The effects of copper toxicity on the photosynthetic activities of Avicennia germinans was investigated using two CuSO 4 concentrations (0.062 and 0.33 M) added in Hoagland's solution in an aerated hydroponic system. Photosynthesis and chlorophyll fl uorescence were measured after 30 h of copper stress. Results obtained in this study show that increasing levels of Cu +2 of 0.062 and 0.33 M Cu +2 resulted in a general reduction of the stomatal conductance (28 and 18%, respectively) and 100% of inhibition of net photosynthesis. Additionally, at these concentrations of Cu +2, reductions of chlorophyll fl uorescence parameters were also observed. These changes suggested that the photosynthetic apparatus of Avicennia germinans was the primary target of the Cu +2 action. It is concluded that Cu +2 ions causes a drastic decline in photosynthetic gas exchange and Chlorophyll fl uorescence parameters in A. germinans leaves.

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The main associated factors were shown to be time from purée preparation to use (>24 hours), use of certain vegetables (borage and chard), and breast-feeding. Nitrate levels in both vegetables implicated as etiological factors in acquired MHb are high.

The toxic effects of cadmium on the photosynthetic apparatus of Avicennia germinans were evaluated by means of the chlorophyll fluorescence transient O-J-I-P. The chlorophyll fluorescence transients were recorded in vivo with high time resolution and analyzed according to the OJIP-test that can quantify the performance of photosystem II. Cadmium-treated plants showed a decrease in yield for primary photochemistry, TR0/ABS. The performance index of photosystem II (PSII), PIABS, decreased due to cadmium treatment. This performance index is the combination of the indexes of three independent parameters: (1) total number of active reaction centers per absorption (RC/ABS), (2) yield of primary photochemistry (TR0/ABS), and (3) efficiency with which a trapped exciton can move an electron into the electron transport chain (ET0/TR0). Additionally, the F0/Fv registered the highest sensitivity to the metal, thus indicating that the water-splitting apparatus of the oxidizing side of PSII is the primary site of action of cadmium. In summary, cadmium affects several targets of photosystem II. More specifically the main targets of cadmium, according to the OJIPtest, can be listed as a decrease in the number of active reaction centers and damage to the activity of the water-splitting complex.

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