N. Lebedev, FLUORESCENCE ANALYSIS OF PROTOCHLOROPHYLL(IDE) TO CHLOROPHYLL(IDE) CONVERSION IN THE GREEN-ALGA CHLAMYDOMONAS-REINHARDTII MUTANTS, Photosynthetica, 32(4), 1996, pp. 569-585
The low-temperature fluorescence spectroscopy allowed to detect three
forms of protochlorophyllide in dark-adapted cells of green alga Chlam
ydomonas reinhardtii mutant yl (which cannot synthesize chlorophyll -
Chl - in the dark), as well as in mutant s48 (which cannot synthesize
Chl b). The pigment fluorescence was located at 630, 638 and 656 nm, a
nd had excitation maxima at 440 and 444 nm, and a double band at about
425 and 470 nm, respectively. The shape of excitation spectra showed
the two former bands belonging to a monomeric pigment while the latter
one to the pigment in an aggregated state. The monomeric protochlorop
hyllide (PChl) was photochemically active and at room temperature it t
ransformed into monomeric chlorophyll(ide). The aggregated PChl was re
latively stable and its fluorescence did not change under irradiation.
Dark-adapted cells of C. reinhardtii ss107 and vf5 mutants, unable to
synthesize light-harvesting complexes (CPLH) or core chlorophyll-prot
eins of photosystems 1 and 2, respectively, had the same PChl fluoresc
ence. Monomeric PChl only was detected in wild-type cells of C. reinha
rdtii in the presence of a substrate for Chl biosynthesis (ALA) or an
inhibitor of chloroplast protein formation (CAP). In ALA-treated plant
s, the accumulation of PChl was accompanied by accumulation of monomer
ic protoporphyrin IX. The latter pigment was the main one detected aft
er the alga cultivation at a chilling temperature (8 degrees C). In wi
ld-type cells, but not in the s48 or y1 mutants, cultivated in the dar
k, fluorescence of monomeric Chi b with the emission maximum at 656 nm
was observed. This fluorescence had excitation maximum at 466 nm and
seemed to belong to a pigment not bonded to CPLH polypeptides. Hence,
in addition to the well-known pathway of Chl formation operating in et
iolated higher plants and extensively studied so far, a monomeric path
way exists and is responsible for the light-dependent Chl synthesis in
cells of C. reinhardtii. This pathway is spectroscopically similar to
the recently discovered new pathway of chlorophyll biosynthesis opera
ting in light-adapted higher plants.