γ-Aminobutyric acid (GABA) accumulation in four strawberry cultivars in response to elevated CO2 storage

Accumulation of γ-aminobutyric acid (GABA) is associated with stress factors in plant systems. The objective of the current study was to compare GABA concentrations in four strawberry (Fragaria × ananassa Duch) cultivars with different tolerances to postharvest CO2 treatment (20% in air) as indicated by accumulation of fermentation products. Color change of fruit of all cultivars was delayed by CO2 treatment. Concentrations of ethanol and ethyl acetate increased in CO2 treated fruit of ‘Jewel’ but not in ‘Allstar’, ‘Earliglow’, and ‘Northeaster’. Higher GABA concentrations were associated with elevated CO2 treatment in all cultivars compared with air, but GABA accumulations were much lower in ‘Allstar’ and ‘Earliglow’ than in ‘Jewel’ and ‘Northeaster’. At harvest, glutamate decarboxylase (GAD) activity was greater in fruit of ‘Jewel’ and ‘Northeaster’ than in ‘Allstar’ and ‘Earliglow’. GAD activity decreased during storage, but it was not affected by CO2. GABA transaminase (GABA-T) activity was lower in CO2 than air treated ‘Jewel’ fruit, but it was not affected consistently by CO2 in the other cultivars. The results indicate that high CO2 treatments increased GABA concentrations in strawberry fruit, but the accumulation is not consistently associated with sensitivity of the fruit to CO2 as indicated by accumulation of fermentation products.