Ja. Homerdixon et al., PIGMENT ORIENTATION CHANGES ACCOMPANYING THE LIGHT STATE TRANSITION IN SYNECHOCOCCUS SP PCC-6301, Photosynthesis research, 40(1), 1994, pp. 35-44
Low temperature (77 K) linear dichroism spectroscopy was used to chara
cterize pigment orientation changes accompanying the light state trans
ition in the cyanobacterium, Synechococcus sp. PCC 6301 and those acco
mpanying chromatic acclimation in Porphyridium cruentum in samples sta
bilized by glutaraldehyde fixation. In light state 2 compared to light
state 1 intact cells of Synechococcus showed an increased alignment o
f allophycocyanin parallel to the cells' long axis whereas the phycobi
lisome-thylakoid membrane fragments exhibited an increased allophycocy
anin alignment parallel to the membrane plane. The phycobilisome-thyla
koid membrane fragments showed less alignment of a short wavelength ch
lorophyll a (Chi a) Qy transition dipole parallel to the membrane plan
e in state 2 relative to state 1. To aid identification of the observe
d Chl a orientation changes in Synechococcus, linear dichroism spectra
were obtained from phycobilisome-thylakoid membrane fragments isolate
d from red light-grown (increased number of PS II centres) and green l
ight-grown (increased number of PS I centres) cells of the red alga Po
rphyridium cruentum. An increased contribution of short wavelength Chi
a Qy transition dipoles parallel to the long axis of the membrane pla
ne was directly correlated with increased levels of PS II centres in r
ed light-grown P cruentum. Our results indicate that the transition to
state 2 in cyanobacteria is accompanied by an increase in the orienta
tion of allophycocyanin and a decrease in the orientation of Chi a ass
ociated with PS II with respect to the thylakoid membrane plane.