The Chl a Carboxylic Biosynthetic Routes: Protochlorophyllide a - Chlorophyll Biosynthesis and Technological Applications - page 221

Fig. 8.6 MV Pchlide a

8.1.1.3 The Monovinyl (MV) Pchlide a Pool

MV Pchlide a has one vinyl group at position 2 and one ethyl group at position 4 of
the tetrapyrrole macrocycle (Fig. 8.6 ). The MV nature of the MV Pchlide a compo-
nent of the Pchlide a pool of higher plants was determined by chemical derivatiza-
tion coupled to analytical fluorescence spectroscopy at 77 K (Belanger and Rebeiz
1980a ). It was confirmed by NMR spectroscopy and field desorption mass spec-
troscopy (Wu and Rebeiz 1984 ). The mechanism of the reactions involved in
cyclopentanone ring formation during conversion of Mpe to Pchlide a was
discussed above in a previous section.

Biosynthetic Heterogeneity of MV Pchlide a in DDV-LDV-LDDV Plants

In Fig. 8.7 , the biosynthesis of MV Pchlide a is depicted to occur in four different
thylakoid environments as suggested by multiple resonance energy transfer fromMV
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 MV
Pchlide a , is accompanied by chemical biosynthetic heterogeneity or not. In other
words, it is unclear whether the proposed biosynthesis of MV Pchlide a via routes
2, 3, 0 and 9 is catalyzed by identical Pchlide cyclases or by different cyclase
isozymes. These biosynthetic routes will be discussed further below.
In addition to DV Pchlide a , etiolated and green DDV-LDV-LDDV plant species
such as cucumber, form smaller amounts of MV Pchlide a during prolonged dark
incubation (Carey and Rebeiz 1985 ; Ioannides et al. 1994 ). This Pchlide a formation
can be accounted for by routes 2 and 3. In route 3, MV Pchlide a formation can
be accounted for by a slow conversion of DV Pchlide a to MV Pchlide a ,a
reaction catalyzed by 4VPideR during prolonged dark-incubations (Tripathy and
Rebeiz 1988 ). Probably, biosynthetic routes 2 and 3 are 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 ).