DARK HETEROTROPHIC GROWTH-CONDITIONS RESULT IN AN INCREASE IN THE CONTENT OF PHOTOSYSTEM-II UNITS IN THE FILAMENTOUS CYANOBACTERIUM ANABAENA-VARIABILIS ATCC-29413
Rm. Mannan et Hb. Pakrasi, DARK HETEROTROPHIC GROWTH-CONDITIONS RESULT IN AN INCREASE IN THE CONTENT OF PHOTOSYSTEM-II UNITS IN THE FILAMENTOUS CYANOBACTERIUM ANABAENA-VARIABILIS ATCC-29413, Plant physiology, 103(3), 1993, pp. 971-977
The filamentous nitrogen-fixing cyanobacterium Anabaena variabilis ATC
C 29413 is capable of heterotrophic growth in complete darkness. After
6 months of continuous dark growth, both the autotrophic and heterotr
ophic cultures were found to have the same doubling time of 14 h. On a
cellular basis, the chlorophyll content remained the same and the phy
cobilin content showed an increase in the dark-grown cultures. Fluores
cence emission spectra at 77 K of dark-grown cells indicated that the
phycobilisomes are functionally associated with photosystem II (PSII).
Moreover, upon transfer to light, the dark-grown cells readily evolve
d oxygen. Although photosystem I (PSI) and whole chain-mediated electr
on transfer rates were comparable in both types or cultures, the rate
of PSII-mediated electron transfer was found to be 20% higher in dark-
grown cells. The PSI to PSII ratio changed from 6:1 in autotrophic cul
tures to 4:1 in the dark-grown cells. These changes in the rate of PSI
I electron transfer and in the stoichiometry between the two photosyst
ems under dark, heterotrophic growth conditions were brought about by
a preferential increase in the number of PSII units while the number o
f PSI units remained unchanged. The advantages of using this organism
in the selection of PSI-deficient mutants are discussed.