EFFECTS OF CHILLING ON RESPIRATION AND INDUCTION OF CYANIDE-RESISTANTRESPIRATION IN SEEDLING ROOTS OF CUCUMBER

The effects of chilling stress on respiration and induction of the alt ernative pathway (AP) were investigated with roots of 3-day-old cucumb er seedlings (Cucrcmis sativus L.) grown at 26 degrees C and then chil led at 2, 10, or 15 degrees C for 24, 48, 96, 144, or 192 hours. Oxyge n uptake by roots exposed to 2 degrees C was significantly lower than by 10 or 15 degrees C-treated roots, and the inhibition of oxygen upta ke in the presence of SHAM (salicylhydroxamic acid) increased from 29% in unchilled tissue to 60% after 96 hours of treatment. At 10 and 15 degrees C, the capacity of the AP was nearly double that of the unchil led control and the 2 degrees C-treated seedlings. A 24 hours, postchi lling treatment at 26 degrees C resulted in greater oxygen uptake at a ll temperatures as treatment time increased up to 96 hours. At 2 degre es C, the capacity of the AP was significantly reduced below the level of the 10 and 15 degrees C-treated tissue and the untreated control. The activity of the AP became fully activated by 96 hours in roots chi lled at 2 degrees C. Results suggest that the capacity of the AP can b e affected by low-temperature treatments, and exposure to 2 degrees C for up to 96 hours leads to a significant loss in capacity of the AP.