| Cadmium (Cd) is one of the most toxic heavy metals in the environment. Cd stress dexterous affects crop yield and quality, and even give a threat on human health via food chain. Although Se is not necessary for plants, it has been found to effectively improve the resistance to various abiotic stresses. Thus, the present study was carried out via hydroponic and pot experiments to explore the effect of external Se on growth parameters, Cd uptake and allocation, photosynthetic performance, nutrition metabolism, reactive oxygen metabolism and tobacco quality in the two constracting genotypes in Cd tolerance under Cd stress. The main results are as follows:1. Pot experiments were conducted to investigate the genotypic difference in effect of external Se on tobacco quality under Cd stress between Guiyanl (Cd sensitive genotype) and Yunyan2(Cd tolerant genotype). There were4treatments:Control, Se (2.5mg kg-1Se), Cd (3mg kg-1Cd), and Cd+Se (2.5mg kg-1Se+3mg kg-1Cd). The results showed that the content of the nicotine, total nitrogen and total protein of Cd treatment were decreased by25.4%,40.2%and29.3%in Guiyanl and23.6%,33.7%and26.4%in Yunyan2, respectively, compared with control. The ratio of sugar/nicotine and nitrogen/nicotine were abnormal under Cd alone treatment, which were important index for evaluating the qualities of tobacco leaves. However, compared with Cd alone treatment, Se addition significantly increased the contents of nicotine, total nitrogen and total protein, being decreased by19.6%,44.8%and38.8%in Guiyanl, and18.5%,31.2%and27.2%in Yunyan2, respectively. These results indicated that external Se could obviously alleviate Cd induced reduction in the tobacco quality.2. Hydroponic experiments were conducted to study the effect of exogenous Se on the two tobacco genotypes Guiyanl and Yunyan2under Cd stress. There were4treatments:Control (BNS), Cd (BNS+50μM Cd), Se (BNS+3μM Se) and Cd+Se (BNS+50μM Cd+3μM Se). The results showed that plants under Cd stress showed leaf chlorosis, brown roots, and growth inhibition. Shoot height, root length, and biomass were apparently reduced. Photosynthesis, reflected by chlorophyll content, net photosynthetic rate (Pn) and the maximum efficiency of photosystem II photochemistry (Fv/Fm), was also inhibated significantly. However, external Se significantly alleviated the Cd-induced inhibition in plant growth, especially in Cd-sensitive genotype. Plant dry weights increased by54.3%/28.6%and12.5%/15.9%in shoots/roots of Guiyanl and Yunyan2, respectively. The chlorophyll content, Pn and Fv/Fm ratio of plants under Cd+Se increased by187.3%,43.7%,9.8%in Guiyanl and by163.4%,38.5%,7.9%in Yunyan2, respectively, compared with the Cd-alone treatments.3. The effect of exogenous Se on transport and accumulation of Cd and other mineral elements under Cd stress and genotypic difference was investigated. The result indicated that Cd-tolerant Yunyan2accumulated more Cd than Cd-sensitive Guiyanl. Exogenous Se markedly suppressed Cd concentration compared with the Cd-alone treatment, with reductions of25.7%/37.2%and25.8%/22.1%in shoots/roots of Guiyanl and Yunyan2, respectively. The Cd-induced negative effect on Zn, Mn, Ca, Cu, Fe, Mg concentration was significantly recovered under Cd+Se treatment.4. The effect of external Se on scavenging system of reactive oxygen species exposed to Cd treatment and genotypic difference was studied. The results showed that exogenous Se dramatically depressed Cd-induced malondialdehyde (MDA), O2-and H2O2accumulation especially in the sensitive genotype, and higher activities of SOD, POD, CAT, APX, GR, and GPX were detected in Cd+Se treatment simultaneously, compared with the Cd-alone treatment. The results of ATPase activities showed that HT-K+-ATPase, Na+-K+-ATPase, and Ca2+-Mg2+-ATPase in shoots and roots of both genotypes were dramatically decreased under the Cd-alone treatment. However, exogenous Se markedly increased the activities of the3types of ATPase in shoots and roots of both genotypes, compared with the Cd-alone treatment. |
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