ABSTRACT
A "Laiyang" pear is a climacteric fruit with a special taste and nutritional value but is prone to a post-harvest aroma compound loss and a loss in fruit quality. In this study, pears were pretreated with 0.5 µl L-1 1-methylcyclopropene (1-MCP) at 20°C for 12 h and then stored at 0 ± 1°C for 150 days to evaluate the influence of 1-MCP on fruit quality and the changes in components of volatile aromas. In addition, pears were further treated with 2 mmol L-1 ethephon. The effects of ethephon on the recovery of aroma production were investigated during the 150 day storage at 0 ± 1°C and the subsequent 7 day shelf life at 20 ± 1°C. Treatment with 1-MCP inhibited firmness loss, increased electrical conductivity, reduced respiration and ethylene production rates as well as the contents of soluble solids, and maintained the storage quality of the fruits. However, 1-MCP treatment inhibited the emission of volatile aromas in pear fruits by decreasing the activities of various enzymes, such as lipoxygenase (LOX), hydroperoxide lyase (HPL), alcohol dehydrogenase (ADH), pyruvate carboxylase (PDC), and alcohol acetyltransferase (AAT). During the shelf-life, activities of the above mentioned enzymes were significantly enhanced, and a higher content of volatile aromas were found in fruits treated with 1-MCP + ethephon, while other qualities were not compromised. These results showed that 1-MCP treatment could effectively maintain the quality of the "Laiyang" pear during cold storage, and the additional application of ethephon on fruits during shelf-life may be a promising way to restore volatile aromas in pear fruits after long-term storage.
ABSTRACT
BACKGROUND: Arginase plays key roles in methyl jasmonate (MeJA)-mediated quality maintenance in vegetables and fruits. MeJA treatment induced the Arginase 2 (SlARG2) expression, which is one of the most important encoding genes of arginase. In addition, the treatment with MeJA induced resistance to pathogenic infection in many plants. However, the functions of SlARG2 in MeJA-induced defense to Botrytis cinerea are unclear. In our work, control and SlARG2-silenced tomato fruits (Solanum lycopersicum) were treated with 0.05 mmoL L-1 MeJA before storage to assay the roles of SlARG2 in MeJA-induced defense responses to Botrytis cinerea. RESULTS: Our results indicated that MeJA treatment induced both pathogenesis-related gene expression (PR1, PR2a, PR2b and PR3b), and the activity of defense-related enzymes, as well as upregulated arginine metabolism. Compared to control fruits, the treatment with MeJA also induced the activity of arginase, arginine decarboxylase (ADC) and ornithine aminotransferase (OAT), and expression of SlARG2, SlADC, ornithine decarboxylase (SlODC) and SlOAT, and consequently increased the accumulation of arginine, proline, glutamate, putrescine and spermine. However, the induction effects by MeJA were significantly reduced in fruits in which SlARG2 was silenced and severe disease symptoms were observed. CONCLUSION: MeJA fumigation could inhibit disease development by inducing pathogenesis-related gene expression (PR1, PR2a, PR2b and PR3b) and defense-related enzymes activity, as well as upregulated arginine metabolism. In addition, SlARG2 silencing could inhibit the functions of MeJA in inducing the accumulation of the above substances. Overall, our study provided strong evidence that SlARG2 was essential for MeJA-induced tomato fruit defense responses to Botrytis cinerea. © 2020 Society of Chemical Industry.
