The Chl a Carboxylic Biosynthetic Routes: Protochlorophyllide a - Chlorophyll Biosynthesis and Technological Applications - page 217

Fig. 8.3 DV Pchlide a
Biosynthetic Heterogeneity of Divinyl Pchlide a in DDV-LDV-LDDV Plants
In Fig. 8.4 , the biosynthesis of DV Pchlide a from DV Mpe is depicted to occur in
two different thylakoid environments as suggested by multiple resonance energy
transfer from DV Pchlide a to various Chl a -Protein complexes (Table 6.1 , Chap. 6 )
and (Kolossov et al. 2003 ), as well as further conversions to Chlides and Chls as
will be discussed later. It is unclear at this stage whether the spatial biosynthetic
heterogeneity of DV Pchlide a , is accompanied by chemical biosynthetic heteroge-
neity or not. In other words, it is unclear whether the proposed biosynthesis of DV
Pchlide a , from DV Mpe via routes 1, and 8 is catalyzed by identical Pchlide
cyclases or by different cyclase isozymes. These biosynthetic routes will be
discussed further later on.
Biosynthesis of DV Pchlide a via Biosynthetic Route 1 in Etiolated DDV- LDV-
LDDV Plants in Darkness, and in Greening DDV-LDV-LDDV Plants During
the Light Phases of the Photoperiod
Formation of the cyclopentanone ring via biosynthetic route 1 (Fig. 8.4 ) in etiolated
DDV-LDV-LDDV plants was demonstrated by conversion of exogenous DV Mpe
to DV Pchlide a in isolated cucumber etiochloroplasts (Tripathy and Rebeiz 1986 ).
DV Mpe was converted into 83 % DV Pchlide a and 17 % MV Pchlide a . The
formation of much smaller amounts of MV Pchlide a can be accounted for by
biosynthetic route 2 (Fig. 8.4 ) and suggests that biosynthetic route 1 (Fig. 8.4 ) is the
predominant biosynthetic route in etiolated DDV-LDV-LDDV plant species in
darkness. biosynthetic route 1 is also active in greening DDV-LDV-LDDV plants
during the first few dark phases of the photoperiod when Pchlide a accumulation is
substantial (Cohen et al. 1977 ; Cohen and Rebeiz 1978 ).
Biosynthesis of DV Pchlide a via Biosynthetic Route 8 in DDV-LDV-LDDV Plants
During the Light and Dark Phases of the Photoperiod
In green DDV-LDV-LDDV plant species such as cucumber, DV Pchlide a is
continuously present during the light cycles of the photoperiod and only trace amounts
of MV Pchlide a areformed(Careyetal. 1985 ; Ioannides et al. 1994 ). Interruption of
the light cycle by a brief dark period (LD) indicated that such plant species formmost
of their Chl via regenerated DV Pchlide a (Abd-El-Mageed et al. 1997 ). These