γ-aminobutyric acid treatment inhibits browning and promotes storage quality by regulating reactive oxygen species and membrane lipid metabolism in fresh-cut stem lettuce.

The effects of γ-aminobutyric (GABA) on enzymatic browning, storage quality, membrane and reactive oxygen species (ROS) metabolism in fresh-cut stem lettuce were investigated. The results illustrated that GABA treatment delayed browning degree, polyphenol oxidase (PPO) activity and the expression of LsPPO. Meanwhile, higher chlorophyll and ascorbic acid contents were exhibited in GABA-treated stem lettuce, as well as the slower microbial propagation. Further investigation revealed that exogenous GABA application declined malondialdehyde content, electrolyte leakage and the enzyme activities of membrane metabolism, and the expression levels of related genes were also downregulated. In addition, GABA treatment scavenged ROS and strengthened the enzyme activities of ROS metabolism, as well as the expression levels of corresponding genes. Taken together, these findings implied that the repressed enzymatic browning and microbial propagation in GABA-treated stem lettuce were due to the inhibition of ROS accumulation, enhancement of membrane stability and increased resistance to oxidation.

Phosphatidylinositol-specific phospholipase C-associated phospholipid metabolism mediates DcGLRs channel to promote calcium influx under CaCl2 treatment in shredded carrots during storage.

The rapid activation of phosphatidylinositol-specific phospholipase C (PI-PLC) occurs early after the stimulation of biotic and abiotic stress in plants, which directly associated with the calcium channel-induced calcium ion (Ca2+) influx. Exogenous calcium chloride (CaCl2) mediates the calcium signaling transduction to promote the γ-aminobutyric acid accumulation and nutritional quality in shredded carrots whereas the generation mechanism remains uncertain. Therefore, the involvement of PI-PLC-associated phospholipid metabolism was investigated in present study. Our result revealed that CaCl2 treatment promoted the expression and activity of PI-PLC and increased the inositol 1,4,5-trisphosphate and hexakisphosphate content in shredded carrots. The transcripts of multi-glutamate receptor-like channels (DcGLRs), the glutamate and γ-aminobutyric acid (GABA) content, and Ca2+ influx were induced by CaCl2 treatment in shredded carrots during storage. However, PI-PLC inhibitor (U73122) treatment inhibited the activation of PI-PLC, the increase of many DcGLRs family genes expression levels, and Ca2+ influx. Moreover, the identification of DcPI-PLC4/6 and DcGLRs proteins, along with the analysis of characteristic domains such as PLCXc, PLCYc, C2 domain, transmembranous regions, and ligand binding domain, suggests their involvement in phospholipid catalysis and calcium transport in carrots. Furthermore, DcPI-PLC4/6 overexpression in tobacco leaves induced the Ca2+ influx by activating the expressions of NtGLRs and the accumulation of glutamate and GABA. These findings collectively indicate that CaCl2 treatment-induced PI-PLC activation influences DcGLRs expression levels to mediate cytosolic Ca2+ influx, thus, highlighting the "PI-PLC-GLRs-Ca2+" pathway in calcium signaling generation and GABA biosynthesis in shredded carrots.

Genome-wide identification and role of HSFs in antioxidant response of hot water treated zucchini fruit during cold storage.

Zucchini squashes are cold-sensitive and vulnerable to chilling injury (CI) resulting from reactive oxygen species (ROS) and hot water (HW) immersing effectively reduce CI symptoms during cold storage. However, mechanism involved in reduced ROS due to HW treatment has not been characterized well. In this study, tender green zucchini fruit were treated with HW for 15 min at 45 ± 1 °C and stored for 15 d at 4 ± 1 °C and above 90 % relative humidity. Results showed substantial reduction in CI index, electrolyte leakage, malonaldehyde (MDA) contents and ROS accumulation along with increased activity of ROS-scavenging enzymes due to HW treatment. To gain insight into the molecular mechanism involved in antioxidant defense system, transcriptomic analysis revealed that heat shock factors (HSF) accumulated due to HW treatment regulated the ROS pathway during cold stress. CpHSFA4a was one of the highly expressed transcription factors (TF) due to HW treatment that regulated the transcription of ROS enzymes related genes. CpHSFA4a bind actively with heat shock element (HSE) in promoter regions of CpSOD, CpCAT, CpAPX1, CpAPX2, and CpAPX3, activated and increased the expression of these genes. In conclusion, HW treatment alleviated the CI by maintaining ROS homeostasis through CpHSFA4a mediated ROS pathway in zucchini squashes during cold storage.

Exogenous CaCl2 reduces the oxidative cleavage of carotenoids in shredded carrots by targeting CAMTA4-mediated transcriptional repression of carotenoid degradation pathway.

