Physiological and biochemical responses of Ulva prolifera and Ulva linza to cadmium stress.

Responses of Ulva prolifera and Ulva linza to Cd(2+) stress were studied. We found that the relative growth rate (RGR), Fv/Fm, and actual photochemical efficiency of PSII (Yield) of two Ulvaspecies were decreased under Cd(2+) treatments, and these reductions were greater in U. prolifera than in U. linza. U. prolifera accumulated more cadmium than U. linza under Cd(2+) stress. While U. linza showed positive osmotic adjustment ability (OAA) at a wider Cd(2+) range than U. prolifera. U. linza had greater contents of N, P, Na(+), K(+), and amino acids than U. prolifera. A range of parameters (concentrations of cadmium, Ca(2+), N, P, K(+), Cl(-), free amino acids (FAAs), proline, organic acids and soluble protein, Fv/Fm, Yield, OAA, and K(+)/Na(+)) could be used to evaluate cadmium resistance in Ulva by correlation analysis. In accordance with the order of the absolute values of correlation coefficient, contents of Cd(2+) and K(+), Yield, proline content, Fv/Fm, FAA content, and OAA value of Ulva were more highly related to their adaptation to Cd(2+) than the other eight indices. Thus, U. linza has a better adaptation to Cd(2+) than U. prolifera, which was due mainly to higher nutrient content and stronger OAA and photosynthesis in U. linza.

[Physiological responses of Enteromorpha linza and Enteromorpha prolifera to seawater salinity stress].

To investigate the physiological responses and adaptation mechanisms of Enteromorpha to seawater salinity stress, a laboratory experiment with Enteromorpha linza and E. prolifera was conducted to study their fresh mass (FM), relative growth rate (RGR), relative electrical conductivity (REC), chlorophyll (Chl) and carotenoid (Car) contents, Chl a/Chl b, Chl/Car, chlorophyll fluorescence parameters, and osmotic adjustment ability (OAA) under the stress of different salinity levels of diluted and concentrated seawater for 10 days. Compared with the control, 10%-200% salinity seawater increased the FM and RGR of the two Enteromorpha species obviously, 100% and 50% salinity seawater made the FM and RGR of E. linza and E. prolifera peaked, respectively, while 300% salinity seawater decreased the FM and RGR of E. linza and E. prolifera significantly, with the decrement being larger for E. linza. The biomass of E. linza and E. prolifer only had an increase in 50% and 100% sanity seawater and in 10%, 50%, 100%, and 200% salinity seawater, respectively. The Chl and Car contents and Chl a/Chl b of E. linza and E. prolifera had a significant increase in 10% salinity seawater, but decreased after an initial increase with the increasing salinity level of seawater. The Chl and Car contents and Chl a/Chl b of E. linza and E. prolifera peaked in 100% and 50% salinity seawater, respectively. With increasing salinity of seawater, the light use efficiency (alpha), maximal photochemical efficiency of PS II (F(v)/F(m)), actual photochemical efficiency of PS II in the light (Yield), maximal relative electron transport rate (rETR(max)), and half-saturation light intensity (I(k)) of E. linza and E. prolifera all showed the same variation trend as Chl. 10% -300% salinity seawater enabled E. linza and E. prolifera to express certain osmotic adjustment ability (OAA), and the OAA of E. linza and E. prolifer peaked in 100% and 50% salinity seawater, respectively. The growth of Enteromorpha had no correlation with Chl/Car, but was significantly negatively correlated with REC and positively correlated with Chl, Car, Chl a/ Chl b, F(v)/F(m), Yield, rETR(max), alpha, I(k), and OAA. To sum up, 100% salinity was the optimal salt concentration for the growth of E. linza, and 50% salinity was optimal for E. prolifera. E. prolifera could adapt to a wider range of salinity than E. linza. The parameters REC, Chl, Car, Chl a/Chl b, F(v)/F(m), Yield, rETR(max), alpha, I(k), and OAA could be used to evaluate the salt adaptation of Enteromorpha.