Effect of a Shading Mesh on the Metabolic, Nutritional, and Defense Profiles of Harvested Greenhouse-Grown Organic Tomato Fruits and Leaves Revealed by NMR Metabolomics

Abstract

Controlling the temperature inside a greenhouse during the summer is a problem of increasing importance in the Mediterranean countries, especially in the Spanish southeast. The metabolic profile of greenhouse tomatoes and leaves grown under conventional conditions and within the presence of a shade mesh (∼50% reduction of sunlight radiation) has been monitored. Tomatoes were weekly harvested from May to July 2017 and analyzed by NMR spectroscopy coupled to multivariate data analysis techniques, together with oxygen radical absorbance capacity (ORAC) assays (for antioxidant activity). Fatty acids and carotenoids profiles were unraveled by GC-FID and HPLC-DAD, respectively. To verify whether it would be possible to take advantage of different light growing conditions to potentiate a plant’s defense system, leaves of the corresponding plants were collected and their methanolic extracts were analyzed by NMR toward deciphering new biomarkers, which were used to assess their antibacterial and antibiofilm activities. The presence of a shading mesh resulted in a reduction in tomato production and in smaller fruits with lower contents of sugars (glucose and fructose) and carotenoids (lycopene and β-carotene) and higher contents of organic acids, amino acids, and polyunsaturated fatty acids (linoleic and oleic acids) and of phenylpropanoids and flavonoids (which contributed to an increased antioxidant activity). Methanolic extracts of leaves of nonshaded plants showed a higher antibiofilm activity than that from shaded plants. This activity was well-correlated with an increase of phenolic compounds, together with some specific amino acids and organic acids from tomato leaves.

Pearl Grey Shading Net Boosts the Accumulation of Total Carotenoids and Phenolic Compounds That Accentuate the Antioxidant Activity of Processing Tomato

“…As reported by Slimestad and Verheul [ 8 ] and Abreu et al [ 75 ], regardless of treatments, rutin was the most abundant flavonoid ( Table 7 ). In contrast, Bertin and Génard [ 2 ] reported that the most abundant flavonoid in tomatoes was naringenin, demonstrating how genotype, cultural practices, environmental conditions, and even analytical determination techniques can influence the content of these compounds.…”

“…Specifically, we evaluated the free radical scavenging activity DPPH, the free radical scavenging activity by ABTS decolorization, and the ferric reducing antioxidant capacity FRAP ( Table 8 ). Our findings showed significant antioxidant activity in fruits grown under pearl grey net, probably related to the higher content of total phenolic compounds ( Table 7 ) [ 75 ].…”

NMR Metabolomics Applied on the Discrimination of Variables Influencing Tomato (Solanum lycopersicum)

“…In untargeted plant metabolomics, methanol–water mixtures with or without acidification (e.g., formic or acetic acid) have become popular extraction solvents, since they allow extracting a wide range of metabolites [ 36 ]. For lycopene extraction, a mixture of methanol and chloroform (80:20, v / v ) was also reported [ 37 ]. Moreover, for high-throughput fingerprinting, the recommended procedure is to perform the extraction directly with deuterated solvents, and so, after extraction and centrifugation, the supernatant can be directly transferred into an NMR tube for data acquisition.…”

“…Their results indicated that the shaded carbon-limited plants decreased their sink carbon demand and showed subtle compositional modifications along a diel cycle, including those directly linked to photosynthesis and photorespiration (in leaves) and, in a lesser extension, in several organic acids (in fruits) [ 75 ]. Similarly, Abreu et al [ 37 ] analyzed the metabolic profile of Almería greenhouse organic tomatoes ( Solanum lycopersicum cv. Delyca) fruits and leaves under different light regimes produced by a shade mesh (control vs. 50% reduction of sunlight radiation).…”

“… Partial least square-discriminant analysis (PLS-DA) ( a ) scores plot and ( b ) Shared and Unique Structures (SUS) plot adapted from Abreu et al [ 37 ]. The SUS-plot clusters the loadings according to their importance [ p(corr )] for the discrimination of the NMR data with the harvest week (Y axis) and with the light condition (X axis, control, and shaded conditions on the right and left sides, respectively), showing that fructose and glucose increased in control tomatoes, while sucrose, cinnamic acids, rutin, fatty acids, most amino acids, and organic acids (malate and citrate) increased in shaded tomatoes.…”