Regulation Of ACC On H₂O₂-induced Horizontal Bending Of Pea Primary Roots

Ethylene is a gaseous hormone, which plays a significant role in the whole growth cycle of plants. Under the treatment of ethylene, the dicotyledonous seedlings showed three distinct phenomena, which were described as that the hypocotyls became shorter and thicker, the horizontal elongation of root was inhibited, the bending degree of the top increased, which were called the typical triple response of ethylene. Exogenous H₂O₂ could inhibit the geotropism of the primary root of pea and induce the horizontal bending. ACC（1-amino-1-carboxylic acid, ACC）, the precursor of ethylene could increase the content of endogenous ethylene. In this study, the pea seeds ―Longwan No.1‖ were used as material, with a variety of physiological and biochemical methods, such as High Phase Liquid Chromatography（HPLC）, the alleviation effect of ACC on H₂O₂-induced horizontal bending of pea primary roots and the regulation of ACC on auxin, gibberellin, starch content and activities of α-amylase and indoleacetic acid oxidase in primary root, so as to explore the mechanism of the primary root bending and the interaction between ethylene and auxin in the primary root. Test results were as follows:1. Effects of exogenous H₂O₂ on the contents of auxin in different parts of the pea primary rootThe pea seeds were treated with different concentrations of H₂O₂, and the auxin contents in each part were determined. The results showed that the content of IAA decreased with the increase of H₂O₂ concentration in the root tip and elongation zone, while the IAA content in shoots increased with the increase of H₂O₂ concentration.2. Effect of ACC on the content of hormones in the curved rootThe pea seeds were treated with different concentrations of ACC and the endogenous hormone contents in bending root were determined with the method of high performance liquid chromatography（HLPC）. Results show that both of the auxin（IAA） and gibberellin（GA3） contents in primary roots were increased, indicating that exogenous ACC could not only improve the content of endogenous ethylene in the primary roots, but also increase the content of hormone related.3. Alleviating effect of ACC on the horizontal bending of pea primary root induced by H₂O₂Under the stress of H₂O₂, the bending degree of pea primary roots was observed after the addition of exogenous ACC. The results showed that the horizontal bending degree and the curved rate of the pea primary root were all decreased, and the alleviating effect enhanced with the increase of ACC concentration. The triple response of ethylene was significant. Therefore, ethylene could alleviate the horizontal bending of pea primary roots in general.4. Effects of ACC on the auxin contents in different parts of the pea primary root induced by H₂O₂After adding ACC, the auxin contents in root tip and elongation zone of pea primary root were determined. Results showed that the IAA content in root tip increased, while the content of IAA in elongation zone decreased with the increase of the exogenous ethylene concentration.5. The inhibitory effect of ACC on the hydrolysis of starch in pea primary root induced by H₂O₂After adding ACC, the starch content, α-amylase activity, soluble sugar content and GA3 content in H₂O₂-induced pea primary root were determined. Results showed that the GA3 content decreased, the α-amylase activity decreased, which led to the increase of starch content and the decrease of soluble sugar content. The mechanism may be that the decrease of GA3 content weakened the promoting effect on α-amylase activity, which could inhibit the degradation of starch in pea root. According to the starch-statolith hypothesis, the increase of starch in the root cap played a role in balancing rocks and led to the recovery of response to gravity for primary root.6. Effects of ACC on the activity of IAAO under the H₂O₂ stressUnder the stress of exogenous ACC and H₂O₂, the activity of IAAO decreased in the root tip but increased in the elongation zone with the increase of ACC concentration, and the activity in the root tip was far stronger than that of elongation zone, showing that ethylene may regulate the horizontal bending of the primary root by inhibiting the degradation of auxin.