Regulation of phycobilisome structure and gene expression by light intensity

The cyanobacterium Agmenellum quadruplicatum PR-6 (Synechococcus sp PCC 7002) was grown turbidostatically in white light at three levels of irradiance: 20, 200, and 1260 microeinsteins per square meter per second. Phycobilisomes were isolated from each culture and analyzed by absorbance, gel electro...

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Bibliographic Details
Published in:Plant physiology (Bethesda) 1992-03, Vol.98 (3), p.1003-1010
Main Authors: De Lorimier, R.M. (University of California, Berkeley, CA), Smith, R.L, Stevens, S.E. Jr
Format: Article
Language:English
Subjects:
Agmenellum quadruplicatum
AZOTE
Biological and medical sciences
COMPOSICION QUIMICA
COMPOSITION CHIMIQUE
CYANOPHYTA
EXPRESION GENICA
EXPRESSION DES GENES
Fundamental and applied biological sciences. Psychology
Gels
Gene expression
Genes
Irradiance
Life Sciences & Biomedicine
LUMIERE
Luminous intensity
LUZ
Marine
Molecular and cellular biology
Molecular genetics
Nitrates
Nitrogen
NITROGENO
Phycobilisome
PIGMENT
PIGMENTOS
Plant Sciences
Plants
PROTEINAS
PROTEINE
Ratios
RNA
Science & Technology
Synechococcus
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Summary:The cyanobacterium Agmenellum quadruplicatum PR-6 (Synechococcus sp PCC 7002) was grown turbidostatically in white light at three levels of irradiance: 20, 200, and 1260 microeinsteins per square meter per second. Phycobilisomes were isolated from each culture and analyzed by absorbance, gel electrophoresis, and electron microscopy. The ratio of phycocyanin to allophycocyanin decreased 1.8-fold from the lowest to highest irradiance. This change was due entirely to an approximately 2.5-fold decrease in one structural unit of rod domains, the complex of phycocyanin, and a 33-kilodalton linker polypeptide (LR33). For a given irradiance, phycobilisomes from cells grown on ammonium as the nitrogen source had 10 to 20% more phycocyanin then those from nitrate cultures. Total RNA was isolated from all cultures and probed with gene fragments specific to phycocyanin and allophycocyanin subunits and LR33. The relative level of RNAs encoding phycocyanin and allophycocyanin was found to vary with light intensity in parallel with the phycobiliprotein ratio. Hence, the light-harvesting capacity of phycobilisomes is directly regulated by relative levels of phycobiliprotein mRNA. The LR33 transcript occurs as a 3' extension on about 10% of phycocyanin transcripts. The ratio of RNA encoding LR33 to that encoding phycocyanin did not vary with irradiance, although the protein ratio changed 1.7- to twofold between extremes. Based on these and other observations, we propose that the LR33 protein is constitutively synthesized at a rate higher than that required to complex with available phycocyanin
ISSN:0032-0889
1532-2548
DOI:10.1104/pp.98.3.1003