Effect of nitric oxide on the activity of phenylalanine ammonia-lyase and antioxidative response in sweetpotato root in relation to wound-healing

We assessed the effect of nitric oxide (NO) on the activity of phenylalanine ammonia-lyase and antioxidative response in sweetpotato root in relation to wound-healing. To find the optimum concentration of sodium nitroprusside (SNP), a NO donor, to promote wound-healing process, sweetpotato root discs were treated with 0, 0.1, 0.5, 1.0 or 5.0mM SNP and 1 mM 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), then allowed to heal in the dark at 28 +/- 1 degrees C and 85% RH for 5 days. SNP at 0.5 mM was most effective in promoting wound-healing and enhanced activities of phenylalanine ammonia-lyase (PAL), superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR). It also maintained higher total phenolics and ascorbic acid contents and total antioxidative capacity, but restrained O-2(-) production and malondialdehyde (MDA) accumulation compared with untreated control discs. The H2O2 peak induced by wounding was significantly elevated by 0.5 mM SNP, but later during healing, when the concentration of H2O2 was relatively higher, H2O2 levels were reduced by NO. The positive promotion of wound-healing in sweetpotato roots with NO was reversed by the NO scavenger cPTIO. The results suggest that NO promotes restoration of wounded sweetpotato by improving PAL activity and potentiating the antioxidative defence system. (C) 2012 Elsevier B.V. All rights reserved.