Effect of Drought Stress on Chlorophyll Fluorescence Parameters, Phytochemical Contents, and Antioxidant Activities in Lettuce Seedlings

Abstract

This study monitored changes in chlorophyll fluorescence (CF), growth parameters, soil moisture content, phytochemical content (proline, ascorbic acid, chlorophyll, total phenol content (TPC), and total flavonoid content (TFC)), and antioxidant activities in 12-day-old lettuce (Lactuca sativa L.) seedlings grown under drought stress (no irrigation) and control (well irrigated) treatments in controlled conditions for eight days. Measurements occurred at two-day intervals. Among ten CF parameters studied, effective quantum yield of photochemical energy conversion in PSII (Y(PSII)), coefficient of photochemical quenching (qP), and coefficient of photochemical quenching of variable fluorescence based on the lake model of PSII (qL) significantly decreased in drought-stressed seedlings from day 6 of treatment compared to control. In contrast, maximum quantum yield (Fv/Fm), ratio of fluorescence (Rfd), and quantum yield of non-regulated energy dissipation in PSII (Y(NO)) were significantly affected only at the end. All growth parameters decreased in drought-stressed seedlings compared to control. Proline started increasing from day 4 and showed ~660-fold elevation on day 8 compared to control. Chlorophyll, ascorbic acid, TPC, TFC, and antioxidant activities decreased in drought-stressed seedlings. Results showed major changes in all parameters in seedlings under prolonged drought stress. These findings clarify effects of drought stress in lettuce seedlings during progressive drought exposure and will be useful in the seedling industry.

Monitoring of Salinity, Temperature, and Drought Stress in Grafted Watermelon Seedlings Using Chlorophyll Fluorescence

“…The magnitude of the effect was dependent on the type of stress and the duration of seedling exposure to stress. We found a significant decrease in growth parameter values under all stress conditions, which was consistent with previous reports in a range of plants, including watermelon ( Hou et al, 2016 ; Bhandari et al, 2018 ; Yanyan et al, 2018 ; Lee et al, 2021 ; Shin et al, 2021a ).…”

“…The magnitude of the effect was dependent on the type of stress and the duration of seedling exposure to stress. We found a significant decrease in growth parameter values under all stress conditions, which was consistent with previous reports in a range of plants, including watermelon (Hou et al, 2016;Bhandari et al, 2018;Yanyan et al, 2018;Lee et al, 2021;Shin et al, 2021a). Similar to several previous studies in various plants (Bhandari et al, 2018;Shin et al, 2020aShin et al, , 2021b, growth parameter values were significantly reduced in all three experiments.…”

“…These results were similar to those of previous studies, which found that the chlorophyll content of plants affected by drought stress was reduced in watermelon, tomato, lettuce, and Arabidopsis affected by drought stress (Banks et al, 2018;FIGURE 6 | Changes in visual appearance of grafted watermelon seedlings grown under different temperature conditions during the progressive treatment time. Yao et al, 2018;Malambane et al, 2021;Shin et al, 2021a). Our results also showed a decrease in growth parameters under high and low temperature conditions, which is in accordance with Hou et al (2016).…”

“…Fresh shoot and root weights were measured using a digital weighing machine (UX420H; Shimadzu Corp., Kyoto, Japan). The relative water content of the soil in a single plug tray was measured by drying the soil samples at 105°C for 72 h according to Shin et al (2021a) . The seedlings from 0, 6, and 12 of treatment time after measuring CF and growth parameters were collected separately, freeze-dried and used for chlorophyll and proline analysis in salinity and temperature stress treatments, whereas the samples from all the treatment times (0, 1, 2, and 3 days after the initiation of treatment) were used in the drought stress experiment.…”

“…In the drought stress experiment, the treatment was conducted for only 3 days as the status of the seedling was poor after that period. Previous reports also showed that chlorophyll levels in plants decrease after severe stress; however, some authors have reported an increase in for some time and decrement after exposure to severe stress conditions (Partelli et al, 2009;Bhandari et al, 2018;Shin et al, 2020bShin et al, , 2021a.…”