Effects of salt stress on salt ion distribution and physiological characteristics of grafted watermelon seedlings
[Objective]This study aimed to investigate the effects of salt stress on salt ion distribution and physiologi-cal characteristics of grafted watermelon seedlings,providing a theoretical reference basis for regulating the growth of wa-termelon under salt stress and rationally developing and utilizing underground brackish water and salinized soil.[Method]The grafted watermelon seedlings were used as experimental materials,and the Hoagland nutrient solution with a nutrient solution salinity of 2.5 g/L as control(CK)was set as the base,supplemented with brackish water solutions with different salinities(3.0,3.5,4.0,and 4.5 g/L),to determine the fresh weight(FW),dry weight(DW),the relative content of chlorophyll(SPAD value),K+,Na+,Cl-accumulation and K+/Na+values in different tissues,as well as various physio-logical indicators[superoxide dismutase(SOD)and catalase(CAT)activities,proline(Pro),and malondialdehyde(MDA)contents)]of watermelon seedlings under the different treatments.Correlation analysis,principal component analysis(PCA),and salt stress threshold evaluation were conducted.[Result]With the increase of brackish water salini-ty,both FW and DW of watermelon seedlings showed a decreasing trend.FW decreased significantly by 33.38％and 38.08％compared with that of CK at salinities of 4.0 and 4.5 g/L respectively(P＜0.05,the same below).Cl-accumula-tion in the root system increased significantly by 348.43％to 492.52％at salinities of 3.0 and 4.5 g/L compared with the CK,while it peaked in stems and leaves under 4.5 g/L salinity.K+accumulation in different tissues decreased with increa-sing salinity,with significant reductions of 52.15％,52.16％and 54.61％in roots,stems and leaves respectively under 4.5 g/L salinity compared with CK.Na+accumulation in different tissues and whole plants of watermelon seedlings increased with increasing salinity of nutrient solution.K+/Na+values in roots,stems and leaves significantly decreased by 59.68％,61.63％and 52.70％under nutrient solution salinity of 4.5 g/L compared to CK respectively.The SPAD value of water-melon seedling leaves gradually decreased with increasing nutrient solution salinity,showing a linear correlation.SOD and CAT activities and Pro content in the leaves of watermelon seedlings showed quadratic,linearly decreasing and para-bolic relationships with the salinity respectively.The MDA content in both roots and leaves of watermelon seedlings in-creased with increasing brackish water salinity,with significant increases of 27.30％and 25.83％in roots,and 19.07％and 12.71％in leaves,compared with CK and 3.5 g/L salinity,respectively.Correlation analysis and PCA results showed a certain correlation between FW and ion accumulation in all tissues of watermelon seedlings.The cumulative contribution rate of the first principal component(PC1)and the second principal component(PC2)reached 67.8％.Salt stress thresh-old analysis and evaluation showed that the salinity thresholds under mild,moderate,and severe salt stress for water-melon seedlings were 2.80-3.91 g/L,3.91-5.32 g/L,and＞5.32 g/L respectively.[Conclusion]Under salt stress,Na+and Cl-accumulation in watermelon seedlings reduces K+uptake and destroys osmoregulatory substances and antioxidant en-zyme systems,causing membrane lipid oxidation and seedling biomass decrease.Leaf Pro content,stem Cl-accumula-tion,and leaf and root MDA contents can be used as comprehensive evaluation indicators for watermelon seedlings sub-jected to salt stress.
salt stresswatermelonsalt ion accumulationphysiological characteristics
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