The objective of this study was to investigate the response of the photosynthetic apparatus of the Venus flytrap (Dionaea muscipula J. Ellis) to UV-A radiation stress as well as the role of selected secondary metabolites in this process. Plants were subjected to 24 h UV-A treatment. Subsequently, chl a fluorescence and gas exchange were measured in living plants. On the collected material, analyses of the photosynthetic pigments and photosynthetic apparatus proteins content, as well as the contents and activity of selected antioxidants, were performed. Measurements and analyses were carried out immediately after the stress treatment (UV plants) and another 24 h after the termination of UV-A exposure (recovery plants). UV plants showed no changes in the structure and function of their photosynthetic apparatus and increased contents and activities of some antioxidants, which led to efficient CO₂ carboxylation, while, in recovery plants, a disruption of electron flow was observed, resulting in lower photosynthesis efficiency. Our results revealed that D. muscipula plants underwent two phases of adjustment to UV-A radiation. The first was a regulatory phase related to the exploitation of available mechanisms to prevent the over-reduction of PSII RC. In addition, UV plants increased the accumulation of plumbagin as a potential component of a protective mechanism against the disruption of redox homeostasis. The second was an acclimatization phase initiated after the running down of the regulatory process and decrease in photosynthesis efficiency.

The aim of this study was to examine the effect of the modified light spectrum of glass containing red luminophore on the performance of the photosynthetic apparatus of two types of lettuce cultivated in soil in a greenhouse. Butterhead and iceberg lettuce were cultivated in two types of greenhouses: (1) covered with transparent glass (control) and (2) covered with glass containing red luminophore (red). After 4 weeks of culture, structural and functional changes in the photosynthetic apparatus were examined. The presented study indicated that the red luminophore used changed the sunlight spectrum, providing an adequate blue:red light ratio, while decreasing the red:far-red radiation ratio. In such light conditions, changes in the efficiency parameters of the photosynthetic apparatus, modifications in the chloroplast ultrastructure, and altered proportions of structural proteins forming the photosynthetic apparatus were observed. These changes led to a decrease of CO₂ carboxylation efficiency in both examined lettuce types.

Dionaea muscipula J. Ellis is a South and North Carolina carnivorous endemic plant with medicinal properties. Its natural habitat is characterized by low availability of nutrients and poor plant cover, resulting in Venus flytrap exposure to various stress factors (especially UV-A radiation). To evaluate the response of Dionaea muscipula photosynthetic apparatus to increased levels of UV-A radiation, plants cultivated in controlled conditions (30–40 % air humidity, temperature 23 ± 1 °C, light intensity 290 μmol m^–2 s^–1, 16 h light/8 h dark) (Control) were treated additionally with 50 μmols m^–2s^–1 UV-A radiation for 24 h (Treated). Measurements of gas exchange, chlorophyll fluorescence and photosynthetic pigment content were conducted immediately after the exposure, both in the Control and Treated plants. Additionally, the same parameters were evaluated in the next 24 hours (Recovery). UV-A treatment (Treated) did not change chlorophyll a + b content and chlorophyll a/b ratio. Furthermore, an increased level of electron carriers (Area, Sm) and increased efficiency of electron transport between Q_A and PSI (ΦR₀, δR₀, ρR₀) was observed. Further, PSI and electron acceptors demonstrated an increased ability to oxidize reduced plastoquinone pool (V_I decrease). As a consequence, the rate of net photosynthesis increased significantly. After 24h from the exposure (Recovery), the chlorophyll a + b content declined but the ratio of chlorophyll a/b did not alter, which indicates a decrease in the size of photosynthetic antennas and the number of active PSII centers. Additionally, inactivation of the reaction centers (F₀ decrease, V_J and V_I increase) and a decrease in the amount of electron carriers, especially PQ poll (Sm), was observed. Moreover, a decrease of electron flux and efficiency of electron transport between Q_A and PSI occurred (decrease of: ΦE₀, ψE₀, ET₀/RC, ET₀/CS₀, ΦR₀, ρR₀). These results may indicate the decrease of PSII photochemical efficiency. Simultaneously, PSI reactions remained unchanged and the rate of net photosynthesis increased significantly. This can be connected with the activation of alternative pathways of electron transport. Activation of these pathways leads to the limitation of NADPH synthesis and an increase in ATP synthesis, what enables the plant’s effective acclimatization to stress conditions.