γ-Aminobutyric acid is involved in overlapping pathways against chilling injury by modulating glutamate decarboxylase and defense responses in papaya fruit.

The effect of γ-aminobutyric acid (GABA) treatment at two concentrations (1 mM or 5 mM) on papaya fruit stored at 4°C and 80%-90% relative humidity for 5 weeks was investigated. The application of GABA at 5 mM apparently inhibited chilling injury, internal browning, electrolyte leakage, malondialdehyde (MDA), hydrogen peroxide (H2O2), polyphenol oxidase (PPO), phospholipase D (PLD), and lipoxygenase (LOX) activities of papaya fruit. Fruit treated with 5 mM GABA enhanced the activities of ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR), superoxide dismutase (SOD), glutamate decarboxylase (GAD), and phenylalanine ammonia-lyase (PAL). In addition, GABA treatment significantly displayed higher levels of proline, endogenous GABA accumulation, phenolic contents, and total antioxidant activity than the nontreated papaya. The results suggested that GABA treatment may be a useful approach to improving the chilling tolerance of papaya fruit by reducing oxidative stress and enhancing the defense system.

Hydrogen Sulfide Mitigates Chilling Injury of Postharvest Banana Fruits by Regulating γ-Aminobutyric Acid Shunt Pathway and Ascorbate-Glutathione Cycle.

This study aimed to determine the effect of hydrogen sulfide on chilling injury (CI) of banana (Musa spp.) during cold storage (7°C). It was observed that hydrogen sulfide application (2 mmol L-1) markedly reduced the CI index and showed significantly higher chlorophyll contents, along with suppressed chlorophyll peroxidase and chlorophyllase enzyme activity. The treated banana fruits exhibited substantially higher peel lightness (L*), along with significantly a lower browning degree and soluble quinone content. The treated bananas had substantially a higher endogenous hydrogen sulfide content and higher activity of its biosynthesis-associated enzymes such as D-cysteine desulfhydrase (DCD) and L-cysteine desulfhydrase (LCD), along with significantly lower ion leakage, lipid peroxidation, hydrogen peroxide, and superoxide anion concentrations. Hydrogen sulfide-treated banana fruits showed an increased proline content and proline metabolism-associated enzymes including ornithine aminotransferase (OAT), Δ1-pyrroline-5-carboxylate synthetase (P5CS), and proline dehydrogenase (PDH). In the same way, hydrogen sulfide-fumigated banana fruits accumulated higher endogenous γ-aminobutyric acid (GABA) due to enhanced activity of glutamate decarboxylase (GAD) and GABA transaminase (GABA-T) enzymes. The hydrogen sulfide-treated fruits exhibited higher total phenolics owing to lower polyphenol oxidase (PPO) and peroxidase (POD) activity and stimulated phenylalanine ammonia lyase (PAL). The treated banana exhibited higher ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR), and superoxide dismutase (SOD) activity, along with higher glutathione (GSH) and ascorbic acid (AsA) concentrations and a significantly lower dehydroascorbic acid (DHA) content. In conclusion, hydrogen sulfide treatment could be utilized for CI alleviation of banana fruits during cold storage.

Effect of postharvest oxalic acid application on enzymatic browning and quality of lotus (Nelumbo nuciferaGaertn.) root slices.

Post-cut surface browning is one of the major constraints for shelf-life extension of lotus root slices. In the present study, lotus roots slices were treated with 0, 5 and 10 mmol L-1 oxalic acid and stored at 20 ± 1 °C for 5 days. Results showed that 10 mmol L-1 oxalic acid treated lotus slices exhibited reduced browning, superoxide anion, hydrogen peroxide, electrolyte leakage and malondialdehyde content than control. The 10 mmol L-1 treated slices had better visual quality and higher ascorbic acid and total phenolic contents. In addition, 10 mmol L-1 treated slices showed reduced total bacterial count along with lower soluble quinones, peroxidase and polyphenol oxidase activities in contrast to control. Similarly, 10 mmol L-1 treatment showed higher superoxide dismutase, catalase and ascorbate peroxidase activities as compared to control. In conclusion, 10 mmol L-1 oxalic acid application could be considered suitable to delay post-cut browning of lotus root slices.

