Changes in the nature of phenolic deposits after re-warming as a result of melatonin pre-sowing treatment of Vigna radiata seeds

Changes in phenolics (PhC – phenolic compounds) measured as UV-absorbing compounds (UVAC) and their localization as well as growth, lipid peroxidation (TBARS level) and proline (Pro) level in three-day-old roots of seedlings (To stage) obtained from hydroprimed (H) and hydroprimed with melatonin (H-MEL) seeds after 2 days of chilling (5 °C) and 2 days of re-warming were examined. H and H-MEL resulted in inhibition of root growth under optimal conditions, but after re-warming, a positive effect of MEL was noted. The results also showed a positive MEL impact on TBARS level already after chilling and especially after re-warming. Exposure of Vigna radiata seedlings to chilling caused a significant increase in Pro level, especially in H-MEL roots, but after re-warming it drastically decreased. Under chilling stress, accumulation of UVAC also decreased. However, after re-warming it returned to the level observed in the roots grown constantly at 25 °C. Even if after re-warming of V. radiata seedlings only slight accumulation of total PhC was observed, phenolic deposits accumulating in the vacuoles of H-MEL roots were completely different from those in the vacuoles of the control and H roots. H-MEL application to the seeds resulted in a significant increase in small granular composite materials, while in the control and H roots, large oval deposits prevailed. Taken together, it is probable that all of these differences were connected with positive effects of MEL on chilled V. radiata seedlings after re-warming.