Short-Term Reaction of Dionaea muscipula J. Ellis Photosynthetic Apparatus after UV-A Radiation Treatment ^†

Abstract

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.