Indole-3-acetic acid, a hormone potentially involved in chilling-induced seed browning of pepper (Capsicum annuum L.) fruit during cold storage

Abstract

Pepper (Capsicum annuum L.) fruit is affected by chilling temperatures below 7–10 °C; thus, there are limitations to maintaining postharvest freshness during its cold storage and distribution. Here, the six endogenous hormones, abscisic acid, gibberellic acid, indole-3-acetic acid (IAA), jasmonic acid, jasmonoyl-isoleucine, and salicylic acid, were quantitatively analyzed, and the genes and amino acids associated with them were investigated under the hypothesis that hormones are primarily involved in chilling injury (CI) of pepper fruit. Pepper fruit of two different genotypes, ‘Takanotsume’ (‘TK’) and ‘Gyeonggiyangpyeong’ (‘GG’), were harvested at the mature-green stage and stored at 2 °C for 21 d. Seed browning was the most visible symptom of CI during storage. Seed browning was rarely observed for ‘TK’; however, it was observed for ‘GG’ with a higher production of reactive oxygen species. Thus, ‘TK’ was less sensitive to chilling than ‘GG’, as demonstrated by the completely different CI levels. IAA levels substantially increased in ‘GG’ on 3 d of cold storage; however, it did not change in ‘TK’ during the entire storage period. Since the pattern between the expression level of CaAMI1 and the IAA content was similar, the IAM pathway was probably involved in the IAA production in ‘GG’. The content of individual amino acids substantially changed in ‘GG’ compared to ‘TK’ but the initial proline content was highest in ‘TK’. ‘GG’ showed a more complex correlation between the analyzed factors compared to ‘TK’. The CI level of ‘TK’ positively correlated with gamma-aminobutyric acid (GABA) and auxin response factor 19 (CaARF19). The CI level of ‘GG’ had a positive, and negative correlation with GABA and alanine, and CaARF6, respectively. These results might help elucidate the mechanism of chilling-induced seed browning in pepper fruit and develop pepper cultivars that are resistant to CI during cold storage and distribution.