The Relationships among Chlorophyll Fluorescence Parameters and Chloroplast Antioxidant Enzymes in Puccinellia tenuiflora Seedlings under Na2CO3 Stress

The relationships among chlorophyll fluorescence parameters, chloroplast antioxidant enzyme and active oxygen in the leaves of P. tenuiflora seedlings under Na₂CO₃ stress was investigated in the article. Results showed that when Na₂CO₃ stress was less than 0.4%, the activity of antioxidant enzymes (APX, GST, SOD) increased along with the increasing Na₂CO₃ stress. However, the changes of actual photochemical efficiency of PSII in the light (Φ PSII), photochemical quenching efficiency (qP), electron transfer rate (ETR) and heat dissipation rate (HDR) were not obvious. When Na₂CO₃ stress was over 0.4%, Φ PSII, qP, ETR and HDR increased with the increasing Na₂CO₃ stress, while the active oxygen and antioxidant enzyme activity of chloroplast decreased. All this suggest that there is refined osmotic regulation mechanisms may exist in the P. tenuiflora seedlings when Na₂CO₃ stress was below 0.4%, and these mechanisms ensure that the photosynthesis can be successfully completed. Chloroplast is quite sensitive to salt stress, Na₂CO₃ stress below 0.4% resulted in the increase of active oxygen and accordingly induced defend reactions in the chloroplast. When Na₂CO₃ stress was over 0.4%, the surplus light energy might probably dissipate through the following two ways: one is increasing heat dissipation rate (HDR); The other is enhancing pesudocyclic photophosphorylation by increasing Φ PSII and ETR. Different mechanisms might exist in this kind of plants to adjust the absorption and utilization of light energy under various Na₂CO₃ stress.