Effects Of Proline And Glutathione On Pigeon Pea Under Cadmium Stress

Heavy metals are environmental toxins and are continuously releasing into environment through anthropogenic,and lithogenic sources.These pollutants seriously affect ecosystems,especially plants,since their habitats are fixed and directly dependent on soil.Among these pollutants,cadmium is the most concerned because it is extremely toxic,inhibits the normal growth of plants and seriously affects their physiological and biochemical processes.Therefore,mitigating cadmium toxicity in plants is a research task worth studying.Pigeon pea（Cajanus cajan）is a multipurpose shrub that has a long history of cultivation for its ability to produce nutrients and active ingredients that are beneficial to human health.As far as we know,there is no relevant research report on pigeon pea in response to cadmium stress.This paper will focus on the inhibitory effect of cadmium on the growth,physiological and biochemical processes of pigeon pea,and the mitigation effect of exogenous proline and glutathione on pigeon pea under cadmium stress.The main research results of this paper are as follows:1.Effects of Cadmium Stress on Morphological,Physiological and Biochemical Parameters of Pigeon Pea SeedlingsMorphological,physiological and biochemical parameters of pigeon pea grown in a natural greenhouse were evaluated after exposure to cadmium 75(mg kg^-1).Compared with the control,cadmium stress significantly inhibited the morphological traits of seedlings,such as a27%decrease in total plant height,a 43%decrease in leaf area,a 48%decrease in leaf dry mass,and a 56%decrease in root dry mass.Root uptake of essential nutrients calcium(Ca²⁺),magnesium(Mg²⁺)and potassium（k⁺）were also reduced by 13%,19%and 17%,respectively,while their transformation from roots to leaves was inhibited by 23%,32%,respectively and26%.Photosynthetic gas properties,namely,net photosynthetic rate,stomatal conductance,transpiration rate,and intercellular carbon dioxide concentration were reduced by 33%,53%,72%,and 21%,respectively,compared with control plants.Cadmium stress significantly hindered photosynthetic pigments and their biosynthetic enzymes.Chlorophyll a and chlorophyll b decreased by 57%and 53%,respectively,and their biosynthesis enzymes chlorophyllase,MDCase,delta-aminolevulinic acid（delta-ALA）,porphobilinogen（PBG）and uroporphyrinogen（Urogen III）were suppressed by 163%,142%,102%,87%and 73%,respectively.2.Effects of cadmium stress on the anatomical structure of root meristem and leaves of pigeon pea seedlingsThe results of pigeon pea root meristem treated with cadmium showed that the majority of cells and their vacuoles were reduced,and the number of plastids,Golgi apparatus,mitochondria and endoplasmic reticulum in cells decreased.In addition,chloroplast ultrastructure was altered,resulting in blurred granule/matrix lamellae and ruptured thylakoid membranes.Cadmium stress also affected stomatal openings on the adaxial and adaxial surfaces of leaves.Compared with the control,the number of stomata per unit area of??pigeon pea leaves decreased in the front and back sides after cadmium stress,and the size and structure of glandular hairs were observed to be different.Compared with the control,the glandular hairs sank downward after cadmium stress Bottom tissue and reduced size.3.Effect of cadmium stress on the antioxidant system of pigeon pea seedlingsCompared with the control,cadmium stress produced significant oxidative stress damage on pigeon pea seedlings,with 183%increase in hydrogen peroxide（H₂O₂）,217%increase in malondialdehyde（MDA）content,and increased electrolyte leakage（EL）96%.Cadmium stress also significantly inhibited the activities of antioxidant enzymes.Compared with the control,the superoxide dismutase（SOD）activity decreased by 231%,the peroxidase（POD）activity decreased by 249%,and the catalase（CAT）activity decreased by 275%in pigeon pea seedlings after cadmium stress.%,glutathione peroxidase（GPX）activity decreased by 319%.In addition,cadmium stress reduced total sugar content in pigeon pea seedlings by 67%,non-reducing sugar by 59%,reducing sugar by 46%,and lipid by 43%.In addition,the release rates of plant hormones such as IAA,ABA and ethylene increased by 117%,84%and 139%,respectively,compared with the control.4.Effects of exogenous proline and glutathione supplementation on morphology,physiology and molecular properties of pigeon pea under cadmium stressSupplementation with exogenous proline and glutathione（PGSH）reversed the inhibitory effects of cadmium at the morphological,physiological and molecular levels in pigeon pea.Supplementation of PGSH significantly restored the adverse effects of cadmium on the morphology of pigeon pea,and the total plant height,leaf area,leaf dry mass and root dry mass were restored by 23%,39%,42%and 49%,respectively.The supplementation of exogenous PGSH significantly reduced the cadmium concentration in roots and shoots,while the uptake of Ca²⁺,Mg²⁺and k⁺in roots increased by 11%,16%and 17%,respectively,and their transformation from roots to leaves compared with the control,they increased by 19%,23%and 27%,respectively.In addition,exogenous PGSH supplementation also increased the content of photosynthetic pigments and the activities of their biosynthetic enzymes.Compared with the control,chlorophyll a and chlorophyll b increased by 47%and 39%,respectively,and the activities of their biosynthetic enzymes chlorophyllase,MDCase,δ-ALA,PBG and Urogen III increased by 149%,127%,97%,83%and 69%Exogenous PGSH supplementation significantly reduced 139%H₂O₂,193%MDA content,and 74%EL to normalize cadmium-induced oxidative stress compared with controls.In addition,exogenous PGSH supplementation reversed the inhibitory effects of cadmium stress on antioxidant enzymes,in which SOD activity increased by 187%,POD activity increased by203%,CAT activity increased by 219%and GPX activity increased by 275%.In addition,exogenous PGSH addition restored the ethylene release rate and ABA content to normal standards,except for IAA.The expression levels of cadmium tolerance-related genes,such as Phyto chelatase-like protein,MYB and WRKY transcription factors,and CYP450,were significantly up-regulated in pigeon pea seedlings supplemented with exogenous PGSH,which proved that the relevant molecular activities of cells resisting cadmium toxicity were effectively controlled.activation.The addition of PGSH significantly increased the GSH/GSSG ratio of proline and glutathione biosynthesis and the activity ofγ-glutamylcysteine??synthetase in shoots and roots.The above results indicated that PGSH could effectively reverse the cadmium-induced toxicity in pigeon pea,which provided a new environmentally friendly method for relieving the crop from coping with metal stress in actual production.