Physiological and biochemical response and related gene expression of Hongyang kiwiftuit seedlings under salt stress

Abstract: 【Objective】Kiwifruit is rich in vitamin C, dietary fiber and a variety of minerals, and has rich nutritional value. It is one of the most popular fruits in the world, but it is also a fruit crop that is sensitive to salt stress. The saline land in China has a wide distribution, and affects plant growth and soil permeability. It results in soil hardening and ion imbalance in plants, limiting the cultivation of kiwifruit seriously. Therefore, it is of great significance to study the salt tolerance of kiwifruit and solve the problem of kiwifruit cultivation in the saline land. In this research, physiological and biochemical response and related gene expression of Hongyang seedlings under salt stress were analyzed.【Methods】 The seedlings under the same growth conditions were transplanted into a pure vermiculite culture dish and cultured in the greenhouse for 1 month. The method of NaCl treatment was to pour Hoagland nutrient solution every 3 days, and the NaCl concentrations of Hoagland nutrient solution were 0, 50, 100, 150 and 200 mmol · L- 1 , respectively. The net photosynthesis rate (Pn) and relative conductivity (REC) was detected immediately after NaCl treatment. The antioxidant enzyme activities, the contents of osmotic adjustment substances, vitamin C (VC) and malondiadehyde (MDA) as well as the expressions of the salt- stress related genes were measured subsequently.【Results】Along with the increase of NaCl concentrations, the growth condition of Hongyang seedlings was gradually deteriorated and limited. Compared with the control, the plants of experimental groups were dwarfed and wilted, and the leafedge became scorched. The treatments of 50 and 100 mmol · L- 1 had relatively little effect on young seedlings. With 150 mmol · L- 1 treatment, the plants began to show obvious yellowing, wilting and dwarfing. When the concentration achieved 200 mmol·L-1 , the plants showed wilted and stunted seriously. Meanwhile, with the increasing of NaCl concentrations, the Pn decreased and the REC increased. The activity of peroxidase (POD) decreased at first and then increased. The activity of superoxide dismutase (SOD) increased, whereas the activity of catalase (CAT) decreased. The contents of soluble sugar and protein ascended first and then descended. The content of malondialdehyde (MDA) increased first and then decreased. The content of VC decreased, and the content of proline (Pro) increased significantly. Real-time quantitative PCR showed that NaCl treatment promoted the expressions of ethylene receptor genes, melatonin responsive genes, salt-tolerance genes, ABA positive feedback genes, osmotic stress response genes and reactive oxygen species (ROS) regulation genes. Meanwhile, the expressions of ABA catabolic genes and VC synthetic genes were inhibited. More importantly, the expressions of genes related to salt stress were consistent with the physiological indexes of plants.【Conclusion】This research explored the intrinsic regulatory mechanisms of Hongyang seedlings at physiological, biochemical and molecular levels. It showed that Hongyang seedlings can withstand 100 mmol·L- 1 NaCl at most without obvious inhibition and damages. Therefore, it provides a reference for the cultivation of kiwifruit in saline land and has great significance for improving the yield and quality of kiwifruit.