Effect of NaCl and harvest time on antioxidant compounds and morphological cell changes in Lollo Bionda and Lollo Rosso lettuces

Abstract

It is known that lettuce (Lactuca sativa L. var. crispa L.) phenological stage and environmental changes can cause changes in the plant cell morphology and an important variation in secondary plant metabolites. Antioxidant compounds are beneficial to health and salinity can increase them. The aim of this study was to determine the effect of salt concentration (NaCl 0.05 and 0.1 mol L -1 ) and harvest time (days 10, 20 and 30) on mass, color parameters, antioxidant compounds and proline concentration as well as the morphological tissue changes on two lettuce cultivars: Lollo Bionda 'Levistro' (green leaves) and Lollo Rosso 'Carmoli' (red leaves). NaCl treatments and time of harvest affected fresh matter (FM), DM and DM%, total phenol content, concentration of anthocyanin and antioxidant capacity of both cultivars. High NaCl concentrations decreased FM (from 16.8 to 8.7 g in 'Levistro' in 3 rd harvest) and the intracellular space of the leaf tissue but increased the concentration of proline (from 19.6 to 292.2 μg 100 g -1 FM in 'Levistro') and antioxidant compounds (from 412.9 to 487.3 mg Trolox eq. 100 g -1 FM in 'Levistro'). In addition, concentrations of antioxidant compounds (from 458.2 to 506.4 mg Trolox eq. 100 g -1 FM in 'Levistro') and cell density were significantly higher in late than early harvested plants. Thus, successive harvesting may lead to higher antioxidant capacities of lettuces leaves. A moderate decline in FM, a higher cell density and proline concentrations may indicate the better adaptability to salinity stress of red 'Carmoli' than the green 'Levistro' lettuces.

Evaluation of alternative substrates for hydroponics based on biological parameters of leaf lettuce (Lactuca sativa L.) and its stress response

“…In the first phase, when vacuoles are filled with Na + and Cl -, the growth of leaves and roots is only partially affected, while in the second phase, when vacuoles are completely filled, the concentration of ions in cytoplasm increases, and the action of enzymes is limited (Munns, 2005;Parihar et al, 2015). Salinity stress on lettuce can manifest itself in a higher total content of phenols, anthocyanin and proline concentrations (Neocleous et al, 2014;Flores et al, 2022). GSH is concentrated in chloroplasts, cytosol, mitochondria, peroxisome and apoplasts.…”

Changes in Agronomic, Antioxidant Compounds, and Morphology Parameters of Green and Red Lettuces (Lactuca sativa L.) by Successive Harvests and UV-B Supplementation

“…Lettuce seeds, obtained from Rijk Zwaan, were germinated on pre-hydrated granulated rock wool and expanded perlite A6 using a dark germination chamber (T: 22 • C; and RH: 80% for 24 h) following the recommendation by [35]. After root emission, the trays were transferred to the greenhouse and irrigated in accordance with the recommendations by [35]. The nutrient solution proposed by [36] for leafy vegetables was used during culture.…”

“…The pH of the nutrient solution was kept between 5.5 and 5.8 to maximize nutrient absorption from the crop using nitric acid solution. Seedlings at the true four-leaf stage were transplanted to a recirculating floating root hydroponic system and established in floating rafts made of high-density expanded polystyrene (25 kg m −3 ) of 0.5•1.5•0.025 m with a density of 50 plants m −2 [35]. Two days after the transplant, the complete nutrient solution was added.…”

“…For fresh (FW) and dry weights (DW) measurements, the recommendations by [35] were followed. Briefly, for each harvest, five biological replicates per repetition (n = 15 per treatment) were randomly selected for FW.…”

“…Color parameters were evaluated as a quality characteristic of the leaves. For this measurement, the recommendation made by [35] was followed. For each harvest, two measurements were taken for each one of the nine biological replicates per treatment repetition (n = 27 plants per treatment).…”