Photosynthesis Research (v.105, #3)

We celebrate Andy Benson’s 93rd birthday on September 24, 2010 through this Editorial. This short account about Andy Benson should serve as a prelude to the short article that Andy has written for the entire photosynthesis community, which gives a glimpse of why he left the field of the “path of carbon in photosynthesis,” when he had already discovered, together with Melvin Calvin, James Alan Bassham, and others, most of the major steps in what we now call the Calvin–Benson cycle.
Keywords: James A. Bassham; Carl B. Benson; Emma C. Alm Benson; Dee Benson; Calvin-Benson cycle; Melvin Calvin; Martin Kamen; Lifetime Achievement Award of the Rebeiz Foundation; Robert A. Millikan; Samuel Ruben; University of California at Berkeley; University of California, San Diego

Govindjee, the founding editor of the Historical Corner of Photosynthesis Research, invited me 3 years ago to tell the story of why I left Melvin Calvin’s laboratory in the mid 1950s long before the 1961 Nobel Prize in Chemistry was awarded to Calvin for the path of carbon in photosynthesis. I have already written my scientific perspective on this topic (see Benson (Photosynth Res 73:29–49, 2002); also see Bassham (Photosynth Res 76:35–52, 2003) as he was also a major player in this research). Here, I present my recollections of my last days in the old radiation laboratory (ORL) at Berkeley, California. References have been added by Govindjee for the benefit of the readers.
Keywords: John Barltrop; Melvin Calvin; R. Clint Fuller; Jacques Mayaudon; J. Rodney Quayle; Thioctic (Lipoic) acid; Sam G. Wildman; Cornelis B. Van Niel

Light, genotype, and abscisic acid affect chloroplast positioning in guard cells of Arabidopsis thaliana leaves in distinct ways by Martina Königer; Brita Jessen; Rui Yang; Dorothea Sittler; Gary C. Harris (213-227).
The goal of this study was to investigate the effects of light intensity, genotype, and various chemical treatments on chloroplast movement in guard cells of Arabidopsis thaliana leaves. After treatment at various light intensities (dark, low, and high light), leaf discs were fixed with glutaraldehyde, and imaged using confocal laser microscopy. Each chloroplast was assigned a horizontal (close to pore, center, or epidermal side) and vertical (outer, middle, inner) position. White light had a distinct effect on chloroplast positioning, most notably under high light (HL) when chloroplasts on the upper leaf surface of wild-type (WT) moved from epidermal and center positions toward the pore. This was not the case for phot1-5/phot2-1 or phot2-1 plants, thus phototropins are essential for chloroplast positioning in guard cells. In npq1-2 mutants, fewer chloroplasts moved to the pore position under HL than in WT plants, indicating that white light can affect chloroplast positioning also in a zeaxanthin-dependent way. Cytochalasin B inhibited the movement of chloroplasts to the pore under HL, while oryzalin did not, supporting the idea that actin plays a role in the movement. The movement along actin cables is dependent on CHUP1 since chloroplast positioning in chup1 was significantly altered. Abscisic acid (ABA) caused most chloroplasts in WT and phot1-5/phot2-1 to be localized in the center, middle part of the guard cells irrespective of light treatment. This indicates that not only light but also water stress influences chloroplast positioning.
Keywords: Abscisic acid; Actin; Chloroplast movement; CHUP; Guard cells; Light intensity; Phototropin; Zeaxanthin

Digalactosyl-diacylglycerol-deficiency lowers the thermal stability of thylakoid membranes by Sashka Boychova Krumova; Sergey Petrovich Laptenok; László Kovács; Tünde Tóth; Arie van Hoek; Győző Garab; Herbert van Amerongen (229-242).
We investigated the effects of digalactosyl-diacylglycerol (DGDG) on the organization and thermal stability of thylakoid membranes, using wild-type Arabidopsis thaliana and the DGDG-deficient mutant, dgd1. Circular-dichroism measurements reveal that DGDG-deficiency hampers the formation of the chirally organized macrodomains containing the main chlorophyll a/b light-harvesting complexes. The mutation also brings about changes in the overall chlorophyll fluorescence lifetimes, measured in whole leaves as well as in isolated thylakoids. As shown by time-resolved measurements, using the lipophylic fluorescence probe Merocyanine 540 (MC540), the altered lipid composition affects the packing of lipids in the thylakoid membranes but, as revealed by flash-induced electrochromic absorbance changes, the membranes retain their ability for energization. Thermal stability measurements revealed more significant differences. The disassembly of the chiral macrodomains around 55°C, the thermal destabilization of photosystem I complex at 61°C as detected by green gel electrophoresis, as well as the sharp drop in the overall chlorophyll fluorescence lifetime above 45°C (values for the wild type—WT) occur at 4–7°C lower temperatures in dgd1. Similar differences are revealed in the temperature dependence of the lipid packing and the membrane permeability: at elevated temperatures MC540 appears to be extruded from the dgd1 membrane bilayer around 35°C, whereas in WT, it remains lipid-bound up to 45°C and dgd1 and WT membranes become leaky around 35 and 45°C, respectively. It is concluded that DGDG plays important roles in the overall organization of thylakoid membranes especially at elevated temperatures.
Keywords: Arabidopsis mutants; Digalactosyl-diacylglycerol; dgd1 mutant; Thermal stability; Thylakoid lipids; Thylakoid membranes

