Melatonin Rescues Photosynthesis and Triggers Antioxidant Defense Response in Cucumis sativus Plants Challenged by Low Temperature and High Humidity

Abstract

Environmental factors such as low temperature (LT) and high humidity (HH) hinder plant growth and development in plastic tunnels and solar greenhouses in the cold season. In this study, we examined the effect of melatonin (MT) on shoot-based tolerance to LT and HH conditions in cucumber (Cucumis sativus) seedlings and explored its underlying mechanism. LT and HH stress inhibited growth and biomass accumulation, produced leaf chlorosis, led to oxidative stress, lowered chlorophyll and carotenoid contents, reduced photosynthetic and photosystem II (PSII) activities, and increased the level of intercellular carbon dioxide and the non-photochemical quenching of photosystem I (PSI) and PSII. However, foliar application of MT significantly improved the morphological indices and photosynthetic efficiency of cucumber seedlings, which entailed the elevation of electrolyte leakage, lipid peroxidation, and reactive oxygen species accumulation by boosting the antioxidant enzyme defense system under LT and HH conditions. Additionally, the measurement of nitrogen (N), magnesium (Mg), and iron (Fe) contents in roots and leaves showed that MT significantly augmented the nutrient uptake of cucumber seedlings exposed to LT and HH stresses. Furthermore, MT application increased the transcripts levels of genes encoding antioxidant enzymes under LT and HH conditions, whereas treatment with LT and HH suppressed these genes, suggesting that MT application increases the LT and HH tolerance of cucumber seedlings. Overall, our results suggest that MT application increases the tolerance of cucumber seedlings to LT and HH stress by enhancing the plant morphometric parameters, regulating PSI and PSII, and activating the antioxidant defense mechanism. Thus, the exogenous application of MT could be potentially employed as a strategy to improve the LT and HH tolerance of cucumber.

Melatonin enhanced low-temperature combined with low-light tolerance of pepper (Capsicum annuum L.) seedlings by regulating root growth, antioxidant defense system, and osmotic adjustment

“…In the present study, pretreated with MT, although the and H 2 O 2 contents in pepper leaves under LL stress were obviously higher than those under CK, but significantly decreased after 6, 12, 24, 48, and 168h compared with LL, which indicated that exogenous MT effectively alleviated the LL-induced damage in pepper plants. Our results are consistent with those of a previous study that in “Zhongnong 37” cucumber ( Cucumis sativus L.) sprayed 200μM MT for 5 days during 2-leaf stage, a significant decrease of 246.1% in MDA contents were observed on 6th day under 15/10°C and 95% humidity, in addition, the H 2 O 2 contents were greatly reduced on the second and fourth day, and the production of was dramatically suppressed, compared to the seedlings without MT treatment ( Amin et al., 2022 ). Membrane stability damage is considered to be a dominant stress caused by low temperature combined with low light as indicated by the accumulations of H 2 O 2 and .…”

“…The key enzyme-encoding genes ( CsSOD , CsPOD ) were dramatically upregulated at day 2, 4, and 6, and the highest expression level was obtained at day 4, increasing by 69.25 and 95.33% in comparison with those of seedlings without MT. However, CsCAT increased from day 0 to day 6 ( Amin et al., 2022 ). In our experiment, MT pretreatment exerted slight effects on the SOD, POD, and CAT activities under control condition.…”

“…(2019b) demonstrated that MT positively upregulated the expression of CsAPX in tea plant under stresses of cold, salt, and drought stresses, leading to increased ROS elimination ( Li et al., 2019b ). The expressions of CsAPX , CsMDHAR , CsDHAR , and CsGR in cucumber were all upregulated by MT under low-temperature and high-humidity stress ( Amin et al., 2022 ). This result was consistent with our findings in which CaAPX , CaDHAR , and CaMDHAR were upregulated by pre-application of MT after 12, 24, 48, and 168h LL stress ( Figure 6 ).…”

Physiological and transcriptomic analysis provides novel insight into growth in Kam sweet rice under different nitrogen supplies

“…The amplification conditions included an initial step at 94°C for 2 min (1 cycle), followed by 40 cycles of 94°C for 30 s, 55°C for 30 s, and 72°C for 30 s, and a final extension at 72°C for 1 min (1 cycle), using the CFX96 Touch qRT‐PCR system (BioRad). Three technical replications were performed, and the relative gene expression was determined using the 2 −ΔΔ Ct method (Amin et al, 2022). The primers used are given in the Table S3.…”

Melatonin-mediated development and abiotic stress tolerance in plants

“…Furthermore, in SNAT1 -deficient Arabidopsis , the gene expression of chloroplast heat shock proteins ( CpHSP70.1 and CpHSP70.2 ) and caseinolytic proteases ( ClpR1 , ClpR4 , and ClpP1 ) is suppressed, while exogenous melatonin application reverses this response, implying that melatonin might participate in the quality control of chloroplast proteins ( Lee and Back, 2018 ). Under the combined stress of low temperature and high humidity, melatonin pretreatment promotes the uptake and translocation of N, Mg, and Fe, which are responsible for chlorophyll biosynthesis and other physicochemical reactions ( Amin et al., 2022 ). Evidence indicates that, when tomato is exposed to darkness for 4 days, melatonin increases the chlorophyll content, Fv/Fm value, and starch content and ameliorates carbon starvation-induced leaf chlorosis by activating the expression of miR171b or inhibiting glucan water dikinase gene expression ( Wang et al., 2022b ).…”