Ionizing radiation impacts photochemical quantum yield and oxygen evolution activity of Photosystem II in photosynthetic microorganisms.

PURPOSE: Long-term space exploration requires biological life support systems capable of coping with the deleterious space environment. The use of oxygenic photosynthetic microorganisms represents an intriguing topic in this context, mainly from the point of view of food and O2 production. The aim of the present study was to assess the effects of space ionizing radiation exposure on the photosynthetic activity of various microorganisms. MATERIALS AND METHODS: Ground-based irradiation experiments were performed using fast neutrons and gamma rays on microorganisms maintained at various light conditions. A stratospheric balloon and a European Space Agency (ESA) flight facility were used to deliver organisms to space at the altitude of 38 and 300 km, respectively. During the balloon flight, the fluorescence activity of the organisms was real-time monitored by means of a special biosensor. RESULTS: The quantum yield of Photosystem II (PSII), measured directly in flight, varied among the microorganisms depending on the light conditions. Darkness and irradiation of cells at 120 and 180 micromol m(-2) s(-1) enhanced the radiation-induced inhibition of photosynthetic activity, while exposure to weaker light irradiance of 20 and 70 micromol m(-2) s(-1) protected the cells against damage. Cell permanence in space reduced the photosynthetic growth while the oxygen evolution capacity of the cells after the flight was enhanced. CONCLUSIONS: A potential role of PSII in capturing and utilizing ionizing radiation energy is postulated.

Detection of herbicide subclasses by an optical multibiosensor based on an array of photosystem II mutants.

Massive use of herbicides in agriculture over the last few decades has become a serious environmental problem. The residual concentration of these compounds frequently exceeds the maximum admissible concentration in drinking water for human consumption and is a real environmental risk for the aquatic ecosystem. Herbicides inhibiting photosynthesis via targeting photosystem II function still represent the basic means of weed control. A multibiosensor was constructed for detecting herbicides using as biosensing elements photosynthetic preparations coupled to an optical fluorescence transduction system (Giardi et al. EU patent EP1134585, 01830148.1-2204); this paper is about its application in the detection of herbicide subclasses in river water. Photosynthetic material was immobilized on a silicio septum inside a series of flow cells, close to diodes so as to activate photosystem II (PSII) fluorescence. The principle of the detection was based on the factthat herbicides selectively modify PSII fluorescence activity. The multibiosensor has the original feature of being able to distinguish the subclasses of the photosynthetic herbicides by using specific immobilized biomediators isolated from mutated organisms. This setup resulted in a reusable, portable multibiosensor for the detection of herbicide subclasses with a half-life of 54 h for spinach thylakoids and limit of detection of 3 x 10(-9) M for herbicides present in river water.