Abstract
Exogenous application of salicylic acid (SA) has been known for delaying ripening in many fruit and vegetables. But the function of endogenous SA in relation to postharvest fruit performance is still unexplored. To understand the role of endogenous SA in postharvest fruit ripening of tomato, 33 tomato lines were examined for their endogenous SA content, membrane stability index (MSI), and shelf life (SL) at turning and red stages of tomato fruit ripening. Six tomato lines having contrasting shelf lives from these categories were subjected further for ethylene (ET) evolution, 1-aminocyclopropane-1-carboxylic acid synthase (ACS), 1-aminocyclopropane-1-carboxylic acid oxidase (ACO), polygalacturonase (PG), pectin methyl esterase (PME), antioxidant assays and lipid peroxidation. It was found that high endogenous SA has a direct association with low ET evolution, which leads to the high SL of fruit. High lycopene content was also found to be correlated with high SA. Total antioxidants, PG, and PME decreased and lipid peroxidation increased from turning to red stage of tomato fruit development. Furthermore, these lines were subjected to expression analysis for SA biosynthesis enzymes viz. Solanum lycopersicum Isochorismate Synthase (SlICS) and SlPAL. Real-time PCR data revealed that high SL lines have high SlPAL4 expression and low SL lines have high SlPAL6 expression. Based on the results obtained in this study, it was concluded that endogenous SA regulates ET evolution and SL with the aid of the antioxidative defense system, and SlPAL4 and SlPAL6 genes play significant but opposite roles during fruit ripening.
Highlights
Tomato is cultivated in outdoor settings, greenhouses, and net houses in nearly every country in the world
The present study suggests that endogenous salicylic acid (SA) has a positive correlation with shelf life (SL), and it regulates postharvest ET production (Table 3)
It works in a concentration-dependent manner, and its optimal concentration to reduce the ripening process varies from cultivar to cultivar and variety to variety in tomato fruit
Summary
Tomato is cultivated in outdoor settings, greenhouses, and net houses in nearly every country in the world. India, USA, Turkey, Egypt, Iran, Spain, Italy, and Brazil are the world’s leading producer of tomatoes. It covers an area of ∼4.73 million hectares and produces 163.96 million tons (FAO, 2016). Tomato is India’s most common crop in terms of revenue and nutrition; it is a very valuable fruit plant. Tomato is a climacteric fruit; its commencement of ripening is directly correlated to ethylene (ET) burst (Gapper et al, 2013). Tomato undergoes six developmental stages of fruit ripening: green, breaker, turning, pink, light red, and red ripe. Tomato fruit ripening is escorted by fruit softening, changes in color from green to red, and increased levels of flavor and aromatic compounds such as sugars, volatiles, and organic acids
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