| During the process of phytoremediation, auxin can increase heavy metal uptake by plants, but the related mechanism is unclear. Organic acids are widely distributed in plants, and play an important role in the detoxification and tolerance to metal stress. Many studies have confirmed that oxalic acid, citric acid and phytic acid etc play an important role in heavy metal accumulation by plants. However, little information is available for pentanoic acids. Our previous work showed that compared to non-hyperaccumulator, a significant exudation of pentanoic acids was observed by arsenic hyperaccumulator when auxin was added. In order to study the effect of 3-indoleacetic acid (IAA) on the exudation of pentanoic acids by the roots of plants with different arsenic-accumulation ability, firstly, the As hyperaccumulator(Pteris cretica var. nervosa) and non-hyperaccumulator(Pteris ensiformis) were treated by different concentrations of IAA (0-60mg·L-1) under the stress of 2 mg·L-1 As(V). Secondarily, we determined the root physiology, plant biomass, arsenic uptake, root activity, activity of cytoplasm membrane ATPase, pentanoic acid contents in plants and root exudates. Lastly, we studied the effect of exogenously-applied pentanoic acid (0-2mg·L-1) on arsenic uptake, chlorophyll content, activities of antioxidant enzymes, contents of malondialdehyde (MDA), soluble sugar and proline in plants with different arsenic-accumulation ability. The results showed as follows.1. The results showed that the biomass of two plants significantly, increased in the presence of 20mg·L-1 IAA compared to the control. At the 20mg·L-1 IAA treatment, As concentrations in fronds and petioles, the root activity and root ATPase activity in cytoplasmic membrane of P. cretica var. nervosa increased significantly, and these indices in P. cretica var. nervosa were significantly higher than those in P. ensiformis. At 20-60mg·L-1 IAA treatments, the activities of three antioxidative enzymes (CAT, SOD and POD) in roots of P. cretica var. nervosa increased significantly, but the CAT activities decreased and SOD activities increased significantly in roots of P. ensiformis. Moreover, POD activities in roots of P. ensiformis showed no significantly change. The contents of MDA in roots of two plants were significantly decreased by 20-40mg·L-1 IAA treatment. However, the MDA contents in roots of P. cretica var. nervosa were significantly lower than those of P. ensiformis. Result from correlation analysis showed that As concentrations in roots of P. cretica var. nervosa were positively related to its root activity, but no correlation was found in P. ensiformis between root As concentrations and the indices determined. Therefore, the As hyperaccumulation of P. cretica var. nervosa was attributed to its high root activity.2. In the low concentration of IAA treatment, no significant difference was observed in the height of P. cretica var. nervosa compared to the control. However, the height of P. cretica var. nervosa was significantly decreased by high concentration of IAA. In the 20mg·L-1 IAA treatment, the height of P. ensiformis increased significantly and reached the maximum. In the 20mg·L-1 IAA treatment, the content of pentanoic acid in shoot of P. cretica var. nervosa reached the maximum, but significantly decreased in P. ensiformis with the increase of IAA concentration compared to the control. The content of pentanoic acid in roots of two plants decreased significantly with increasing concentration of IAA. The root exudation of pentanoic acid by P. cretica var. nervosa was significantly increased with IAA addition, but significantly decreased in P. ensiformis. The content of pentanoic acid exudation in P. cretica var. nervosa increased significantly with IAA addition compared to the control, especially in the 60mg·L-IAA treatment. A significant positive correlation was found between pentanoic acid exudation by roots and arsenic contents, indicating that arsenic hyperaccumulator have a higher ability to activate arsenic than non-hyperaccumulator.3. The fresh weight of two plants increased significantly under 0.5 mg·L-1 pentanoic acid treatment, and the total arsenic concentration in P. cretica var. nervosa was also increased significantly. Accordingly, the arsenic concentration in culture medium significantly decreased compared to the control. In addition, the total arsenic concentration in P. ensiformis and arsenic concentration in culture medium showed no significant difference compared to the control in different concentrations of pentanoic acid treatment4. The activities of antioxidant enzymes in fronds of P. cretica var. nervosa increased significantly with pentanoic acid addition, but a significant decrease or insignificant change was found in P. ensiformis. The MDA content in P. cretica var. nervosa was much lower than P. ensiformis under pentanoic acid treatment Under pentanoic acid treatment, the chlorophyll content in P. cretica var. nervosa was significantly lower than that in P. ensiformis. The contents of proline and soluble sugar of two plants were significantly increased by 0.5 mg·L-1 pentanoic acid. Therefore, a suitable concentration of pentanoic acid played an important role of plant arsenic detoxification and tolerance. Furthermore, it can promote plant arsenic uptake and maintain biomass. |
PDF Full Text Request