Effect Of Tryptophan On Cadmium Ion Uptake And Transport In Rice

Rice is one of the main food crops in China.However,with the acceleration of urbanization,the rapid development of industry and agriculture,and the increasing discharge of waste water as well as waste gas,the cadmium pollution in soil has been aggravated.the incidents of rice cadmium exceeded the standard have occurred from time to time,which causes a potential threat to human health.Developing new inhibitors is an effective method to reduce the cadmium content in rice.In this study,main rice varieties were used in field trials to compare effects of low molecular acids on the absorption and transport of cadmium ion in rice.Mechanism of tryptophan regulating the absorption and transport of cadmium ion in rice was discussed in combination with in vitro leaf experiment and seedling experiment.The main results were as follows:1.Spraying malic acid,citric acid and tryptophan at anthesis stage of rice decreased the content of cadmium in all organs of rice,and the effect of malic acid and citric acid on cadmium reduction was more obvious than that of tryptophan.The cadmium content in panicle neck and flag leaf of panicle was significantly reduced.The most obvious reduction of Cd was taken place in grains by 76.49%.When citric acid concentration reached 5 mM,Cd content of grain decreased by 83.51%.The cadmium content in rice organs also decreased with spraying tryptophan on leaf surface,but the reduction amount was less than those with spraying citric acid and malic acid.2.Spraying malic acid,citric acid and tryptophan also significantly affected the transport and accumulation of essential elements.After spraying 2 mM malic acid,5 mM citric acid and 0.01mM tryptophan,the Mn content in rice organs was significantly increased.The contents of Ca and Zn in grains and spikes decreased obviously.Malic acid,citric acid and tryptophan may indirectly inhibit the transport of Cd in rice by regulating the transport of essential elements,such as Ca,Mn,Zn,and so on.3.In the 1.1 mg/L cadmium stress environment,the difference of Cd accumulation in the leaves of high accumulation rice and low accumulation rice was largest in about 11 hours.There was a positive correlation between the rate of chlorosis and the concentration of Cd in leaves of low-accumulation cultivar X24,and the content of photosynthetic pigment decreased by about70%.4.Under the treatment of 1.1 mg/L Cd solution,the addition of 0.2².0 mM tryptophan could significantly reduce the Cd content in rice detached leaves.The Cd content in leaves of 4genotypes under Cd stress without tryptophan was in the range of 277.69³64.99 mg/kg,and R705 showed the highest Cd content and X24 the lowest.After adding tryptophan inhibitor,there was no significant difference in Cd content among the three genotypes（R705,65 and 80）.However,Cd content in detached leaves from X24 was slightly lower than that from the above three genotypes.X24 was the most sensitive genotype to tryptophan,and its Cd reduction caused by tryptophan was about 44.5%.The next sensitive genotype was R705,and its cadmium reduction caused by tryptophan was about 34.77%.Cadmium content in 80 was less influenced by tryptophan.The activity of Ca²⁺Mg²⁺ATPase in X24 detached leaves was decreased by adding0.2².0 mM tryptophan.5.In a medium containing 0.3 mg/L cadmium,addition of tryptophan reduced the cadmium accumulation in rice seedlings.When the concentration of tryptophan is 0.2mM,the effect of reducing cadmium is obvious.Among them,the accumulation of cadmium in the underground part decreased with the increase of the concentration of tryptophan,and the decrease of cadmium accumulation in the aboveground part decreased.0.2 mM tryptophan can alleviate the toxic effects of cadmium on the root system.The addition of tryptophan can increase the Mn²⁺content and reduce the K⁺content in rice seedlings.