Reversible phytochrome regulation influenced the severity of ozone-induced visible foliar injuries in Trifolium subterraneum L.

In Trifolium subterraneum, oxidative stress caused by ozone has been shown to result in more severe visible foliar injuries when plants were kept in dim broadband white light during the night (i.e. a long photoperiod) compared to darkness during the night (a short photoperiod). As phytochrome signalling is involved in photoperiod sensing, the effect of night-time red and far-red illumination on the ozone-induced response was studied. T. subterraneum plants were treated with ozone enriched air (70?ppb) for either 1?h for a single day or 6?h for three consecutive days. After the first ozone exposure, plants were separated into six night-time light regimes during the two subsequent nights (10?h?day, 14?h night): (1) darkness, (2) far-red light (FR), (3) a short night-break of red followed by far-red light during an otherwise dark night (R FR), (4) a short night-break of red, far-red and finally red light during an otherwise dark night (R FR R), (5) dim white light (L) and (6) red light (R). The treatments L and R resulted in significantly more severe ozone-induced visible foliar injuries relative to D and FR treatments, indicating a phytochrome-mediated response. The night-breaks resulted in a photoreversible and significantly different ozone response depending on the light quality of the last light interval (R FR or R FR R), supporting a photoreversible (between P_r and P_fr) phytochrome signalling response. Thus, in T. subterraneum, the outcome of oxidative stress due to ozone appears to depend on the photoperiod mediated by the night-time conformation of phytochrome.     

Effects of 50 Hz electric currents and magnetic fields on the prokaryote Propionibacterium acnes

The effects of 50 Hz sinusoidal electric currents and magnetic fields on the Gram-positive skin bacterium Propionibacterium acnes were investigated. Intracellular free calcium ([Ca(2+)](i)), intracellular pH (pH(i)), and cell viability were examined, based on their relevance to ELF field studies and on previous studies conducted on P. acnes (UVA irradiation, photosensitization using porphyrin-based sensitizers, and broad-band red light). The [Ca(2+)](i) and the pH(i) were measured spectrofluorimetrically using the fluorescent probes fura-2 and BCECF, respectively. Sham-exposed controls were used to assess the field exposed samples. Cell suspensions were exposed to 50 Hz, 0.2 mT sinusoidal magnetic fields generated by using Helmholtz coils for up to 30 min. The estimated maximum induced electric field was 0.2 mV/m. Changes in [Ca(2+)](i) and cell viability were not detected. Ag/AgCl electrodes were used to expose cell suspensions to 50 Hz sinusoidal electric currents. The current densities were in the range 0.015-1500 A/m(2) (corresponding electric fields congruent with0.01-1000 V/m). Changes in [Ca(2+)](i) were not observed after current exposure. Current densities of 800 A/m(2) (electric field E congruent with550 V/m) were required for a 50% reduction in cell viability. Current densities greater than 800 A/m(2) were required for a reduction in pH(i). However, a pH gradient across the cell membrane (inside alkaline) was maintained even when exposure resulted in less than 0. 2% survival (1400 A/m(2), E congruent with950 V/m). Thus, dissipation of the pH gradient across the cell membrane and changes in [Ca(2+)](i) were not a consequence of cell inactivation by 50 Hz electric currents. This is in contrast to inactivation of P. acnes by UVA irradiation or photosensitization, where such changes have been obtained.     

Photomorphogenesis and pigment induction in lentil seedling roots exposed to low light conditions

Although roots are normally hidden in soil, they may inadvertently be exposed to low light levels in experiments or in natural conditions through cracks or light transmittance through the soil. Light has been implicated in root morphogenesis. Thus, effects of low light conditions on lentil (Lens culinaris L. cv. Verte du Puy) root morphology and root pigmentation were studied. Lentil seedlings were grown in peat or transparent, nutrient-fortified agar at a 12-h light (PAR 240 μmol · m(-2) · s(-1)), 12-h dark cycle. Roots were exposed to low levels (≈ 1-10 μmol · m(-2) · s(-1)) of broadband white light, either directly or indirectly by aboveground light penetrating the growth medium. Control roots were grown in darkness. In situ spectroscopy was used to measure transmittance and reflectance spectra of intact root tissue by mounting the upper part of the primary root directly in a spectrophotometer equipped with an integrating sphere attachment. The transmittance and reflectance spectra were used to calculate the in situ root absorbance spectrum. Absorbance bands were found in the regions 480-500 nm and 650-680 nm, possibly due to low levels of root-localised carotenoids and chlorophylls, respectively. Low light levels (≈ 1-10 μmol · m(-2) · s(-1) ) transmitted through the growth medium significantly increased root pigment concentration and root biomass, and altered root morphology by enhancing lateral root formation and inhibiting root elongation relative to roots grown in complete darkness. The light-induced changes in root morphogenesis and pigmentation appear to be primarily due to upper root light perception.     

A growth chamber for idealized studies of seedling root growth dynamics and structure

A root growth chamber is described which allows seedling root growth dynamics and structure to be monitored continuously under a variety of conditions for several weeks. The chamber consists of two cells with inner dimensions 18×20×0.12 cm. To simulate the soil matrix, each cell was filled with spherical glass beads of 0.1 cm diameter. Given the 0.12 cm width of each cell, the glass bead matrix was approximately one bead layer thick. Roots were therefore grown in a quasi -two-dimensional and transparent environment. This enabled root images of high spatial and temporal resolution to be collected and analysed quantitatively using standard image analysis techniques. The chamber was constructed such that the root environment could be manipulated with regard to nutrient distribution, `soil' matrix structure and other perturbations to the system. Preliminary experiments of the growth dynamics of lentil roots (Lens culinaris L. cv. Verte du Puy) in the chamber were conducted. The majority of the primary and lateral roots followed a similar growth pattern with high growth rates between days 5 and 9 and days 14 and 18 separated by a period of low growth rate between days 10 and 12 after seeding in the chamber. Thus, primary and lateral root growth was to a certain extent synchronized. Lateral roots developed after 3 to 8 days on the outer curve (convex side) of the primary root. The roots shared many of the characteristics of roots developed in three-dimensional systems indicating that the chamber did not induce artificial root behaviour. Thus, the idealized and quantitative studies that can be conducted in the chamber may enable many aspects of the complex interactions between the root system and environment to be studied.