Carotenoid oxidative cleavage is a significant factor contributing to the color changes of shredded carrots and treatment with calcium chloride (CaCl2, 1% w/v) has been observed to alleviate the whitening symptom and color loss. However, the specific mechanism by which CaCl2 treatment suppresses carotenoid degradation remains unclear. In this study, the effect of CaCl2 and EGTA (calcium ion chelating agent) treatment on carotenoid biosynthesis and degradation in shredded carrots and the mechanism involved was investigated. CaCl2 treatment promoted the expression and activity of carotenoid biosynthetic enzyme (phytoene synthase, PSY), but inhibited the increases of the degradative enzyme activity of carotenoid cleavage dioxygenase (CCD) and down-regulated the corresponding transcripts, thus delayed the degradation of total carotenoid and maintaining higher levels of major carotenoid compounds including ß-carotene, α-carotene, lycopene, and lutein in shredded carrots during storage. However, EGTA treatment promoted the gene expression and enzyme activity of CCD and increased the degradation of carotenoid compounds in shredded carrots during storage. Furthermore, the CaCl2 treatment induced DcCAMTA4, identified as a calcium decoder in shredded carrots, which, in turn, suppressed the expressions of DcCCD1 and DcCCD4 by interacting with their promoters. The transient overexpression of DcCAMTA4 in tobacco leaves led to reduced expression of NtCCD1 and NtCCD4, maintaining a higher content of carotenoids. Thus, CaCl2 alleviated the oxidative cleavage of carotenoids in shredded carrots through the DcCAMTA4-mediated carotenoid degradation pathway.

Exogenous chlorogenic acid inhibits quality deterioration in fresh-cut potato slices.

Fresh-cut potatoes are prone to surface browning and physiological degradation. Chlorogenic acid (CGA), a natural phenolic antioxidant, has demonstrated preservative properties in various postharvest products. However, the underlying mechanisms of its application on maintaining quality remain unclear. Therefore, the effect of exogenous CGA treatment on quality deterioration of potato slices and the mechanisms involved were investigated. Results revealed CGA treatment retarded the browning coloration, suppressed microbial growth and inhibited the declines in starch, and ascorbic acid contents in potato slices. Meanwhile, the treatment activated the phenylpropanoid pathway but decreased the activities of phenolic decomposition-related enzymes such as polyphenol oxidase (PPO) and tyrosinase and downregulated StPPO expression. Moreover, the treated slices exhibited reduced accumulation of reactive oxygen species and increased activity of antioxidant enzymes. Additionally, they displayed enhanced 2,2-diphenyl-1-picrylhydrazyl radicals scavenging capacity and higher ATP levels. Therefore, these findings indicated that CGA treatment was effective for quality maintenance and antioxidant capacity enhancement in fresh-cut potatoes, thereby providing potential strategies for the preservation and processing of fresh-cut produce.

Glutamate application maintains quality and antioxidant capacity of fresh-cut carrots by modulating GABA shunt, phenylpropanoid and ROS metabolism.

The effects of exogenous glutamate treatment on the quality attributes, γ-aminobutyric acid (GABA) shunt, phenylpropanoid pathway, and antioxidant capacity of fresh-cut carrots were investigated. Results showed that glutamate treatment suppressed the increases in lightness and whiteness values, inhibited the degradation of total carotenoids and maintained better flavor and taste in fresh-cut carrots. Moreover, glutamate treatment rapidly promoted the activities of glutamate decarboxylase and GABA transaminase, thus improving the GABA content. It also significantly enhanced the activities of phenylalanine ammonia-lyase, cinnamate-4-hydroxylase, and 4-coumarate coenzyme A ligase and promoted the accumulation of total phenolics as well as the main individual phenolic compounds, including chlorogenic and caffeic acid. In addition, glutamate application activated the reactive oxygen system-related enzyme including peroxidase, superoxide dismutase, ascorbate peroxidase, and catalase activities to maintain higher antioxidant capacity in fresh-cut carrots. These results demonstrated that exogenous glutamate treatment maintained better nutritional quality and alleviated color deterioration by accelerating the accumulation of GABA and phenolics and enhancing the antioxidant capacity in fresh-cut carrots.

CmCML11 interacts with CmCAMTA5 to enhance γ-aminobutyric acid (GABA) accumulation by regulating GABA shunt in fresh-cut cantaloupe.

The effect of calcium chloride (CaCl2) treatment on γ-aminobutyric acid (GABA) accumulation in fresh-cut cantaloupe and the involved mechanisms were investigated. The result showed that 1% (w/v) CaCl2 treatment increased GABA content and activities of glutamate decarboxylase (GAD) and succinate semialdehyde dehydrogenase (SSADH), while decreased glutamate (Glu) content and GABA transaminase (GABA-T) activities in fresh-cut cantaloupe. CmCML11 and CmCAMTA5 expressions of CaCl2-treated fruit increased by 187.4% and 165.6% than control fruit in the initial 6 h. Besides, expressions of GABA shunt genes, including CmGAD1, CmGAD2, CmGABA-T and CmSSADH were also up-regulated by CaCl2 treatment during early storage. Moreover, acting as a transcriptional activator, CmCAMTA5 could bind to the CG-box in promoters of CmGAD1, CmGABA-T and CmSSADH and activate their transcription. Furthermore, the interaction between CmCML11 and CmCAMTA5 could enhance the transcriptional activation on GABA shunt genes which were regulated by CmCAMTA5. Collectively, our findings revealed that CaCl2 treatment promoted GABA accumulation in fresh-cut cantaloupe via the combined effect of CmCML11 and CmCAMTA5 in the regulation of expressions of CmGAD1, CmGABA-T, and CmSSADH in GABA shunt.