'Rocha’ Pear ripening under the 1-mcp evergreen effect: the impact of the auxin 1-naphthaleneacetic acid treatment

‘Rocha’ pear (Pyrus communis L. cv. Rocha), is a DOP cultivar from the West region of Portugal that is appreciated worldwide. Combined with controlled atmosphere storage, 1-methylcyclopropene (1-MCP) application, an antagonist of ethylene action, has been one of the most applied techniques to extend the storage of ‘Rocha’ pear. However, fruit industry is facing a problem resulting from 1-MCP application: it prevents the normal ripening of the fruit and affects the final quality at the consumer level. In this study, we exposed 1-MCP treated fruits to an auxin 1-naphthaleneacetic acid (1- NAA) solution (2 mM) and analyzed the efficacy in restoring the ripening of ‘Rocha’ pear. First, during the first 24 h, we determined the primary impact of 1-NAA on the expression of genes encoding ethylene receptors (PcETRs) and ethylene biosynthesis enzymes (PcACS and PcACO), combined with lipid peroxidation and reactive oxygen species. We also studied the effect of 1-NAA on ethylene production, respiration, and other ripening markers (firmness and sugars) across shelf life. Herein, the expression of PcACS1 and PcACS4 increased in 1-MCP fruit treated with 1- NAA compared to pear treated only with 1-MCP. Additionally, the expression of PcETR2 and PcETR5 was enhanced, revealing the potential of the 1-NAA treatment in inducing the production of new ethylene receptors. Time course physicochemical analysis revealed that fruit ripening was accelerated by 1- NAA treatment, as judged by ethylene evolution and respiration associated with softening. The 1-NAA treatment increased firmness loss (ca. 60%) and internal ethylene production (ca. 50%). Also, exogenous 1-NAA treatment increased 1- aminocyclopropane carboxylic acid (ca. 28%) and ACC oxidase activity (ca. 15%) corroborating the increased in gene expression. Our findings reveal that 1-NAA treatment may circumvent 1-MCP effect providing valuable information for ripening studies in pear.