Growth conditions determine different melatonin levels in Lupinus albus L.

Melatonin, an indoleamine, which has recently been assigned several roles in plant physiology as a growth promoter, as rooting agent, and as antioxidant in senescence delay and cytoprotection, seems to have a relevant function in plant stress situations. The presence of melatonin increases the resistance of lupin plant tissues (Lupinus albus L.) against natural or artificially induced adverse situations. In this work, we studied the response of lupin plants in controlled stress situations (drought-, anaerobic-, pH-, and cold stress and using ZnSO4, NaCl, and H2O2 as chemical stressors) and measured the changes in endogenous melatonin levels in lupin plants. Also, the effect of abscisic acid, ethylene, and natural environmental conditions were evaluated. In general, nearly all stressful factors caused an increase in melatonin in the investigated organs. The chemical stress provoked by ZnSO4 or NaCl caused the most pronounced changes in the endogenous level of melatonin, followed by cold and drought stressors. In some cases, the level of melatonin increased 12-fold with respect to the levels in control plants, indicating that melatonin biosynthesis is upregulated in common stress situations, in which it may serve as a signal molecule and/or as a direct antistress agent due to its well-known antioxidative properties.