The Resistance Mechanism Of Lolium Perenne To Heavy Metal Cd²⁺ Stress

In the present work, the accumulation characteristics of Cadmium (Cd) and the toxiceffect of Cd²⁺on the growth and physiological characteristics of perennial ryegrass(Loliumperenne) was studied. Moreover, the role of GSH and PCs in the Cd²⁺detoxification ofperennial ryegrass was proved, and the resistance of perennial ryegrass to Cd²⁺was increasedthrough exogenous GSH regulation. The results were summarized as follows.1.Treated with5,10,20mg/L Cd²⁺for18days, the Cd concentration reached4.65,4.71,6.21mg/gDW in root of perennial ryegrass, and0.34,0.43,0.62mg/gDW in shoot. Thetransport index of Cd reached0.07,0.09,0.10respectively, the bioconcentration index of shootreached67.68,43.15,31.22, and the distribution proportion of shoot reached27.05%,32.24%,42.52%, the total Cd accumulation in shoot reached0.20,0.24,0.31mg/10plants. With the treatment concentration rising, the Cd transport index, shootdistribution proportion and total Cd accumulation in shoot are significantly increased, thecontinuous enrichment capacity to Cd is showed in perennial ryegrass. Though the Cdconcentration of shoot of perennial ryegrass exceeds the Cd hyperaccumulator standard, thetransport index is less than1, therefor, it is a high enrichment plant rather than Cdhyperaccumulator.2.Treated with0(CK),5,10,20mg/L Cd²⁺for18days, the absolute growth rate of5,10,20mg/L Cd²⁺treatment significantly decreased by33.94%,45.23%,53.89%compared with CKrespectively. The absolute water content, shoot biomass, root biomass and ration of root toshoot were also significantly decreased. The root growth parameter was significantly inhibitedby Cd²⁺.Under Cd²⁺treatment, the concentration of K and Mg in shoot was significantlydecreased compared with CK.3.Treated with5mg/L Cd²⁺for6ds, the results showed that photosynthetic pigmentscontents of perennial ryegrass did not change significantly, whereas the gas exchange parameters and the chlorophyll fluorescence parameters were affected significantly. When3and6d after treatment, Pn significantly decased by24.4%and23.4%compared with0d, thedecreasing was caused by non-stomatal limitation factors.ΦPSII, rETR and qP significantlydecreasd when6d after treatment compared with0d, the PSII light reaction ability reduced.The qN and Y(NPQ) incerased significantly when6d after treatment, the increasing of heatdissipation energy strengthened the photo protective role.4. Treated with5mg/L Cd²⁺for6ds, the reduced glutathione (GSH) concentration in leafincreased significantly, whereas increased significantly firstly and then decreased in root, theacceleration of phytochelatins(PCs) synthesis lead to excessive consumption of GSH. With thetreatment time increasing, the concentration of PCs in leaf and root gradually elevating, andconcentration in root was much larger than leaf. The thiol proportion of PC3in total thiol wasmaximum in root, when6d after treatment, the proportion reached83.35%, whereas the thiolproportion of GSH was maximum in leaf, reached46.08%when6d after treatment. With thetreatment time increasing, the T-SH concentration in root and leaf of perennial ryegrassincreased significantly, the relationship between T-SH concentration and Cd concentration wasvery significantly positive correlation.5.The perennial ryegrass were treated in the solution consisted of0.1,0.5,1mMGSH and5mg/L Cd²⁺. The results showed that the regulation of exogenous GSH could improve theresistance of perennial ryegrass to Cd²⁺stress. Exogenous GSH promotes the growth ofperennial ryegrass under Cd²⁺stress. When24ds after treatment, compared with Cd²⁺treatment,the shoot biomass, root biomass and ratio of root to shoot increased significantly under thetreatment of Cd²⁺+0.5mMG and Cd²⁺+1mMG. Exogenous GSH reduces the oxidative stress ofroot caused by Cd²⁺, when12ds after treatment, the MDA content of root under Cd²⁺+0.5mMGand Cd²⁺+1mMG treatment was significant lower than Cd²⁺treatment. Exogenous GSHreduces the inhibition effect of Cd²⁺on Ca2+absorption, improves the photosynthetic capacityof perennial ryegrass under Cd²⁺treatment.6.In order to verify the detoxification role of GSH and PCs, perennial ryegrass weretreated in the solution consisted of5mg/LCd²⁺and0.25mM BSO. The results showed that the content of chlorophyllb and carotenoid decreased significantly compared with Cd²⁺treatment,the photosynthetic pigment is protected by PCs. The MDA content of leaf and root weresignificant higher than Cd²⁺treatment. The activity of activity of SOD, POD, CAT, APX,MDHAR, GR,GPX in leaf and POD, CAT activity in root were lower than Cd²⁺treatment. TheASA content of leaf and root were lower than Cd²⁺treatment, the DHA content were oppositeto ASA. GSH and PCs have a protective effect on antioxidant system in perennial ryegrass,thereby reducing the oxidative stress caused by Cd²⁺. When24ds after treatment, the gasexchange parameters of Pn, Gs, Tr and Mg concentration of shoot including K concentration ofroot decreased significantly compared with Cd²⁺treatment. When6,12,24ds after treatment,the root biomass decreased by3.65%,3.77%,17.86%compared with Cd²⁺treatment, and theratio of root to shoot decreased by5.00%,5.56%,22.22%respectively. GSH and PCs have aprotective effect on growth of perennial ryegrass under Cd²⁺stress. Under the treatment ofCd²⁺and BSO, the Cd concentration of root and shoot were both lower than Cd²⁺treatment,and the transport index was higher than Cd²⁺treatment, GSH and PCs involve in the absorptionand transport of Cd²⁺in perennial ryegrass.In summary, the accumulation ability of Cd of perennial ryegrass is evaluated, thetoxic effect of Cd²⁺on perennial ryegrass is clarified, the improving Cd²⁺-resistancemethod by exogenous GSH is established, and the role of GSH metabolism inresistance mechanism of perennial ryegrass to Cd²⁺is revealed.