Table 1.

Overview of small-molecule compounds that induce adventitious root (AR) formation and development under no stress in plants.

Small-Molecule Compounds	Plant Species	Small Signal Molecule Mediated Effects	References
NO	Marigold	NO can trigger AR development and enhances endogenous H2O2 levels	[23]
		IAAO, POD, and PPO↑	[27]
		NR and NOS can contribute to NO production to induce AR development	[16]
	Cucumber	NO induces AR formation through NOS and NR pathways	[24,25]
		NO can trigger AR development in a cGMP-dependent manner	[17]
		NO can induce AR formation and up-regulate cell cycle-related genes	[7]
		PPO↑; POD and IAAO↓	[30]
		Two NO-releasing compounds, NOS-like and DAO, trigger AR formation	[19]
		NR and NOS promote AR development and up-regulate their gene relative expression levels	[10]
	Ground-cover chrysanthemum	PPO, IAAO, WSC, and total nitrogen↑; total polyphenol content↓	[28]
	Mountain ginseng	CAT, POD, APX, DHAR, GR, NADPH, and O2−↑	[29]
H2	Cucumber	H2 upregulates cell cycle-related genes and promotes AR formation	[7]
		50% HRW significantly induces adventitious rooting and POD, PPO, and IAAO↑	[30]
	Marigold	RWC, WSC, starch, soluble protein content, POD, PPO, and IAAO↑; stomatal aperture and electrolyte leakage↓	[5]
H2S	Cucumber	10 μM NaHS triggers AR development	[16]
		H2S can induce AR primordia	[40]
	Willow	Endogenous H2S, IAA, and NO↑	[38]
	Soybean	Endogenous H2S, IAA, and NO↑	[38]
CO	Mung bean	NO fluorescence↑	[41]
	Cucumber	10 μM hemin and hematin can significantly induce AR development in cucumber	[17,42]
CH4	Cucumber	80% MRW increases root length and number	[19]
		CH4-induced adventitious rooting of cucumber explants requires γ-glutamyl cysteine SGH	[40,47]
ETH	Cucumber	Exposure of cucumber explants to ETH up-regulated NOS and NR activity and their gene relative expression levels	[10]
	Marigold	IAAO, POD, and PPO↑	[27]
H2O2	Cucumber	10–50 and 20–40 μM H2O2, respectively, increases the weight and number of AR respectively	[59]
	Marigold	200 μM H2O2 significantly induces root length and root number	[23]
		IBA and H2O2 may act synergistically to mediate adventitious rooting	[26]
	Ground-cover chrysanthemum	PPO, IAAO, WSC, and total nitrogen↑; total polyphenol content↓	[28]