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PHOTOPHYSIOLOGICAL RESPONSES OF FRAGILARIOPSIS CYLINDRUS (BACILLARIOPHYCEAE) TO NITROGEN DEPLETION AT TWO TEMPERATURES1
Article first published online: 20 DEC 2011
© 2011 Phycological Society of America
Journal of Phycology
Volume 48, Issue 1, pages 127–136, February 2012
How to Cite
Petrou, K., Kranz, S. A., Doblin, M. A. and Ralph, P. J. (2012), PHOTOPHYSIOLOGICAL RESPONSES OF FRAGILARIOPSIS CYLINDRUS (BACILLARIOPHYCEAE) TO NITROGEN DEPLETION AT TWO TEMPERATURES. Journal of Phycology, 48: 127–136. doi: 10.1111/j.1529-8817.2011.01107.x
Received 11 October 2010. Accepted 5 June 2011.
- Issue published online: 1 FEB 2012
- Article first published online: 20 DEC 2011
- Fragilariopsis cylindrus;
- QB nonreducing PSII centers
The photosynthetic efficiency and photoprotective capacity of the sea-ice diatom, Fragilariopsis cylindrus (Grunow) W. Krieg., grown in a matrix of nitrogen repletion and depletion at two different temperatures (−1°C and +6°C) was investigated. Temperature showed no significant effect on photosynthetic efficiency or photoprotection in F. cylindrus. Cultures under nitrogen depletion showed enhanced photoprotective capacity with an increase in nonphotochemical quenching (NPQ) when compared with nitrogen-replete cultures. This phenomenon was achieved at no apparent cost to the photosynthetic efficiency of PSII (FV/FM). Nitrogen depletion yielded a partially reduced electron transport chain in which maximum fluorescence (FM) could only be obtained by adding 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). reoxidation curves showed the presence of QB nonreducing PSII centers under nitrogen depletion. Fast induction curves (FICs) and electron transport rates (ETRs) revealed slowing of the electrons transferred from the primary (QA) to the secondary (QB) quinone electron acceptors of PSII. The data presented show that nitrogen depletion in F. cylindrus leads to the formation of QB nonreducing PSII centers within the photosystem. On a physiological level, the formation of QB nonreducing PSII centers in F. cylindrus provides the cell with protection against photoinhibition by facilitating the rapid induction of NPQ. This strategy provides an important ecological advantage, especially during the Antarctic spring, maintaining photosynthetic efficiency under high light and nutrient-limiting conditions.