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Table 15.2 Calculated distances R, that Separate Proto, Mp(e) and Pchlide
a
Donors from Chl
a
-
Protein complexes acceptors in barley and cucumber chloroplasts at 77 K
in situ
Proto
Mp(e)
Barley cucumber Barley Cucumber
R(
˚
)
MV Pchlide
a
barley
DV Pchlide
a
cucumber
Chl
a
species
Chl
a
F685 (LHCI-
680 + outer half of
LHCII)
38.24
29.6
35.06
38.16
37.31
34.79
Chl
a
F695
(CP47) + CP29)
40.6
29.48
34.62
40.91
38.97
38.14
Chl
a
F735 (LHCI-730) 22.34 16.26 19.07 23.41 23.06 21.84
Note
: The distances “R” were determined from [(R
6
)
1/6
cm]10
8
˚
.cm
1
. The R
6
values were
calculated in Table 9 of Kopetz et al.
2004
(Adapted from Kopetz et al.
2004
)
First analytical tools were developed to calculate the distances separating Proto,
Mp(e), and DV and MV Pchlide
a
from Chl
a
acceptors (Table
15.2
) (Kopetz
et al.
2004
). The calculated distances were next compared to current concepts of the
photosynthetic unit structure (Allen and Forsberg
2001
; Anderson
2002
; Staehelin
2003
) and the Chl-thylakoid biogenesis models proposed in Figs.
15.1
,
15.2
, and
15.3
(see above). The calculated distances separating Proto, Mp(e) and DV and MV
Pchlide
a
from various Chl
a
acceptors
in situ
are reported in Table
15.2
.
The early concept of a PSU consisting of about 500 antennas Chl per reaction
center has evolved into two pigment systems each with its own reaction center and
antennas Chl (Allen and Forsberg
2001
; Anderson
2002
; Staehelin
2003
). The early
visualization of the two photosystems consisted of various pigment-protein
complexes arrayed into a linear PSU (the continuous array model), about 450
˚
in length and 130
˚
in width (Bassi et al.
1990
). Within the PSU, the LHCII was
considered shared between the two photosystems. More recent models favored the
concept of a laterally heterogeneous PSU (Allen and Forsberg
2001
; Anderson
2002
; Staehelin
2003
). In this model LHCII was considered to shuttle between PSI
and PSII upon phosphorylation and dephosphorylation (Allen and Forsberg
2001
).
Furthermore while PSII is mainly (but not exclusively) located in appressed thyla-
koid domains, PSI is located in non-appressed stroma thylakoids, grana margins,
and end membranes (Anderson
2002
; Staehelin
2003
). The calculated distances
separating Proto, Mp(e) and DV and MV Pchlide
a
from various Chl
a
acceptors in
situ are reported in Table
15.2
.
Distances separating anabolic tetrapyrroles from various Chl-protein complexes
ranged from a low of 16.26
˚
for Proto-Chl
a
separation in cumber, to a high of
40.91
˚
for Proto-Chl
a
-F695 separation in barley (Table
15.2
). The magnitude of
these distances is certainly compatible with the observation of intense resonance
excitation energy transfer reported in Kolossov et al. (
2003
).
In cucumber, a DDV-LDDV plant species (Abd-El-Mageed et al.
1997
), the
distances that separate Proto were shorter than those that separate Mp(e) and DV
Pchlide
a
from the Chl
a
species (Table
15.2
). Since Proto is an earlier intermediate
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