Nitric oxide effect on root architecture development in Malus seedlings

The time-dependent production of nitric oxide (NO) in roots induced by indole-3-butyric acid (IBA) and the effect of sodium nitroprusside (SNP) on root architecture development were investigated, using Malus hupehensis Rehd. seedlings. Following IBA application, a very rapid increase in NO formation and a subsequent second wave of NO burst was observed, which was related to the induction of lateral roots (LRs) and the organogenesis of lateral root primordia (LRP), respectively. The first NO burst was correlated with the second and the two peaks of NO burst induced by IBA were totally abolished by 3,3',4',5,7-pentahydroxyflavone (quercetin). Exogenous NO promoted the emergence and elongation of LR and inhibited the elongation of primary root (PR) in a dose-dependent manner: low concentrations of SNP promoted both the amounts and the elongation of LR but inhibited the elongation of LR and PR at higher concentrations. It was concluded that (i) the rapid production of NO induced by IBA was correlated with the IBA-induced initiation of LR; (ii) quercetin inhibition of IBA-induced LR formation was correlated with the quercetin inhibition of IBA-induced NO biosynthesis, and (iii) exogenous NO affects the development of root system architecture in a dose-dependent manner.