
in Greening Plants
Two MV Chlide b pools are putatively formed form MV Pchlide
b
via routes 9, and
11. These two putative biosynthetic routes are discussed below.
Possible Formation of MV Chlide b from MV Pchlide b in Green
DDV-LDV-LDDV Plants via Biosynthetic Route 9
The operation of this hypothetical route is suggested by (a) the formation of MV
Pchlide
b
in green cucumber seedlings, and (b) the structural relationship between
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