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The unprecedented rate of depletion of the stratospheric ozone layer will likely lead to appreciable increases in the amount of ultraviolet-B radiation (UV-B, 280–320 nm) reaching the earth's surface. In plants, photosynthetic reactions and nucleic acids in the mesophyll of leaves are deleteriously affected by UV-B. We used a fiber-optic microprobe to make(More)
Global-change scenarios suggest a trend of increasing diffuse light due to expected increases in cloud cover. Canopy-level measurements of plant-community photosynthesis under diffuse light show increased productivity attributed to more uniform distribution of light within the forest canopy, yet the effect of the directional quality of light at the leaf(More)
Light-mediated chloroplast movements are common in plants. When leaves of Alocasia brisbanensis (F.M. Bailey) Domin are exposed to dim light, mesophyll chloroplasts spread along the periclinal walls normal to the light, maximizing absorbance. Under high light, the chloroplasts move to anticlinal walls. It has been proposed that movement to the high-light(More)
Action spectra for chromatic adaptation in Fremyella diplosiphon Drouet have been determined using techniques previously described. Action maxima are at 540 nm, with a half-band width of 80 nm, for induction of phycoerythrin synthesis (green action) and at 650 nm, with a half-band width of 90 nm, for reversal of induction of phycoerythrin synthesis (red(More)
The alga Chlamydomonas nivalis lives in a high-light, cold environment: persistent alpine snowfields. Since the algae in snow receive light from all angles, the photon fluence rate is the critical parameter for photosynthesis, but it is rarely measured. We measured photon irradiance and photon fluence rate in the snow that contained blooms of C. nivalis. On(More)
Many understory plants rely on diffuse light for photosynthesis because direct light is usually scattered by upper canopy layers before it strikes the forest floor. There is a considerable gap in the literature concerning the interaction of direct and diffuse light with leaves. Some understory plants have well-developed lens-shaped epidermal cells, which(More)
Photoacoustic methods offer unique capabilities for photosynthesis research. Phenomena that are readily observed by photoacoustics include the storage of energy by electron transport, oxygen evolution by leaf tissue at microsecond time resolution, and the conformational changes of photosystems caused by charge separation. Despite these capabilities,(More)
Mesophyll structure has been associated with the photosynthetic performance of leaves via the regulation of internal light and CO(2) profiles. Differences in mesophyll structure and chlorophyll distribution within three ontogenetically different leaf types of Eucalyptus globulus ssp. globulus were investigated. Juvenile leaves are blue-grey in color,(More)
A fiber optic microprobe, 5.5 μm in diameter, was used as a detector to measure the light intensity profile at the distal cell surface of Phycomyces blakesleeanus (Burgeff) sporangiophores that were irradiated unilaterally by a collimated xenon source. The light intensity at a fixed location of the cell surface showed large random variations over time which(More)
Measuring leaf light absorptance is central to many areas of plant biology including photosynthesis and energy balance. Absorptance is calculated from measured values of transmittance and reflectance, and most such measurements have used direct beam light. However, photosynthesis and other processes can differ under direct and diffuse light. Optical(More)