Effects of UV radiation on five marine microphytobenthic Wadden sea diatoms isolated from the Solthörn tidal flat (Lower Saxony, southern North Sea) – Part I: growth and antioxidative defence strategies

Figures & data

Table 1. Characteristics of the Solthörn tidal flat isolates. all grown in f/2 medium (Guillard, 1975). Sampling locations in the Solthörn tidal flat, sampling dates, cell volumes (*¹) and growth medium.

Species	Sampling location	Sampling date	Diff. in cell volume [%]*^1
Achnanthes exigua	station 1	07.07.2008	5.1 ± 2.3
Amphora exigua	station 2	22.07.2008	4.9 ± 2.4
Cocconeis peltoides	station 2	22.07.2008	2.6 ± 1.3
Diploneis littoralis	station 2	07.07.2008	5.5 ± 3.0
Navicula digitoradiata	station 1	07.07.2008	6.1 ± 3.2

* ¹Obtained from the UVR-assays, including means ± SD. Differences were calculated according to the data given in Scholz & Liebezeit (2012a).

Fig. 1. Maximum specific growth rate (µ_max, A), specific growth rate (µ, B), chl a content (C, D) and protein content (E, F) of Achnanthes exigua, Amphora exigua, Cocconeis peltoides, Diploneis littoralis and Navicula digitoradiata obtained from short- (6 h) and long-term UV (30 days) experiments. All values are means ± SD.

Table 2. Antioxidant effects of methanol extracts on different radical screening tests, expressed as µmol g^–1 DW (mean ± SD. Assays: A1 = PAR, A2 = PAR+UV-A, A3 = PAR+UV-B, A4 = PAR+UV-A+UV-B). Abbreviations: DPPH = 2,2-diphenyl-1-picrylhydrazyl-free-radical-scavenging activity, SAS = superoxide-anion-scavenging assay, HPS = hydrogen-peroxide-scavenging activity, HRS = hydroxyl-radical-scavenging activity, FRAP = ferric-reducing antioxidant power assay, FIC = ferrous-ion chelating assay, n.d. = not determined, – = not detected.

