Melatonin acts as a growth‐stimulating compound in some monocot species

TLDR

Melatonin, a well‑studied animal molecule, has been shown to act as a growth‑promoting hormone in lupin hypocotyls. The study investigates melatonin’s growth‑promoting activity in the coleoptiles of canary grass, wheat, barley, and oat. Melatonin and IAA were quantified in etiolated coleoptiles using liquid chromatography with electrochemical detection and tandem mass spectrometry, revealing comparable concentrations. Melatonin exhibited auxin‑like growth promotion in coleoptiles (10–55% of IAA activity) and inhibited root growth similarly to auxin, indicating that melatonin and auxin coexist and may act together as auxinic hormones.

Abstract

Abstract: In a recent study melatonin ( N ‐acetyl‐5‐methoxytryptamine), a well‐investigated animal molecule but minimally studied in plants, was seen to have a physiological role as growth‐promoting molecule in lupin hypocotyls. In the present study, the role of melatonin as a growth promoter is extended to coleoptiles of canary grass, wheat, barley and oat, in which it shows a relative auxinic activity [with respect to indole‐3‐acetic acid (IAA), the main auxin in plants] of between 10 and 55%. In addition, melatonin is seen to have an important inhibitory growth effect on roots similar to that played by auxin. The quantitation by liquid chromatography with electrochemical detection and identification by tandem mass spectrometry of melatonin and IAA in etiolated coleoptiles of the monocots assayed showed that both compounds are present in similar levels in these tissues. These results point to the co‐existence of auxin and melatonin in tissues and raises the possibility of their co‐participation in some physiological actions as auxinic hormones in plants.