Effects of long-term magnesium stress on chlorophyll fluorescence characteristics and antioxi-dant properties of celery
In order to study the effects of long-term magnesium deficiency and magnesium excess stress on chloro-phyll fluorescence characteristics and antioxidant system of celery,American celery was used as the material,and the Yamazaki total nutrient solution was used as the control(CK,1.0 mmol·L-1 Mg2+),magnesium deficiency(0,0.5 mmol·L-1)and magnesium excess(2.5 mmol·L-1)treatments were set.After 65 days of treatment,the chlo-rophyll content,chlorophyll fluorescence parameters and antioxidant related indicators of celery were determined.The results showed that the chlorophyll content,the maximum photochemical efficiency(Fv/Fm)of PSⅡ,the pho-tochemical quenching coefficient(qP),the photochemical quenching(qL),the photosynthetic electron transfer rate(ETR),the light energy absorbed per unit reaction center(ABS/RC)and the light energy absorbed per unit area(ABS/CSm)of celery leaves were significantly reduced by magnesium deficiency and magnesium excess stress,while the relative variable fluorescence(Vj)of J point,the dissipated energy per unit reaction center(DIo/RC),the thermal dissipation energy per unit area(DIo/CSm)were significantly increased,and the OJIP curve was signifi-cantly deformed.Excessive magnesium leads to the performance index(PI abs)based on the absorption of light en-ergy,and the quantum yield of the electron transport flux from QA to QB(φEo)significantly decreased,and non-pho-tochemical quenching(qN)significantly increased.The activities of phenylalanine ammonia-lyase(PAL),cin-namate hydroxylase(C4H),4-coumaryl coenzyme A ligase(4CL)and the content of flavonoids in celery leaves were significantly increased under magnesium excess stress.The activities of superoxide dismutase(SOD),catalase(CAT)and ascorbic acid peroxidase(APX)in celery leaves and petioles decreased significantly under deficiency and excess stress of magnesium,while the contents of malondialdehyde(MDA),proline(Pro)and hydrogen perox-ide(H2 O2)increased significantly.The peroxidase(POD)activity of celery leaves was significantly increased and the content of superoxide anion was significantly decreased under magnesium deficiency stress.The effect of magnesi-um excess stress on chlorophyll fluorescence characteristics and antioxidant capacity of celery was significantly greater than that of magnesium deficiency stress.
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