The Effect Of Bicarbonate Use On Photorespiration Under Submerged Macrophytes

Photorespiration,occurs in all oxygen-producing photosynthetic organisms,is one of the most important carbon metabolism in the biogeosphere,which commences with the formation of phosphoglycolate under oxygenation of Ru Bis CO（ribulose-1,5-bisphosphate carboxylase/oxygenase）.To alleviate the effect of photorespiration for photosynthesis,terrestrial plants have evolved the C4 pathway and CAM（crassula acid metabolic）.Compared to terrestrial plants can directly obtain CO₂ from the atmosphere,submerged macrophytes face the effects of CO₂ deficiency.Therefore,the effect of photorespiration on photosynthesis could be more significant in submerged plants.To obtain sufficient CO₂,submerged plants have formed different CCM（CO₂ concentration mechanism）.HCO₃^-utilization is the CCM possessed by more than 50%of submerged plants.In this study,the effect of HCO₃^-use on photorespiration were investigated in four submerged plants,Cabomba caroliniana,Ceratophyllum demersum,Egeria densa and Ottelia alismoides,via the p H-drift experiment,oxygen inhibition,the rate of O₂ exchange and photorespiration-related enzymes.Then,we focuses mainly on the O.alismoides.The results showed that C.demersum,E.densa and O.alismoides possessed the ability of HCO₃^-use in p H-drift,but not C.caroliniana.The oxygen inhibition of 4 submerged plants were increased significantly under low CO₂ condition.In addition,after four different submerged plants were treated with AZA（acetamidoamine,an extracellular CA enzyme inhibitor）,the GLO（Glycolate oxidase）and CAT（Catalase）activity of C.demersum,E.densa and O.alismoides raised significantly except for C.caroliniana.simultaneously,the results indicate that adding AZA+DIDS（4,4’-Diisothiocyano-2,2’-stilbenedisulfonic acid,an anion exchange inhibitor）promoted obviously the oxygen inhibited ratio and the rate of O₂exchange under low CO₂ condition on O.alismoides.After AZA+DIDS treatment,the activity of GLO,CAT,SGAT（serine-glyoxylate aminotransferase）,GGAT（Glutamate-Glyoxylate Aminotransferase）and GS（Glutamine synthetase）were increased significantly except for Ru Bis CO.In addition,compared with Blyxa japonica,when O.alismoidesis was induced from high CO₂to low CO₂,there is no significant change under the activity of its photorespiration enzymes.Our all results show that HCO₃^-utilization can diminish the photorespiration of submerged plants and contribute them to adapt the low CO₂environment in the water.