Zinc affects differently growth, photosynthesis, antioxidant enzyme activities and phytochelatin synthase expression of four marine diatoms

Abstract

Zinc-supplementation (20 μM) effects on growth, photosynthesis, antioxidant enzyme activities (superoxide dismutase, ascorbate peroxidase, catalase), and the expression of phytochelatin synthase gene were investigated in four marine diatoms (Amphora acutiuscula, Nitzschia palea, Amphora coffeaeformis and Entomoneis paludosa). Zn-supplementation reduced the maximum cell density. A linear relationship was found between the evolution of gross photosynthesis and total chlorophyll content. The Zn treatment decreased the electron transport rate except in A. coffeaeformis and in E. paludosa at high irradiance. A linear relationship was found between the efficiency of light to evolve oxygen and the size of the light-harvesting antenna. The external carbonic anhydrase activity was stimulated in Zn-supplemented E. paludosa but was not correlated with an increase of photosynthesis. The total activity of the antioxidant enzymes did not display any clear increase except in ascorbate peroxidase activity in N. palea. The phytochelatin synthase gene was identified in the four diatoms, but its expression was only revealed in N. palea, without a clear difference between control and Zn-supplemented cells. Among the four species, A. paludosa was the most sensitive and A. coffeaeformis, the most tolerant. A. acutiuscula seemed to be under metal starvation, whereas, to survive, only N. palea developed several stress responses.

Figure 1

Gross photosynthesis versus irradiance curves in Amphora coffeaeformis, Amphora acutiuscula, Entomoneis paludosa, and Nitzschia palea grown in ASW (control) or in the presence of 20 μM Zn added to ASW. Mean values ± SE (n = 3–5).

Figure 2

(a) Relationship between α ^B calculated from gross photosynthesis versus light intensity curves (P/E in Figure 1) and Chl a/Chl c ratio (Table 1) in Amphora coffeaeformis, Amphora acutiuscula, Entomoneis paludosa, and Nitzschia palea grown in ASW in the absence (□) or the presence (◊) of Zn supplementation. (b) Relationship between the total Chl content (Table 1) and the maximum gross photosynthesis (P _max⁡ ^B) (Figure 1) in Amphora coffeaeformis, Amphora acutiuscula, Entomoneis paludosa, and Nitzschia palea grown in ASW in the absence (■) or the presence (◆) of Zn supplementation.

Figure 3

Relative electron transport rate (rETR) versus irradiance curves in Amphora coffeaeformis, Amphora acutiuscula, Entomoneis paludosa, and Nitzschia palea grown in ASW (control) or in the presence of 20 μM Zn added to ASW. Mean values ± SE (n = 3–5).

Figure 4

Relationship between the relative intensity of rETR and the relative intensity of P ^B in Amphora coffeaeformis, Amphora acutiuscula, Entomoneis paludosa, and Nitzschia palea grown in the absence (□) or the presence (■) of a Zn supplementation.

Figure 5

External, internal, and total carbonic anhydrase (CA) activities in Amphora coffeaeformis, Amphora acutiuscula, Entomoneis paludosa, and Nitzschia palea grown in ASW (control) or in the presence of 20 μM Zn added to ASW. Mean values ± SE (n = 3–5). Significant differences are indicated by an asterisk (P ≤ 0.05).

Figure 6

Antioxidant enzymes activities (superoxide dismutase, SOD; catalase, CAT and ascorbate peroxidase, APX) in Amphora coffeaeformis, Amphora acutiuscula, Entomoneis paludosa, and Nitzschia palea grown in ASW (control) or in the presence of 20 μM Zn added to ASW. Significant differences are indicated by an asterisk (P ≤ 0.05). Mean values ± SE (n = 3–5).

Figure 7

Alignment of the amino acid sequences of phytochelatin synthase fragments isolated from Amphora acutiuscula (FN995989), Amphora coffeaeformis (FN995985), Entomoneis paludosa (FN995987) and Nitzschia palea (FN995985) grown in ASW. Black boxes indicated 100% identity, dark grey 80%, and light grey 60%. The cysteine residues are indicated by asterisks.