Abstract:

This study aimed to clarify the regulatory mechanism of exogenous glycine betaine(GB)on the antioxidant and photosynthetic systems of maize seedling leaves under combined heat and drought stress(TD),providing a theoretical basis for alleviating crop stress under extreme environments.Using the maize variety Xianyu 335 as experimental material,different concentrations of GB(0,50,100,200,and 400 mmol/L)were applied to the leaves at the three-leaf-one-heart stage.After 24 hours,combined stress was simulated in a climate chamber with high temperature(day/night temperature of 40 ℃/28 ℃)and 20% PEG-6000 to induce moderate drought,exploring the regulatory effects of GB on the antioxidant system and photosynthesis of maize seedlings.The results showed that 100 mmol/L GB significantly promoted plant growth.Compared with the TD treatment,plant height,leaf area,shoot dry weight,and root dry weight increased by 27.48%,27.45%,28.33%,and 78.26%,respectively,while the root-to-shoot ratio increased by 14.91 percentage points.On the 5th day after stress,100 mmol/L GB significantly enhanced antioxidant enzyme activities,with superoxide dismutase(SOD),peroxidase(POD),and catalase(CAT)activities increasing by 69.09%,69.02%,and 41.81%,respectively.Simultaneously,the contents of malondialdehyde(MDA),superoxide anion($\mathrm{O}^{\bar{.}}_{2}$),and hydrogen peroxide(H₂O₂)decreased by 21.92%,6.50%,and 25.33%,respectively.Furthermore,soluble sugar(SS)and soluble protein(SP)contents increased by 31.69% and 18.98%.Photosynthetic characterization analysis indicated that GB effectively improved the lamellar system structure of chloroplast grana and stroma thylakoids,thereby significantly increasing the SPAD value under combined stress and alleviating damage to the photosystem Ⅱ(PSⅡ)reaction center.This was manifested by a decrease in minimal fluorescence(F0)and increases in variable fluorescence(Fv)and maximum fluorescence(Fm).Additionally,by mitigating the stomatal and non-stomatal limitations caused by combined stress,GB treatment significantly enhanced photosynthetic performance,increasing the net photosynthetic rate(Pn)by 24.14% on the 5th day after stress.In conclusion,under combined heat and drought stress,exogenous GB can protect the photosynthetic system by enhancing antioxidant enzyme activities and osmotic adjustment capacity,thereby alleviating stress damage and promoting the growth of maize seedlings.

Key words: Maize, Glycine betaine, Combined heat and drought stress, Antioxidant system, Photosynthesis

CLC Number: 

• S513玉米(玉蜀黍)