Physiological, phytochemical and structural changes of multi-leaf lettuce caused by salt stress.

Abstract

Environmental stress due to salt has been described to enhance lettuce processability, shelf life and consumer acceptability. Moderate salinity causes altered leaf carotenoid, lignin, phenolic and flavonol levels without noticeable changes in the green colour and morphology of lettuce. The aim of this study was to understand the improvements in processability, due to salt stress, related to textural properties and structural characteristics. Physiological, phytochemical and structural changes were observed that were of significant relevance to salt stress (50, 100 and 150 mmol L(-1) NaCl). Fresh weight per plant, fresh weight per leaf, leaf area, water content, colour saturation, chlorophyll a and b and the area of the intercellular spaces decreased when the concentration of salt was increased. Solute concentration, elasticity, total and individual phenolic acids and the areas occupied by the palisade and spongy parenchyma cells increased when the concentration of salt was increased. These data illustrate that salt stress can have a positive impact on certain structural parameters, especially tissue elasticity, that can be closely linked to a higher number of cells, of lower size and high leaf strength, explaining the postharvest longevity of lettuce. However, leaf growth and visual quality could be negatively affected by salt stress.