Molecular And Physiological Mechanisms Of Proline Metabolism In Lycium Ruthenicum Murr. Under NaCl Stress

Salinity stress harms plant growth by interfering with a number of biochemical and physiological processes.Plants,in turn,have evolved complex physiological and molecular processes to survive and protect themselves in these harsh environments.The accumulation of cellular osmolytes is the commonest responses of plants to abiotic stresses.Proline is the most commonly accumulated osmolyte,and it is now widely recognized that proline has many functions under abiotic stresses.Lycium ruthenicum is a common native halophyte and perennial shrub found in arid and semi-arid areas,and it is an ideal plant for exploring the mechanism of salt tolerance.The previous study showed that proline content was more accumulated in L.ruthenicum under salinity.However,there is still limited literature about proline metabolism in L.ruthenicum,also the related molecular mechanism is unknown.Hence,this study analyzed the effect of salt(NaCl)on physiological indexes,antioxidants,proline related enzymes activities,proline related genes expression patterns of L ruthenicum.The main results are as follows:1.The results showed L.ruthenicum growth is influenced by increasing concentration of NaCl and the symptoms of salt damage gradually became visible.Under 50 mmol/L and 150 mmol/L NaCl concentration,the shoot height and root length remained constant compared with control,whereas the roots,stem and leaves biomass significantly increased.L.ruthenicum can withstand NaCl stress,and moderate NaCl can stimulate its growth.2.With NaCl concentrations increasing,the soluble proteins,the activities of SOD and CAT significantly increased firstly,and reached maximum under 150 mmol/L NaCl concentration,then were declined.Differently,proline showed an obvious increasing trend with the increase of NaCl concentration compared with control(21.5,26.6 and 25.5 times higher under 300 mmol/L NaCl condition in leaves,roots and stem)and played a leading role in salt tolerance.Besides,POD activity decreased with the increase of NaCl.3.The proline related enzymes activities(P5CS,P5 CR and δ-OAT)increased with NaCl addition,while Pro DH increased and decreased at 300 mmol/L.The proline content was positive correlated with P5 CS,P5CR δ-OAT and Pro DH,thus suggesting Glutmate pathway as a main synthesis pathway of proline in L.ruthenicum,but it was switched to Ornithine pathway with the increase of salt concentration.4.A total of five LrP5 CS,one LrP5 CR,three LrOAT,four LrPro DH and two LrP5 CDH putative candidates of proline related genes were searched in L.ruthenicum.All of them were expressed in all tissues,and which were induced significantly by NaCl addition compared to the control.5.The expression of LrP5CS2,LrP5CS3,LrP5CR1,LrOAT2,LrP5CDH2,LrPro DH2 and LrPro DH3 was promoted higher(0.7,23.9,26.1,24.4,6.7,32.1 and 26.1 times)under 50 mmol/L compared with 250 mmol/L NaCl.Under 250 mmol/L NaCl,only LrP5CS1 and LrOAT1 expressed higher(9.4 and 1.7 times)compared with 50 mmol/L NaCl.This proposed that 50 mmol/L NaCl is ideal for most proline related genes during proline accumulation in L.ruthenicum.In conclusion,the following results confirmed that physiological indexes,antioxidants and metabolic enzymes activities play a crucial role during proline accumulation and NaCl stress tolerance of L ruthenicum.