PHOTOPHYSIOLOGICAL RESPONSES OF FRAGILARIOPSIS CYLINDRUS (BACILLARIOPHYCEAE) TO NITROGEN DEPLETION AT TWO TEMPERATURES¹

Abstract

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.

Impacts of nitrogen and phosphorus starvation on the physiology of Chlamydomonas reinhardtii

“…Compared to other experimental conditions, fluorescence intensity for the J-I-P steps declines in microalgal cells exposed to higher irradiances (Petrou et al 2011). A decline of the P step was also registered for Ndepleted microalgal cells (Petrou et al 2012). In addition, Solovchenko et al (2013) reported that changes in O-J-I-P under different light treatments and N-deprived cells could be related to changes in pigment (Chl a and carotenoids) composition.…”

Photophysiological responses of Southern Ocean phytoplankton to changes in CO2 concentrations: Short-term versus acclimation effects

“…Each data point represents an individual NPQ value. and nutrient limitation (Alderkamp et al, 2012;Petrou et al, 2012), but not yet under low CO 2 concentration.…”

Southern Ocean phytoplankton physiology in a changing climate

“…Comparison of the photoacclimation strategies of F. cylindrus and P. antarctica provides an excellent example of how the photoprotective capacity of these two important SO species can be linked with their ecological niche occupancy. F. cylindrus has been shown to utilise rapid and dynamic NPQ under a range of environmental conditions (Mock and Hoch, 2005;Kropuenske et al, 2009Kropuenske et al, , 2010Petrou et al, 2011aPetrou et al, , 2012Petrou and Ralph, 2012), balancing growth with light acquisition through the modulation of their carotenoid pigments (Petrou et al, 2011a(Petrou et al, , 2012Petrou and Ralph, 2012). This species is highly resilient to changes in irradiance, possessing a large chlorophyll a specific optical cross sectional area (useful in low light), yet able to keep excitation pressure low under high light by rapid induction of xanthophylldriven NPQ and regulation of the functional cross sectional area of PSII ( PSII ) Petrou et al, 2011aPetrou et al, , 2012Petrou and Ralph, 2012).…”

“…F. cylindrus has been shown to utilise rapid and dynamic NPQ under a range of environmental conditions (Mock and Hoch, 2005;Kropuenske et al, 2009Kropuenske et al, , 2010Petrou et al, 2011aPetrou et al, , 2012Petrou and Ralph, 2012), balancing growth with light acquisition through the modulation of their carotenoid pigments (Petrou et al, 2011a(Petrou et al, , 2012Petrou and Ralph, 2012). This species is highly resilient to changes in irradiance, possessing a large chlorophyll a specific optical cross sectional area (useful in low light), yet able to keep excitation pressure low under high light by rapid induction of xanthophylldriven NPQ and regulation of the functional cross sectional area of PSII ( PSII ) Petrou et al, 2011aPetrou et al, , 2012Petrou and Ralph, 2012). This plasticity is not common to all SO diatoms, instead other species exposed to the same stressors, have shown to be less plastic to changes in light, exhibiting limited NPQ capacity and no dynamic control over excitation pressure (Petrou et al, 2011a, highlighting how photoacclimation strategy may be an important determinant of the success of F. cylindrus in polar marine environments (Kang and Fryxell, 1992;Lizotte, 2001;Kopczynska et al, 2007).…”