Mechanism Of Trehalose Regulating Cadmium Accumulation In Rice Seedlings

Cadmium is one of the most widely used metals.In the past half-century,the average soil Cd concentration on southwestern China and coastal areas has increased by more than 50%,and the annual average growth rate far exceeds other heavy metals in the soil.The soil in the southern part of China is acidic,which makes it easy about crops to accumulate cadmium.Rice,which is the main food crop in the south,also has a strong accumulation capacity for cadmium,which seriously threatens human health.Plants can accumulate compatible solutes to counteract the damage caused by stress through osmotic adjustment.Trehalose has been shown to play an important role in plant stress resistance due to its stability to molecules and membranes.In this study,the T705 variety of rice was used as the experimental material.The hydroponic test was used to investigate the cadmium accumulation characteristics of trehalose on rice seedlings,its physiological level and the response to the antioxidant defense system.The main research results are as follows:（1）Effect of trehalose on cadmium accumulation in rice seedlingsCompared with seedlings contaminated with cadmium alone,cadmium contaminated solution to trehalose added can effectively inhibit the absorption and accumulation of cadmium in rice.The time-kinetic absorption of cadmium in rice showed that exposure to cadmium solution could cause direct damage to rice roots,while the absorption of cadmium in stems and leaves showed two leaping periods.In the second leaping stage,the serious damage to plant cell membrane was not enough to alleviate coercion.In the concentration dynamics absorption test,the test results were fitted according to the Michaelis-Menten equation.With the increase in trehalose concentration,the Vmax value of cadmium accumulation in rice seedling leaves gradually decreased.When the trehalose concentration was 13.21 mmol·L^-1,the Vmax value of stems and leaves was the smallest.When the concentration of trehalose was2.64 mmol·L^-1,the Vmax value of roots was the smallest.Trehalose promoted the transport of roots to stems and leaves while inhibiting the total amount of cadmium accumulation in rice seedlings.（2）Effects of trehalose on physiological levels of rice seedlings under cadmium stressthe growth and development of rice seedlings were observed and tested.It was found that trehalose had no adverse effects on rice growth,but it did not have a good alleviation effect on rice seedlings under cadmium stress.Under cadmium stress,the growth of rice seedlings was blocked,the root activity decreased,and the direct damage to roots also indirectly caused a negative reaction to the photosynthesis effect of leaves,resulting in decreased chlorophyll,damage to the cell membrane and increased relative conductivity of the leaves,and lipid peroxidation levels upgrade.When the concentration of trehalose is higher(50 mmol·L^-1)under cadmium stress,the inhibition of rice seedlings is more obvious.The application of exogenous trehalose promoted the accumulation of trehalose in rice seedlings.In addition,a small amount of trehalose accumulated in the case of cadmium stress,indicating the necessity of trehalose for abiotic stress in plants,but in the case of 50 mmol·L^-1 trehalose,rice trehalose accumulation was reduced compared to low concentration exogenous trehalose administration.（3）Effects of trehalose on antioxidant defense of rice seedling cells under cadmium stressUnder cadmium stress,the superoxide anion radical（O₂.^-）production rate and H₂O₂ content in the stems and roots of rice seedlings increased with the increase of trehalose level.The activities of superoxide dismutase（SOD）,catalase（CAT）and peroxidase（POD）increased first and then decreased to the increase in trehalose concentration,spray treatment group showed an upward trend.It indicates that low concentration of exogenous trehalose can promote the plant antioxidant system,while high concentration of exogenous trehalose may cause damage to rice seedlings.At the same time,with the application of exogenous trehalose,the activity of intracellular trehalase is significantly increased,the decomposition of trehalose is accelerated,and the balance of trehalose in the cells is maintained.