162 research outputs found
UV-B Physiological Changes Under Conditions of Distress and Eustress in Sweet Basil
UV-B radiation has been previously reported to induce protective or deleterious effects on plants depending on the UV-B irradiation doses. To elucidate how these contrasting events are physiologically coordinated, we exposed sweet basil plants to two UV-B doses: low (8.5 kJ m-2 day-1, 30 min exposure) and high (68 kJ m-2 day-1, 4 h exposure), with the plants given both doses once continuously in a single day. Physiological tests during and after both UV-B exposures were performed by comparing the stress-induced damage and adverse effects on photosynthetic activity, the concentration and composition of photosynthetic and non-photosynthetic pigments, and stress-related hormones biosynthesis in basil plants. Our results showed that upon receiving a high UV-B dose, a severe inactivation of oxygen evolving complex (OEC) activity at the PSII donor side and irreversible PSII photodamage caused primarily by limitation of the acceptor side occurred, which overloaded protective mechanisms and finally led to the death of the plants. In contrast, low UV-B levels did not induce any signs of UV-B stress injuries. The OEC partial limitation and the inactivation of the electron transport chain allowed the activation of photoprotective mechanisms, avoiding irreversible damage to PSII. Overall results indicate the importance of a specific response mechanisms regulating photoprotection vs irreversible photoinhibition in basil that were modulated depending on the UV-B doses
Transformation of electromagnetically induced transparency into absorption in a thermal potassium optical cell with spin preserving coating
We report a new experimental approach where an order of magnitude enhancement of the electromagnetically induced absorption (EIA) resonance contrast, thus making it similar to that of the EIT resonance contrast is observed under the same conditions. The EIA signal results from the interaction of a weak probe beam with a ground state that has been driven by the pump (counter-propagating) beam. Probe absorption spectra are presented where the laser frequency is slowly detuned over the D 1 line of 39 K vapor contained in a cell with a PDMS antirelaxation coating. In addition to the frequency detuning, a magnetic field orthogonal to the laser beams is scanned around zero value at a higher rate. With both laser beams linearly polarized, an EIT resonance is observed. However, changing the pump beam polarization from linear to circular reverses the resonance signal from EIT to EIA
Light-induced potassium desorption from polydimethylsiloxane film
Potassium photoejection from polydimethylsiloxane surfaces has been
observed and analyzed in detail. By diode laser absorption spectroscopy
the K concentration in a sealed measurement cell without buffer gas has
been monitored as a function of the environment variables, like
temperature, flooding light wavelength and power. The dynamic evolution
of the process has been measured too, showing differences compared to
previous measurements with different alkali-metal atoms.
Saturation spectroscopy on the K D1 line has been performed at room
temperature by taking advantage of this phenomenon
Collisional broadening and shifting of ammonia absorption lines at 790 nm
By using a diode laser spectrometer based on a commercial
heterostructure diode laser operating in free-running mode, line
shape parameters of some ammonia ro-vibrational overtones at
790 nm have been measured at room temperature. These weak absorption
lines have been detected by using the wavelength modulation
spectroscopy technique with second-harmonic detection.
The broadening and shifting coefficients have been obtained for
ten absorption lines by fitting the collected second-harmonic
absorption features and varying the pressure of different buffer gases
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