Species Assay	Achnanthes exigua				Amphora exigua				Cocconeis peltoides				Diploneis littoralis				Navicula digitoradiata
	A1	A2	A3	A4	A1	A2	A3	A4	A1	A2	A3	A4	A1	A2	A3	A4	A1	A2	A3	A4
A. Short-term experiment (6 h)
DPPH	1.2 ± 0.3	1.8 ± 0.6	30.5 ± 3.7	32.4 ± 4.6	‒	‒	11.2 ± 1.9	10.3 ± 1.8	‒	2.2 ± 0.7	16.7 ± 1.9	16.3 ± 1.5	‒	‒	10.5 ± 1.0	11.1 ± 2.3	‒	1.7 ± 0.3	14.9 ± 1.6	17.3 ± 2.2
SAS	‒	‒	23.1 ± 3.9	26.5 ± 4.2	‒	1.4 ± 0.4	37.9 ± 8.3	42.9 ± 7.4	‒	1.0 ± 0.2	56.3 ± 11.1	55.2 ± 10.6	‒	9.2 ± 0.8	68.7 ± 9.4	73.5 ± 10.6	‒	‒	15.3 ± 4.5	16.9 ± 3.2
HPS	‒	‒	16.0 ± 1.8	16.9 ± 2.3	‒	1.9 ± 0.3	12.6 ± 1.2	14.1 ± 1.1	‒	0.7 ± 0.09	3.2 ± 0.3	3.5 ± 0.4	‒	0.3 ± 0.08	2.2 ± 0.3	3.7 ± 0.3	‒	0.5 ± 0.03	8.4 ± 1.3	10.2 ± 1.9
HRS	‒	0.9 ± 0.05	8.6 ± 0.7	9.1 ± 0.4	‒	0.8 ± 0.03	7.2 ± 0.8	7.9 ± 1.0	‒	n.d	0.6 ± 0.1	‒	‒	‒	0.9 ± 0.1	1.1 ± 0.2	‒	‒	2.2 ± 0.4	3.6 ± 0.8
FRAP	‒	28.7 ± 9.4	333.0 ± 14.6	326.9 ± 19.4	‒	199.5 ± 11.7	209.1 ± 10.3	208.4 ± 14.5	‒	169.5 ± 15.7	242.7 ± 19.1	236.3 ± 18.5	‒	38.2 ± 5.1	233.5 ± 21.3	236.2 ± 14.6	‒	10.5 ± 1.9	242.6 ± 18.9	249.0 ± 16.4
FIC	‒	3.2 ± 1.1	13.1 ± 2.6	12.4 ± 1.5	‒	8.6 ± 1.3	9.4 ± 1.0	9.6 ± 2.1	‒	1.4 ± 0.3	5.5 ± 0.9	6.3 ± 1.2	‒	5.5 ± 1.1	10.3 ± 2.0	11.7 ± 1.9	‒	‒	12.4 ± 2.0	11.1 ± 1.7
B. Long-term experiment (30 days)
DPPH	3.9 ± 0.4	57.6 ± 11.3	68.7 ± 10.6	66.2 ± 10.3	‒	22.6 ± 2.1	44.1 ± 5.4	37.5 ± 4.3	‒	12.3 ± 1.0	42.9 ± 6.1	48.9 ± 2.3	‒	14.2 ± 1.7	35.7 ± 5.2	31.5 ± 4.3	‒	12.3 ± 1.4	42.7 ± 3.6	40.1 ± 3.9
SAS	‒	276.1 ± 14.9	516.9 ± 29.3	506.4 ± 25.2	‒	198.3 ± 19.7	526.6 ± 27.0	511.8 ± 25.3	‒	113.7 ± 11.5	522.7 ± 22.6	518.4 ± 20.3	‒	157.2 ± 12.8	799.5 ± 31.2	808.1 ± 28.9	‒	204.7 ± 19.4	615.9 ± 22.6	627.3 ± 27.1
HPS	‒	18.4 ± 1.5	38.9 ± 3.2	36.1 ± 3.9	‒	12.5 ± 1.8	28.3 ± 2.4	29.4 ± 3.1	‒	10.6 ± 1.3	22.5 ± 2.4	23.0 ± 1.6	‒	4.1 ± 0.08	15.2 ± 1.9	17.1 ± 2.0	‒	8.3 ± 1.1	19.5 ± 1.8	22.3 ± 2.1
HRS	‒	14.3 ± 1.7	27.2 ± 2.5	29.6 ± 2.4	‒	8.1 ± 1.0	16.2 ± 1.7	19.7 ± 2.2	‒	8.5 ± 0.1	10.3 ± 0.9	11.6 ± 1.1	n.d.	‒	2.6 ± 0.1	5.8 ± 0.8	‒	4.7 ± 0.2	11.1 ± 1.3	11.0 ± 1.2
FRAP	‒	136.5 ± 14.4	327.4 ± 27.6	323.8 ± 22.5	‒	291.0 ± 10.4	566.8 ± 28.1	442.7 ± 24.3	‒	251.3 ± 19.2	321.8 ± 21.5	304.6 ± 18.3	‒	88.5 ± 9.2	343.2 ± 19.0	359.4 ± 22.5	0.3 ± 0.1	95.6 ± 9.3	351.8 ± 18.2	362.3 ± 26.5
FIC	‒	11.3 ± 1.7	22.1 ± 3.0	16.3 ± 2.6	‒	13.7 ± 1.9	26.3 ± 6.4	33.4 ± 5.5	‒	10.1 ± 1.2	23.5 ± 5.9	29.2 ± 6.4	‒	11.8 ± 1.6	20.7 ± 3.4	26.3 ± 4.8	‒	12.7 ± 1.9	33.6 ± 8.3	35.9 ± 9.0

Fig. 2. Results from phytochemical screening. Presence of phenolic compounds (A), flavonoids (B: dark grey) and tannins (B: light grey) in biomass extracts of the five isolates. Data were obtained from short- and long-term exposure to PAR, PAR+UV-A, PAR+UV-B and PAR+UV-A+UV-B. The dimensions of circles indicate slight (small circles), medium (small-medium circles), medium-strong (large-medium circles) and strong (large circles) colorimetric reactions.

