Different Responses of Two Contrasting Strawberry Cultivars to Heat Exposure Associated with Antioxidative Enzyme Protection and γ‐Aminobutyric Acid Metabolic Pathway

In this study, two cultivars of strawberry (Fragaria × ananassa Duch.) were compared for their response to different levels
of heat stress (30, 35, and 40 °C, categorized as mild, moderate, and severe heat stress, respectively) with controls growing
at 25 °C. At temperatures of 25 °C and mild heat stress, there were no obvious differences in symptoms between the
cultivars Camarosa and Kurdistan. At 40 °C, Camarosa exhibited more severe damage compared to Kurdistan, indicating that
Kurdistan had greater heat stress tolerance. No significant difference in γ-aminobutyric acid (GABA) content was observed
in Camarosa until 35 °C, where GABA content significantly decreased compared to the control. In contrast, GABA levels
in Kurdistan steadily increased as the heat stress intensified from 25 to 40 °C. The concentration of total soluble sugars
(TSS) and activities of catalase, ascorbate peroxidase, and superoxide dismutase in both cultivars initially increased under
heat stress but declined at 40 °C in Camarosa. In Kurdistan, elevated temperatures triggered the expression of GABA shuntrelated
genes, including glutamate decarboxylase (GAD1) and two catabolic enzymes (GABA-T1, GABA-T3, and SSADH),
suggesting that under heat stress, GABA and succinate act as temporary storage metabolites to supply the tricarboxylic acid
cycle when the stress is mitigated.