Impacts Of Osmotic Regulation Responses To Salinity Stress On Soil Cd Uptake By Edible Amaranth Cultivars

The deteriorating of soil environmental quality is most principal factor, affecting the sustainable development of agriculture, especially soil salinization and heavy metal pollution which have caused conspicuous damage to soil structure and the safety of agricultural products. The mechanisms of effect metal accumulation about salinity should be discussed, provide theory basis for screening and breeding of salinity tolerant cultivars with low metal accumulation.A pot-grown plant experiment was conducted in sewage-irrigated garden soil(mean 2.28 mg kg-1Cd) pretreated with different salinity concentrations(0, 0.2%, and 0.4% Na Cl). The experimental plants had been screened by our research group, they were Quanhong(low-Cd accumulation cultivar) and Liuye(high-Cd accumulation cultivar).After about 70 d, mature plants were harvested and used for determination of Cd content of plants tissues and rhizosphere solution, main osmotic adjustment substances, chlorophyll content, MDA and pectin content. The study was aimed to investigate differences of the osmotic-response about high/low-Cd accumulation edible amaranth cultivars under salinity stress, QH and LY, and the effect of which to Cd accumulation. And result showed that:(1) Under salinity stress, the Cd content in roots and leaves of two cultivars significantly increased compared with the control(p<0.05), and Cd content in QH was obviously lower than in LY. QH roots had stronger Na+ and Cl- retention ability than LY, decreasing the transportation of them from roots to leaves. In 0.4%Na Cl treatment, the K+/Na+ ration decreased by 31.94% in leaves of QH, and by 70.34% in leaves of LY. The Mg2+/Na+ and Ca2+/Na+ ration have similar regularities. The continually increasing inorganic ions could induce disorder of the plant metabolism, and increase the possibility that soil Cd entered into cells.(2) More proline accumulated in roots and leafs of both cultivars compared to the control(P<0.05) and QH exhibited stronger proline synthesization ability than LY. Under salinity stress, the contents of free amino acids and soluble protein in cultivar QH significantly increased in comparison with the control(P<0.05), and the contents of free amino acids decreased in LY. The cultivar QH tended to produce more harmless organic matter in response to salinity stress. Many organic matter could form Cd- chelate conjugate in the cell, thus decreasing the Cd accumulation of leaf. The process might be an important aspect resulting in low Cd-accumulating cultivar.(3) Under salinity stress, the pectin content, chlorophyll content and chlorophyll a/b decreased in comparison with the control, but MDA content and membranc permeability increased in two cultivars. The pectins could bind to the Cd by negatively charged groups, thus intercepting more Cd in cell wall, moreover, the destruction of membrane structure and function raised transmembrane probability of Cd. In addition, the osmotic potential(Ψ) of the roots and leaves of both cultivars decreased with an increasing salt concentration, and the relative contribution of inorganic ions to ΨT in LY was more than in QH. This would increase the risk of plant’s ions and Cd ingestion, thus leading to a variety of poisoning symptoms.