Comprehensive evaluation of salt tolerance in ginger at seedling stage and expression pattern of aquaporin protein

【Objective】To investigate the effects of salt stress on morphological changes and physiological indexes of ginger at seedling stage，establish a salt-tolerant evaluation system for ginger，explore salt-tolerant germplasm resources， which could provide theoretical reference for the selection and breeding of salt-tolerant varieties of ginger.【Method】The main plant varieties from 5 major ginger producing areas in China were used as experimental materials，and 2 treatments， control （CK）and salt stress（NaCl），were set up. Principal component analysis was used to integrate the physiological and biochemical indexes and other individual indexes into 3 comprehensive indexes，and combined with the method of the membership function to carry out a comprehensive evaluation of salt tolerance，and to analyze the expression of the aquaporin protein（AQP）gene in the salt-tolerant varieties and the sensitive varieties.【Result】The increase in plant height，stem thickness，number of leaf，root vigour，leaf water potential and leaf osmotic potential decreased in all ginger varieties under salt stress. Hydrogen peroxide（H₂O₂）content，malondialdehyde（MDA）content and peroxidase（POD）activity of leaves were increased. Superoxide dismutase（SOD）activity was significantly increased in Guizhou ginger（P<0.05， the same below）but decreased in the other 4 varieties. Catalase（CAT）activity was decreased in Shandong big ginger but elevated in the other 4 varieties. Phenylalanine deaminase（PAL）activity decreased in Shandong big ginger and Zhugen ginger，but increased in the other 3 varieties. Plant height，stem diameter and number of leaf were significantly and positively correlated with the comprehensive evaluation value（D value）. Leaf MDA content，H₂O₂ content，water potential and osmotic potential were negatively correlated with D values，root vigour was extremely significantly and positively correlated withD value（P<0.01）. The salt tolerance of ginger was ranked from the strongest to the weakest as Shandong big ginger，Guizhou yellow ginger，Fengtou ginger，Luoping small yellow ginger and Zhugen ginger. Expression pattern analysis of 8 AQP genes showed that 7 AQP genes were down-regulated in Shandong big ginger leaves and 4 AQP genes were down-regulated in roots after salt stress treatment；3 AQP genes were down-regulated in leaves and 6 AQP genes were down-regulated in roots of Zhugen ginger.【Conclusion】Salt tolerance evaluation of 5 ginger varieties at seedling stage indicates that Shandong big ginger has the strongest salt tolerance and Zhugen ginger has the weakest salt tolerance. Plant height，stem diameter，number of leaf and root vigour can be the main reference indexes for screening ginger salt-tolerant varieties.