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Finally, the proposal that Pchlide b does not occur in nature goes counter to the
recent finding of Xu et al. ( 2002 ). These authors reported the accumulation of a
putative Pchlide b in a triple Synechocystis mutant (PS I-less/ chl L / lhcb + /cao + )
grown under light activated heterogeneous growth (LAHG) conditions that also led
to the accumulation of pheophorbide b ( i.e . demetalated Chlide b ). The putative
Pchlide b exhibited an absorbance spectrum very similar to that reported by Schoch
et al. ( 1995 ) for their synthetic putative Pchlide b . In this case too, it is very
probable that the accumulated putative Pchlide b reported by Xu et al. ( 2002 ),
was demetalated along with the reported demetalation of Chlide b .
Although the mass spectroscopic data reported by Schoch et al. ( 1995 ) and Xu
et al. ( 2002 ) is compatible with the molecular weight of MV Pchlide b, it is very
possible that this is due to the vagary of mass spectroscopy caused by the formation
of a protopheophytin a adduct having the same molecular weight as MV Pchlide b .
12.3 Divinyl Protochlorophyllide
b
(DV Pchlide
b
)
So far it has not been possible to detect DV Pchlide b in plants (Fig. 12.2 ).
12.4 Monovinyl Chlorophyllide
b
(MV Chlide
b
)
Monovinyl chlorophyllide b was first detected in greening (Duggan and Rebeiz
1981 , 1982 ) and green higher plant tissues (Aronoff 1981 ). The pool of MV Chlide
b exhibited the spectrofluorometric properties of MV Chl b in diethyl ether at
298 and 77 K, but had the chromatographic mobility and solubility of a monocar-
boxylic phorbin. The presence of a free carboxylic group and a formyl group was
demonstrated by methylation with diazomethane and conversion to a Chlide
b oxime upon reaction with hydroxylamine (Duggan and Rebeiz 1982 ). The
concentration of Chlide b in green tissues was in the same range as that of MV
Pchlide a and MV Chlide a . It was estimated that less than 15 % of the Chlide b pool
could have arisen from chlorophyllase activity in vitro as confirmed by the extent of
hydrolysis of 14 C-labeled MV Chl b added to green tissues just before pigment
extraction (Duggan and Rebeiz 1982 ) (Fig. 12.3 ).
12.5 Divinyl Chlorophyllide
b
(DV Chlide
b
)
DV Chlide b has so far been detected only in the Nec 2 maize mutant (that used to
be known as the ON 8147 mutant) (C. A. Rebeiz, unpublished). This mutation is a
lethal mutation, the leaves are pale yellow, and accumulate only DV Chl a and
b (Bazzaz 1981 ). Nec2 maize leaves accumulate DV Chlide b to the extent of about
1.00 nmoles per gram of fresh leaves (C. A. Rebeiz, unpublished) (Fig. 12.4 ).
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