Studies On Effects Of Cadmium On Seedling Growth And Some Physiological Traits Of Various Crops

Cadmium is a toxic heavy metal, and its pollution is one of the most harmful farmland contaminations as well. Soil Cd contamination not only inhibits the growth and development of crops, leading to reduced yield and quality, but also poses a great threat to human health via food chain due to the uptake and accmulation by crops. Rice is one of the most important cereals in China and worldwide, and it is well documented that there is a great difference among genotypes in Cd uptake, accumulation and tolerance. However, the differences among indica rice, japonica rice and waxy rice in Cd accumulation, distribution and tolerance have rarely been studied so far. Tomato is a favorable summer fruit and vegetable. In western countries, tomato and its product ranks the second in the consumed vegetables. Tomato, originated in tropic and subtropics, is sensitive to low temperature, and a great deal of researches have been done about the effect of low temperature on its physiological and biochemical characteristics up to now, whereas studies about the influence of Cd stress on tomato seedling growth and physiological characteristics remain poorly understood. Seed germination and seedling growth are the beginning of lifecycle as well as the first growth stage of perceiving external environment. A sand culture and a hydroponic experiment were carried out to study the effect of various Cd levels on seedling growth and some physiological characteristics of rice and tomato, focusing on Cd toxicity and its physiological mechanism of rice and tomato under various Cd treatments. The main results are as follows:1. Genotypic variation in seed germination, seedling growth and physiological characteristics of rice under Cd stressA sand culture was employed in the experiment to investigate the genotypic variation in the effect of Cd on seed germination, seedling growth and physiological characteristics of rice. The result showed that the germination was slightly stimulated under low Cd concentration (0.01-0.1 mM Cd), while severely inhibited under higher Cd concentrations (2.0 mM). Rice seedlings exposed to 0.01mM Cd showed slight increases in plant height, root volume, biomass and chlorophyll content. These parameters were significantly reduced when Cd level in the medium was increased to 0.5 mM, and meanwhile corresponding increases in superoxide Dismutase (SOD) and peroxidase (POD) activities, and malondialdehyde (MDA) content were observed, indicating enhancement of lipid peroxidation when the plants were exposed to Cd stress. Cadmium addition lowered chlorophyll content, and the concentrations of such microelements, as Fe, Cu and Mn in roots and shoots, while increased proline contents. There was a significant genotypic difference in the response of these parameters to Cd stress, with the highest resistance for Xiushui 110,...