Contribution of pre-storage melatonin application to chilling tolerance of some mango fruit cultivars and relationship with polyamines metabolism and γ-aminobutyric acid shunt pathway

The efficacy of pre-storage application of 100 mu M melatonin on conferring chilling tolerance in fruit of four mango cultivars stored at 5 +/- 1 degrees C for 28 d was investigated. Tangra' and 'Gulab Jamun' mangoes had maximum and minimum chilling tolerance, respectively. Accumulation of endogenous polyamines and gamma-aminobutyric acid (GABA) in the peel and the pulp of Tangra' fruit treated with melatonin was a possible reason for its chilling tolerance. Accumulation of endogenous polyamines was associated with higher arginine decarboxylase (ADC) and ornithine decarboxylase (ODC), and lower diamine oxidase (DAO) and polyamine oxidase (PAO) activities in the peel and pulp. Additionally, higher GABA shunt (Glutamate decarboxylase and GABA-transaminase) activity was associated with elevated GABA content in Tangra' mangoes. The limited effectiveness of melatonin treatment for chilling injury alleviation in 'Chaunsa' was probably due to higher polyamines accumulation accompanied with lower PAO and DAO activity in the peel and pulp of the fruit, in addition to higher ADC and ODC in the peel.