Photosynthesis Research (v.87, #3)
Ilya Vassiliev (January 12, 1959–August 10, 2005) by Bridgette A. Barry (245-246).
Remembering Lee McIntosh (1949–2004), a pioneer in the molecular biology of chloroplast and mitochondrion function by Hans Kende (247-251).
Left- and right-handed LHC II macroaggregates revealed by circularly polarized chlorophyll luminescence by Eugene E. Gussakovsky; Maksim V. Ionov; Yuri E. Giller; Kira Ratner; Takhir F. Aripov; Yosepha Shahak (253-265).
Circularly polarized chlorophyll luminescence (CPL) may serve as a measure of chiral macroaggregates of the light-harvesting chlorophyll-protein complexes (LHC II) in both isolated chloroplasts and intact leaves (Gussakovsky et al (2000) Photosynth Res 65: 83–92). In the present work, we applied the CPL approach to study the effect of fast (1–2 min) thermal impacts on LHC II macroaggregates. The results revealed unexpected temperature-response kinetics, composed of initial bell-shaped changes in the CPL signal, followed by degradation down to a steady state (equilibrium). The bell-shape effect was dependent upon illumination, and vanished in the dark. A mathematical analysis of the temperature-response kinetics uniquely indicated that LHC II chiral macroaggregates may persist in both left- and right-handed forms. These forms differ in their response to high temperatures. Both forms are more thermostable in leaves than in isolated chloroplasts. The cooperative degradation of LHC II macroaggregates, which is induced by the thermal impact, is irreversible. It is therefore suggested that the native LHC II macroaggregates are stable, stationary, non-equilibrium, spatially heterogeneous (dissipative) structures. The dissipative properties probably allow the interconversion between left- and right-handed forms under perturbation by certain factors. Illumination probably serves as one such perturbation factor, initiating the interconversion of dark-adapted, left-handed to light-dependent, right-handed LHC II macroaggregates. The chiral heterogeneity of the LHC II macroaggregates is a newly revealed aspect which needs to be taken into consideration in future circular dichroism or CPL studies.
Keywords: pea (Pisum sativum); isolated chloroplasts; intact leaves; light effect; thermal impact
Excitation energy transfer in the LHC-II trimer: a model based on the new 2.72 Å structure by Juha Linnanto; Jari Martiskainen; Viivi Lehtovuori; Janne Ihalainen; Robertas Kananavicius; Roberto Barbato; Jouko Korppi-Tommola (267-279).
Energy transfer of the light harvesting complex LHC-II trimer, extracted from spinach, was studied in the Qy region at room temperature by femtosecond transient absorption spectroscopy. Configuration interaction exciton method [Linnanto et al. (1999) J Phys Chem B 103: 8739–8750] and 2.72 Å structural information reported by Liu et al. was used to calculate spectroscopic properties and excitation energy transfer rates of the complex. Site energies of the pigments and coupling constants of pigment pairs in close contact were calculated by using a quantum chemical configuration interaction method. Gaussian random variation of the diagonal and off-diagonal exciton matrix elements was used to account for inhomogeneous broadening. Rate calculations included only the excitonic states initially excited and probed in the experiments. A kinetic model was used to simulate time and wavelength dependent absorption changes after excitation on the blue side of the Qy transition and compared to experimentally recorded rates. Analysis of excitonic wavefunctions allowed identification of pigments initially excited and probed into later. It was shown that excitation of the blue side of the Qy band of a single LHC-II complex results in energy transfer from chlorophyll b’s of the lumenal side to chlorophyll a’s located primarly on one of the monomers of the stromal side.
Keywords: energy transfer; exciton; femtosecond; LHC-II; light harvesting
Visible foliar injury caused by ozone alters the relationship between SPAD meter readings and chlorophyll concentrations in cutleaf coneflower by Howard S. Neufeld; Arthur H. Chappelka; Greg L. Somers; Kent O. Burkey; Alan W. Davison; Peter L. Finkelstein (281-286).
