Dataset Information

Short flashes and continuous light have similar photoinhibitory efficiency in intact leaves.

ABSTRACT: Lincomycin-treated pumpkin leaves were illuminated with either continuous light or saturating single-turnover xenon flashes to study the dependence of photoinactivation of photosystem II (PSII) on the mode of delivery of light. The flash energy and the time interval between the flashes were varied between the experiments, and photoinactivation was measured with oxygen evolution and the ratio of variable to maximum fluorescence (F(v)/F(m)). The photoinhibitory efficiency of saturating xenon flashes was found to be directly proportional to flash energy and independent of the time interval between the flashes. These findings indicate that a low-light-specific mechanism, based on charge recombination between PSII electron acceptors and the oxygen-evolving complex, is not the main cause of photoinactivation caused by short flashes in vivo. Furthermore, the relationship between the rate constant of photoinactivation and photon flux density was similar for flashes and continuous light when F(v)/F(m) was used to quantify photoinactivation, suggesting that continuous-light photoinactivation has a mechanism in which the quantum yield does not depend on the mode of delivery of light. A similar quantum yield of photoinhibition for flashes and continuous light is compatible with the manganese-based photoinhibition mechanism and with mechanisms in which singlet oxygen, produced via a direct photosensitization reaction, is the agent of damage. However, the classical acceptor-side and donor-side mechanisms do not predict a similar quantum yield for flashes and continuous light.

SUBMITTER: Sarvikas P

PROVIDER: S-EPMC2955740 | biostudies-literature | 2010 Oct

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Short flashes and continuous light have similar photoinhibitory efficiency in intact leaves.

Sarvikas Päivi P Hakala-Yatkin Marja M Dönmez Sirin S Tyystjärvi Esa E

Journal of experimental botany 20100719 15

Lincomycin-treated pumpkin leaves were illuminated with either continuous light or saturating single-turnover xenon flashes to study the dependence of photoinactivation of photosystem II (PSII) on the mode of delivery of light. The flash energy and the time interval between the flashes were varied between the experiments, and photoinactivation was measured with oxygen evolution and the ratio of variable to maximum fluorescence (F(v)/F(m)). The photoinhibitory efficiency of saturating xenon flash ...[more]

PMID: 20643811

Similar Datasets

Project description:It has been theorized that photosynthetic radiation use efficiency (PhRUE) over the course of a day is constant for leaves throughout a canopy if leaf nitrogen content and photosynthetic properties are adapted to local light so that canopy photosynthesis over a day is optimized. To test this hypothesis, 'daily' photosynthesis of individual leaves of Solanum melongena plants was calculated from instantaneous rates of photosynthesis integrated over the daylight hours. Instantaneous photosynthesis was estimated from the photosynthetic responses to photosynthetically active radiation (PAR) and from the incident PAR measured on individual leaves during clear and overcast days. Plants were grown with either abundant or scarce N fertilization. Both net and gross daily photosynthesis of leaves were linearly related to daily incident PAR exposure of individual leaves, which implies constant PhRUE over a day throughout the canopy. The slope of these relationships (i.e. PhRUE) increased with N fertilization. When the relationship was calculated for hourly instead of daily periods, the regressions were curvilinear, implying that PhRUE changed with time of the day and incident radiation. Thus, linearity (i.e. constant PhRUE) was achieved only when data were integrated over the entire day. Using average PAR in place of instantaneous incident PAR increased the slope of the relationship between daily photosynthesis and incident PAR of individual leaves, and the regression became curvilinear. The slope of the relationship between daily gross photosynthesis and incident PAR of individual leaves increased for an overcast compared with a clear day, but the slope remained constant for net photosynthesis. This suggests that net PhRUE of all leaves (and thus of the whole canopy) may be constant when integrated over a day, not only when the incident PAR changes with depth in the canopy, but also when it varies on the same leaf owing to changes in daily incident PAR above the canopy. The slope of the relationship between daily net photosynthesis and incident PAR was also estimated from the photosynthetic light response curve of a leaf at the top of the canopy and from the incident PAR above the canopy, in place of that measured on individual leaves. The slope (i.e. net PhRUE) calculated in this simple way did not differ statistically from that calculated using data from individual leaves.

Project description:The human circadian timing system is most sensitive to the phase-shifting effects of light during the biological nighttime, a time at which humans are most typically asleep. The overlap of sleep with peak sensitivity to the phase-shifting effects of light minimizes the effectiveness of using light as a countermeasure to circadian misalignment in humans. Most current light exposure treatments for such misalignment are mostly ineffective due to poor compliance and secondary changes that cause sleep deprivation. Using a 16-day, parallel group design, we examined whether a novel sequence of light flashes delivered during sleep could evoke phase changes in the circadian system without disrupting sleep. Healthy volunteers participated in a 2-week circadian stabilization protocol followed by a 2-night laboratory stay. During the laboratory session, they were exposed during sleep to either darkness (n = 7) or a sequence of 2-msec light flashes given every 30 sec (n = 6) from hours 2 to 3 after habitual bedtime. Changes in circadian timing (phase) and micro- and macroarchitecture of sleep were assessed. Subjects exposed to the flash sequence during sleep exhibited a delay in the timing of their circadian salivary melatonin rhythm compared with the control dark condition (p < 0.05). Confirmation that the flashes penetrated the eyelids is presented by the occurrence of an evoked response in the EEG. Despite the robust effect on circadian timing, there were no large changes in either the amount or spectral content of sleep (p values > 0.30) during the flash stimulus. Exposing sleeping individuals to 0.24 sec of light spread over an hour shifted the timing of the circadian clock and did so without major alterations to sleep itself. While a greater number of matched subjects and more research will be necessary to ascertain whether these light flashes affect sleep, our data suggest that this type of passive phototherapy might be developed as a useful treatment for circadian misalignment in humans.

Dataset Information

Short flashes and continuous light have similar photoinhibitory efficiency in intact leaves.

Publications

Short flashes and continuous light have similar photoinhibitory efficiency in intact leaves.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets