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Effects of Arsenic Stress on Activities of Antioxidant Enzymes and Photosynthesis Process in Plants with Different Abilities to Accumulate Arsenic

Author: XieFei
Tutor: WangHongZuo
School: Kunming University of Science and Technology
Course: Ecology
Keywords: Arsenic Antioxidative enzymes Photosynthesis Light reaction Dark reaction Enhanced phytoextraction
CLC: X173
Type: Master's thesis
Year: 2009
Downloads: 67
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Abstract

Arsenic(As) is a non-essential element for plant growth, with toxic, carcinogenic and mutagenic properties. Arsenic pollution problem has received close attention from the public. With the discovery of some As hyperaccumulators, such as Pteris vittata, Pityrogramma calomelanos, Pteris cretica var. nervosa, Pteris fauriei and so on, the biocontrol of As-contaminated soil and water has been highlighted. At the same time, some non-hyperaccumulators such as Pteris semipinnata and Pteris ensiformis have also been explored. However, many researches were conducted with Pteris vittata, a famous As hyperaccumulator, and the absorption, transloation, accumulation and detoxification of As in this plant has been well documented. Because arsenic accumulation and photosynthesis are conducted in plant leaves, plant should keep the normal metabolic mechanism and deal with the relationship between arsenic accumulation and photosynthesis. To our knowledge, little information was available on the photosynthesis process of plants with different abilities to accumlate As under As stress.In present research, firstly, the effects of As stress (0,5,25,50 mg As L-1) on activities of catalase (CAT), peroxidase (POD), superoxide dismulasc (SOD) and ascorbate peroxidase (APX) as well as malondialdehyde (MDA) content and production rate of free radical O2-·in the fronds of As hyperaccumulator (P. cretica var. nervosa) and non-hyperaccumulator (P. ensiformis) were evaluated by hydroponic experiments. In addition, the variations of these six indexes along with time under 25 mg As L-1 stress were also studied. Secondly, the maximum quantum yield(Fv/Fm), effective quantum yield (Yield), ATPase, Rubisco and Glyceraldehyde-3-phosphate dehydrogenase GAPDH activity and As concentration in plant leaves were also evaluated by hydroponic and pot experiments. Furthermore, the variations of these six indexes along with time under 100 mg As kg-1 and 20 mg As L-1 stress were also studied, respectively. Thirdly, the effects of enhanced-phytoextraction of As such as phosphate addition, CDTA addition and pH adjustment on those indexes mentioned above were studied before plant harvest.The results indicate as follows:1. For P. ensiformis, the activities of CAT, POD and SOD were maintained, and POD activity was enhanced under the stress of As. MDA contents in the fronds of P. cretica var. nervosa were depressed by As, but P. ensiformis showed the opposite trend. The production rate of free radical O2-·in the fronds of P. ensiformis increased more significantly compared with P. cretica var. nervosa in the presence of As. For P. cretica var. nervosa, CAT and APX activities decreased followed by an increase with extended time, POD activity increased significantly, but no significant change in SOD activity was observed with time. In the case of P. ensiformis, the activities of POD and SOD decreased significantly, CAT activity decreased and then increased, while APX activity did not show any significant change along with time. MDA contents in both plants decreased significantly starting from the sixth day. O2-·production rate in the fronds of P. cretica var. nervosa increased significantly in the sixth day, then decreased to the initial level with extended time. These findings indicate that the antioxidative ability of P. cretica var. nervosa is superior to that of P. ensiformis under As stress, and POD plays an important role in the antioxidative system.2. With increasing As concentration, the non-hyperaccumulators failed to regulate the Fv/Fm and Yield by themselves, but As hyperaccumulators could keep the Fv/Fm very well. Under low concentration of As stress, ATPase and Rubisco activity of the hyperaccumulators increased significantly, but opposite trend was shown under high As concentration treatment. However, there was no significant change of ATPase and Rubisco activity in non-hyperaccumulators. Under As stress condition, GAPDH activity of hyperaccumulators did not change, but significant decrease was observed in non-hyperaccumulator. Therefore, decreased ATPase and Rubisco activity of hyperaccumulators may lead to their low biomass, but high activity of GAPDH produce As resistance.3. There was no significant change of Fv/Fm, Yield and Rubisco activity in As hyperaccumulators and non-hyperaccumulators after using enhanced-phytoextration methods for As methods except for high P concentration. Under high P concentration treatment, the Fv/Fm increased significantly in non-hyperaccumulators. ATPase activity in the fronds of P. cretica var. nervosa and P. semipinnata increased significantly under basic conditions. GAPDH activity in the fronds of hyperaccumulators increased significantly under high CDTA concentration and basic conditions, but there was no significant change in non-hyperaccumulators.4. With increasing As concentration, As concentration in the fronds of hyperaccumulators increased significantly. For non-hyperaccumulators, only P. ensiformis increased As concentration but did not reach the standard for As hyperaccumulator. There was no significant change of As concentrations in P. cretica var. nervosa under CDTA and phosphate addition treatments, but significant increase of As was observed in P. semipinnata exposed to low or middle CDTA (0.5-1 g·kg-1) and phosphate(50-600 mg·kg-1) concentrations, respectively.

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