Table 1.

Effects of HMs on the levels of endogenous melatonin accumulation in plants.

HMs	Plant Species	Exposed Organs	Concentration (µM)	Exposure Duration	MT Level	Reference
Al	Glycine max	Root	50	24 h	↑	[74]
Al	Nicotiana tabacum	Leaves	100	15 days	↑	[71]
Al	Oryza sativa	Seedlings	500	72 h	↓	[71]
Cd	Medicago sativa	Root	50, 100, and 200	15 h	↑	[67]
Cd	Solanum lycopersicum	Root	100	15 days	↑	[68]
Cd	Solanum lycopersicum	Leaves	100	15 days	↑	[70]
Cd	Nicotiana tabacum	Leaves	500	15 days	↑	[71]
Cd	Arabidopsis thaliana	Leaves	300	24 h	↑	[69]
Cd	Oryza sativa	Seedlings	500	72 h	↑	[71]
Zn	Hordeum vulgare	Root	100	15 h	↑	[65]
Zn	Hordeum vulgare	Root	100	72 h	↑	[65]
Zn	Lupinus albus	Root	100	24 h	↑	[66]

↑ (increase), ↓ (decrease), h (hour).