Effect of pre-storage ascorbic acid and Aloe vera gel coating application on enzymatic browning and quality of lotus root slices.

The effect of ascorbic acid [AA (1%)] and Aloe vera gel [AVG (50%)] coating alone and in combination was investigated on enzymatic browning and quality of lotus root slices during storage at 20 ± 1°C. The combined application of AA and AVG coating delayed surface browning, reduced increase in relative electrolyte leakage (REL) and showed higher overall visual quality (OVQ). Similarly, AA and AVG combined treatment reduced superoxide anion ( O2-· ) and hydrogen peroxide (H2 O2 ) production and malondialdehyde (MDA) content, and suppressed peroxidase (POD) and polyphenol oxidase (PPO) activities. In addition, AA and AVG treatment conserved higher AA content, ascorbate peroxidase (APX), superoxide dismutase (SOD) and catalase (CAT) enzymes activities along with higher total phenolics and radical scavenging activity. In conclusion, the combined application of AA and AVG coating could be an appropriate treatment to delay surface browning and quality loss of lotus root slices. PRACTICAL APPLICATIONS: Lotus root is an aquatic rhizome vegetable. The fresh-cut slices of lotus roots are prone to post-cut enzymatic browning and quality deterioration during postharvest storage. Browning induced loss of visual quality and microbial infestations are the leading constraints in extending storage and/or shelf life of lotus root slices. Surface browning results in loss of characteristic color eventually leading to significant reduction in market potential and visual quality. However, quality deterioration and development of browning could be delayed with some suitable postharvest treatments. So, the effect of AA and Aloe vera gel based coating was investigated for quality conservation of lotus root slices. The findings of the current work are of global importance in reducing browning and conserving visual quality of lotus root slices in particular and fresh-cut produce in general.

Better salinity tolerance in tetraploid vs diploid volkamer lemon seedlings is associated with robust antioxidant and osmotic adjustment mechanisms.

Tetraploids are usually more tolerant to environmental stresses than diploids. Citrus plants face numerous abiotic stresses, including salinity, which negatively affect growth and yield. Double diploid citrus rootstocks have been shown to be more tolerant to abiotic stresses than their diploid relatives. In this study, we evaluated the antioxidative and osmotic adjustment mechanisms of diploid (2x) and double diploid (4x) volkamer lemon (Citrus volkameriana Tan. and Pasq.) rootstocks, which act against salt stress (75 and 150 mM). Results indicated that, under salt stress, all physiological variables (photosynthesis, stomatal conductance, transpiration rate, and leaf greenness) decreased, and these decreases were more noticeable in 2x plants than in 4x plants. On the other hand, accumulation of oxidative markers (malondialdehyde and hydrogen peroxide) was greater in the leaves and roots of 2x seedlings than in 4x seedlings. Similarly, the activities of antioxidative enzymes (peroxidase, ascorbate peroxidase, glutathione reductase, and catalase) were higher in the leaves and roots of 4x plants than in 2x plants. However, superoxide dismutase activity was higher in the roots of 2x seedlings than 4x seedlings. Double diploid plants affected by salt stress accumulated more osmolytes (i.e. proline and glycine betaine) in their leaves and roots than that by 2x plants. Total protein content, antioxidant capacity, and total phenolic content were also higher in 4x plants than 2x plants under salinity. At 150 mM, both 2x and 4x plants showed more symptoms of stress than those at 75 mM. Sodium content was the highest in the roots of 2x plants and in the leaves of 4x plants, while chloride content peaked in the leaves of 2x plants and in the roots of 4x plants. Overall, our results demonstrate that the active antioxidative defence mechanisms of 4x plants increase their tolerance to salinity compared to their corresponding 2x relatives. Thus, the use of newly developed tetraploid rootstocks may be a strategy for enhancing crop production in saline conditions.