Effect of exogenous γ-aminobutyric acid on physiological property, antioxidant activity, and cadmium uptake of quinoa seedlings under cadmium stress

Abstract

Increasing cadmium (Cd) pollution has negative effects on quinoa growth and production. Gamma-aminobutyric acid (GABA) confers plants with stress resistance to heavy metals; however, the mechanism remains unclear. We explored the effects of exogenous GABA on the physiological characteristics, antioxidant capacity, and Cd accumulation of quinoa seedlings under Cd stress using hydroponic experiments. Partial least-squares regression was used to identify key physical and chemical indices of seedlings affecting Cd accumulation. Compared with those of the CK group, exposure to 10 and 25 µmol·L-1 Cd significantly reduced the photosynthetic pigment contents, photosynthesis, and biomass accumulation of quinoa seedlings; resulted in shorter and thicker roots; decreased the length of the lateral roots; decreased the activities of superoxide dismutase (SOD) and peroxide (POD); and increased H2O2 and malondialdehyde (MDA) contents. Exogenous GABA reduced the Cd content in the stem/leaves and roots of quinoa seedlings under Cd stress by 13.22-21.63% and 7.92-28.32%, decreased Cd accumulation by 5.37-6.71% and 1.91-4.09%, decreased the H2O2 content by 38.21-47.46% and 45.81-55.73%, and decreased the MDA content by 37.65-48.12% and 29.87-32.51%, respectively. GABA addition increased the SOD and POD activities in the roots by 2.78-5.61% and 13.81-18.33%, respectively, under Cd stress. Thus, exogenous GABA can reduce the content and accumulation of Cd in quinoa seedlings by improving the photosynthetic characteristics and antioxidant enzyme activity and reducing the degree of lipid peroxidation in the cell membrane to alleviate the toxic effect of Cd stress on seedling growth.

Keywords: antioxidant system; cadmium(Cd) stress; physiological characteristics; quinoa; γ-aminobutyric acid.

Figure 1. Effects of exogenous GABA on the H₂O₂ and MDA contents of quinoa seedlings under cadmium (Cd) stress

Different lowercase letters indicate a significant difference among the five treatments (P<0.05).

Figure 2. Effect of exogenous GABA on the activities of the antioxidant enzymes

(A) SOD and (B) POD in quinoa seedlings under Cd stress. Different lowercase letters indicate a significant difference between treatments (P<0.05).

Figure 3. Analysis of factors influencing cadmium accumulation in quinoa seedlings based on the PLS regression model

a1, c2: stem-leaf length; a2, c4: stem and leaf dry weight; a3, c7: stem-leaf tolerance index; a4, c8: net photosynthetic rate; a5, c9: stomatal conductance; a6, c10: intercellular CO₂ concentration; a7, c11: transpiration rate; a8, c12: chlorophyll a; a9, c13: chlorophyll b; a10, c14: carotenoids; a11, c15: chlorophyll (a + b); a12, c21: above-ground MDA content; a13, c23: above-ground H₂O₂ content; a14, c25: above-ground SOD activity; a15, c27: above-ground POD activity; a16, c29: above-ground Cd content; b1, c1: root length; b2, c3: root dry weight; b3, c5: root-crown ratio; b4, c6: root tolerance index; b5, c16: total root length; b6, c17: root surface area; b7, c18: root volume; b8, c19: average root diameter; b9, c20: total root tip number; b10, c22: under-ground MDA content; b11, c24: under-ground H₂O₂ content; b12, c26: SOD activity in under-ground tissues; b13, c28: POD activity in under-ground tissues; b14, c30: Cd content in under-ground tissues.

Figure 4. Correlation analysis of the changes in each indicator in response to exogenous GABA treatment of quinoa seedlings under Cd stress

1. Above-ground SOD activity. 2. Root-shoot ratio 3. Under-ground SOD activity. 4. Root mean diameter. 5. Above-ground Cd accumulation. 6. Above -ground Cd content. 7. Total Cd accumulation. 8. Under-ground Cd accumulation. 9.Under-ground Cd content. 10. Above-ground MDA content. 11. Above-ground H₂O₂ content. 12. Under-ground H₂O₂ content. 13. Under-ground MDA content. 14. Above-ground POD activity. 15. Chlorophyll b. 16. Stem and leaf length. 17. Intercellular CO₂ concentration. 18. Under-ground POD activity. 19. Root dry weight. 20. Root tolerance index. 21.Transpiration rate. 22. Net photosynthetic rate. 23. Chlorophyll a. 24. Chlorophyll (a+b). 25. Carotenoid. 26.Total root length. 27. Root surface area. 28.Root length. 29. Root volume. 30. Stem and leaf dry weight. 31. Stem and leaf tolerance index. 32. Stomatal conductance. 33. Total number of root tips.