Effects Of Exogenous Glycerol On Growth And Physiology Of Maize Seedlings Under Water Stress

Maize is a significant crop that integrates grain production,economic benefits,and food security.Heilongjiang Province,located in one of the three primary maize production belts globally,has the largest planting area in the country,playing a vital role in ensuring national food security.However,seasonal and unpredictable droughts frequently affect Heilongjiang Province due to climatic reasons,resulting in reduced maize production.Therefore,exploring effective ways to improve maize drought tolerance is essential for maize production in Heilongjiang Province and food security in China.Glycerol（Gly）is a nontoxic,harmless,and degradable sugar alcohol that can promote plant growth and play a crucial role in regulating plant response to adversity.However,few studies have explored the mechanism of glycerol in regulating maize adaptation to water stress.This experiment used maize variety"Zhengdan 958"in a hydroponics experiment,using 20%polyethylene glycol（PEG-6000）to simulate water stress.The effects of exogenous glycerol on the growth,photosynthetic characteristics,antioxidant system,and osmotic adjustment of maize seedlings under water stress were studied to clarify the regulation mechanism of exogenous glycerol on drought resistance of maize seedlings.The results provide theoretical basis and technical support for drought resistance cultivation of maize.The main results are as follows:（1）3 mM is the best concentration of exogenous glycerol to alleviate the growth inhibition of maize seedlings under water stress.The effects of glycerol with different concentrations of 0,0.5,1,3 and 5 m M on the morphology,biomass and root characterization of maize seedlings under water stress were studied.It was found that with the increase of glycerol concentration,the growth indexes of maize seedlings all showed a trend of increasing at first and then decreasing,among which 3 m M glycerol had the best regulation effect.（2）Exogenous glycerol can alleviate the effect of water stress on the growth of maize seedlings.By studying the effects of exogenous glycerol on the aboveground morphology,root characterization and biomass of maize seedlings under water stress,it was found that exogenous glycerol increased the plant height,leaf area,aboveground dry weight,root dry weight,total root length,root surface area and root volume of maize seedlings under water stress,among which 3 m M glycerol increased the indexes by 26.57%,33.01%,53.01%and 20.72%respectively.（3）Exogenous glycerol can effectively alleviate the damage of water stress to photosynthetic system of maize seedlings.By studying the effect of exogenous glycerol on photosynthetic indexes of maize seedlings under water stress,it was found that exogenous glycerol increased the stomatal opening of maize seedlings under water stress by 321.57%.The Pn、Gs、Ci、Tr、F_v/F_m and F_v/F_owere increased by 52.84%,28.49%and 22.24%respectively.The Chl a and Chl b in leaves of maize seedlings were increased by 13.85%and 6.67%respectively.The activities of Rubisco and PEPCase in maize seedlings were increased by 16.92%～177.96%and 11.61%～107.02%respectively.The results showed that exogenous glycerol reduced the damage to the photosynthetic system of maize seedlings under water stress,maintained the photosynthetic capacity of maize seedlings,and promoted the growth and biomass accumulation of maize seedlings under water stress.（4）Exogenous glycerol enhances the antioxidant capacity of leaves and roots of maize seedlings under water stress.By studying the effects of exogenous glycerol on active oxygen metabolism and related indexes of antioxidant system in maize seedlings under water stress,it was found that exogenous glycerol significantly reduced the production rate of O₂^·-、the content of H₂O₂and MDA in membrane lipid of maize seedlings under water stress.The leaves reduced by4.34%～15.96%,9.58%～16.16%and 3.24%～18.71%respectively,and the roots reduced by12.01%～30.23%,14.22%～17.10%and 13.06%～18.94%respectively.The activities of SOD、POD、CAT、APX、MDHAR and DHAR in leaves and roots of maize seedlings were enhanced.The contents of As A and GSH in the antioxidant system of leaves and roots of maize seedlings were increased by6.85%～45.54%and 4.03%～29.17%respectively,and by 8.71%～50.14%and 6.63%～24.99%respectively.The results showed that exogenous glycerol maintained the high antioxidant enzyme activity and the stability of As A-GSH cycle of maize seedlings under water stress,which was beneficial to the removal of intracellular reactive oxygen species and improved the resistance of maize seedlings to water stress.（5）Exogenous glycerol enhances osmotic adjustment ability of leaves and roots of maize seedlings under water stress.The effects of exogenous glycerol on osmotic adjustment substance content and RWC of leaves and roots of maize seedlings under water stress were studied.It was found that exogenous glycerol treatment further increased proline and soluble protein content of leaves and roots of maize seedlings under water stress,with the increase ranges of 4.68%～26.25%and 1.95%～27.19%for leaves and 4.14%～6.68%for roots respectively.The RWC was increased by7.88%～16.01%,indicating that exogenous glycerol maintained the osmotic pressure of maize seedlings under water stress and enhanced the osmotic adjustment ability of maize seedlings,thus improving the drought resistance of maize seedlings.