The Response Characteristics Of Winter Wheat To Molybdenum Pollution In Soil And Mechanisms For Resistance

As one of the essential trace minerals for plants, animals, and microorganisms, Molybdenum（Mo）is also a very important strategic resource. Current research mainly focuses on the effects of Mo deficienency on the yield and quality of crops, and the study of environmental problems caused by Mo pollution is rare. In fact, excess Mo in soil can cause serious damage to animal and human health through the food web, and the influence of Mo pollution on the ecological system should not be ignored. Therefore, the study of the response characteristics of plants and its regulatory mechanismsto excess Mo, could not only provide theoretical guidance for the selection of resistant and hyperaccumulator plants, but at the same time could provide technical support for phytoremediation of polluted soil. Based on the results of earlier studies,soiland hydroponic culture experiments were conducted to investigatethe response of winterwheats to soil pollution of Mo and their resistant mechanisms.The main results are as follows.1. Pot and hydroponic culture experiments were conducted to investigate the effects of different pollution levels of Mo on the growth and development of winter wheat. The results showed that the yield of winter wheat showed an initial increase up to a maximum at 500 mg·kg^-1, followed by a downward trend at high concentration. The chlorophyll content, photosynthetic rate （P_n）, transpiration rate（Tr） and stomatal conductance（Gs） were decreased within the range of Mo levels 0.15²000 mg·kg^-1; With the decline of P_n, the decreases inintercellular CO₂ concentration（Ci） and Gs indicated that stomatal limitation was the main factor causing P_n decline; TheChla/b decreased with an increase of Mo pollution levels, which indicated that the transformation from Chla to Chlb was blocked under Mo pollution condition, at the same time, photosynthesis was inhibited as a result of chloroplast structuredisorder; Respiration was effected because of the shape of mitochondria. The life cycle of winter wheats was not completed when the Mo level reached 3000⁴000 mg·kg^-1.2. A pot culture experiment was conducted to investigate the absorption and distributionof excess Mo in winter wheat. The results showed that Mo concentration in different organs were in the ordes: roots>leaves>stems>glumes>grains, indicating that the roots could accumulate a certain amount of Mo and inhibit its translocation to shoots. The distribution into glumes and grains decreased with an increase of Mo pollution levels, which indicated that excess Mo inhibited its translocation from vegetative organs to reproductive organs, thus reducing its threat to human health. Excess Mo mainly accumulated in stems within the range of Mo levels 100¹000 mg·kg^-1, but in leaves within the range of Mo levels 1000²000 mg·kg^-1. However the concentration of Mo in grains still reached up to 6.43³20.19 μg·g^-1, the health risk indexs were 0.98⁴8.67, and the relationships between Mo concentration in grains and available Mo in soils were y=0.942e0.009x（ r=0.881 p<0.01）, which indicated that excess Mo in soil could threaten human health through the food webs.3. Pot and hydroponic culture experiments were conducted to investigate the resistance mechanisms to Mo pollution in winter wheat. The results showed that the concentrarions of Mo and its distribution percentages in cell walls and vacuoles were enhanced significantly, which indicated that winter wheat mainly distributed excess Mo in cell walls and vacuoles and which might be an important resistance mechanism. The MDA concentration increased with an increase of Mo pollution levels and was significantly different compared with appropriate Mo application(0.15 mg·kg^-1), and indicated that cell membrane structures of winter wheat were damaged under Mo pollution. Proline concentrations imcreased with the increase of Mo pollution levels, which indicated that winter wheat could reduce cell water potential by accumulating proline under Mo pollution. The activity of antioxidant enzymes（SOD、POD、CAT、APX） remained stable, which indicated that Reactive oxygen species kept a dynamic balance between generation and removal, which might be another important resistance mechanism.4. A hydroponic culture experiment was conducted to investigate the changes in abundance of metabolitesthe in Mo pollution of winter wheat. The results showed that winter wheats producted many different metabolites including organic acids, fatty acid, amino acids and phytohormones under Mo pollution, which took part in tricarboxylic acid cycle, fatty acid metabolism, amino acidmetabolism and signal transduction. The concentrations of malic acid, arachidonic acid, corticosterone, androsterone, MG, DG, cAMP, methyl jasmonate and γ-aminobutryic acid were enhanced most significantly, which minght be metabolic biomarkers under Mo pollution and should be verified and analyzed in the following study.