Analysis of antioxidant enzyme activity in the leaves of 3 species of Pyrus as rootstock

Abstract: 【Objective】P. betulaefolia, P. ussuriensis and P. xerophila are the main rootstocks in the North, Northeast and Northwest of China. Antioxidant enzymes have close connection with plant growth and development. The aim of the study was to investigate the antioxidant enzyme (SOD, POD and CAT) activities among 3 species of pyrus and the connection between the antioxidant enzyme (SOD, POD and CAT) activities and the salt resistance.【Methods】Six accessions of each species were collected from“National Repository of Apple and Pear”in Research Institute of Pomology, Chinese Academy of Agricultural Sciences in August 2019. The seeds of 8 accessions were collected and strati-fied and then sown in the soil for germination. 60-day old seedlings were treated with saline-alkali solu-tion. The activities of SOD, POD and CAT of both the leaves from the adult trees of 18 accessions and from the leaves seedlings of 8 accessions were measured at about 25 ℃ through ultraviolet spectropho-tometer. The mean value and standard error of antioxidant enzyme activities and relevance were calcu-lated with SPSS 26.0 software, one-way ANOVA was used to analyze the significant differences, and LSD (minimum significance method) was used to test the significant differences among the accessions at α=0.05 level. Origin 2019b APP was used for principal component analysis.【Results】Among the 18 wild pear accessions, the activity range of SOD was 37.55- 206.64 U · mL^-1, with the average level 121.57 U·mL-1, and the highest SOD activity was detected in the leaves of P. betulaefolia-Wujiazhuang1. The activity range of POD was 32.71-455.60 U·mL^-1, with the average level 177.55 U·mL^-1, and the highest POD activity was found in P. xerophila-Huangtupo. The CAT activity range was 58.72-237.71  U·mL^-1, with the average level 101.41 U·mL-1, and the highest CAT activity was found in P. xerophila-Lingkong 1. Among the activities of POD, SOD and CAT of the 18 wild pear accessions, POD was the highest, followed by SOD and CAT in turn. There were significant differences in SOD and POD activi-ties among 18 accessions, but the differences in CAT activity among some accessions were not obvious. The average activity of SOD, POD, and CAT for P. betulaefolia were 155.99, 98.78 and 89.26 U·mL^-1,respectively, the level were 94.39, 189.73 and 138.43 U·mL^-1 respectively, as for P. ussuriensis, the lev-el were 114.31, 257.27 and 79.68 U·mL-1 for P. xerophila, respectively. The overall levels of SOD activ-ity in the leaves of three wild pear species were P. betulaefolia > P. ussuriensis > P. xerophila. There were significant differences between P. betulaefolia and P. xerophila. The overall levels of POD activity were, P. ussuriensis > P. xerophila > P. betulaefolia, and the significant differences existed among P. ussuriensis, P. xerophila and P. betulaefolia. The overall levels of CAT activity were P. xerophila > P. betu-laefolia > P. ussuriensis. According to principal component analysis, the first discriminant function explained 44.7% of the activities of the three antioxidant enzymes in wild rootstock accessions in the data-set, whereas the second function explained 38.8%. Therefore, the two principal components could repre-sent the information content of 83.5%, which could well represent the data information. Examination of the coefficients of the discriminant functions indicated that CAT and SOD were the highest contributors to the first function. But in terms of second function the highest contributors were SOD and POD. Then we discovered that P. betulaefolia and P. xerophila could be distinguished by PC1 (CAT and SOD). The accessions of P. betulaefolia mainly clusted in the first quadrant, while P. xerophila mainly clusted in the quadrant 3 and 4. PC2 (SOD and POD) could distinguish the accessions of P. betulaefolia and P. ussuriensis. The accessions of P. ussuriensis clusterd in the quadrant 2 and 3, and the accessions of P. sus suriensis and P. xerophila clustered in the same quadrant，mainly due to the POD activity. Based on the principal component analysis and we calculated the score of each accession using the comprehensive evaluation function. At first, we calculated the average scores of the accessions of P. ussuriensis, P. xerophila and P. betulaefolia, and found that the scores of the accessions of P. betulaefolia were signifi-cantly higher than those of P. ussuriensis and P. xerophila, and the scores of accessions of P. xerophila were slightly higher than those of P. ussuriensis, and P. betulaefolia-Wujiazhuang 1 was the highest，while the score of P. ussuriensis-Sunwu 10 was the lowest. After saline-alkali treatment, P. ussuriensis and P. xerophila appeared wilting first, and P. betulaefolia was the most resistant. The SOD activities of P. betulaefolia, P. ussuriensis and P. xerophila showed upward trends, P. betulaefolia rose by 525.69 U·mL^-1, P. xerophila increased by 447.52 U·mL^-1, P. ussuriensis rose by 569.32 U·mL^-1. At the same time, their POD activities also presented rising trends, P. betulaefolia rose by 102.17 U · mL^-1, P. xerophila in-creased by 472.19 U·mL^-1, P. ussuriensis rose by 408.05 U·mL^-1. However, the CAT activity of P. betulaefolia only increased by 52.95 U·mL^-1, the CAT activity of P. ussuriensis decreased slightly by 18.60U·mL^-1, and the CAT activity of P. xerophila decreased the most, by 104.51 U·mL^-1. The average activity of SOD increased significantly, with an average increase of 507.28 U·mL^-1, and the average activity of POD also showed an upward trend, with an average increase of 317.34 U · mL^-1, which was signifi-cantly lower than the SOD activity. But the average activity of CAT showed a downward trend, with an average decrease of 23.98 U · mL^-1.【Conclusion】There were differences in antioxidant enzyme activi-ties among various wild pear species and accessions. The highest SOD activity was found in P. betulae-folia-Wujiazhuang 1, the highest POD activity in P. xerophila-Huangtupo, and the highest CAT activity in P. xerophila-Lingkong 1. The antioxidant enzyme activities in leaves of P. betulaefolia were higher than those of P. ussuriensis and P. xerophila as a whole, and the antioxidant enzyme activities of P. ussu-riensis was slightly higher than that of P. xerophila. The antioxidant enzyme activities of P. betulaefolia-Wujiazhuang 1 was the highest，while P. ussuriensis-Sunwu 10 the lowest. The activity of SOD and POD showed a trend of increase after the high-concentration salt-alkali treatment. The CAT activity ofP. betulaefolia showed an increase trend, and the salt-alkali resistance of P. betulaefolia was stronger than that of the other two species.