Effects Of Cadmium On Seed Germination, Seeding Growth And Antioxidant System Of Thellungiella Hallophila

Cadmium （Cd） is one of the particular biotoxicity heavy metals due to its highmobility and great solubility character. Cd pollution becomes more and more serious,and has severe effects on the agricultural production and human health. High level ofCd affects seed germination, growth and development of plants, causing lipidperoxidation and oxidative stress. Plants have developed several protectionmechanisms to cope with cadmium stress. For example, plants can tolerate cadmiumstress by scavenging ROS using non-enzymatic components such as ascorbate （AsA）,glutathione （ GSH） and enzymatic components such as superoxide dismutase （SOD）,peroxidase （POD） and so on.In the present study, Thellungiella hallophila was used to study effects ofdifferent concentration of cadmium on seed germination parameters such asgermination rate, germination potential, germination index and vigor index, inaddition, growth of cotyledons was also measured. On the other hand, content of Cd²⁺,AsA , GSH，activity of SOD, glutathione reductase （GR）, POD, ascorbate peroxidase（APX） and catalase （CAT） were measured, and isoenzymes of SOD, GR, POD, APXand CAT were also analyzed using native gel electrophoresis to examine responses ofantioxidants of enzymatic components to the tolerance of T. hallophila to Cd stress.The main results are showed as follows:Under condition of 0.3 mmol·L-1of cadmium, seed germination rate,germination potential，germination index, vigor index and growth of cotyledons wereless affected. The inhibition increased with the increase of Cd²⁺ concentration, and thevigor index and growth of cotyledons was 0 when Cd²⁺ concentration was 0.9mmol·L-1. Furthermore, cadmium had more inhibition on root than on shoot. Theseeds didn’t germinate any more on normal culture medium after un-germinated seedstreated with 0.9 mmol·L-1Cd²⁺. It suggested that the damage of Cd stress to seed germination is irreversible. The root length, bud length and biomass of T. Hallophilaseedlings were decreased with the increase of the Cd2+concentrationCd stress reduced biomass, number and area of leaf, root length of T.Hallophila seedlings. Content of chlorophyll and carotene declined with the increaseof Cd2+concentration, and photosynthetic oxygen release rate was markedly reduced.High concentration of Cd can increase membrane permeability and damage integrityof cell membrane. Content of MDA and H2O2increased with the increase of Cd2+concentration.Content of Na+, K+were less affected under the treatment of differentconcentration of Cd. Content of Ca2+in the shoot had no significant change. However,content of Ca2+in the roots significantly reduced with the increase of the Cd2+concentration. Proline is one of the important compatible solutes, which can alsoprotect the membrane damage caused by Cd stress. Proline contents markedlyincreased in the shoot and roots of T. hallophila with the increase of Cd2+concentration suggesting that proline was the main osmotic adjustment solutes inT.hallophila.T. hallophila accumulated Cd under Cd stress. Cd content in the roots and shootgradually increased with the increase of Cd2+concentration. Since Cd concentration inthe roots and shoot was 255.5 mg kg-1DW and 189.35 mg kg-1DW, respectively, T.hallophila was considered as a kind of Cd stress resistant plant. However, T.hallophila was not a Cd-hyperaccumulator, for Cd concentration is higher in the rootthan in the shoot. Cd accumulated in the roots and was prevented from transport toshoot, which reduced damage to shoot of T. hallophila under Cd stress.The contents of GSH and AsA of T. hallophila were gradually increased withthe increase of Cd2+concentration. Meanwhile, GSH and AsA were necessary todecompose the H2O2. The activities of SOD, GR and APX in leaves had no significantchange. However, activity of CAT was enhanced when Cd2+concentration was 0.9mmol·L-1. POD activity showed an upward trend with increasing of Cd2+concentration. The relative activities of Fe-SOD and Cu/Zn-SOD1 were significantlyenhanced. The relative activity of POD increased rapidly under condition of high Cd concentration treatment, the relative activity of POD after 0.3, 0.6 and 0.9 mmol·L^-1Cd treatments was 1.2-, 1.8- and 2.5-folds higher than that in control. Moreover,activity of CAT2 increased significantly with the increase of Cd²⁺ concentration.These results suggest that SOD, POD and CAT involved in scavenging of reactiveoxygen species caused by Cd stress, and POD played a main role in removal of H₂O₂.