The Regulation Of Jasmonic Acid And Gibberellin In Response To Cadmium Toxicity In Rice Seedlings

As one of the most important food crops in C hina, rice plays a key role in both people’s daily life and the national economy as a whole. The pollution of heavy metal Cd will not only affect the growth and quality of rice, but also transfer through food chain, thus risking the human health. Therefore, it’s of great significance to investigate the mechanism whereby Cd toxicity affects on the growth and development of rice. With the Oryza sativa rice 9311 as the experiment material, which is widely grown in C hina, we investigated the effects of Cd toxicity on the rice seedling growth and the regulation of Jasmonic acid and Gibberellin in response to Cd toxicity in rice seedlings. The main results are as follows:1.Cd toxicity inhibits the growth of rice seedlings. In the experiment, rice seedlings were treated with different level of Cd(0、0.625、1.25、2.5、5、10 μM Cd Cl2) for 4 days, with the results as follows: low level of Cd(0.625 μM) inhibits the elongation growth of seminar roots in rice seedlings at significant level(P<0.05), while the inhibition of shoot elongation growth is not at significant level(P<0.05); with the increase in Cd treatment concentration, the inhibitory effect on the elongation growth of seminar roots and shoots becomes more and more obvious; Cd toxicity can greatly reduce the fresh weight of the roots and shoots of rice seedlings, and this effect is even more obvious with the increase in Cd treatment concentration; Cd toxicity has greater inhibitory effects on root growth than on shoots in rice seedlings, thus leading to root/shoot ratio reduced in rice seedlings with Cd toxicity.2. The increase of Jasmonic acid content induced by Cd toxicity reduces the root activity, enhances the Cd absorption by the roots and inhibits the root growth of rice seedlings. In the experiment, the rice seedlings were treated with 10μM Cd Cl2, with the results shown as follows: the Cd toxicity induced the expression of Jasmonic acid biosynthesis related genes, therefore promoting the increase of Jasmonic acid content in the rice seedling roots; the Cd toxicity enhanced the expression of phospholipid hydrolase related genes(Phospholipases D genes) in the cell membrane, thereby damaging the cell membrane structure of the roots, increasing the permeability of the cell membrane and reducing the root activity; the Cd toxicity enhanced the expression of Cd absorption related genes, thus increasing the Cd absorption by the roots of rice seedlings; the Cd toxicity inhibited the expression of cell division and cell elongation related genes, thus inhibiting the growth of rice seedling roots. After the addition of 7.5μM IBU, the biosynthesis of Jasmonic acid in the roots of rice seedlings with Cd toxicity was inhibited, with the content of Jasmonic acid decreased in the roots; the enhancement of the expression of Phospholipases D genes by Cd toxicity was alleviated, with the root activity increased; the enhancement of the expression of Cd absorption related genes by Cd toxicity was alleviated, with the Cd absorption by the roots reduced; the inhibition of the expression of cell division and cell elongation related genes in the roots of rice seedlings as well as the inhibition of root growth was alleviated. It’s shown from the results above that, the decrease of root activity, increase of Cd absorption by the roots and the inhibition of the root growth of rice seedlings affected by Cd toxicity are associated with the increase of Jasmonic acid level in the rice seedling roots, which is induced by Cd toxicity. This will further reduce the root activity, increase the Cd absorption by the roots and inhibit the root growth of rice seedlings.3.The increase of Jasmonic acid content induced by Cd toxicity inhibits the shoot growth of rice seedling. Cd toxicity can greatly promote the expression of Gibberellin catabolic genes(Os GA2ox1、Os GA2ox6、Os GA2ox8、Os GA2ox9) in the second leaf of rice. Cd toxicity may enhance the transformation of active Gibberellin into inactive Gibberellin, therefore inhibiting the growth of the second leaf in rice seedlings. In the experiment, 10 μM GA3 sprayed exogenously can greatly alleviate the inhibition of the shoot growth of rice seedlings suffering from Cd toxicity, including the inhibition of first leaf, the second leaf and the shoot. GA3 sprayed exogenously can stimulate the shoot growth of rice seedlings and reduce the Cd level per unit mass of the shoots, therefore allevating the inhibition of the shoot growth of rice seedlings suffering from Cd toxicity.