Table 3.

Hormones and their involvement in root growth and development

Phytohormone	Function	References
Auxin (IAA) NAA	Increases CRP initiation and outgrowth	Sreevidya et al. (2010)
2,4-D	Increases CRP initiation through cell division (but does not promote cell elongation and root outgrowth)	Sreevidya et al. (2010) and Debi et al. (2005)
Kinetin, trans-zeatin	Stimulates elongation of LRs	Sreevidya et al. (2010), Ashikari et al. (2005), Jain et al. (2006), Kurakawa et al. (2007) and Debi et al. (2005)
Kinetin, trans-zeatin	Stimulates CRP formation	Debi et al. (2005), Hirose et al. (2007) and Zhao et al. (2009)
Gibberellins (GA3)	Interacts with ethylene to promote CRP outgrowth and elongation	Steffens et al. (2006)
Gibberellins	Controlling root development by regulating local auxin biosynthesis and polar auxin transport by modulating the expression of OsYUCCA6 and PIN	Li et al. (2020a, b)
Ethylene	Promotes CR formation at submerged nodes–internodes	Lorbiecke and Sauter (1999)
Ethylene	Promotes CR emergence at submerged nodes through induction of epidermal cell death	Mergemann and Sauter (2000)
Strigolactones (SLs)	Promote CR elongation by inducing meristematic cell division	Arite et al. (2012)
Abscisic acid	Promotes root hair elongation by regulating auxin homeostasis in root tips	Wang et al. (2017)
Auxin and melatonin	Regulates root architecture by modulating auxin response in rice	Liang et al. (2017)