Table 1.

Effects of melatonin and serotonin on vegetative growth.

Effect	Concentration range	Species	Proposed mechanism of action	Reference
Melatonin
Delayed leaf senescence	20 µM – 10 mM	Malus sp., Arabidopsis thaliana, Hordeum vulgare, Oryza sativa	Antioxidant activity, inhibition chlorophyll degradation, upregulation ascorbic acid and glutathione pathways, down-regulation of senescence related genes, modification of photosynthesis and sugar metabolism, modification of nitrogen metabolism, decreased protein degradation	58,106-109,121,127
Increased number of lateral roots	50 – 500 uM	Arabidopsis thaliana, Lupinus albus, Cucumis sativus	Modification of expression levels of transcription factors, cell wall and peroxidase-related genes	62,63,90,94,156
Increased root elongation	0.05 – 100 uM	Virginia radiata, Prunus sp, Lupinus albus, rice, Arabidopsis thaliana, Helianthus annus	Antioxidant activity, increased carbohydrate concentration, interaction with calcium/calmodulin signaling cascades	48,52,90-93,158
Increased root number	0.1 – 200 uM	Brassica juncea, Hypericum perforatum, Prunus rootstocks, Punica granatum	Interaction with 5HT and auxin	8,31,88,89,91,92,159
Increased incidence somatic embryogenesis	100 uM	Coffea canephora	Interaction with calcium signaling cascades	102
Enhanced microspore development		Hypericum perforatum	Modification of calcium distribution	8
Increased plant biomass	0.05 – 10 µM	Prunus avium x Prunus cerasus, Oryza sativa, Arabidopsis thaliana	Enhancement of carbohydrate and proline metabolism	48,91,93,160
Increased number adventitious roots	0.5–100 µM	Lupinus albus, Oryza sativa, Prunus rootstocks		90,92,93,161
Increased seedling growth	10 µM	Oryza sativa, Lupinus albus, Brassica olereacea rubrum, Zea mays	Modification of calicium/calmodulin signaling pathways, enhancement of sugar metabolism, biosynthesis, hydrolysis and transport, enhanced photosynthesis and starch catabolism.	53,95,98,101,115,126
Inhibition of seedling growth	100 µM	Zea mays	Inhibition of sugar metabolism, starch accumulation, reduced sucrose biosynthesis, hydrolysis and transport	101
Increased shoot production	5.71 µM – 1.16 mg/L	Punica granatum, Vaccinium corymbosum, Mimosa pudica	Interaction with calcium signaling pathways	114,159,162
Inhibition of primary root formation	high concentration	Brassica juncea, Oryza sativa, Lupinus albus, Arabidopsis thaliana		48,89,93,115
Modification of stem and leaf branching patterns		Oryza sativa, Solanum lycopersicum	Interaction with auxin signaling genes	103,104
Chronoregulator	10 uM	Eichhornia crassipes, vitis vinifera, Prunus avium, Ulva sp, Chara australis, Chenopodium rubrum, Oryza sativa	Antioxidant activity, support of photosynthetic apparatus, light signaling	44,97,110,121,123,125,133,163
Increased hypocotyl elongation	5–40 uM	Helianthus annus, Lupinus albus		52,115
Promotion coleoptile growth		Phalaris canariensis, Avena sativa, Triticum aestivum, Hordeum vulgare	Interaction with polyamines and auxin, antioxidant activity	95
Promotion of germination	100–500 M	Cucumis sativus	Antioxidant	129
Serotonin
Increased incidence somatic embryogenesis	100 uM	Coffea canephora	Interaction with calcium signaling cascades	102
Increased shoot production	100–200 uM	Hypericum perforatum, Mimosa pudica	Interaction with MEL, auxin, and calcium signaling pathways	88,114
Delayed senescence	0.8 µM	Oryza sativa	Antioxidant	116
Increased root length	0.8 M – 20 uM	Hordeum vulgare, Helianthus annus		52,112
Increased root weight	0.8 µM	Hordeum vulgare		112
Increased coleoptile weight	0.8 µM	Hordeum vulgare		112
Increased mitotic index	0.8 µM	Hordeum vulgare		112
Increased lateral root formation	10–160 uM	Arabidopsis thaliana	Inhibition of auxin activity and transport, modification of auxin gene expression	111
Increased adventitious root formation	> 160 uM	Arabidopsis thaliana	Inhibition of auxin activity and transport, modification of auxin gene expression	111
Inhibition of primary root formation	10–160 uM	Arabidopsis thaliana	Inhibition of auxin activity and transport, modification of auxin gene expression	111
Increased hypocotyl elongation	5–15 uM	Helianthus annus		52
Induction of root formation		Juglans nigra x regia		113
Promotion germination		Hippeastrum hybridium		164