Putrescine (1,4-diaminobutane) as an indicator of pollution-induced stress in higher plants: barley and rape stressed with Cr(III) or Cr(VI).

The performance of the free polyamines as plant stress indicators is studied in barley and rape plants grown in nutrient culture, by exposure to Cr(VI) or Cr(III) in concentrations ranging from 0 to 100 ppm. Putrescine levels are elevated up to 10 times in the leaves of stressed plants compared to those of control plants, but neither spermidine nor spermine show any consistent reactions on the stress. Cr(VI) is more toxic than Cr(III) and induces putrescine accumulation quicker than Cr(III). Chromium concentrations in leaves reach 3000-5000 ppm (dry wt) after exposure to 100 ppm Cr(VI) and 300-400 ppm (dry wt) following exposure to 100 ppm Cr(III). Simultaneously with, or following shortly after the putrescine induction, reductions in root growth, chlorosis, induction of leaf chitinase activity, and, later, reduced shoot growth and lowered water content in leaves are observed. The pattern of the effects indicates that the basal toxicity mechanism of the two chromium species is connected to disturbance of the normal function of the root. Putrescine induction is an integrated part of the response mechanism of the stressed plants, appearing as an early sign of stress. However, the chromium concentration of the leaves as a warning of chromium-induced stress is judged to be an even more sensitive indicator.