Effects Of Exogenous Methyl Jasmonate On Water Absorption Capacity Of Maize(Zea Mays L.) Seedling Root Under Drought Stress

Maize is an important grain crop grown extensively in China.Drought stress can cause a severe reduce of yield as maize is a kind of hydrophilous plant which is susceptive to water loss.It is of great significance to explore the underlying mechanism of drought adaptation and find the method of improving drought tolerance of maize.Jasmonates（JAs）,an environmental signaling molecule,are involved in regulating plant development and responding environment stress.It has been reported that exogenous methyl jasmonate（MeJA）can enhance the stress resistance of plant.However,to our knowledge,there is hardly any study about the effect of MeJA on maize root under abiotic and biotic stress.To find out the effect of exogenous MeJA on water absorption of maize root,we determined the gas exchange parameters,the contents of H₂O₂ and MDA,the activity of antioxidant enzymes,water content of leaves,root hydrau-lic conductivity,activity and expression level of aquaporins in water-cultured‘Zhengdan 958’（a maize conventional variety）at seedling stage.The main results are listed as follows:1.The photosynthetic rate,stomatal conductance and transpiration rate of maize seed-ing roots was increased under normal water condition but droped under drought stress.These decreased characters caused by drought stress can be mitigated by exogenous MeJA,along with increased leaf water content and potential.Under normal water condition,root hydraulic conductivity maiz seedling had a significant increase after exogenous MeJA treatment.On the contrary,plants under drought stress presented 40.7%of root hydraulic conductivity of con-trol ones,and it can be partly restored by exogenous MeJA treatment（74.2%of root hydraulic conductivity of control ones）.These results suggested that exogenous MeJA could reduce water loss of plant aerial portion by regulating the stomatal closure and promote water uptak-ing by enhancing root hydraulic conductivity,which contributing to maintain a high level of water content and abating drought stress.2.No matter treated with MeJA or not,the transpiration rate of plants under normal water condition dropped to the same level when aquaporins were inhibited by HgCl₂.This result indicated that aquaporins were involved in MeJA-mediated water regulation.In view of this,the expression levels of aquaporins were determined and the result showed partial aqua-porins were up-regulated after exogenous MeJA treated.Thus,we can conclude that aqua-porins probably play an important role in MeJA-mediated water regulation.3.Exogenous MeJA made an increase of activity of antioxidant enzymes in maize seed-ling roots under drought stress,which could reduce the accumulation of reactive oxygen spe-cies（ROS）and the contents of H₂O₂ and MDA caused by drought stress.As a result,the oxi-dation resistance of plant was improved remarkably.On the other side,the declined accumu-lation of ROS maybe had an effect on plant root hydraulic conductivity by mitigating the ROS-induced inhibition of aquaporins,thereby resulting decreased effect of drought stress.