Effects Of Root Anatomy On Hg Absorption Of Rice

Mercury is an important pollutant because its organic compounds have strong neurotoxicity and high enrichment in organisms through food chain, exerting serious threat to human health. Since1950s, with the incident of methylmercury poisoning in Minamata Bay of Japan mercury transformation and accumulation in ecosystem has drawn a lot of attention. Mercury can enter human bodies by skin contact, water and food consumption. Grown with Hg contaminated water and soil is one of the most important way for Hg accumulation in crops, such as rice. Rice quality and safety is an important social issue as rice is the staple food for Chinese people. Unfortunately, mercury pollution of paddy soil is an increasing problem, causing high risks for food safety and human health. It's of great significance to understand the mechanisms for Hg accumulation in crops, so that measures can be taken to reduce Hg level in edible tissues. Being the major absorption organs for contaminants as well as nutrients, the root system, especially its anatomy has great effect on mercury accumulation and translocation. Root anatomy has been found to be varied with species, genotypes and rhizosphere conditions. The present study was conducted in hydroponics to investigate root anatomy and its effect on Hg uptake in different genotypes and induced rhizosphere conditons. The results are as followings.1. Five genotypes, i.e. You-728, Xieyou-728, You-92, Wuyun-23, Xiushui123, of rice have been studied. Root anatomy differed greatly among genotypes. Japonica rice developed more adventitious roots and higher root porosity than the indica ones. The two indica genotypes of Ⅰ-1and Ⅰ-2showed generally longer roots than the japonicas.2. The results indicated that mercury absorption and translocation differed greatly between genotype. Among them, two japonica genotypes (Wuyun23and Xiushui123) showed a little bit less Hg accumulation in low concentrations, but significantly higher absorption and translocation in high levels than the other three indica rice.3. Xieyou-728is selected as the research object to study the effects of environmental factors on root anatomy and Hg accumulation. Root anatomy was induced by environmental factors and therefore changed the Hg absorption in Xieyou-728seedlings. Excessive phosphate induced more adventitious roots and root length, but had little effect on diameter. On the contrary, phosphate starvation increased root diameter greatly but had little effect on other parameters. Rhizosphere oxygenation significantly increased the root elongation and root porosity but inhibit the development of adventitious roots and root diameter. All the treatments did not affect root surface area.4. Rhizosphere treatments had great effect on Hg uptake and translocation. Comparing with P starvation, excessive P treatment increased both Hg accumulation and translocation in rice seedlings. Due to the high porosity and inhibition of adventitious root development, seedlings treated by oxygenation showed lower ability in Hg uptake than those treated by deoxygenation.