The Regulatory Mechanism For The Effect Of Zinc On Cadmium Uptake And Accumulation By Pakchoi

Cadmium(Cd) is a toxic element, while zinc(Zn) is an essential element. However, in spite of the similar physical and chemical properties of Zn and Cd, the view that Zn alleviates Cd toxicity in plants remains controversial. Here, we used two different genotype varieties of pakchoi(cultivars HG and HXW) to study the effect of different Zn levels on Cd uptake, transport, subcellular distribution and tolerance to Cd, and revealed the regulatory mechanism of Zn on Cd uptake and accumulation and further provide a theoretical basis for remediating mildly polluted soil. The main results were as follows.1.The effects of Zn on growth of two pakchoi cultivars exposed to Cd were investigated by hydroponic and field culture experiments. The results showed that in the absence of Cd, relative chlorophyll contents and photosynthetic rates were reduced gradually as Zn concentration increased; while in the presence of Cd, higher Zn levels relieved leaf chlorosis caused by Cd, and the relative chlorophyll content and photosynthetic rate increased with an increase in Zn level. In mildly polluted soil, the biomass of two pakchoi cultivars showed no significant change with the increased Zn supply.2.The effects of Zn on Cd uptake, accumulation and distribution in two pakchoi cultivars were investigated by hydroponic and field culture experiments. The results showed that with an increase in Zn concentration in nutrient solution, the Cd content of shoots and roots were reduced, and the reductions were more significant in roots; The Cd accumulation in shoots showed no significant changes with Zn levels, but significantly decreased in roots. The results of non-invasive micro-test technology revealed that net Cd2+ influx into roots were significantly suppressed by Zn2+ and extent of suppression was increased when Zn2+ concentration increased. A field experiment further verified that Zn decreased Cd contents both in shoots and roots of two pakchoi cultivars.3.The effects of Zn on subcellular Cd contents and distribution in two pakchoi cultivars were investigated by hydroponic culture experiment. The results showed that Cd contents in subcellular fractions of leaves and roots in two pakchoi cultivars were decreased with an increase in Zn levels, and the decreases were more significant in roots. In leaves, the proportions of Cd in the soluble fraction of two pakchoi cultivars were increased with an increase in Zn concentration, and this tendency was reversed in the cell wall fraction. However in roots, the Cd distribution in subcellular fractions of cultivar HG showed no significantly changes with an increase in Zn, but decreased the proportion in the soluble fraction and increased the proportion in the cell wall fraction of cultivar HXW.4.The effects of Zn on antioxidant enzyme activities of the two pakchoi cultivars were investigated by hydroponic culture experiment. The results showed that when plants were exposed to Cd, Zn maintained stable SOD, CAT, APX activities in leaves and roots of the HG cultivar; while for the HXW cultivar, the three antioxidant enzyme activities were decreased in leaves but improved in roots with an increase in Zn.