The Chl a Carboxylic Biosynthetic Routes: Conversion of Chlide a to Chl a - Chlorophyll Biosynthesis and Technological Applications - page 259

10.1.4.4 Biosynthesis of MV Chlorophyll via Route 13 in Etiolated

DMV-LDV-LDMV Plants After Exposure to Light,
and in Greening DMV-LDV-LDMV Plants During
the Initial Dark Phases of the Photoperiod

a

Etiolated DMV-LDV-LDMV plants accumulate mostly MV Pchlide a . In addition
in some plant species such as corn, they accumulate smaller yet significant amounts
of DV Pchlide a . Upon exposure to light, the small amounts of DV Pchlide a are
converted to DV Chlide a by POR-A as described in Sect. IIIA of Chap. 9 . Thus In
etiolated DMV-LDV-LDMV plants subjected to illumination small amounts of MV
Chlide a are formed from DV Chlide a by 4-vinyl reduction as discussed for
DDV-LDV-LDDV plants in section IV A of Chap. 9 . Since in etiolated tissues,
MV Chlide a conversion to MV Chl a takes place via esterification with GG
(Schoch 1978 ), it is our guess that, conversion of the nascent MV Chlide a to
MV Chl a via route 13 takes place via Chl a -GG followed by stepwise hydro-
genation to Chl a -Phytol as described in Sect. 1.1 . This route is also most probably
functional in DDV-LDV-LDDV plants growing under photoperiodic conditions,
at the onset of illumination, during the first few dark cycles of the photoperiod
when t-LW-Pchlide a accumulation is substantial (Cohen et al. 1977 ; Cohen and
Rebeiz 1978 ).
Since during the initial phases of greening of etiolated tissues, most of the
Chl consists of MV Chl a , located in PSI and PSII (Akoyunoglou et al. 1981 ;
Alberte et al. 1972 ), we propose that the MV Chl a formed via route 13 is destined
to PSI and/or PSII Chl-protein complexes.

10.1.5 Biosynthetic Heterogeneity of DV Chlorophyll a

In normal higher plants DV Chl a is a transient intermediate during MV Chl a
formation. Under certain circumstances however, DV Chl a is the main Chl
a that accumulates and participates in photosynthesis. This heterogeneity is
discussed below.

10.1.5.1 Transient Formation of DV Chlorophyll via Route

1 in Etiolated DDV-LDV-LDDV Plants After Exposure
to Light, and in Greening DDV-LDV-LDDV Plants During
the Initial Dark Phases of the Photoperiod

a

In etiolated DDV-LDV-LDDV tissues, it has been repeatedly observed that when
the mixed MV-DV Pchlide a is photoconverted into a mixed MV-DV Chlide a pool
by a 2.5 ms light pulse, some of the nascent DV Chlide a is rapidly converted to DV
Chl a during the first 30 s of dark incubation (Rebeiz et al. 1983 ). More recently we