Response to Salt Stress in Lettuce: Changes in Chlorophyll Fluorescence Parameters, Phytochemical Contents, and Antioxidant Activities

Abstract

Chlorophyll fluorescence (CF), growth parameters, phytochemical contents [proline, chlorophyll, ascorbic acid, total phenol content (TPC), total flavonoid content (TFC)], and antioxidant activities were investigated in lettuce (Lactuca sativa L.) seedlings grown under different sodium chloride (NaCl) concentrations (0, 50, 100, 200, 300, and 400 mM) in a controlled environment for eight days. The parameters were evaluated at two days intervals. Almost of the CF and growth parameters as well as phytochemicals were significantly affected by both NaCl concentrations and progressive treatment schedule. The maximum quantum yield (Fv/Fm), effective quantum yield of photochemical energy conversion in PSII [Y(PSII)], coefficient of photochemical quenching (qP), coefficient of non-photochemical quenching (qN), and ratio of fluorescence decline (Rfd) showed decrements only at the highest saline concentration (400 mM), whereas the quantum yield of non-regulated energy dissipation in PSII [Y(NO)] exhibited a dissipation trend. All the growth parameters decreased with increasing NaCl concentrations, showing the highest decrease (~8 fold) in shoot fresh weight, compared to control seedlings. Proline significantly increased with increasing NaCl concentration and treatment time. Other phytochemicals decreased with the increase in NaCl concentration and reached their lowest at 400 mM. Overall, the results showed major changes in all parameters when the seedlings were grown at a NaCl concentration of 400 mM. The present findings will be useful for understanding the differential effect of NaCl concentrations in lettuce seedlings, and also might be useful to optimize the NaCl concentrations in other crops grown in controlled environmental conditions.

MGIDI and WAASB indices: The useful approaches for selection of salt-tolerant barley genotype at the early growth and maturity stages

“…As a contrast result, salinity stress slightly increased chlorophyll content in some barley seedlings. This finding is agreement with the results reported in cotton (Higbie et al 2010), sunflower (Heidari et al 2014, Thellungiella sals (Goussi et al 2018), and lettuce (Shin et al 2020). It has been reported that increasing salt solutions in leaf tissue decreases leaf area index and leads to increase in specific leaf weight (Sohan et al 1999).…”

“…Chlorophyll as a green-colored pigment is a vital component of the photosynthetic apparatus, and its role in capturing light energy, energy transduction, and stabilization of membranes has been investigated extensively (Porcar-Castell et al 2014;Shah et al 2017;Shin et al 2020;Abrar et al 2020). The relative chlorophyll content is likely to decline under salt treatment compared with control condition.…”

Light and Autofluorescence, Multitasking Features in Living Organisms

“…Various factors can influence optical properties of chlorophyll as well as other pigments, making the overall absorption, reflectance and fluorescence signals of plants and leaves to act as valuable intrinsic biomarkers exploitable for various studies. Investigations can vary from the basic mechanisms of photosynthetic processes to the noninvasive characterization of leaf growing or plant adaptation to stress inducing factors such as changes in light irradiation and soil components, for applications ranging from industry and farming to environmental surveillance [25][26][27][28].…”

Regulated Salinity Eustress in a Floating Hydroponic Module of Sequentially Harvested Lettuce Modulates Phytochemical Constitution, Plant Resilience, and Post-Harvest Nutraceutical Quality

“…Moreover, an electrical conductivity of 3.8 and especially 4.8 mS cm −1 in the nutrient solution was able to enhance the properties of fresh-cut lettuce, reducing respiration, browning phenomena, the decay process, and prolonging its shelf life [32]. Therefore, while a mild salinity, 5 mM < [NaCl] < 30 mM, can exert beneficial effects with a minimal impact on lettuce growth and biomass, high salinity concentrations (NaCl > 30 mM) can limit plant growth and development by affecting ions and water uptake, thus causing oxidative stress with a consequent negative impact on photosynthesis, growth/yield, and quality [33]. Obviously, a low NaCl concentration (NaCl~5mM), does not affect growth and biomass and does not elicit a defence response [34].…”