The Physiological And Ecological Response Of Catharanthus Roseus To Soil Cadmium Stress And The Regulation Of Exogenous Nitric Oxide

Recently, human activities have led to increasingly serious pollution of urban soil cadmium (Cd), which direct harm to the urban ecological environment and human health. It has become a global problem urgently to be solved. In phytoremediation of heavy metal polluted soil, the landscape plants, comparing with hyperaccumulator, have relatively large biomass, many kinds, and fast growth and not cause secondary pollution, and have a good ecological and landscape effect. Therefore, discussing the cadmium stress response mechanisms of the ground cover plants and the mitigation effects of cadmium contamination will provide theoretical basis and practical significance in the plants screened for the remediation of urban cadmium contamination soil. Accordingly, this research choose the valuable ornamental plant Catharanthus roseus, which is an important landscaping and anticancer drug source plant which is widely distributed in city gardens and on roadsides in China, as the experimental material. A controlled pot-experiment was arranged with different treatments of different cadmium concentrations (0,5,10,25,50and100mg·kg-1) and exogenous NO with the sodium nitroprusside (SNP, an exogenous NO donor) to investigate the effect of different level of cadmium treatment, and the physiological and ecological response of the SNP treatment under cadmium concentrations on C. roseus.The results showed that C. roseus has a strong capability in cadmium accumulation, which resulted in roots higher than shoots, the cadmium treatments of<10mg·kg-1didn’t affect the malondialdehyde (MDA) content, H2O2content, superoxide (O2-) production rate and the activities of antioxidative enzymes. Also, it only has little influence on the plasma membrane ATPase (H+-ATPase and Ca2+-ATPase) and the5’-AMPase activity. However,25-100mg·kg-1cadmium treatments induced the accumulation of MDA, H2O2and O2·-both in shoots and roots of C. roseus. Meanwhile, high levels of cadmium significantly enhanced the activities of catalase (CAT), superoxide dismutase (SOD), peroxidase (POD) and glutathione (GSH) content in shoot, as well as the activities of POD and SOD in root possessing the same trend, and but had no obvious effects on the activities of CAT and GSH content in root. As the same time, the damage of the plasma membrane ATPase and5’-AMPase is worsed. The treatments with higher cadmium concentrations (≥25mg·kg-1) significantly inhibited C. roseus growth, biomass and C, N, P and K accumulation, as well as altered their distribution patterns, while the treatment with lower cadmium concentration (<10mg·kg-1) had no significant effects. In the pot experiment, all plants were not withered and died. The experiment result has a gap with defined hyperaccumulators, but it revealed that C. roseus has stronger tolerance to cadmium contamination to a certain extent as for the stronger cadmium accumulation capacity in roots and the reasonably accumulation and distribution pattern of biomass and nutrient. These results implied that C. roseus is a possible for urban landscaping and purification of heavy metal contaminated soil, and has some potential applications in the remediation of cadmium polluted soil.Simultaneously, the addition of100μmol·L-1exogenous SNP can alleviate the inhibitory effects of25mg·kg-1of cadmium stress on the growth of C. roseus seedlings. What’s more, SNP increased the leaf length, leaf width, plant height, basal diameter and biomass (fresh weight and dry weight).Compared with cadmium stress, applying SNP decreased the contents of MDA, H2O2, GSH and the production rate of O2·-, significantly promoted the activities of CAT, POD and SOD in shoot and root. While SNP alleviated the inhibitory of chlorophyll a (Chla), chlorophyll b (Chlb) and total chlorophyll, increased the net photosynthetic rate (Pn), stomatal conductivity degrees (Gs), transpiration rate (Tr) and stomatal limit value (Ls), and decreased the intercellular CO2concentration (Ci) and instantaneous light use efficiency (LUE). Simultaneously, SNP can induce H+-ATPase and Ca2+-ATPase activity of plasma membrane increased to normal level in shoot and root. However, applying100μmol·L-1sodium nitrate or nitrite (the decomposition products of NO) or the same concentration of sodium ferrocyanide (an analog of SNP) had no significant alleviation effects on cadmium stress. The applied100μmol·L-1SNP can mitigate the cadmium toxic effects, and reduce the cadmium accumulation on the C. roseus. The possible mechanisms of action are as follow. Firstly, compared with cadmium stress, applying SNP decreased the contents of MDA, H2O2, GSH and the production rate of superoxide anion radical (O2-), significantly promoted the activities of CAT, POD and SOD in shoot and root, and eliminate or balance cellsoxygen levels. Secondly, While SNP alleviated the inhibitory of chlorophyll a (Chla), chlorophyll b (Chlb) and total chlorophyll, increased the net photosynthetic rate (Pn), stomatal conductivity degrees (Gs), transpiration rate (Tr) and stomatal limit value (Ls), and decreased the intercellular CO2concentration (Ci) and instantaneous light use efficiency (LUE).That is to say, SNP can increase the chlorophyll content and improve the photosynthetic capacity of mesophyll cells under cadmium stress. Thirdly, SNP enhance the plasma membrane H+-ATPase, Ca2+-ATPase and5’-AMPase activity, strengthen the transport of ions across the membrane, Ca2+signal transduction and metabolism, protect the plasma membranes under cadmium stress. At last but not the least, SNP maintain normal growth of plants by improving the activity of nitrate reductase (NR), glutamine synthetase (GS) and glutamate-oxoglutarate aminotransferase (NADH-GOGAT), reducing the activity of glutamate dehydrogenase (NADH-GDH), increasing the content of nitrate nitrogen (NO3-N), and accelerating the assimilation of ammonium (NH4+).Therefore, appropriately increasing the NO content into plant might be a viable way to alleviate the cadmium pollution soil for modern agricultural production and contaminated soil remediation in urban. Pathways of plant obtaining NO may have the following methods. On the one hand, the use of chemical and genetic control means will regulatie the generation of endogenous NO in plants. On the other hand, improving the composition of bacteria in the soil will make the soil released more nitrogen oxides, promote plant root system to absorb NO. Thirdly, the development of friendly fertilizers which can release NO will increase the NO volume for plants roots absorbing.