Nitric oxide implication in cadmium-induced programmed cell death in roots and signaling response of yellow lupine plants

The sequence of events leading to the programmed cell death (PCD) induced by heavy metals in plants is still the object of extensive investigation. In this study we showed that roots of 3-day old yellow lupine (Lupinus luteus L.) seedlings exposed to cadmium (Cd, 89 μM CdCl2) resulted in PCD starting from 24 h of stress duration, which was evidenced by TUNEL-positive reaction. Cd-induced PCD was preceded by a relatively early burst of nitric oxide (NO) localized mainly in the root tips. Above changes were accompanied by the NADPH-oxidase-dependent superoxide anion (O2−) production. However, the concomitant high level of both NO and O2− at the 24th h of Cd exposure did not provoke an enhanced peroxynitrite formation. The treatment with the NADPH-oxidase inhibitor and NO-scavenger significantly reduced O2− and NO production, respectively, as well as diminished the pool of cells undergoing PCD. The obtained data indicate that boosted NO and O2− production is required for Cd-induced PCD in lupine roots. Moreover, we found that in roots of 14-day old lupine plants the NO-dependent Cd-induced PCD was correlated with the enhanced level of the post-stress signals in leaves, including distal NO cross-talk with hydrogen peroxide.