Table 3. Total polyphenolic and flavonoid content obtained from the short- and long-term UVR experiments. Data are expressed as mg 100 g^-1, including mean values ± SD. Assays: A1 = PAR, A2 = PAR+UV-A, A3 = PAR+UV-B, A4 = PAR+UV-A+UV-B. Abbreviations: TPPC = total polyphenolics, TFC = total flavonoid content, – = not detected.

Species Assay	Achnanthes exigua				Amphora exigua				Cocconeis peltoides				Diploneis littoralis				Navicula digitoradiata
	A1	A2	A3	A4	A1	A2	A3	A4	A1	A2	A3	A4	A1	A2	A3	A4	A1	A2	A3	A4
A. Short-term Experiment (6 h)
TPPC	26.5 ± 1.5	124.7 ± 3.6	131.9 ± 3.7	142.2 ± 4.6	19.6 ± 2.0	83.3 ± 2.7	127.1 ± 3.3	127.8 ± 4.2	–	–	151.4 ± 3.7	161.0 ± 4.3	51.6 ± 1.3	–	181.3 ± 5.7	187.2 ± 6.2	14.5 ± 0.9	53.9 ± 2.4	111.2 ± 3.8	113.1 ± 4.7
TFC	–	–	8.4 ± 0.3	10.1 ± 2.3		–	5.7 ± 0.9	9.4 ± 1.0	–	–	3.6 ± 0.2	5.1 ± 0.2	–	–	3.9 ± 0.3	5.8 ± 0.4	–	–	6.2 ± 1.1	9.1 ± 0.8
B. Long-term experiment (30days)
TPPC	95.4 ± 4.4	218.4 ± 12.6	251.3 ± 11.1	283.1 ± 10.0	55.2 ± 3.9	236.4 ± 12.9	244.7 ± 9.1	254.3 ± 10.6	59.3 ± 5.1	281.5 ± 11.6	299.4 ± 15.3	316.4 ± 13.2	87.6 ± 4.7	473 ± 11.9	518.2 ± 14.9	521.4 ± 13.7	72.5 ± 8.3	136.2 ± 11.9	604.5 ± 14.1	622.1 ± 12.4
TFC	‒	‒	19.1 ± 2.2	21.6 ± 3.4	‒	‒	18.5 ± 1.3	19.2 ± 1.6	‒	4.5 ± 0.6	26.2 ± 3.1	30.1 ± 2.7	‒	‒	39.2 ± 1.8	40.7 ± 2.5	‒	‒	22.3 ± 1.7	20.4 ± 1.9

Fig. 3. Enzyme activities of Achnanthes exigua, Amphora exigua, Cocconeis peltoides, Diploneis littoralis and Navicula digitoradiata after 6 h exposure to PAR, PAR+UV-A, PAR+UV-B and PAR+UV-A+UV-B. (A) Superoxide dismutases (= SOD), (B) Ascorbate peroxidase (= APX), (C) Monodehydroascorbate reductase (= MDHAR) and (D) Glutathione reductase (= GR).

Fig. 4. Enzyme activities of Achnanthes exigua, Amphora exigua, Cocconeis peltoides, Diploneis littoralis and Navicula digitoradiata after 30 days exposure to PAR, PAR+UV-A, PAR+UV-B and PAR+UV-A+UV-B. (A) Superoxide dismutases (= SOD), (B) Ascorbate peroxidase (= APX), (C) Monodehydroascorbate reductase (= MDHAR) and (D) Glutathione reductase (= GR).

Fig. 5. DMSP content of Achnanthes exigua, Amphora exigua, Cocconeis peltoides, Diploneis littoralis and Navicula digitoradiata after 6 h (A) and 30 days exposure (B) to PAR, PAR+UV-A, PAR+UV-B and PAR+UV-A+UV-B. Values are means ± SD.

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