Photoinactivation of photosystem II in leaves.

Photosynth Res

Research School of Biological Sciences, Australian National University, GPO Box 475, Canberra, ACT 2601, Australia.

Published: June 2005

Photoinactivation of Photosystem II (PS II), the light-induced loss of ability to evolve oxygen, inevitably occurs under any light environment in nature, counteracted by repair. Under certain conditions, the extent of photoinactivation of PS II depends on the photon exposure (light dosage, x), rather than the irradiance or duration of illumination per se, thus obeying the law of reciprocity of irradiance and duration of illumination, namely, that equal photon exposure produces an equal effect. If the probability of photoinactivation (p) of PS II is directly proportional to an increment in photon exposure (p = kDeltax, where k is the probability per unit photon exposure), it can be deduced that the number of active PS II complexes decreases exponentially as a function of photon exposure: N = Noexp(-kx). Further, since a photon exposure is usually achieved by varying the illumination time (t) at constant irradiance (I), N = Noexp(-kI t), i.e., N decreases exponentially with time, with a rate coefficient of photoinactivation kI, where the product kI is obviously directly proportional to I. Given that N = Noexp(-kx), the quantum yield of photoinactivation of PS II can be defined as -dN/dx = kN, which varies with the number of active PS II complexes remaining. Typically, the quantum yield of photoinactivation of PS II is ca. 0.1micromol PS II per mol photons at low photon exposure when repair is inhibited. That is, when about 10(7) photons have been received by leaf tissue, one PS II complex is inactivated. Some species such as grapevine have a much lower quantum yield of photoinactivation of PS II, even at a chilling temperature. Examination of the longer-term time course of photoinactivation of PS II in capsicum leaves reveals that the decrease in N deviates from a single-exponential decay when the majority of the PS II complexes are inactivated in the absence of repair. This can be attributed to the formation of strong quenchers in severely-photoinactivated PS II complexes, able to dissipate excitation energy efficiently and to protect the remaining active neighbours against damage by light.

Download full-text PDF

Source
http://dx.doi.org/10.1007/s11120-005-0410-1DOI Listing

Publication Analysis

Top Keywords

photon exposure
28
quantum yield
12
yield photoinactivation
12
photoinactivation
9
photoinactivation photosystem
8
irradiance duration
8
duration illumination
8
directly proportional
8
number active
8
active complexes
8

Similar Publications

Photon-counting mammography is an emerging modality that allows for spectral imaging and provides a differentiation of material compositions. The development of photon-counting mammography-specific contrast agents has yet to be explored. In this study, the contrast, sensitivity, and organ dose between silver sulfide nanoparticles (AgS-NPs) and a clinically approved iodinated agent (iopamidol) were investigated using a contrast-embedded gradient ramp phantom and a prototype scanner.

View Article and Find Full Text PDF

Background: Elemental analysis of teeth allows for exposure assessment during critical windows of development and is increasingly used to link early life exposures and health. The measurement of inorganic elements in teeth is challenging; laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is the most widely used technique.

Objective: Both synchrotron x-ray fluorescence (SXRF) and LA-ICP-MS have the capability to measure elemental distributions in teeth with each having distinct advantages and disadvantages.

View Article and Find Full Text PDF

Reduced cerebral blood flow occurs early in the development of Alzheimer's disease (AD), but the factors producing this reduction are unknown. Here, we ask whether genetic and lifestyle risk factors for AD-the ε4 allele of the Apolipoprotein (APOE) gene, and physical activity-can together produce this reduction in cerebral blood flow which leads eventually to AD. Using in vivo two-photon microscopy and haemodynamic measures, we record neurovascular function from the visual cortex of physically active or sedentary mice expressing APOE3 and APOE4 in place of murine APOE.

View Article and Find Full Text PDF

Molecularly imprinted hydrogels embedded with two-dimensional photonic crystals for the detection of dexamethasone/betamethasone sodium phosphate.

Mikrochim Acta

January 2025

Key Laboratory of New Energy & New Functional Materials, Shaanxi Key Laboratory of Chemical Reaction Engineering, College of Chemistry and Chemical Engineering, School of Medicine, Yan'an University, Yan'an, Shaanxi, 716000, People's Republic of China.

Dexamethasone sodium phosphate (DSP) and betamethasone sodium phosphate (BSP) imprinted hydrogels embedded with two-dimensional photonic crystals (2DPC) were developed as hormones-sensitive photonic hydrogel sensors with highly sensitive, selective, anti-interference and reproducible recognition capability. The DSP/BSP molecularly imprinted photonic hydrogels (denoted as DSP-MIPH and BSP-MIPH) can specifically recognize DSP/BSP by rebinding the DSP/BET molecules to nanocavities in the hydrogel network. This recognition is enabled by the similar shape, size, and binding sites of the nanocavities to the target molecules.

View Article and Find Full Text PDF

Cardiac Positron Emission Tomography (PET) can be used for the assessment of myocardial perfusion. Compared to other cardiac imaging techniques, notably Single Photon Emission Computer Tomography (SPECT), cardiac PET offers superior image resolution, higher accuracy, quantitative measures of myocardial perfusion, lower radiation exposure, and shorter image acquisition time. However, PET tends to be costlier and less widely available than SPECT due to the specialized equipment needed for generating the necessary radiotracers.

View Article and Find Full Text PDF

Want AI Summaries of new PubMed Abstracts delivered to your In-box?

Enter search terms and have AI summaries delivered each week - change queries or unsubscribe any time!