Photosynthesis Research (v.95, #1)

The very personal touch of Professor Martin Gibbs as a worldwide advocate for photosynthesis and plant physiology was lost with his death in July 2006. Widely known for his engaging humorous personality and his humanitarian lifestyle, Martin Gibbs excelled as a strong international science diplomat; like a personal science family patriarch encouraging science and plant scientists around the world. Immediately after World War II he was a pioneer at the Brookhaven National Laboratory in the use of 14C to elucidate carbon flow in metabolism and particularly carbon pathways in photosynthesis. His leadership on carbon metabolism and photosynthesis extended for four decades of working in collaboration with a host of students and colleagues. In 1962, he was selected as the Editor-in-Chief of Plant Physiology. That appointment initiated 3 decades of strong directional influences by Gibbs on plant research and photosynthesis. Plant Physiology became and remains a premier source of new knowledge about the vital and primary roles of plants in earth’s environmental history and the energetics of our green-blue planet. His leadership and charismatic humanitarian character became the quintessence of excellence worldwide. Martin Gibbs was in every sense the personification of a model mentor not only for scientists but also shown in devotion to family. Here we pay tribute and honor to an exemplary humanistic mentor, Martin Gibbs.
Keywords: Martin Gibbs; CO2 fixation; Gibbs effect; Triose phosphate dehydrogenases; Photophosphorylation; Light intensity; CO2 compensation point; 14C-sugar labeling; Photorespiration; Oxyhydrogen reaction; Mentoring; Sugar metabolism; Chloroplast respiration; Glycolate synthesis

Eukaryotes arose from an endosymbiotic association of an α-proteobacterium-like organism (the ancestor of mitochondria) with a host cell (lacking mitochondria or plastids). Plants arose by the addition of a cyanobacterium-like endosymbiont (the ancestor of plastids) to the two-member association. Each member of the association brought a unique internal environment and a unique genome. Analyses of recently acquired genomic sequences with newly developed algorithms have revealed (a) that the number of endosymbiont genes that remain in eukaryotic cells—principally in the nucleus—is surprisingly large, (b) that protein products of a large number of genes (or their descendents) that entered the association in the genome of the host are now directed to an organelle derived from an endosymbiont, and (c) that protein products of genes traceable to endosymbiont genomes are directed to the nucleo-cytoplasmic compartment. Consideration of these remarkable findings has led to the present suggestion that contemporary eukaryotic cells evolved through continual chance relocation and testing of genes as well as combinations of gene products and biochemical processes in each unique cell compartment derived from a member of the eukaryotic association. Most of these events occurred during about 300 million years, or so, before contemporary forms of eukaryotic cells appear in the fossil record; they continue today.
Keywords: Chloroplasts; Endosymbiosis; Eukaryotic cell evolution; Gene transfer; Mitochondria; Protein reassortment

The vast structural and functional information database of photosynthetic enzymes includes, in addition to detailed kinetic records from decades of research on physical processes and chemical reaction-pathways, a variety of high and medium resolution crystal structures of key photosynthetic enzymes. Here, it is examined from an engineer’s point of view with the long-term goal of reproducing the key features of natural photosystems in novel biological and non-biological solar-energy conversion systems. This survey reveals that the basic physics of the transfer processes, namely, the time constraints imposed by the rates of incoming photon flux and the various decay processes allow for a large degree of tolerance in the engineering parameters. Furthermore, the requirements to guarantee energy and electron transfer rates that yield high efficiency in natural photosystems are largely met by control of distance between chromophores and redox cofactors. This underlines a critical challenge for projected de novo designed constructions, that is, the control of spatial organization of cofactor molecules within dense array of different cofactors, some well within 1 nm from each other.
Keywords: Chlorophylls; Concentration quenching; Electron tunneling; Förster resonance energy transfer; Light harvesting; Reaction center; Redox chains

