Effect Of La(Ⅲ) On Endogenous Hormones And Metabolism Of Flavonoids In Soybean Seedlings(Glycine Max) Under UV-B Radiation Stress

Atmospheric pollutants such as chlorofluorocarbons have caused severe depletion of stratospheric ozone, particularly in the Antarctic, where the Springtime"Ozone Hole"has greatly increased the amounts of damaging ultraviolet-B radiation reaching the Earth's surface. This study used the method of water culture, and oil-bearing crops of soybean (Glycine max), as the test material, to explore the effect of La(III) and UV-B radiation on endogenous hormones and flavonoids metabolism and mechanism within the seedlings. Research methods used involve physiology, biochemistry, molecular spectroscopy technology and simulation technology. This study investigated the effects of La(III) on the content of endogenous hormones and aromatic amino acids, mechanism of key enzymes of flavonoid metabolism in soybean seedlings under UV-B radiation stress. It revealed the effects and mechanism of La(III) on endogenous hormones and metabolism of flavonoids in plants under UV-B radiation stress from an environmental and ecological perspective, physiological, biochemical and enzyme conformation levels.The main research results of this dissertation were shown as follows:(1) UV-B radiation stress effected grouth in soybean seedlings.The lack of green areas on leaf surfaces and rate of leaf folding were increased, leaf area, chlorophyll content, mineral elements, root activity, root length, fresh(dry) weight were decreased in soybean seedlings under UV-B radiation stress. This decline is related with UV-B radiation dosage. La(III)(20 mg/L) could increase soybean root activity, chlorophyll content, mineral elements, in order to promote photosynthesis; increased leaf area and fresh (dry) weight of leaves of soybean seedling promotes growth. seedlings was able to maintain absorption and utilization of light energy to meet the energy demand and materials needed for plant self-repair, to alleviate UV-B radiation on leaf damage after La(III)(20 mg/L) intervention. High doses of La (III)(60 mg/L)could reduce soybean root activity, chlorophyll content, mineral elements, thereby inhibiting photosynthesis; and lower leaf area and fresh (dry) weight of leaves in soybean seedling, thus inhibiting the growth of soybean seedlings. La(III)(20 mg/L) could alleviate the UV-B radiation stress on plant growth inhibition, La(III)(20 mg/L) could increase inhibition of UV-B radiation stress on plant growth.(2) UV-B radiation stress causes a decrease in IAA, GA and CTK content and increased ABA content, IAAO activity and ETH content, plant growth, organ growth and development of mitigation, change in morphology, decrease in biomass, and thus harming the plants. La(III)(20 mg/L) in plants exposed to UV-B radiation stress can increase IAA, GA and CTK content and reduce ABA content, IAAO activity and ETH content, reduced inhibition caused by UV-B radiation on plant growth, and to plant growth and ease the contradiction of flavonoid synthesis, reduce UV-B radiation on plant injury. The effect of La(III)(20 mg/L) on plants may be related to La(III)(20 mg/L) causing an increase in flavonoids, reducing damage caused by UV-B radiation, stability of membrane structure, maintenance of plant water potential, and a lower intensity of stress response in plants. La(III)(60 mg/L) in soybean seedlings exposed to UV-B radiation stress, showed an decrease in IAA, GA and CTK content, increase in ABA content and IAAO activity, thus increasing plant injury caused by UV-B radiation. Combined stress leads to decreased cell proliferation and growth, organ growth and development of mitigation, morphology change, and a decrease in biomass. Endogenous ETH productionwas reduced in soybean seedlings under the action of La(III)(20 mg/L)+UV-B radiation stress, showed a decrease in 1-amino-cyclopropane-1-carboxylic acid (ACC) content and that of amino-cyclopropane carboxyl acid synthase activity, which reduces the amount of ethylene converted from 1-aminocyclopropane-1-carboxylic acid (ACC). La(III)(20 mg/L) accelerates the removal of free radicals to increase cell membrane protection system activity and maintain cell membrane permeability to inhibit ethylene production. However, La(III)(60 mg/L) shows opposite results.(3) Trp content in soybean seedlings decreased, while Phe, Tyr, and DAHPS activity increased in soybean seadlinngs under UV-B stress. As a result, IAA content in plants was decreased and plant growth was inhibited. La(III)(20 mg/L) increases Trp, Phe, Tyr content and DAHPS activity, is beneficial for increasing plant IAA content, while by increasing the activity of soybean seedlings DAHPS and Phe, Tyr content to promote the synthesis of flavonoids. Increase of flavonoids would reduce the amount of UV-B radiation absorbed by the plant, thus reducing damage caused by UV-B radiation on soybean seedling. La(III)(60 mg/L) of soybean seedlings inhibited flavonoids synthesis by inhibiting Trp, Phe, Tyr content and DAHPS activity. This decrease in flavonoids thus increased the amount of UV-B radiation absorbed in the plant and damage on soybean seedling was increased.(4) The PAL activity, C4H activity, 4CL activity, CHS activity and flavonoid content were increased in soybean seedlings under UV-B radiation stress, but declined sharply in the recovery period. La(III)(20 mg/L) effectively enhanced PAL activity, C4H activity, 4CL activity, CHS activity and flavonoid content to provide barriers against UV-B radiation stress in plants. La(III)(60 mg/L) inhibited PAL activity, C4H activity, 4CL activity, CHS activity and flavonoid content, and played a negative role under UV-B radiation stress of the plants. La(III)(20 mg/L) and UV-B radiation could promote the activities of key enzymes of flavonoid metabolism, and increased flavonoid content, but the mechanism was inconsistent, the former is a stress response by the plants, which has a passive increase.(5) The method of physical chemistry, molecular dynamics simulation was used in the in vitro experiments. It showed that changes in molecular structure of CHS under UV-B radiation stress is UV-B radiation reduced the molecular basis of CHS activity; it was found that a large number of negative charge clusters on CHS protein surface, indicating that La(III) may be a relationship directly with the CHS proteins. La(III) acted with acylamino group O, or N atom on CHS peptide chain directly, which lead to change CHS micro structure, increase/decrease CHS activity, promote/inhibit the synthesis of flavonoids.