The ability of the SPAD-502 chlorophyll meter to quantify chlorophyll amounts in ozone-affected leaves of cutleaf coneflower (Rudbeckia laciniata var. digitata) was assessed in this study. When relatively uninjured leaves were measured (percent leaf area affected by stipple less than 6%), SPAD meter readings were linearly related to total chlorophyll with an adjusted R 2 of 0.84. However, when leaves with foliar injury (characterized as a purple to brownish stipple on the upper leaf surface affecting more than 6% of the leaf area) were added, likelihood ratio tests showed that it was no longer possible to use the same equation to obtain chlorophyll estimations for both classes of leaves. Either an equation with a common slope or a common intercept was necessary. We suspect several factors are involved in altering the calibration of the SPAD meter for measuring chlorophyll amounts in visibly ozone-injured leaves, with the most likely being changes in either light absorption or scattering resulting from tissue necrosis.
Keywords: chlorophyll; correlation; foliar stipple; ozone; Rudbeckia laciniata ; SPAD meter
A photoacoustic method for rapid assessment of temperature effects on photosynthesis by Stephen K. Herbert; Karl Y. Biel; Thomas C Vogelmann (287-294).
The photosynthetic and photoacoustic properties of leaf samples were studied using a photoacoustic system modified for precise temperature control. Data were collected over a temperature range of −10 °C to +60 °C. A distinct acoustic noise transient marked the freezing temperature of the samples. A positive absorption transient and a brief period of oxygen uptake marked the thermal denaturing temperature of the samples. Between these extremes, the effects of temperature on light absorption, oxygen evolution, and photochemical energy storage were quantified quickly and easily. Oxygen evolution could be measured as low as −5 °C and showed a broad temperature peak that was 10 °C lower under limiting light intensity than under saturating light intensity. Photochemical energy storage showed a narrower temperature peak that was only slightly lower for limiting light intensities than for saturating light intensities. In a survey of diverse plants, temperature response curves for oxygen evolution were determined readily for a variety of leaf types, including ferns and conifer needles. These results demonstrate that temperature-controlled photoacoustics can be useful for rapid assessment of temperature effects on photosynthesis and other leaf properties.
Keywords: leaf freezing point; oxygen evolution; photoacoustics; photosynthesis; Photosystem II; temperature stress
Simultaneous collection of rapid chlorophyll fluorescence induction kinetics, fluorescence quenching parameters, and environmental data using an automated PAM-2000/CR10X data logging system by Dennis W. Gray; Zoe G. Cardon; Louise A. Lewis (295-301).
The PAM-2000 portable chlorophyll fluorometer represents one of the first commercially available instruments utilizing the Pulse Amplitude Modulation (PAM) measurement principle, and has become a widely used platform for measuring chlorophyll fluorescence in a wide range of study systems. In this paper, we describe a new method for externally driving and gathering data from the PAM-2000, a method that allows the user to execute a pre-defined user run (or runs) and capture (1) rapid induction kinetics (at 2 ms frequency) during all saturating pulses, (2) measures of F, Fo, Fo′, Fm, and Fm′ associated with those same pulses, and (3) changes in fluorescence F at user-defined intervals between pulses, for the entire user run, with all data compressed into a single, manageable data logger file. Practically, the method makes possible, for example, a post-hoc evaluation of the appropriateness of saturation pulse lengths and intensities during a user run. More importantly it captures, during entire user runs, the varied information contained in slow changes in fluorescence between saturating pulses, as well as rapid induction kinetics, quenching coefficients and quantum yields all gathered simultaneously from all saturating flashes.
Keywords: automated data collection; chlorophyll fluorescence; desert algae; fluorescence induction kinetics; PAM-2000; P-peak shift, desiccation/rehydration
A simple low-cost microcontroller-based photometric instrument for monitoring chloroplast movement by Robert Berg; Martina Königer; Brit-Maren Schjeide; George Dikmak; Susan Kohler; Gary C. Harris (303-311).