Oscillations with a period of 1–2 min in the rate of photosynthesis have been found in leaves of C3 and C4 land plants under invariant, saturating, light and carbon dioxide. This article reports the occurrence of similar oscillations with a period of 2–2.5 min in individual cells of the marine diatom Coscinodiscus wailesii. These oscillations were determined by measurements of both oxygen (oxygen microelectrode) and carbon dioxide (pH microelectrode) just outside the plasmalemma. These oscillations were found in less than 1% of the cells examined. The occurrence of oscillations in unicelluar diatoms rules out for these organisms hypotheses as to the origin of oscillations in land plant leaves that are based on cell–cell interactions.
Keywords: Coscinodiscus wailesii ; Diatom; Photosynthetic oscillation

Effect of dichromate on photosystem II activity in xanthophyll-deficient mutants of Chlamydomonas reinhardtii by Nadia Ait Ali; Philippe Juneau; Olivier Didur; François Perreault; Radovan Popovic (45-53).
The photosystem II activity and energy dissipation was investigated when algal Chlamydomonas reinhardtii genotypes were exposed to dichromate toxicity effect. The exposure during 24 h to dichromate effect of two C. reinhardtii mutants having non-functional xanthophylls cycle, as npq1 zeaxanthin deficient and npq2 zeaxanthin accumulating, induced inhibition of PSII electron transport. After dichromate-induced toxicity, PSII functions of C. reinhardtii mutants were investigated under different light intensities. To determine dichromate toxicity and light intensity effect on PSII functional properties we investigated the change of energy dissipation via PSII electron transport, non-photochemical regulated and non-regulated energy dissipation according to Kramer et al. (Photosynth Res 79:209–218, 2004). We showed the dependency between dichromate toxicity and light-induced photoinhibition in algae deficient in xanthophyll cycle. When algal mutants missing xanthophylls cycle were exposed to dichromate toxicity and to high light intensity energy dissipation via non-regulated mechanism takes the most important pathway reaching the value of 80%. Therefore, the mutants npq1 and npq2 having non-functional xanthophylls cycle were more sensitive to dichromate toxic effects.
Keywords: Photosystem II energy dissipation; Xanthophyll cycle; Zeaxanthin; Dichromate; Chlamydomonas reinhardtii ; MAXI-IMAGING-PAM fluorometry

Acaryochloris marina is an oxygen-evolving organism that utilizes chlorophyll-d for light induced photochemistry. In photosystem I particles from Acaryochloris marina, the primary electron donor is called P740, and it is thought that P740 consist of two chlorophyll-d molecules. (P740+-P740) FTIR difference spectra have been produced, and vibrational features that are specific to chlorophyll-d (and not chlorophyll-a) were observed, supporting the idea that P740 consists chlorophyll-d molecules. Although bands in the (P740+-P740) FTIR difference spectra were assigned specifically to chlorophyll-d, how these bands shifted, and how their intensities changed, upon cation formation was never considered. Without this information it is difficult to draw unambiguous conclusions from the FTIR difference spectra. To gain a more detailed understanding of cation induced shifting of bands associated with vibrational modes of P740 we have used density functional theory to calculate the vibrational properties of a chlorophyll-d model in the neutral, cation and anion states. These calculations are shown to be of considerable use in interpreting bands in (P740+-P740) FTIR difference spectra. Our calculations predict that the 31 formyl C–H mode of chlorophyll-d upshifts/downshifts upon cation/anion formation, respectively. The mode intensity also decreases/increases upon cation/anion formation, respectively. The cation induced bandshift of the 31 formyl C–H mode of chlorophyll-d is also strongly dependant on the dielectric environment of the chlorophyll-d molecules. With this new knowledge we reassess the interpretation of bands that were assigned to 31 formyl C–H modes of chlorophyll-d in (P740+-P740) FTIR difference spectra. Considering our calculations in combination with (P740+-P740) FTIR DS we find that the most likely conclusions are that P740 is a dimeric Chl-d species, in an environment of low effective dielectric constant (∼2–8). In the P740+ state, charge is asymmetrically distributed over the two Chl-d pigments in a roughly 60:40 ratio.
Keywords: Chlorophyll; Chlorophyll-d ; Density functional theory; Fourier transform infrared; Normal-mode; Vibrational frequencies; Formyl group

