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9.4.5.2 Formation of MV Chlide
a
by Vinyl Reduction of DV Chlide
a
via Route 8 in Greening DDV-LDV-LDDV Plants During
the Light Phases of the Photoperiod
Formation of MV Chlide a by rapid vinyl reduction of transient DV Chlide a via
route 8, is justified by the detection of 4VCR activity in photoperiodically grown
green tissues, which has been recently documented by Abd El-Mageed et al. ( 1977 ),
and more recently by Kolossov and Rebeiz ( 2001 ).
9.4.6 Formation of MV Chlide a by Vinyl Reduction of DV
Chlide a via Route 13 in Greening DMV-LDV-LDMV
Plants During the Light Phases of the Photoperiod
Formation of MV Chlide a by rapid vinyl reduction of transient DV Chlide a via
route 13, has been documented in barley etioplasts after a light flash of 2.5 ms (Adra
and Rebeiz 1998 ) (Fig. 9.7 ).
9.5 Photoreduction Intermediates and Spectral Shifts
During Photoreduction of Protochlorophyll(ide)
a
H (E550 F655)
In etiolated tissues, the photoreduction of t-LW-Pchlide a H (E550 F655) by PORA
is accompanied by complex spectral shifts (Fig. 9.8 ) of intermediates and end
products that eventually result in the conversion of the crystalline prolamellar
body and prothylakoids to thylakoid membranes. It appears that some of the
spectral shifts may be regulated by protein phosphorylation (Wiktorsson
et al. 1996 ). At the present stage, the significance of the postillumination spectral
shifts to Chl biosynthetic heterogeneity is unclear (Fig. 9.8 ).
9.5.1 Spectral Shift I
Spectral shift I is light-dependent. It was reported by Thorne ( 1971 ) in etiolated
bean leaves. It occurs as a result of fractional photoconversion of LW t-Pchlide a H
(E650 F655), to a dark-stable pigment-apoprotein complex (E668 F674), with 77 K
red excitation and maxima at 668 and 674 nm, respectively. This intermediate
yields a mixture of Pchlide a and Chlide a after dark-ethanol extraction. The
photoconversion rate for Chlide a H (E668 F674) was twice the rate for the
photoconversion of the next intermediate, thus suggesting that, in vivo,
photoconversion of Pchlide a to Chlide a is a two step two photon process.
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