Effect of chilling on antioxidant enzymes and DPPH-radical scavenging activity of high- and low-vigour cucumber seedling radicles

The chilling tolerance of cucumber seedling radicles was influenced by their relative levels of vigour. Radicles of high-vigour seedlings grew to 20 mm in length in 36 h at 25 degreesC, whereas it took 60 h for low-vigour seedling radicles to reach that length. Chilling at 2.5 degreesC for 48 h inhibited the subsequent growth of high- and low-vigour seedlings by 39 and 68%, respectively. The 2,3,5-triphenyltetrazolium chloride (TTC) viability index, and alpha,alpha-diphenyl-beta -picrylhydrazyl (DPPH)-radical scavenging activity were higher in high than low-vigour radicles. Higher ascorbate peroxidase (APX) and catalase (CAT) enzyme activity, DPPH-radical scavenging activity, and recovery of CAT activity after chilling in high-vigour radicles corresponded with their higher level of chilling tolerance in comparison with low-vigour radicles. In contrast, elevated levels of superoxide dismutase, glutathione reductase and guaiacol peroxidase appear to be correlated with chilling injury since they only showed substantial increases in activity in the more chilling-sensitive low-vigour radicles after chilling. Manipulation of APX, CAT, and/or DPPH activity could produce plants with superior and persistent chilling tolerance.