Combined Kinetin and Spermidine Treatments Ameliorate Growth and Photosynthetic Inhibition in Vigna angularis by Up-Regulating Antioxidant and Nitrogen Metabolism under Cadmium Stress

Abstract

Pot experiments were conducted to investigate the probable beneficial role of the individual as well as combined application of kinetin (50 μM Kn) and spermidine (200 μM Spd) on Vigna angularis under cadmium (Cd) stress. Cd treatment reduced growth by declining the content of chlorophylls and carotenoids, photosynthesis, and gas exchange parameters. Exogenously, Kn and Spd application enhanced the photosynthetic parameters and up-regulated the antioxidant system by improving the activities of antioxidant enzymes and the content of non-enzymatic components. In addition, the application of Kn and Spd resulted in significant improvement in the content of sugars, proline, and glycine betaine, ameliorating the decline in relative water content. Oxidative stress parameters including hydrogen peroxide, superoxide, lipid peroxidation, lipoxygenase activity, and electrolyte leakage increased due to Cd stress; however, the application of Kn and Spd imparted a significant decline in all these parameters. Further, reduced Cd uptake was also observed due to Kn and Spd application. Total phenols and flavonoids also increased due to Kn and Spd treatments under normal as well as Cd stress conditions, which may have further helped with the elimination of reactive oxygen species. Reduction in the activity of nitrate reductase and the content of nitrogen was ameliorated due to the exogenous application of Kn and Spd. Therefore, the exogenous application of Kn and Spd benefited Vigna angularis counteracting the damaging effects of Cd stress by up-regulating the tolerance mechanisms, including antioxidant and osmolyte metabolism.

Keywords: Vigna angularis; antioxidants; cadmium; osmolytes; oxidative damage; secondary metabolites.

Figure 1

Effect of cadmium stress on (A) hydrogen peroxide, (B) superoxide, and (C) lipoxygenase activity in Vigna angularis seedlings treated with exogenous kinetin (Kn), superoxide dismutase (Spd), or Kn + Spd application. Data is mean (± SE) of four replicates and different letters represent significant difference at p < 0.05.

Figure 2

Effect of cadmium stress on (A) lipid peroxidation, and (B) electrolyte leakage in Vigna angularis seedlings treated with exogenous Kn, Spd, or Kn + Spd application. Data is mean (±SE) of four replicates and different letters represent significant difference at p < 0.05.

Figure 3

Effect of cadmium stress on (A) proline, (B) glycine betaine, and (C) sugar content in Vigna angularis seedlings treated with exogenous Kn, Spd, or Kn + Spd application. Data is the mean (±SE) of four replicates, and different letters represent a significant difference at p < 0.05.

Figure 4

Effect of cadmium stress on the activity of (A) superoxide dismutase, (B) catalase, and (C) glutathione S-transferase in Vigna angularis seedlings treated with exogenous Kn, Spd, or Kn + Spd application. Data is the mean (±SE) of four replicates, and different letters represent a significant difference at p < 0.05.

Figure 5

Effect of cadmium stress on activity of (A) ascorbate peroxidase, (B) glutathione reductase, and (C) dehydroascorbate reductase in Vigna angularis seedlings treated with exogenous Kn, Spd, or Kn + Spd application. Data is the mean (±SE) of four replicates, and different letters represent a significant difference at p < 0.05.

Figure 6

Effect of cadmium stress on content of (A) ascorbic acid, (B) reduced glutathione, and (C) tocopherol in Vigna angularis seedlings treated with exogenous Kn, Spd, or Kn + Spd application. Data is the mean (±SE) of four replicates, and different letters represent a significant difference at p < 0.05.

Figure 7

Effect of cadmium stress on content of (A) total phenol and (B) flavonoids in Vigna angularis seedlings treated with exogenous Kn, Spd, or Kn + Spd application. Data is the mean (±SE) of four replicates, and different letters represent significant differences at p < 0.05.

Figure 8

Effect of cadmium stress on activity of (A) nitrate reductase, and content of (B) nitrogen and (C) potassium in Vigna angularis seedlings treated with exogenous Kn, Spd, or Kn + Spd application. Data is the mean (±SE) of four replicates, and different letters represent significant differences at p < 0.05