Sensitivity of cyanobacterial antenna, reaction center and CO2 assimilation transcripts and proteins to moderate UVB: light acclimation potentiates resistance to UVB.
We tested the hypothesis that cyanobacterial cells have sufficient acclimation potential to tolerate UVB when it is applied in a natural quantum ratio to growth photosynthetically active radiation (PAR). We grew Synechococcus under 50 (Low) or 300 (High) micromol PAR m(-2) x s(-1) and then exposed the cells to 0.125 (Low) or 0.75 (High) micromol UVB m(-2) x s(-1). The PAR:UVB quantum ratios were near natural for both the Low-PAR:Low-UVB and the High-PAR:High-UVB treatments, but UVB was in excess of typical aquatic PAR:UVB for Low-PAR:High-UVB treatments. The cellular light history determined the UVB responses of Synechococcus. High-PAR cells initially had fewer cpc transcripts encoding phycocyanin, lower phycocyanin content, and more psbAII/AIII transcripts encoding the D1:2 photosystem II (PSII) protein isoform. Higher PAR potentiated them to tolerate an appropriate UVB level without short-term inhibition of PSII or growth. Low-PAR cells rapidly altered psbAII/AIII and cpc gene expression and tolerated appropriate Low UVB. Low-PAR:High-UVB cells, in contrast, suffered short-term inhibition of PSII and growth. In all treatments UVB induced transient loss of cpc transcripts, possibly to free resources for psbAII/AIII expression, which is important for UVB resistance. The drop in cpc transcripts was not part of a general shock response because rbcL transcript pools were stable upon UVB exposure.
Department of Biology and Coastal Wetlands Institute, Mount Allison University, Sackville, NB, Canada.
Tara M
TM
MacDonald
Luc
L
Dubois
Laura C
LC
Smith
Douglas A
DA
Campbell
D000222:Adaptation, Physiological; D001483:Base Sequence; D002245:Carbon Dioxide / Q000378:metabolism*; D000458:Cyanobacteria / Q000378:metabolism / Q000528:radiation effects*; D017931:DNA Primers; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism / Q000528:radiation effects*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D014466:Ultraviolet Rays
D017931:DNA Primers; D045322:Photosynthetic Reaction Center Complex Proteins; D012333:RNA, Messenger; D002245:Carbon Dioxide