Biology Reference
In-Depth Information
The direct conversion of DV Mpe to DV Pchlide
a
in organello, in DMV-LDV-
LDMV plants has been reported (Tripathy and Rebeiz
1986
). DVMpe was converted
to 17 %DV and 83 %MV Pchlide
a
. These results suggested that the fate of DVMpe
in DMV-LDV-LDMV in etiolated plants and during the dark phases of the photope-
riod is conversion to MV Pchlide
a
rather than DV Pchlide
a
, via routes 10 and 11 as
shown in Fig.
8.5
. This is achieved by reduction of DV Pchlide
a
to MV pchlide
a
(Tripathy and Rebeiz
1988
). This in turn suggests that biosynthetic routes 10 and
11 are highly active in etiolated tissues of this greening group of plants. These results
also caution against assuming that conversion of exogenous DV substrates to Pchlide
a
in organello is likely to yield DV Pchlide
a
exclusively, without specific analysis of
DV and MV components as has been often assumed (Walker and Weinstein
1991
;
Wong and Castelfranco
1985
). The operation of routes 10 and 11 in DMV-LD-
LDMV plant species is also compatible with the detection of strong 4-vinyl Pchlide
a
reductase (4VPideR) activity that converts DV Pchlide
a
to MV Pchlide
a
in barley
etiochloroplasts (Tripathy and Rebeiz
1988
).
Biosynthesis of DV Pchlide a via Biosynthetic Route 13 in Greening DMV-LDV-
LDMV Plants During the Light Phases of the Photoperiod
DV Pchlide
a
is formed via route 13 in light-grown DMV-LDV-LDMV plant
species during the light phases of the photoperiod. Biosynthetic route 13 is active
in greening DMV-LDV-LDMV plants during the first few light phases of the
photoperiod when Pchlide a accumulation is substantial (Cohen and Rebeiz
1978
).
Metabolism of DV Pchlide
a
in DDV-LDV-LDDV Plant Species via Routes
1 and 8
Precursor-product relationships between DV Pchlide
a
and DV Chlide
a
(Fig.
8.4
,
routes 1, and 8) were established by demonstrating the photoreduction of DV Pchlide
a
to DVChlide
a
in etiolated cucumber cotyledons induced to accumulate DV Pchlide
a
exclusively (Duggan and Rebeiz
1982
). DV Pchlide
a
is probably converted to DV
Chlide
a
by PORA in etiolated DDV-LDV-LDDV plants (Armstrong et al.
1995
).
During photoperiodic greening, in the light, DV Pchlide
a
is converted to DV Chlide
a
(Abd-El-Mageed et al.
1997
) probably by PORB which is active in the light in light
grown DDV-LDV-LDDV plants (1981; Runge et al.
1996
).
Metabolism of MVPchlide
a
in DMV-LDV-LDMV Plant Species via
Biosynthetic Route 13
During photoperiodic greening of LMV-DDV-LDMV plant species small amounts
of DV Pchlide
a
are always detectable (Abd-El-Mageed et al.
1997
) and are
probably converted to MV Chlide
a
via DV Chlide
a
(Fig.
8.5
).
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