Light-dependent binding of labeled ADP and ATP to noncatalytic sites of chloroplast ATP synthase and the effect of light-exposed thylakoid membrane preincubation with ADP or ATP on ATPase activity were studied. ADP binding during the preincubation was shown to inactivate the chloroplast ATPase, whereas ATP binding caused its activation. The rate and equilibrium constants of ATPase inactivation and activation were close to those of ADP and ATP binding to a noncatalytic site, with K d values of 38 and 33 μM, respectively. It is suggested that ADP- or ATP-binding to one of the noncatalytic sites affects the ATPase activity of chloroplast ATP synthase through a mechanism that modulates tightness of ADP binding to a catalytic site.
Keywords: ATP synthase; Chloroplast ATPase; CFoCF1 ; Noncatalytic sites; Nucleotide binding

The effect of high salt stress on PS II heterogeneity was investigated in wheat (Triticum aestivum) leaves. On the basis of antenna size, PS II has been classified into three forms, i.e., α, β, and γ centers while on the basis of electron transport properties of the reducing side of the reaction centers, two distinct forms of PS II have been suggested, i.e., QB reducing centers and QB non-reducing centers. The chlorophyll a (Chl a) fluorescence transients, which can quantify PS II behavior, were recorded using PEA to derive OJIP in vivo with high time resolution and further analyzed according to JIP test. Our results showed that with an increase in the salt concentration during growth, the number of QB non-reducing centers increased. In antenna size heterogeneity the number of β and γ centers increased while the number of α centers decreased. A change in the energetic connectivity between the PS II units was also observed. Recovery studies showed that antenna heterogeneity was completely recovered from damage at 0.5 M NaCl concentration and partially recovered at 1 M NaCl concentration while reducing side heterogeneity showed no recovery at all after 0.5 M onwards.
Keywords: Photosystem II; Heterogeneity; High salt stress; Antenna size

The 3- and 7-formyl groups of chlorophyll-d (Chl-d) and bacteriochlorophyll-e (BChl-e), respectively, were regioselectively labeled with an isotopically stable oxygen-18 (18O) atom to give 31-18O-labeled Chl-d and 71-18O-labeled BChl-e (ca. 90% 18O) by exchanging the carbonyl oxygen atoms in the presence of acidic H2 18O (ca. 95% 18O). Another photosynthetically active chlorophyll, BChl-a possessing the 3-acetyl group was treated under similar acidic conditions to afford a trace amount of 31-18O-labeled BChl-a and further demetallated compound, the corresponding 31-18O-labeled bacteriopheophytin-a as the major product with 55% 18O-degree. The FT-IR spectra of 18O-(un)labeled chlorophylls in the solution and the solid states showed that the 3- and 7-carbonyl stretching vibration modes moved to about a 30-cm−1 lower wavenumber by 18O-labeling at the 31- and 71-oxo moieties. In artificial chlorosome-like self-aggregates of BChl-e, the 18O-labeled 7-carbonyl stretching mode was completely resolved from the specially hydrogen-bonded 13-C=O stretching mode, evidently indicating no interaction of the 7-CHO with other functional groups in the supramolecules.
Keywords: Bacteriochlorophyll; Chlorophyll; Isotope-18O-labeling; Photosynthetic pigment; Self-aggregation; Vibrational spectroscopy

SPAD chlorophyll meter reading can be pronouncedly affected by chloroplast movement by Jan Nauš; Jitka Prokopová; Jiří Řebíček; Martina Špundová (265-271).
Non-destructive assessment of chlorophyll content has recently been widely done by chlorophyll meters based on measurement of leaf transmittance (e.g. the SPAD-502 chlorophyll meter measures the leaf transmittance at 650 and 940 nm). However, the leaf transmittance depends not only on the content of chlorophylls but also on their distribution in leaves. The chlorophyll distribution within leaves is co-determined by chloroplast arrangement in cells that depends on light conditions. When tobacco leaves were exposed to a strong blue light (about 340 μmol of photons m−2 s−1), a very pronounced increase in the leaf transmittance was observed as chloroplasts migrated from face position (along cell walls perpendicular to the incident light) to side position (along cell walls parallel to the incoming light) and the SPAD reading decreased markedly. This effect was more pronounced in the leaves of young tobacco plants compared with old ones; the difference between SPAD values in face and side position reached even about 35%. It is shown how the chloroplast movement changes a relationship between the SPAD readings and real chlorophyll content. For an elimination of the chloroplast movement effect, it can be recommended to measure the SPAD values in leaves with a defined chloroplasts arrangement.
Keywords: Chlorophyll content; Chloroplast movement; Leaf transmittance; SPAD meter

Mahalanobis distance screening of Arabidopsis mutants with chlorophyll fluorescence by Marius C. Codrea; Marja Hakala-Yatkin; Anna Kårlund-Marttila; Ladislav Nedbal; Tero Aittokallio; Olli S. Nevalainen; Esa Tyystjärvi (273-283).
Rapid nondestructive screening of mutants is a common step in many research projects in plant biology. Here we report the development of a method that uses kinetic imaging of chlorophyll fluorescence to detect phenotypes that differ from wild-type plants. The method uses multiple fluorescence features simultaneously in order to catch different types of photosynthesis-related mutants with a single assay. The Mahalanobis distance was used to evaluate the degree of similarity in fluorescence features between the wild-type and test plants, and plants differing strongly from the wild-type were classified as mutants. The method was tested on a collection of photosynthesis-related mutants of Arabidopsis thaliana. The plants were evaluated from images in which the color of each pixel depended on the Mahalanobis distance of the fluorescence features. Two parameters of the color-coding procedure were used to adjust the trade-off between detection of true mutants and erratic classification of wild-type plants as mutants. We found that a large percentage of photosynthesis-related mutants can be detected with this method. Scripts for the free statistics software R are provided to facilitate the practical application of the method.
Keywords: Arabidopsis thaliana ; Chlorophyll fluorescence; Fluorescence imaging; Mutant detection; Outlier detection