Protective Function Of Photorespiration In Kosteletzkya Virginica(l.)presl Under Salt Stress

Seedlings of Kosteletzkya virginica (L.) Presl under salt stress were sprayed with INH or Na2S,then a combined physiological indicators measurement of chlorophyll fluorescence was conducted to evaluate the protective functions of photorespiration on K. virginica (L.) Presl under salt stress. The results are as follows:1.Effect of INH and Na2S on the growth of Kosteletzkya virginica under NaCl stresssThe fresh weight, dry weight and leaf area of K. virginica decreased with the increase of NaCl concentrations.Treatment with 2 mmol/L Na2S reduced these criteria, though not significantly. However, treatment with 4 mmol/L INH further decreased these indices.2.Effect of INH and Na2S on the photosynthetic characteristics of Kosteletzkya virginica under NaCl stresssThe net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO2 concentration (Ci) of K. virginica leaves decreased with the increase of NaCl concentrations. After spraying the seedling leaves with Na2S,Pn, Gs became quite smaller than the control, while Ci showed no significant difference. Furthermore, when sprayed with INH, Pn, Gs and Ci both decreased than the control, and even got smaller than those sprayed with Na2S under 300 mmol/L NaCl.The content of Chla, Chlb in K. virginica under salt stress increased first and then decreased with the increase of NaCl concentrations.Compared to the control, Chla, Chlb content were larger after sprayed with 2.0 mmol/L Na2S,while got smaller after sprayed with 4.0 mmol/L INH, indicating that photorespiration can alleviate the degradation of chlorophyll. The ratio of chlorophyll a/b increased with the salt concentration. But the seedlings sprayed with Na2S had a higher chlorophyll a/b ratio while those sprayed with INH showed just the opposite result.3.Effect of INH and Na2S on cell membrane permeability of Kosteletzkya virginica under NaCl stresssMDA content in leaves of K. increased with with NaCl concentrations, Na2S spraying lowered MDA content while INH increased it. The relative electric conductiveity showed the same trend as MDA content4. Effect of INH and Na2S on photorespiration rate of Kosteletzkya virginica under NaCl stresssUnder salt stress, photorespiration rate of K. virginica decreased with NaCl concentrations. Under the same NaCl concentrateion, photorespiration with Na2S treatment was stronger, while photorespiration with INH treatment was weaker.5.Effect of INH and Na2S on the activity of reactive oxygen scavenging enzymes of Kosteletzkya virginica lunder NaCl stresssSOD,CAT and POD are all very important reactive oxygen scavenging enzymes under salt stress,and all increased in activity under salinity to some extent. However, the influences of INH and Na2S to their activities were not the same, with the activities of SOD and POD decreased under Na2S,and the activities of SOD,CAT and POD increased under INH.6.Effect of INH and Na2S on the photochemical properties of Kosteletzkya virginica under NaCl stresssWk of Kosteletzkya virginica increased with the increase of NaCl concentrations.Wk of leaves sprayed with Na2S had no significant difference. Wk became higher when sprayed with INH under salt stress.PIABS and D.F. are important indices of plant photosynthetic abilityies,which all decreased significantly with the increase of NaCl concentrations.Spraying Na2S and INH further lowered PIABS and D.F.,with INH exerting the most remarkable effect.RC/CSo decreased with NaCl concentrations.Spraying Na2S elevated RC/CSo,while spraying INH even lowered it, implying that photorespiration protected reaction centers significantly.ABS/RC increased with NaCl concentration. The leaves sprayed with Na2S showed no significant difference, whileithose sprayed with INHs howed higher ABS/RC than the control.TRo/RC and ETo/RC both decreased with NaCl concentrations.Spraying Na2S and INH can make TRo/RC and ETo/RC lower than the control. DIo/RC increased with NaCl concentrations.After spraying Na2S,the DIo/RC was smaller than the control. DIo/RC became higher after spraying INH. Furthermore, TRo/CSm also decreased with NaCl concentrateion. TRo/CSm became higher with Na2S treatment but it lowered with INH treatment. Indicates the quantum yield in electron transfer, which became lower under NaCl stress. After spraying INH,φEo became lower than the control and Na2S treatment.φDo indicates the quantum yield of heat dismisson, which increased with NaCl content. Spraying Na2S made it lower and INH made it higher.In conclusion, plants adapt to saline environments with many effective mechanisms, their basic growth declines with the increase of salt concentration in saline environment for the cost of more energy. After spraying Na2S to promote photorespiration, the net photosynthetic rate of Kosteletzkya virginica was competitively inhibited, but photosynthesis center of K. virginica was protected, with MDA content decreased, chlorophyll content increased and relative electrical conductivity became lower. All these results showed that the photorespiration under salt stress have some positively protective effect. However, INH treatment inhibited photorespiration under saline environment. Excessive light energy under salinity could damage the plant through damaging the photosynthrtic center, membrane integrity and so on, which exacerbated the injury to plants in saline environment. All these showed that photorespiration had important protective effect on K. virginica under salt stress,and the protective effect of photorespiration can not be ignored.