Exogenous Melatonin Enhances Photosynthetic Capacity and Related Gene Expression in A Dose-Dependent Manner in the Tea Plant (Camellia sinensis (L.) Kuntze)

Abstract

The enhancement of photosynthesis of tea leaves can increase tea yield. In order to explore the regulation mechanism of exogenous melatonin (MT) on the photosynthetic characteristics of tea plants, tea variety ‘Zhongcha 108’ was used as the experimental material in this study. The effects of different concentrations (0, 0.2, 0.3, 0.4 mM) of melatonin on the chlorophyll (Chl) content, stomatal opening, photosynthetic and fluorescence parameters, antioxidant enzyme activity, and related gene expression of tea plants were detected and analyzed. The results showed that under 0.2-mM MT treatment, chlorophyll (Chl) content, photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO2 concentration (Ci), and transpiration rate (Tr) improved, accompanied by a decrease in stomata density and increase in stomata area. Zero point two millimolar MT increased Chl fluorescence level and superoxide dismutase (SOD) activity, and reduced hydrogen peroxide (H2O2) and malondialdehyde (MDA) contents, indicating that MT alleviated PSII inhibition and improved photochemical efficiency. At the same time, 0.2 mM MT induced the expression of genes involved in photosynthesis and chlorophyll metabolism to varying degrees. The study demonstrated that MT can effectively enhance the photosynthetic capacity of tea plants in a dose-dependent manner. These results may promote a comprehensive understanding of the potential regulatory mechanism of exogenous MT on photosynthesis in tea plants.

Mechanistic Approach on Melatonin-Induced Hormesis of Photosystem II Function in the Medicinal Plant Mentha spicata

“…Under non-stressed conditions, exogenous MT application in Chara australis increased the number of open RCs of PSII, thus improving Φ PSII [87], as we also observed in Mentha spicata plants. In contrast to our results, in which 100 µM MT reduced Fv/Fm due to donor-side photoinhibition, Yang et al [115] suggested that the application of MT might alleviate PSII inhibition and partially display a direct antioxidant effect. They concluded that the application of 200 µM MT in the tea plant (Camellia sinensis (L.) Kuntze) stimulated photosynthesis and the expression of genes related to chlorophyll metabolism in a dosedependent manner [115].…”

“…In contrast to our results, in which 100 µM MT reduced Fv/Fm due to donor-side photoinhibition, Yang et al [115] suggested that the application of MT might alleviate PSII inhibition and partially display a direct antioxidant effect. They concluded that the application of 200 µM MT in the tea plant (Camellia sinensis (L.) Kuntze) stimulated photosynthesis and the expression of genes related to chlorophyll metabolism in a dosedependent manner [115]. A dose-dependent increase in chlorophyll content was also noticed in our experiments (Figure 1), and enriched chlorophyll content by MT priming under high-temperature stress was observed in the tall fescue [116].…”

Synergistic effects of calcium and melatonin on physiological and phytochemical attributes of Dracocephalum kotschyi genotypes under salinity stress

“…Since a major function of MT is to scavenge ROS and to maintain the oxidative status (Liu et al, 2018), it is not surprising to observe a MT‐induced enhancement in F v /F m in the D. kotschyi plants. Indeed, the positive effects of exogenous MT on SOD activity, ROS scavenging, and F v /F m led the researchers (Yang et al, 2022) to propose that MT is capable of mitigating PSII inhibition mainly through exerting antioxidative effects. Interestingly, external MT exerts its ROS‐detoxifying effects in stressed plants when applied together with other molecules, including sulfur (Siddiqui et al, 2019) and potassium (Siddiqui et al, 2022).…”

Influence of Melatonin Coating on Physiochemical Qualities and Enzymatic Activities in Banana Pericarp under Cold Storage

“…Application of MT on plants stored under chilling sensitive temperatures activated the expression of genes associated with a cold response and antioxidant activities [26]. MT treatment on tea plants exhibits reduced ROS and MDA levels, alongside diminished lipid peroxidation, and this is mainly achieved by the enhanced level of AA and GSH, which helps contribute to the overall antioxidant systems [27]. MT treatments have demonstrated efficacy in mitigating CI symptoms, decreasing EL, MDA content, hydrogen peroxide (H 2 O 2 ), and superoxide anion (O 2…”