S. Tan et al., DECREASE OF POLYPEPTIDES IN THE PS-I ANTENNA COMPLEX WITH INCREASING GROWTH IRRADIANCE IN THE RED ALGA PORPHYRIDIUM-CRUENTUM, Photosynthesis research, 45(1), 1995, pp. 1-10
Thylakoids isolated from cells of the red alga Porphyridium cruentum e
xhibit an increased PS I activity on a chlorophyll basis with increasi
ng growth irradiance, even though the stoichiometry of Photosystems I
and II in such cells shows little change (Cunningham et al. (1989) Pla
nt Physiol 91:1179-1187). PS I activity was 26% greater in thylakoids
of cells acclimated at 280 mu mol photons . m(-2). s(-1) (VHL) than in
cells acclimated at 10 mu mol photons . m(-2). s(-1) (LL), indicating
a change in the light absorbance capacity of PS I. Upon isolating PS
I holocomplexes from VHL cells it was found that they contained 132 +/
- 9 Chl/P700 while those obtained from LL cells had 165 +/- 4 Chl/P700
. Examination of the polypeptide composition of PS I holocomplexes on
SDS-PAGE showed a notable decrease of three polypeptides (19.5, 21.0 a
nd 22 kDa) in VHL-complexes relative to LL-complexes. These polypeptid
es belong to a novel LHC I complex, recently discovered in red algae (
Wolfe et al. (1994a) Nature 367:566-568), that lacks Chl b and include
s at least six different polypeptides. We suggest that the decrease in
PS I Chl antenna size observed with increasing irradiance is attribut
able to changes occurring in the LHC I-antenna complex. Evidence for a
Chl-binding antenna complex associated with PS II core complexes is l
acking at this point. LHC II-type polypeptides were not observed in fu
nctionally active PS II preparations (Wolfe et al. (1994b) Biochimica
Biophysica Acta 1188:357-366), nor did we detect polypeptides that sho
wed immunocross-reactivity with LHC II specific antisera (made to Chla
mydomonas and Euglena LHC II).