Stoichiometry of photosystem I, photosystem II, and phycobilisomes in the red alga Porphyridium cruentum as a function of growth irradiance

Journal Article · Wed Nov 01 04:00:00 EST 1989 · Plant Physiology; (USA)

DOI:https://doi.org/10.1104/pp.91.3.1179· OSTI ID:5925636

Cunningham, Jr, F X; Mustardy, L; Gantt, E ^[1]; Dennenberg, R J; Jursinic, P A ^[2]

---

1. Univ. of Maryland, College Park (USA)
2. Department of Agriculture, Peoria, IL (USA)

Cells of the red alga Porphyridium cruentum (ATCC 50161) exposed to increasing growth irradiance exhibited up to a three-fold reduction in photosystems I and II (PSI and PSII) and phycobilisomes but little change in the relative numbers of these components. Batch cultures of P. cruentum were grown under four photon flux densities of continuous white light; 6 (low light LL), 35 (medium light, ML), 180 (high light, HL), and 280 (very high light, VHL) microeinsteins per square meter per second and sampled in the exponential phase of growth. Ratios of PSII to PSI ranged between 0.43 and 0.54. About three PSII centers per phycobilisome were found, regardless of growth irradiance. The phycoerythrin content of phycobilisomes decreased by about 25% for HL and VHL compared to LL and ML cultures. The unit sizes of PSI (chlorophyll/P{sub 700}) and PSII (chlorophyll/Q{sub A}) decreased by about 20% with increase in photon flux density from 6 to 280 microeinsteins per square meter per second. A threefold reduction in cell content of chlorophyll at the higher photon flux densities was accompanied by a twofold reduction in {beta}-carotene, and a drastic reduction in thylakoid membrane area. Cell content of zeaxanthin, the major carotenoid in P. cruentum, did not vary with growth irradiance, suggesting a role other than light-harvesting. HL cultures had a growth rate twice that of ML, eight times that of LL, and slightly greater than that of VHL cultures. Cell volume increased threefold from LL to VHL, but volume of the single chloroplast did not change. From this study it is evident that a relatively fixed stoichiometry of PSI, PSII, and phycobilisomes is maintained in the photosynthetic apparatus of this red alga over a wide range of growth irradiance.

• OSTI ID: 5925636
• Journal Information: Plant Physiology; (USA), Journal Name: Plant Physiology; (USA) Vol. 91:3; ISSN 0032-0889; ISSN PLPHA
• Country of Publication: United States
• Language: English

Related Subjects

550200* -- Biochemistry
59 BASIC BIOLOGICAL SCIENCES
ALGAE
CELL CONSTITUENTS
GROWTH
IRRADIATION PROCEDURES
MEMBRANES
PHOTOSYNTHETIC MEMBRANES
PHYCOBILISOMES
PLANTS
PORPHYRA
RHODOPHYCOTA
STOICHIOMETRY