Ecophysiological responses of Jussiaea rapens to cadmium exposure

Shoots of Jussiaea rapens Linn were exposed to nutrient solutions containing 0, 7, 15, 30, 60 mg L-1 cadmium (Cd2+) and the effects on plant physiology investigated after treatment for 2 and 5 days. The net photosynthesis rate was inhibited by 54.8-62.7%, but only at the two highest [Cd2+]. Stomatal conductance showed an initial decline from 0.01 to 0.07 mol m(-2) s(-1) after a 2-d exposure to high [Cd2+] but recovered after a 5-d exposure. The Chl fluorescence parameters F-v/F-m, qP and ETR also declined by 16, 87, and 90%, respectively, after 5-d at the highest [Cd2+], which is consistent with damage to the activity of Photosystem II. Chlorophyll a (Chl a), and b and total chlorophyll (Chl) all exhibited content reductions, though in the case of Chl b it required a 5-d exposure. Significant increases in superoxide dismutase (SOD) activity were observed at all. [Cd2+], the greatest increase being 149%. Likewise, carotenoid content increased by five-fold relative to the untreated control values. The increase in SOD activity and carotenoid suggests that one effect of the Cd2+ caused oxidative stress in J. rapens. Root vitality was also negatively influenced by all Cd2+ treatments. However, the [Cd2+] values inhibiting the photosynthetic parameters were greater than those reported for several other species, which suggests that J. rapens may have some degree of tolerance to this toxic metal. (c) 2008 Published by Elsevier B.V.