The growth of photosynthetic organisms is a dynamic process continuously shaped by environmental conditions. The most rapidly changing environmental factor affecting the photosynthesis is light which is a source of energy for carbon fixation (Gilstad et al. 1993; Flameling, Kromkamp 1997; Walters, Horton 1995). During the day, the quality and quantity of photosynthetically active radiation (PAR) changes. Photosynthetic organisms maintain a balance between the photosynthetic energy supply in thylakoid membranes and the energy consumption within the Calvin cycle (Carvalho et al. 2011; Bailey et al. 2008). When algae and some species of higher plants are moved from light to dark conditions, the PSII activity is reduced, probably due to the low rate of reduction of primary electron acceptors (Dau 1994). Furthermore, when the light intensity is too high, the photosynthetic apparatus can be damaged due to the chlorophyll photooxidation.
Photobiological responses and adaptations of
Chlorophyll fluorescence provides information about the physiological state of the organism, the amount of energy absorbed by the chlorophyll molecule and dissipated in the form of heat (Murchie, Lawson 2013). Stress factors lead to increased power dissipation in the PSII center and may in time lead to irreversible damage. Changes in chlorophyll
Interactions between temperature and light have a significant impact on photosynthesis and the growth rate of algae (Butterwick et al. 2005). Low temperature may induce structural and functional changes in the photosynthetic apparatus and RuBisCo activity allowing to maintain the energy balance (Mortain-Bertrand et al. 1988). Levasseur et al. (1990) showed that a temperature-induced decrease in the carbon fixation rate was correlated with a decrease in the energy-transfer efficiency between the antenna and the reaction center of PSII. Thompson et al. (1992) reported that the chlorophyll content in algae decreases with decreasing temperature. Measurement of chlorophyll
The aim of the present study was to determine the efficiency of the photosynthetic apparatus of
Green strains of
The photosynthetic activity of symbionts was measured by chlorophyll
Chlorophyll
Technical fluorescence parameters
Chlorophyll fluorescence intensity measured when all photosystem II reaction lefts are open
Maximal chlorophyll fluorescence intensity measured when all photosystem II reaction lefts are closed
Variable chlorophyll fluorescence (Fm/F0)
Maximum quantum yield of PSII
Efficiency of the water-splitting complex on the donor side of PSII
Dissipated energy flux per cross section (CS) at t = 0
Electron transport flux per cross section (CS) at t = 0
Indicator of the PSII functioning
Index expression as the density of reaction centers (RC)
Time needed to reach Fm (ms)
Trapped energy flux per cross section (CS) at t = 0
The results were presented as mean values for 3 independent replicates. Statistical significance between mean values was assessed by Duncan’s multiple range test using STATISTICA 10.0 statistical software (StatSoft Inc.). A probability of
The results obtained in the present study revealed significant changes in PSII in algae strains incubated at 18°C compared to algae from lower temperatures in the light and dark conditions.
The maximum quantum yield of PSII (Fv/Fm) is used to estimate changes in the functioning of reaction centers, as well as to determine the photosynthetic activity (Büchel, Wilhelm 1993). According to Masojidek et al. (2011), the PSII efficiency varies depending on the time of day, which is related to the intensity of light. The photoinhibition is induced not only due to the excess of unused energy by chlorophyll (Osmond et al. 1999), but also by low temperature stress (Germino, Smith 2000a,b). The research conducted by Gómez et al. (2001) revealed that
Some chlorophyll Different letters indicate significant differences according to Duncan’s test (
Treatment
Endosymbionts of
Ard7
KD64
T(°C)
Light conditions
F0
Fm
Fv
Fv/Fm
Fv/F0
F0
Fm
Fv
Fv/Fm
Fv/F0
18
12L/12D
161.00c
348.30b
187.30a
0.54a
1.16a
45.30c
105.70b
60.30a
0.58a
1.33ab
24D
192.30b
312.00c
119.70c
0.39bc
0.62bcd
63.30b
99.30c
36.00c
0.36cd
0.57bc
15
12L/12D
241.00a
415.70a
174.70b
0.42b
0.72bcd
71.70a
119.70a
48.00b
0.40bcd
0.67abc
24D
91.30d
162.00d
70.70d
0.44b
0.77bc
37.70d
58.70d
21.00d
0.36cd
0.56bc
12
12L/12D
70.00e
105.00e
35.30e
0.34c
0.50cd
39.00d
59.00d
20.00d
0.34d
0.51bc
24D
40.30f
68.30f
28.00ef
0.41bc
0.69bcd
37.70d
58.70d
21.00d
0.36cd
0.56bc
9
12L/12D
34.30g
59.70f
25.30f
0.42b
0.74bcd
27.30e
40.70e
13.30e
0.33d
0.49bc
24D
25.30h
40.70g
15.30g
0.38bc
0.60bcd
20.30f
29.00f
8.70f
0.30d
0.43c
6
12L/12D
5.30j
9.70h
4.30h
0.45b
0.83b
10.70g
16.30g
5.70g
0.35cd
0.55bc
24D
11.00i
16.30h
5.30h
0.33c
0.49d
4.70h
8.00h
3.30g
0.32cd
0.43c
The decrease in the Fv/Fm ratio under varying light intensity can be due to changes in the level of F0 and Fm. This indicates the loss of energy dissipated in the form of heat, which may result from the inability of PSII to reduce the complete electron acceptors (Magnusson 1997; Saakov 2002). The F0 fluctuations include changes at the level of the main antenna as light-harvesting complexes, from the trimeric form to the monomeric form. They also include physical dissociation of the core part of LHCII in PSII. The highest intensity of chlorophyll fluorescence F0, when all PSII reaction centers are open, was observed under 12L/12D conditions at 15°C in both
In the present study, the highest Fm value was determined at 15°C under 12L/12D. These significant differences between two strains may be due to different conditions in which they live. The Fm values for the strains kept under 12L/12D were higher compared to the strains incubated in constant darkness. The lowest values of Fm for both strains were observed at 6°C, regardless of the light conditions (Table 2).
