Free radical production in roots of Phaseolus vulgaris subjected to phosphate deficiency stress

Abstract We subjected bean plants ( Phaseolus vulgaris L. cv. ‘Zlota Saxa’) to phosphate deficiency stress and studied free radical production in whole root extracts. Starting from the 12th day of growth a carbon-centred free radical was detected, by means of electron spin resonance (ESR) after spin trapping with 5,5-dimethyl-L-pyrroline- N -oxide (DMPO), only in phosphate-deficient plants. The simulated hyperfine coupling constants of this spectrum ( a N  = 16.2 G; a H  = 23.6 G) are consistent with an aliphatic or an aromatic carbon-centred radical; this species could derive from lipid peroxidation or phenol oxidation processes, respectively. Hydrogen peroxide production was also enhanced. Production of both H 2 O 2 and DMPO adduct were related to the length of growth on the phosphate-deficient medium. Roots from phosphate-deficient plants showed increased content of phenols and a redox state of ascorbate similar to the control. These results indicate that phosphate starvation imposes a mild oxidative stress.