Environmental and Experimental Botany 65 (2009) 63–71 Contents lists available at ScienceDirect Environmental and Experimental Botany journal homepage: www.elsevier.com/locate/envexpbot Hydrogen peroxide acts as a signal molecule in the adventitious root formation of mung bean seedlings Shi-Weng Li a,∗ , Lingui Xue a , Shijian Xu b , Huyuan Feng b , Lizhe An b a School of Chemical and Biological Engineering, Lanzhou Jiaotong University, 88 West Anning Road, Lanzhou 730070, Gansu Province, PR China b School of Life Sciences, State Key Lab of Arid and Grassland Ecology of MOE, Lanzhou University, 222 South Tianshui Road, Lanzhou 730000, Gansu Province, PR China article info Article history: Received 7 January 2008 Received in revised form 9 June 2008 Accepted 12 June 2008 Keywords: Hydrogen peroxide Signaling Adventitious roots Mung bean Mucuna pruriens L abstract Hydrogen peroxide (H 2 O 2 ), an active oxygen species, is widely generated in many biological systems and mediates various physiological and biochemical processes in plants. In this study we demonstrated that the exogenous H 2 O 2 was able to promote the formation and development of adventitious roots in mung bean seedlings. Treatments with 1–100 mM H 2 O 2 for 8–18 h significantly induced the formation and development of adventitious roots. Catalase (CAT) and ascorbic acid, which are H 2 O 2 scavengers or inhibitors, eliminated the adventitious root-promoting effects of exogenous H 2 O 2 .H 2 O 2 may have a down- stream signaling function in the auxin signaling pathway and be involved in auxin-induced adventitious root formation. 2,3,5-Triiodobenzoic acid (TIBA), an inhibitor of auxin polar transport, strongly inhib- ited adventitious rooting of mung bean seedlings; however, the inhibiting effects of TIBA on adventitious rooting can be partially reversed by the exogenous IBA or H 2 O 2 . Diphenylene iodonium (DPI) strongly inhibits the activity of NADPH oxidase, which is one of the main sources of H 2 O 2 formation in plant cells. DPI treatment strongly inhibited the formation of adventitious roots in mung bean, but the inhibitory effects of DPI on rooting can be partially reversed by the exogenous H 2 O 2 or IBA. This indicates that the formation of adventitious roots was blocked once the generation of H 2 O 2 through NADPH oxidase was inhibited, and H 2 O 2 mediated the IBA-induced adventitious root formation. Furthermore, a rapid increase in the endogenous level of H 2 O 2 was detected during incubation with water 12–36 h after the primary root removal in mung bean seedlings. Three hours after the primary root removal, the generation of endoge- nous H 2 O 2 was markedly induced in IBA-treated seedlings in comparison with water-treated seedlings. This implies that IBA induced overproduction of H 2 O 2 in mung bean seedlings, and that IBA promoted adventitious root formation via a pathway involving H 2 O 2 . Results obtained suggest that H 2 O 2 may func- tion as a signaling molecule involved in the formation and development of adventitious roots in mung bean seedlings. © 2008 Elsevier B.V. All rights reserved. 1. Introduction For many years, hydrogen peroxide (H 2 O 2 ), a form of reactive oxygen, was mainly viewed as a toxic cellular metabolite. How- ever, it is now clear that it functions as a signaling molecule that mediates responses to various stimuli in both plant and animal cells (Neill et al., 2002). Hydrogen peroxide is continually gener- ated from various sources during normal metabolism in plant cells. The electron transport processes during photosynthesis and respi- ration generate basal levels of H 2 O 2 . It is also produced in plant cells in response to a wide variety of abiotic and biotic stresses (Laloi et al., 2004). In addition, there are enzymatic sources of H 2 O 2 including NADPH (nicotinamide adenine dinucleotide phosphate) ∗ Corresponding author. Tel.: +86 931 4938702; fax: +86 931 7667661. E-mail address: Lishweng@yahoo.com.cn (S.-W. Li). oxidases, cell wall peroxidases, amine oxidases, as well as other flavin containing enzymes (Neill et al., 2002). Hydrogen peroxide mediates various physiological and bio- chemical process, including systemic acquired resistance (SAR) and hypersensitive resistance (HR) (Alvarez et al., 1998; Melillo et al., 2006), senescence (Hung et al., 2006), programmed cell death (PCD) (Levine et al., 1994; Desikan et al., 1998; Houot et al., 2001), stomatal closure (Pei et al., 2000; Zhang et al., 2001; Bright et al., 2006), root gravitropism (Joo et al., 2001), lateral root develop- ment (Su et al., 2006), cell wall development (Potikha et al., 1999), and pollen–stigma interactions and development (McInnis et al., 2006a,b). However, to date, we do not know whether hydrogen per- oxide is a messenger in IAA-induced adventitious root formation, or a mediator of the events responsible for adventitious rooting. Adventitious roots are post-embryonic roots that arise from the stem and leaves and from non-pericyclic tissues in old roots. Adventitious root formation is one of the most important means 0098-8472/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.envexpbot.2008.06.004