The Iron and Magnesium Branches of the Porphyrin Biosynthetic Pathway - Chlorophyll Biosynthesis and Technological Applications - page 183

Since the Chl biosynthetic heterogeneity will be discussed at length throughout
this monograph, a brief overview of this heterogeneity will be presented below.
Three figures and one table that will be referred to throughout this monograph will
be presented below.
6.2.1 Biosynthetic Heterogeneity of the Chlorophyll
Biosynthetic Pathway: An Overview
Since the 1963 seminal review of Smith and French ( 1963 ), our understanding of
the Chl biosynthetic pathway has changed dramatically. Several factors have
contributed to this phenomenon, among which: (a) development of systems capable
of Chl and thylakoid membrane biosynthesis in organello and in vitro, (Daniell and
Rebeiz 1982 ; Kolossov et al. 1999 ; Rebeiz and Castelfranco 1971a , b ; Rebeiz
et al. 1984 ), (b) powerful analytical techniques that allowed the qualitative and
quantitative determination of various intermediates of the Chl biosynthetic pathway
(Rebeiz 2002 ), (c) recognition that the greening process proceeds differently in
etiolated and green tissues, in darkness and in the light and in plants belonging to
different greening groups (Abd-El-Mageed et al. 1997 ; Carey and Rebeiz 1985 ;
Ioannides et al. 1994 ) and (d) recognition of the probability that the structural and
functional complexity of thylakoid membranes is rooted in a multibranched, het-
erogeneous Chl biosynthetic pathway (Rebeiz et al. 1999 ).
Chlorophyll biosynthetic heterogeneity (Rebeiz et al. 1981 , 1983 , 1994 , 1995 ,
2003 ) refers either (a) to spatial biosynthetic heterogeneity, (b) to chemical biosyn-
thetic heterogeneity, or (c) to a combination of spatial and chemical biosynthetic
heterogeneities.
Spatial biosynthetic heterogeneity refers to the biosynthesis of an anabolic
tetrapyrrole or end product by identical sets of enzymes, at several different
locations of the thylakoid membranes. On the other hand, chemical biosynthetic
heterogeneity refers to the biosynthesis of an anabolic tetrapyrrole or end product at
several different locations of the thylakoid membranes, via different biosynthetic
routes, each involving at least one different enzyme.
6.2.1.1 Chemical Heterogeneity
As mentioned above, spatial biosynthetic heterogeneity refers to the biosynthesis of
an anabolic tetrapyrrole or end product by identical sets of enzymes, at several
different locations of the thylakoid membranes
Figure 6.3 summarizes the Chl biosynthetic routes that take place in DDV-LDV-
LDDV plant species such as cucumber (Kolossov and Rebeiz 2010 ). Figure 6.4
summarizes the Chl biosynthetic routes that take place in DMV-LDV-LDMV plant
species such as corn, wheat and barley (Kolossov and Rebeiz 2010 ). Figure 6.5 ,
summarizes the fully esterified Chl biosynthetic routes that take place in all
greening groups (Rebeiz et al. 2003 ).