Physiological And Quantitative Proteomics Analysis Of Puccinellia Tenuiflora Chloroplast In Response To Na₂CO₃

Alkali-salinity is one of the most significant abiotic stresses and it limits the productivity and geographical distribution of plants. Alkali-salinity stress imposed severe effects on plant by causing water deficit, which subsequently reduce the stomatal conductance, disturbances in osmotic and oxidative homeostasis. Photosynthesis is inhibited, such as the recuction of light energy utility and CO2assimilation in plants.Puccinellia tenuiflora is a halophytic species belonging to the Gramineae, and capable of completing its life cycle under salt environment with pH9-10. Therefore, P. tenuiflora is considered as an ideal model plant for studying the salt-tolerant mechanisms in plants. In this study, the Na2CCO3responsive molecular mechanisms in P. tenuiflora chloroplast was investigated using a combined physiological and proteomic approach., we found the chloroplast structure was affected, and light reaction acitivity and CO2assimilation were inhibited Under various Na2CO3treatments (150mM-12h,200mM-12h,150mM-24h, and200mM-24h). These led to the growth of P. tenuiflora seedling reduced. Accumulation of Na+causes ion-specifis stress and dissipates the membrane potential. Altered K+/Na+ration and reduced Ca2+and Mg2+contents can inhibit the activity of many essential enzymes and metabolism pathways, which finally lead to growth inhibition. The remarkable increased result of malondialdehyde (MDA) and relative electrolyte leakage further illustrated the increase of membrane lipid peroxidation and membrane permeability. Moreover, the accumulation of proline and soluble sugar enhance the ability of osmotic regulation are helpful to preserve the integrity of cell structure. In addition, dynamic changes of antioxidant system play important roles in the protection of plant/chloroplast response to Na2CO3. Furthermore, using an isobaric tags for relative and absolute quantitation (iTRAQ) approach,68differentially expressed proteins were identified in P. tenuiflora chloroplast in response to Na2CO3. These proteins were mainly involved in the formation of light harvest complex, photosystem â…¡, photosynthetic electron transfer chain, and photosystem â… , energy metabolism, Calvin cycle, photosynthetic pigment metabolism, metabolism, stress and defence, transcription, protein synthesis and fate, as well as signaling transduction.Taken together, our physiological and proteomics results reveal that P. tenuiflora chloroplast may utilize various strategies to cope with Na2CO3treatment. They include:(1) reduce excessive light energy absorption by decreasing chlorophyll content and inhibiting chlorophyll a/b binding protein expression;(2) enhance the heat dissipation by increasing photochemical quenching and accelerating xanthophyll cycle, and thereby reduce the damage of photosynthetic apparatus caused by excessive light energy;(3) minimize the oxidative injury by elevating the specific antioxidant system and enhancing the dissolution of xanthophyll synthetic substrates and intermediate products. In addition, the considerable accumulation of proline and soluble sugar can alleviate osmotic stress, as well as scavenge reactive oxygen species (ROS) to maintain oxidative balance.This study lays a solid foundation for further research on salt-tolerant mechanisms in the Gramineae.