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

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 (aN = 16.2 G; aH = 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 H2O2 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.