Effet Of Ethylene On The Morphology And Hysiological Characteristic Of Soybean Eedlings Under Phosphate Deficiency

Phosphorus is well known as an essential nutrient important in many processes.Due to the low utilization of phosphorus, phosphate deficiency is a common stresscondition experienced in many different environments. Plants may acclimate to low Pnutrition by adequate modifications in root growth, such as increased lateral root numberand root hair density. Plant will also make use of the protective enzyme system and theantioxidant system to protect them from poison. The adverse effects induced by lowphosphorus stress on plant growth and development involve biochemical disturbancemainly through oxidative damage.An exaggerate dincrease in the production of reactiveoxygen species (ROS), triggers acomplex detoxification mechanism which may involvenon-enzymatic and enzymatic systems capable of preventing the cascades ofuncontrolled oxidation.There was numerous reports published which tend to support the involvement ofethylene in the response of plants to several stresses. In this study, we have examinedsome aspects of the biochemical basis of oxidative stress in the soybean, when it isexposed to P stress. Plants grown in phosphorus-deficient solutions often exhibitenhanced ethylene production.Here we studied whether the ethylene signaling modulatethe biochemical pathways of oxidative stress in a tissue dependent manner, and that thissignaling may be important in P stresse.We have investigated the effects of ethylenedonor ethephon and ethylene synthesis antagonists (CoCl2) on P concentrations in rootsof soybean seedlings grown in P-sufficient (1mmol·L-1H2PO4) and P-deficient(10μmol·L-1H2PO4) solution. The main results are as follows:1. Phosphorus deficiency affects the shoot dry mass accumulation and almost hasno effects on accumulation of root dry mass. The root/stem is enhanced by ethylene. Themain root length under the low phosphorus application treatment is about50%lower than that of the control, and the main root length of soybean seedlings grown inP-sufficient solutions was insensitive to Co2+, while Co2+enhanced main root length forthose grown in P-deficient solutions, suggesting that P deficiency-induced decrease inroot length can be reversed by inhibiting ethylene production. The lateral root number isincreased by64%, and the longest lateral root is increased by46%compared with thecontrol.2. There was an increase in ethylene production when seedlings grown inP-deficient solutions, CoCl2abolished the P deficiency-induced ethylene production.Ethylene make P-sufficient growing soybean seedlings the same root architecture withwhich grown under P-deficient conditions. The lower root length and higher lateral rootnumber induced by ethylene were reversed by Co2+.3. P concentration was significantly reduced under P-deficient solutions. There wasan increase in root activity and acid phosphatase (APase) activity when seedlings grownin P-deficient solutions, and the increase in root activity and APase activity weremarkedly induced by ethylene. Ethylene had greater accelerant effect on P concentrationof P-deficient seedlings than that of P-sufficient seedlings.4．The extent of the phosphorus-deficiency damaging effects of reactive oxygenspecies (ROS) depends on the effectiveness of the antioxidative systems which includelow molecular mass antioxidants (ascorbate, glutathione) as well as several antioxidativeenzymes (SOD, APX, CAT, POD). The increased rate of production of ROS was muchfaster than the antioxidative systems, so there is accumulation of ROS, and thedamaging of membrane is increasing. When ethephon were entered, plants grown underP-sufficient conditions accumulate large amounts of ROS and the activities of SOD andAPX were enhanced to the level of P-defficient treatment. In the contrary, plants grownunder P-defficient conditions has little ROS accumulated and the activities of SOD andCAT were reduced when Co2+were entered.These results indicate that ethylene plays an important role in modulation of Pacquisition. Taken together, these findings suggest that ethylene induced by P deficiencymay play an important role in accommodate plants to P-stress.