A new microcontroller-based photometric instrument for monitoring blue light dependent changes in leaf transmission (chloroplast movement) was developed based on a modification of the double-beam technique developed by Walzcak and Gabrys [(1980) Photosynthetica 14: 65–72]. A blue and red bicolor light emitting diode (LED) provided both a variable intensity blue actinic light and a low intensity red measuring beam. A phototransistor detected the intensity of the transmitted measuring light. An inexpensive microcontroller independently and precisely controlled the light emission of the bicolor LED. A typical measurement event involved turning off the blue actinic light for 100 μs to create a narrow temporal window for turning on and measuring the transmittance of the red light. The microcontroller was programmed using LogoChip Logo (http://www.wellesley.edu/Physics/Rberg/logochip/) to record fluence rate response curves. Laser scanning confocal microscopy was utilized to correlate the changes in leaf transmission with intercellular chloroplast position. In the dark, the chloroplasts in the spongy mesophyll exhibited no evident asymmetries in their distribution, however, in the palisade layer the cell surface in contact with the overlying epidermis was devoid of chloroplasts. The low light dependent decrease in leaf transmittance in dark acclimated leaves was correlated with the movement of chloroplasts within the palisade layer into the regions previously devoid of chloroplasts. Changes in leaf transmittance were evident within one minute following the onset of illumination. Minimal leaf transmittance was correlated with chloroplasts having retreated from cell surfaces perpendicular to the incident light (avoidance reaction) in both spongy and palisade layers.
Keywords: chloroplast movement; laser scanning confocal microscopy; leaf transmittance; LogoChip; photometer
Absence of the psbH gene product destabilizes the Photosystem II complex and prevents association of the Photosystem II-X protein in the thermophilic cyanobacterium Thermosynechococcus elongatus BP-1 by Masako Iwai; Mitsunori Katayama; Masahiko Ikeuchi (313-322).
PS II-H is a small hydrophobic protein that is universally present in the PS II core complex of cyanobacteria and plants. The role of PS II-H was studied by directed mutagenesis and biochemical analysis in the thermophilic cyanobacterium Thermosynechococcus elongatus BP-1. The psbH disruptant could grow photoautotrophically; however, its growth was much slower than that of the wild type cell. Chromatography enabled the isolation of active oxygen-evolving PS II complexes from both the mutant and the wild type. The mutant yielded a relatively large amount of inactive PS II complex that lacked the following extrinsic proteins: the 33-kDa protein, the 12-kDa protein, and cytochrome c 550 . There were differences between the psbH disruptant and the wild type in terms of the oxygen evolution activities of the cells, thylakoids, and PS II complexes. At high concentrations of 2,6-DCBQ, the activity was much lower in the mutant than in the wild type. Gel filtration chromatography of the PS II complexes showed that both active and inactive PS II complexes isolated from the mutant were mostly in the monomeric form, while the active PS II complex from the wild type was in the dimeric form. The polypeptide composition of both active and inactive PS II complexes from the mutant showed the absence of another small polypeptide, PS II-X. These results suggest that the PS II-H protein is essential for stable assembly of native dimeric PS II complex containing PS II-X.
Keywords: cyanobacterium; Thermosynechococcus elongatus ; psbH ; psbX ; Photosystem II; dimer
Uphill energy transfer from long-wavelength absorbing chlorophylls to PS II in Ostreobium sp. is functional in carbon assimilation by Christian Wilhelm; Torsten Jakob (323-329).
From the algal genus Ostrobium two species are known which express a chlorophyll antenna absorbing between 710 and 725 nm to a different extent. In a comparative study with these two species it is shown that quanta absorbed by this long wavelength antenna can be transferred to PS II leading to significant PS␣II-related electron transfer. It is documented that under monochromatic far red light illumination growth continues with rather high efficiency. The data show that the uphill-energy transfer to PS II reduces the quantum yield under white light significantly. It is discussed that this strategy of energy conversion might play a role in special environments where far red light is the predominant energy source.
Keywords: energy transfer; far red light; light harvesting; uphill