Exogenous γ-Aminobutyric Acid Treatment That Contributes to Regulation of Malate Metabolism and Ethylene Synthesis in Apple Fruit during Storage

Abstract

Organic acid is an important indicator of fruit quality, and malate is the predominant organic acid in apple fruit. However, the regulation of malate metabolism in postharvest fruit is rarely reported. Here, we found that, compared with a control treatment, a 10 mM γ-aminobutyric acid (GABA) treatment remarkably delayed the loss of tiftratable acidity and malate and increased the succinate and oxalate contents in “Cripps Pink” fruit stored in polyethylene bags at room temperature. The higher malate levels in GABA-treated fruit were accompanied by higher activities of cytosolic nicotinamide adenine dinucleotide-dependent malate dehydrogenase (cyNAD-MDH) and phosphoenolpyruvate carboxylase (PEPC) but lower cytosolic NAD phosphate-dependent malic enzyme (cyNADP-ME) and phosphoenolpyruvate carboxykinase (PEPCK) activities than those seen in control fruit. Notably, ethylene production was significantly reduced by GABA treatment, paralleling the downregulation of MdACS, MdACO, and MdERF expression. Meanwhile, GABA treatment also enhanced the activity of the GABA shunt and promoted the accumulation of GABA. This study provides new insights into the regulation of malate metabolism and reports for the first time the possible interplay between GABA and ethylene signaling pathways in apple fruit during postharvest storage.

Application of γ-Aminobutyric Acid Treatment Differently Affects Physicochemical Characteristics of Tomato Fruits during Post-harvest Storage

“…A value of 10 mM of GABA treatment not only reduced the respiratory rate but also inhibited the ethylene production in apple fruits. Moreover, the expression levels of MdACO, MdACS and MdERF were restricted to varying degrees by 10 mM GABA treatment; this revealed that GABA participates in the regulation of ethylene biosynthesis and signal transduction at the molecular level (Han et al, 2018). It was recently suggested that higher fruit firmness in response to GABA may result directly from GABA treatment or indirectly from lower ethylene biosynthesis or higher level of cell wall hydrolysing enzymes such as PG and PL.…”

γ-Aminobutyrate Improves the Postharvest Marketability of Horticultural Commodities: Advances and Prospects

“…The temporal patterns for GABA (i.e., slow decrease of approximately 60% from 10 to 40 days, followed by a dramatic increase at 70 days, presumably due to fruit aging and cellular disintegration at the end of storage), succinate and malate (slow decrease of 40 and 20%, respectively, from 30 to 70 days) indicate that GABA does not accumulate under storage at RT, and that GABA is probably catabolized to succinate and malate ( Han et al, 2018 ). The application of exogenous GABA increases the expression of MdGAD1 , MdGAD2, MdGABA-T1,2 and MdSSADH1 , restrains the decrease in malate and succinate levels, decreases respiration and ethylene production rates, and delays the ethylene production peak ( Han et al, 2018 ; Table 3 ).…”

“…The temporal patterns for GABA (i.e., slow decrease of approximately 60% from 10 to 40 days, followed by a dramatic increase at 70 days, presumably due to fruit aging and cellular disintegration at the end of storage), succinate and malate (slow decrease of 40 and 20%, respectively, from 30 to 70 days) indicate that GABA does not accumulate under storage at RT, and that GABA is probably catabolized to succinate and malate ( Han et al, 2018 ). The application of exogenous GABA increases the expression of MdGAD1 , MdGAD2, MdGABA-T1,2 and MdSSADH1 , restrains the decrease in malate and succinate levels, decreases respiration and ethylene production rates, and delays the ethylene production peak ( Han et al, 2018 ; Table 3 ). Notably, the application of exogenous Ca 2+ decreases the Glu level (before 30 days), increases the levels of GABA, succinate and malate (10–60 days) and expression of MdGAD1 (before 30 days), MdGAD2 (20–40 days), MdGABA-T1/2 (10–20 days) and MdSSADH (20–40 days), suppresses the respiration rate, and decreases the ethylene production peak ( Han et al, 2021 ).…”

Isolation, sequencing, and expression analysis of 30 AP2/ERF transcription factors in apple

“…is one of the most important tree fruits in the world. However, progress on the ERF transcription factors in apple is more limited than that in model plants like Arabidopsis thaliana, and most researches about apple are focused on fruit ripening and softening (Wang et al, 2007;Tacken et al, 2010;Li et al, 2016;An et al, 2017;Li et al, 2017;Han et al, 2018a;Han et al, 2018b). In this study, we obtained the AP2/ERF transcription factor in apple based on previous results (Girardi et al, 2013) and from the Plant Transcription Factor Database (http://planttfdb.cbi.pku.edu.cn/).…”