Inhibition of etiolated lupin hypocotyl growth and rooting by peroxides, ascorbate and glutathione

The influence of two oxidants (H2O2 and m-chloroperoxibenzoic acid (mCPBA)) and two reductants (ascorbate (ASC) and glutathione (GSH)) on growth and rooting of the etiolated Lupinus albus L. hypocotyls has been studied. Lupin seedlings were derooted and the hypocotyls treated for 24 h with aqueous solutions containing different concentrations (from 10 mu M to 50 mM) of the above compounds. The hypocotyl length and the number and length of the adventitious roots were determined periodically. All the assayed compounds showed a capacity to inhibit growth and rooting of the hypocotyls, the effect being dependent on the compound and its concentration. As a rule, the greater the concentration, the higher the inhibition. The compounds can be classified from higher to lower efficiency as inhibitors as follows: mCPBA, GSH, ASC and H2O2; therefore, inhibitory efficiency is seemingly dependent on the compound per se rather than on its redox nature. The higher effectiveness as inhibitor of mCPBA and GSH is discussed in light of their capacity to inactivate enzymes such as peroxidases, which are involved in plant development and in the protective mechanism against oxidative stress. The fact that younger, actively growing tissues were less sensitive than older hypocotyl tissues to the toxicity of mCPBA and GSH supports the view of a changing endogenous redox state during growth. Data presented here suggest that regulation of the redox balance is decisive in regulating plant morphogenesis.