The Physiological Characteristics Of Rice Seedling Responding To Inorganic Arsenic Stress

In this paper, rice accession Shanyou-63 was employed as the main material to study the detoxification mechanism and physiological characteristics of rice seedling responding to inorganic arsenic (As2O3-As(III) and HAsNa2O4-As(V)) stress. The experiment was constituted by four parts: First, the toxic effects of different species of inorganic arsenic on germinating of rice seed. Second, the physiological characteristics of rice seedling responding to inorganic arsenic stress. Third, molecular responses of rice seedling to inorganic arsenic stress. Fourth, the mechanism of nutrition regulation to decrease the toxicity of arsenic on rice seedling.1. Analysis of the inorganic arsenic toxic effects on rice germination suggested that the seed germination, coleoptile length, root length, fresh weight, dry weight, and water content of rice seed were all decreased significantly, under inorganic arsenic treatment. In addition, the results also showed that seed germination, coleoptile length, root length in rice were more inhibited under As(III) treatment than those under As(V) treatment.2. The results of physiological characteristics of rice seedling responding to inorganic arsenic indicated that the activity of SOD, POD, and CAT in rice roots and leaves was significantly inhibited as the concentration of arsenic increased, especially in roots. The results of nutrition physiology showed that the uptake and utilization efficiencies of nitrogen, phosphorus and potassium were descended as arsenic concentration increased. The results suggested that arsenic could inhibit the nutrition uptake and utilization of rice seedling. Furthermore, the results also indicated that the effects of two species of inorganic arsenic on the nutrition uptake and utilization in rice seedling were different. It was suggested that the uptake and utilization efficiency of phosphorus and potassium in rice seedling were more affected by As (III), but As (V) mainly affected uptake and utilization efficiency of nitrogen.3. Molecular response of nutrition uptake and utilization in rice seedlings under inorganic arsenic stress showed that the expression of gene related to the uptake and utilization of nitrogen, phosphorus, and potassium were down regulated in roots and leaves of rice seedling under inorganic arsenic treatment. In addition, the results also suggested that the expression of gene related to the uptake and utilization of phosphorus and potassium was more inhibited by As (III) than As (V). But As (V) inhibited the uptake and utilization of nitrogen greater. The results were consistent with the conclusion mentioned above.4. Analysis of the mechanism of nutritional regulation to mitigate arsenic toxicity in rice showed that the inhibited effects of morphology indexes and antioxidase activity in rice seedling after inorganic arsenic treatment were all decreased, when the rice seedlings were planted in the solution with high-nitrogen (2N), high-phosphate (2P). But the inhibited effects of the same indexes were enhanced under inorganic arsenic treatment, when the rice seedlings were planted in the solution with high-potassium (2K), low-nitrogen (0.5N), low-phosphorus (0.5P), and low-potassium (0.5K). Furthermore, analysis of arsenic contents in rice tissue also showed that high-nitrogen (2N), high-phosphate (2P) treatments could decrease the arsenic accumulated in rice. But the reverse was true, when the rice was under high-potassium (2K), low-nitrogen (0.5N), low-phosphorus (0.5P), and low-potassium (0.5K) treated.In summary, inorganic arsenic stress has significantly inhibited the growth of rice and the effect of As (III) on rice seedlings was greater than that of As (V). As (III) mainly affects the uptake and utilization of phosphorus and potassium in rice seedling, and As (V) mainly affects that of the nitrogen. In addition, enhance nitrogen and phosphorus contents in culture solution, can reduce arsenic toxic effect on rice.