Physiological Responses Of Different Salt-Tolerant Grape Rootstocks To NaCl Stress

Object:Grape is a popular fruit in the world,but salt stress restricts the development of grape industry.The research on the salt tolerance of grape rootstocks in China started late,and the identification of salt tolerance,the types and mechanisms of salt tolerance still need to be further explored.This experiment was conducted to study the effects of 100 mmol·L-1 NaCl stress on the growth and morphological indexes,antioxidant system,photosynthetic fluorescence characteristics,transport and distribution of mineral elements in potted seedlings of different salt-tolerant grape rootstocks’101-14’and’SO4’.Real-time quantitative fluorescence PCR（RT-PCR）was used to detect the expression levels of genes related to antioxidant enzymes,providing theoretical reference for exploring the physiological response mechanism under NaCl stress.Methods:Different annual grape rootstocks were used as test materials,and potted salt-infused culture method was used.Two treatments were set up:（1）control（CK）:irrigating water;（2）Treatment（T）:100mmol·L-1 NaCl solution was irrigated once every 5 days with 500 m L each time.After the vines grew to8-10 leaves,they were treated,and samples were taken on the 5d,10d and 15d after NaCl stress for determination.Results:（1）Under NaCl stress,the values of MDA,H₂O₂,O^2-and electrical conductivity of salt-sensitive grape rootstock’SO4’were significantly higher than those of salt-tolerant variety’101-14’during the treatment,while the root activity was significantly lower than’101-14’,indicating that under salt stress,The salt-tolerant variety’101-14’could maintain the stability of cytoplasmic membrane and root activity,and its membrane lipid damage was small,so it had strong salt tolerance.（2）Compared with’SO4’,’101-14’can maintain higher activities of superoxide dismutase（SOD）,peroxidase（POD）,catalase（CAT）and other enzymes under NaCl stress.The high activities of ascorbase（APX）,glutathione reductase（GR）,mono dehydroascorbate reductase（MDHAR）,dehydroascorbate reductase（DHAR）,reduced ascorbic acid（ASA）,reduced glutathione（GSH）,dehydroascorbic acid（DHA）and other enzymes in the ascorbate-glutathione circulation system were maintained.The content of oxidized glutathione（GSSG）was also significantly higher than that of SO4.At the same time,NaCl stress significantly up-regulated the expressions of APX,GR,DHAR,SOD,POD and CAT genes in the leaves of’101-14’and’SO4’,but the up-regulated amplitude was different,and the increased amplitude of 101-14’was significantly higher than that of’SO4’.In conclusion,The expression of antioxidant enzyme gene of’101-14’with strong salt tolerance was significantly higher than that of’SO4’with weak salt tolerance under NaCl stress.These results indicated that the grape rootstock’101-14’with strong salt tolerance could maintain high antioxidant enzyme activity and the operating efficiency of the ascorbate-glutathione circulatory system under NaCl stress,and had high efficiency of ROS removal from stress damage,thus having strong salt tolerance.（3）Under NaCl stress,the net photosynthetic rate（P_n）,stomatal conductivity（G_s）and transpiration rate（T_r）of grape rootstocks’101-14’and’SO4’decreased,and the decrease range of’101-14’was significantly less than that of’SO4’,while the intercellular carbon dioxide concentration（C_i）showed varying degrees of increase.The increase of’101-14’was significantly less than that of’SO4’,indicating that the photosynthetic rate of’SO4’was significantly affected by NaCl stress.Under NaCl stress,if the activity of the photosystem is inhibited,it will lead to the decline of plant photosynthesis,thus affecting the growth of plants.The experimental results showed that F_v/F_m,F_v/F₀and PI_ABSof’SO4’decreased significantly,while those of’101-14’decreased slightly,indicating that the light energy conversion rate of’101-14’leaves did not change significantly,and light suppression phenomenon probably did not occur.（4）Under NaCl stress,the content of Na⁺in roots of’101-14’was higher than that in’SO4’,while the content of Na⁺in stems and leaves was lower.The leaves of’101-14’could maintain high contents of K⁺,Ca²⁺and Mg²⁺,and the ratio of K⁺/Na⁺,Ca²⁺/Na⁺to Mg²⁺/Na⁺,and maintain relatively high values of SK,Na,SCa,Na,SMg and Na.’101-14’absorbed less Na⁺content and had a strong ability to exhalate Na⁺.The root system had a strong Na⁺interception effect,and could better maintain the contents of K⁺,Ca²⁺and Mg²⁺in the leaves,so as to better maintain the ion balance inside the plant.（5）Through the correlation analysis of 27 physiological indexes of grape salt tolerance,it was concluded that relative electrical conductivity,F_v/F_m,G_sand PI_ABScould be used as the optimal indexes for salt tolerance evaluation of rootstocks.Conclusion:Under NaCl stress,compared with SO4,the salt-tolerant variety’101-14’could better guarantee the stability of cytoplasmic membrane and root activity,maintain higher antioxidant enzyme activity and the operating efficiency of the ascorbate-glutathione circulatory system,and clear the stress damage and produce ROS efficiently.The photosynthetic rate and leaf light energy conversion rate were less affected by NaCl stress,and compared with’SO4’,’101-14’root system had stronger Na⁺interception effect,which could better maintain the ion balance inside the plant.The correlation analysis of physiological indexes of grape salt tolerance showed that relative electrical conductivity,F_v/F_m,G_sand PI_ABScould be used as optimal indexes for salt tolerance evaluation of rootstocks.