Nitric oxide and hydrogen peroxide are important signals mediating the allelopathic response of Arabidopsis to p‐hydroxybenzoic acid

Abstract Both nitric oxide ( NO ) and hydrogen peroxide ( H 2 O 2 ) are important signals that mediate plant response to environmental stimulation. Their role in plants' allelopathic interactions has also been reported, but the underlying mechanism remains little understood. p ‐Hydroxybenzoic acid (p HBA ) has been proposed to be an allelopathic chemical. Here, we found that pHBA at 0.4 m M efficiently suppressed Arabidopsis growth. Meanwhile, p HBA rapidly induced the accumulation of NO and H 2 O 2 , where such effect could be reversed by NO or H 2 O 2 metabolism inhibitors or scavengers. Also, p HBA ‐induced NO and H 2 O 2 could be compromised in NO synthesis mutants noa1 , nia1 and nia2 , or H 2 O 2 metabolism mutant rbohD/F , but suppressing NO accumulation with a NO synthesis inhibitor or using NO synthesis‐related mutants did not reduce p HBA ‐induced H 2 O 2 accumulation. Furthermore, we found that the effect of pHBA on allelopathic inhibition of growth was aggravated in NO / H 2 O 2 metabolism‐related mutants or reducing NO / H 2 O 2 by different inhibitors, whereas the addition of an NO / H 2 O 2 donor could partly relieve the inhibitory effect of pHBA on the growth of wild type. However, adding only an NO donor, but not low concentration of H 2 O 2 as the donor, could relieve the inhibitory effect of p HBA on root growth in NO metabolism mutants. On the basis of these results, we propose that both NO and H 2 O 2 are important signals that mediate Arabidopsis response to the allelopathic chemical p HBA , where during this process H 2 O 2 may work upstream of the NO signal.