Growth, Physiological And Biochemical Response Of Macroalgae Ulva To Cadmium And Nitrogen Application And Their Mechanism

The experiments were carried out to study on the characteristics of morphology and molecular biology, effects of applied Cd2+on growth, physiology and biochemistry of Ulva prolifera, U. linza and U. clathrata, and effects of interactions between Cd2+and N on their growth, physiology and biochemistry. Through these experiments, we comparative’ studied their biological characteristics, cadmium tolerance and nitrogen regulation on Cd damage in these Ulva. These studies provide theoretical bases for forecasting, early warning and control of green tide, screening seaweed for marine environmental bioremediation, and accelerating seaweed development and utilization. The main results showed that:(1) U. prolifera is filamentous, more branches, above the branch also has two or three level of branches. U. linza are long ribbon, no branch or less branch. In the cell ultrastructure, there has a sheet chloroplast which close to the cell wall distribution, more starch grains and nucleus. U. prolifera’s cell wall is thicker, while U. linza’s is thin. From the cell surface structure, U. prolifera has more branches, each cell is clearly visible, but U. linza cell surface attach a wax nature level, cell visibility is not high even under high power electron microscope. The ITS sequences of both Ulva were blast in NCBI, and the results show that higher homologous species have the same name.(2) With the increase of Cd2+concentrations, fresh weight (FW), relative growth rate (RGR), chlorophyll (Chl) and carotenoid (Car) content, Chl a/Chl b, chlorophyll fluorescence parameters and soluble protein (SP) of U. clathrata, U. prolifera and U. linza were declined. However, inhibiton of these indexes in U. clathrata and U. prolifera were more serious than that in U. linza except Chi content. Under Cd2+stress, Na+, Ca2+, soluble sugar (SS) and proline (PRO) of U. prolifera and U. linza were increased, but K+, Mg2+, Cl", K+/Na+, Ca2+/Na+, free amino acids (FAAS) and organic acid (OA) were decreased. U. prolifera and U. linza maintain a certain level of osmotic adjustment ability (OAA) when Cd2+concentration is5and10μmol·L-1, and the former was lower than the latter. U. linza still maintained a certain level of OAA with Cd2+at20μmol·L-1, but U. prolifera lost OAA. Ulva maintained their OAA due to their higher Na+, K+, Ca2+, FAAS and PRO contents under lower Cd2+. Cd accumulation in U. prolifera and U. linza were increased with the increase of Cd2+concentrations, and U. prolifera accumulated more Cd than U. linza. N and P content in both Ulva first increased than declined, U. linza absorbed more N and P content than U. prolifera under high Cd2+stress. Correlation analysis showed that RGR was a significant positive correlation (P<0.01) with Chl content, Car content, Chl a/Chl b, Yield, rETRmax, a, OAA, Cl-content, K+/Na+, FAAS content, OA content and SP content, was a significant negative correlation (P≤0.01) with contents of Cd2+, Ca2+and SS. The above results leads us to a conclusion that U. clathrata, U. prolifera and U. linza were sensitive to Cd2+, better adaptation of U. linza to Cd2+was mainly achieved by its higher RGR, Car, Chla/Chlb, Fv/Fm, Yield, rETRmax, a, OAA, N and P content, osmotica upon exposure to Cd2+stress.(3) Interactions between Cd2+and N significantly effected the growth, photosynthetic pigments, OAA, Cd accumulation, subcellular distribution of Cd and chemical forms of Cd. In non-Cd (0Cd) treatment, FW and RGR in U. prolifera were declined with the increase of N concentrations, but U. linza were increased. Saturated osmotic potential of each Ulva was decreased. In low Cd2+(LCd:20μmol L-1Cd2+) and high Cd (HCd:80μmol L-1Cd2+) treatment, with the increase of N concentrations, FW and RGR of both Ulva were increased. Saturated osmotic potential of U. prolifera was increased when N concentrations increasing in LCd treatment, while that of U linza was declined. Saturated osmotic potential in both Ulva were increased with the increase of N concentrations in HCd treatment. In the same Cd2+level, Chl content, Car content, Fv/Fm, Yield, Pm, α, K+, Mg2+, Cl", NO3-, SP, FAAS, OA, Cd accumulation, subcellular distribution of Cd and chemical forms of Cd, N and P content were increased when N enrichment, while Na+, Ca2+, SS and PRO contents decreased. In the same N level, saturated osmotic potential of U. prolifera declined gradually, saturated osmotic potential of U. linza rised in LCd treatment, but declined in HCd treatment. FW, RGR, Chl, Car, Fv/Fm, Yield, Pm, α, K+, Mg2+, Cl-, SP, FAAS, OA, P content were all decreased with the increase of Cd2+concentrations, the indexes of U. prolifera declined more than those of U. linza, Na+, Ca2+, Cl", NO3-, SS, PRO, Cd accumulation, subcellular distribution of Cd and chemical forms of Cd increase with the increase of Cd2+concentrations. Subcellular distribution of Cd is:cell wall> nucleus> soluble fraction> chloroplast> mitochondria. Chemical forms of Cd were mianly NaCl and HAC extractable. The above results leads us to a conclusion that U. prolifera grow better than U. linza under lack of N condition. N enrichment alleviated Cd2+toxicity to U. prolifera and U. linza, and the mitigation effect of U. linza is better than U. prolifera.