The Physiological Mechanism Of Chitosan Relieves Cadmium Toxicity In Maize Seedlings

Cadmium?Cd?is a non-essential element for plant growth,and which is highly toxic.With the large-scale emissions of industrial waste?wastewater,waste gas,and solid waste?and the application of cadmium-containing products,the problem of farmland cadmium pollution has received a high degree of attention.At present,the area of farmland that has been contaminated with cadmium has reached 2×10⁴hm².As a major food crop in China,maize?Zea mays L.?is increasingly affected by cadmium pollution,so ensuring the safety of maize production is crucial.Chitosan??-?1,4?poly-2-amino-D-glucose?is deacetylated from chitin,and which is the only naturally occurring polysaccharide in nature.Because chitosan has the advantages of being non-toxic,inexpensive and highly efficient,it has an excellent application prospect in agricultural production.Chitosan can relieve crops from stress.In order to investigate the physiological mechanism of chitosan in relieving cadmium toxicity in maize seedlings,a hybrid variety‘Zhengdan 958'was used as experimental material and cultivated via Hoagland hydroponics in plant growth chamber.Maize seedlings were treated with chitosan of 100 mg·L^-1under Cd²⁺stress at different time points?0,24,48,72,96 h?.The aim of the experiment was to examine the effects of chitosan on the growth,cadmium content,photosynthetic characteristics,chlorophyll fluorescence parameters,cell membrane stability,active oxygen metabolism,antioxidant enzyme activity and endogenous hormone levels under cadmium stress.The results showed that:1.The application of chitosan increased the dry fresh weight,root length,root surface area and root volume of maize seedlings under cadmium stress,and increased root activity and root tolerance index.Chitosan alleviated the inhibition of maize seedling growth under cadmium stress.2.The application of chitosan reduced the transport coefficient of cadmium to the shoot and the enrichment coefficient of the shoot,reduced the cadmium content in shoots and roots of maize seedlings,and which had a more obvious relief effect on the shoots of maize seedlings.3.The application of chitosan increased the leaf area of maize seedlings,increased the photosynthetic rate,chlorophyll content and photosynthetic enzyme activity of seedling leaves under cadmium stress,which reduced photosynthetic system disorders and maintained the ability of photosynthetic production.4.The application of chitosan reduced the generation rate of superoxide radical O₂^-· and the content of H₂O₂,increased the activities of antioxidant enzymes?SOD,POD,CAT,APX,GR,DHAR,MDHAR?and antioxidants?AsA,GSH?content promotes the regeneration of AsA and GSH,maintains the redox state of the cells?AsA/DHA and GSH/GSSG?of maize seedling leaves under cadmium stress,chitosan maintained a higher operating efficiency of the AsA-GSH cycle,and increased the resistance oxidative capacity,which effectively alleviated the inhibition of growth of maize seedlings under cadmium stress.5.The application of chitosan promoted the production of IAA,ZR and GA in maize seedlings under cadmium stress,increased the ratio of IAA/ABA,ZR/ABA and GA/ABA,regulated the content and balance of endogenous hormones,and improved the ability to resist cadmium stress of maize seedlings.6.Chitosan can alleviate the damage of seedlings caused by cadmium stress,and chitosan alone can also promote the growth of seedlings.Chitosan can be used as an exogenous substance in the field of crop resistance to cadmium stress.