Table 2.

Summary of plant hormones, their role in relation to tree-ring formation.

Plant hormone	Roles	References
Auxin (IAA)	Auxin gradient may provide location information for tissue differentiation, and the concentration of auxin is related to the fate of cells. High concentration of auxin can maintain cell meristem, while low concentration of auxin will lead to its differentiation into xylem or phloem	(Bhalerao and Fischer, 2014; Bürger and Chory, 2020)
Gibberellins (GAs)	Promote the division of cambium cells and enhance polar transport; Regulate xylem division and differentiation	(Israelsson et al., 2005; Jasinski et al., 2005; Tal et al., 2016; Ikematsu et al., 2017; Johnsson et al., 2019)
Cytokinins (CTKs)	Plays a central role in the initiation and development of cambium, which can promote the division of vascular stem cells	(Randall et al., 2015; De Rybel et al., 2013; Smet et al., 2019)
Strigolactones (SLs)	Positive regulation of cambium activity and conservation among species	(Hayward et al., 2009; Bürger and Chory, 2020)
Ethylene	Promote cambium division and wood formation	(Etchells and Turner, 2010; Etchells et al., 2012)
Jasmonic acid (JAs)	Promote secondary growth, accelerate the start of cambium, and thicken the stem.	(Sehr et al., 2010)
Brassinosteroid (BRs)	Critical signals to promote procambium division during plant primary growth	(Wang et al., 2022)