Slight differences between Fm and F0 represent low Fv values, which indicate the low PSII activity and the energy dissipation in the form of heat. This parameter is determined by the maximum quantum yield of PSII. In the present study, the highest Fv was observed at 18°C and 15°C for Ard7 kept under 12L/12D conditions. The significantly highest Fv values were observed in KD64 incubated under similar light conditions. Fv of symbiotic algae cultured under 24D conditions were statistically lower compared to the cultures grown under 12L/12D conditions. When the temperature decreased, the Fv decreased significantly. The lowest Fv values were determined at a temperature of 6°C under both light conditions (Table 2). It seems that photoinhibition includes at least two inactivation steps. The first phase is considered reversible and develops for about one hour without causing any damage to the PSII (Leitsch et al. 1994). The second stage probably begins with damage in the PSII reaction centers (Aro et al. 1993; Leitsch et al. 1994; Mishra, Singhal 1992; Vass et al. 1992). The highest Fv/F0 values were noticed in algae strains incubated at a temperature of 18°C, regardless of the light conditions. At temperatures of 12°C, 9°C and 6°C, these values ranged from 0.49 to 0.83 under 12L/12D conditions and from 0.43 to 0.77 under 24D conditions (Table 2). Changes in Fv/F0 values reveal disturbances in the water dissipating complex, which is very sensitive to environmental changes and determines the resistance of plants (Jiang et al. 2006). Similar changes in Fv/F0 were observed in barley (Kalaji et al. 2012).
The specific parameters of fluorescence, such as RC/ABS, TRo/CSo, Eto/CSo, DIo/CSo and PI, are used to explain the gradual flow of energy through single PSII reaction centers (Force et al. 2003; Xu et al. 2014). These parameters allow to determine the photosynthetic activity of endosymbiotic algae of
PI is a biophysical parameter indicating changes in PSII, which is calculated by multiplying ABS/Cs × TRo/Cs × ETo (Strasser, Strasser 1995; Force et al. 2003; Stefanov et al. 2011). PI is one of the fluorescence parameters that provides useful information about the state of the vitality of photosynthetic organisms. The PI values were lower under 12L/12D conditions compared to the control. At a temperature of 15°C, the PI values were similar to the control for Ard7 and higher than the control for KD64 under 24D conditions (Fig. 1). According to Ferrante & Maggiore (2007), however, PSII centers are not damaged at low temperatures but at high temperatures. On the other hand, low temperature may indicate a decrease in the accumulation of electron acceptors and in the activity of PSII reaction centers (Vonshak, Novoplansky 2008). Low temperature stress and light stress have synergistic effects and clearly increase the PSII photodamage (Allakhverdieva, Murataa 2004; Nishiyama et al. 2008). These reactions are similar to those observed in algae exposed to various types of stress, such as high salinity (Vonshak 2002), photoinhibition (Lu, Vonshak 1999; Sonoike et al. 2001), bleaching (Hill et al. 2004) or insecticides (Jena et al. 2012).
The time needed to reach the maximum fluorescence (Tf(max)) may be useful to identify early changes in photosynthetic activity. For
In natural aquatic ecosystems, the toxic effect of environmental factors on algae depends on the depth of their occurrence and the temperature conditions (Oukarroum et al. 2012). The temperature differences connected with the light factor affect the photosynthetic activity. In some organisms, these factors cause a decrease in the PSII activity, while in others they do not cause significant changes or they are quickly regenerated. This tolerance may result from various repair mechanisms, including the ability to quench the ROS activity or to produce photoprotective compounds, such as mycosporine amino acids (MAAs) and carotenoids (Teoh et al. 2013).
The time of stressor treatment is the most important factor that affects the photosynthetic activity. The parameters of chlorophyll fluorescence used in the present study allow to visualize early changes in PSII under the influence of temperature and light. The ability of endosymbionts from two
Based on the obtained results, we can conclude that all of the chlorophyll fluorescence parameters were related to the decreasing temperature and light conditions. In the case of