Effects of Gamma-aminobutyric Acid Treatment on Postharvest Chilling Injury on Tomato Fruit

In recent years, γ-aminobutyric acid (GABA), a non-proteinogenic four-carbon signaling amino acid, has been employed as a safe strategy for attenuating chilling injury and fungal decay, delaying senescence and keeping sensory and nutritional quality of fruits and vegetables during postharvest life. In addition to applying GABA as exogenous safe procedure, heightening cellular GABA shunt pathway activity also is pivotal for attenuating chilling injury and fungal decay, delaying senescence and keeping sensory and nutritional quality of fruits and vegetables during postharvest life. Low temperature storage is widely employed for prolonging postharvest life of fruits and vegetables accompanying by keeping sensory and nutritional quality. Tomato is one of the most important horticultural crops, which exhibits higher benefits for human health but being endemic to subtropical climates, they are very vulnerable to chilling injury. Cold storage application is normally employed as a regular low-cost real postharvest technology. Owing to its great socio-economic significance, great efforts have been done by researchers to attenuating chilling injury in tomato fruits during low temperature storage employing safe strategies such as melatonin, brassinosteroids, salicylic acid, nitric oxide, and gibberellic acid. Attenuating chilling injury in tomato fruits by postharvest treatments may attribute to keeping safe membrane integrity representing by lower electrolyte leakage and malondialdehyde (MDA) accumulation occurring by eliciting endogenous polyamines, proline and nitric oxide accumulation by activating CBF1 signaling pathway, hampering phospholipase D (PLD) and lipoxygenase (LOX) enzymes activity, activating reactive oxygen species (ROS) scavenging enzymes activity resulting in higher ascorbic acid and glutathione accumulation, maintaining endogenous GA3 homeostasis occurring by higher CBF1 signaling pathway concurrent with higher endogenous salicylic acid accumulation, which not only are pivotal for conferring chilling tolerance in tomato fruits but also are crucial for preserving sensory and nutritional quality.

Tomato fruits (Solanum lycopersicum cv. Izmir) were picked at the mature green stage in Zanjan Province, Iran, and transported to the fruit analysis laboratory at Zanjan University. In the laboratory, the fruit was screened for uniform size, maturity, and absence of mechanical damage. Fruits (1440) were divided into four groups, each consisting of 360 fruits. The experiment was done in triplicate in which each replicate consisted of 120 fruits. The exogenous GABA applying was done by immersing of fruits in GABA at 0, 0.1, 1, and 5 mM for 15 min at 20 ˚C. Then, fruits were air dried at room temperature and stored at 4 ± 0.5 ºC (85–90 % RH) for 28 days. After assessment of chilling injury every 7 days during storage at 4 ˚C followed by shelf life at 25 ºC for 3 days, biochemical analyses were performed.

In recent experiment, we showed that the exogenous GABA applying, especially at 5 mM, is beneficial for attenuating chilling injury in tomato fruits during storage at 4 ºC for 28 days which was associated with higher membrane integrity representing by lower electrolyte leakage and malondialdehyde (MDA) accumulation. Keeping safe membrane integrity in tomato fruits in response to exogenous GABA applying may ascribe to triggering reactive oxygen species (ROS) scavenging catalase (CAT), superoxide dismutase (SOD) and ascorbate peroxidase (APX) enzymes activity giving rise to higher endogenous ascorbic acid accumulation concomitant with promoting phenylpropanoid pathway activity representing by higher phenylalanine ammonia lyase (PAL) enzyme activity giving rise to higher phenols and flavonoids accumulation and superior DPPH scavenging capacity.

Therefore, exogenous application of GABA not only is proficient for attenuating chilling injury but also is beneficial for preserving nutritional quality of tomato fruits during storage at 4 ºC for 28 days.