Selenite transiently represses transcription of photosynthesis-related genes in potato leaves by Valeria Poggi; Valerio Del Vescovo; Claudio Di Sanza; Rodolfo Negri; Alejandro Hochkoeppler (63-71).
A striking response of potato leaves to aspersion with selenite was observed at the transcriptional level by means of cDNA microarrays analysis. This response is characterized by a general transient repression of genes coding for components of photosynthetic systems and of other light-regulated genes. In particular, maximal repression was observed 8 h after selenite aspersion, while 24 h after the treatment a complete recovery of normal transcriptional levels was detected. Another general feature of the transcriptional response to selenite is represented by the transcriptional induction of genes related to amino acid metabolism, and to stress defense; interestingly, two genes coding for glutathione S-transferases were found early-induced upon selenite treatment.
Keywords: Selenite; Photosynthesis; Transcription; Microarrays; Potato

Subcellular localization of ferredoxin-NADP+ oxidoreductase in phycobilisome retaining oxygenic photosysnthetic organisms by Fatthy Mohamed Morsy; Masato Nakajima; Takayuki Yoshida; Tatsuki Fujiwara; Toshio Sakamoto; Keishiro Wada (73-85).
Ferredoxin-NADP+ oxidoreductase (FNR) catalyzing the terminal step of the linear photosynthetic electron transport was purified from the cyanobacterium Spirulina platensis and the red alga Cyanidium caldarium. FNR of Spirulina consisted of three domains (CpcD-like domain, FAD-binding domain, and NADP+-binding domain) with a molecular mass of 46 kDa and was localized in either phycobilisomes or thylakoid membranes. The membrane-bound FNR with 46 kDa was solublized by NaCl and the solublized FNR had an apparent molecular mass of 90 kDa. FNR of Cyanidium consisted of two domains (FAD-binding domain and NADP+-binding domain) with a molecular mass of 33 kDa. In Cyanidium, FNR was found on thylakoid membranes, but there was no FNR on phycobilisomes. The membrane-bound FNR of Cyanidium was not solublized by NaCl, suggesting the enzyme is tightly bound in the membrane. Although both cyanobacteria and red algae are photoautotrophic organisms bearing phycobilisomes as light harvesting complexes, FNR localization and membrane-binding characteristics were different. These results suggest that FNR binding to phycobilisomes is not characteristic for all phycobilisome retaining oxygenic photosynthetic organisms, and that the rhodoplast of red algae had possibly originated from a cyanobacterium ancestor, whose FNR lacked the CpcD-like domain.
Keywords: CpcD; Cyanobacterium; Ferredoxin-NADP+ oxidoreductase (FNR); Phycobilisome; Red alga

To evaluate the acclimative ability of current-year and previous-year needles of a shade tolerant conifer Taxus baccata L. to contrasting irradiance conditions, seedlings were raised under 27% solar irradiance and at 3 years of age they were transferred to an experimental garden and grown for one season under full irradiance (HL), 18% irradiance (ML) or 5% irradiance (LL). Whereas previous year needles did not change anatomically, current year needles in HL were thicker and had a thicker palisade and spongy mesophyll, and greater leaf mass per area than ML or LL needles. LL needles had greater nitrogen concentration than HL needles irrespective of age but only previous year LL needles also had an increased N per area content, thanks to their lack of reduction in LMA. Adjustment of chlorophyll and carotenoid content occurred in both needle age classes with LL and ML needles having much higher concentrations but, in current year needles, only slightly higher per area content than HL needles. Chlorophyll a/b ratio was not affected by age or irradiance. These modifications had no significant effect on photosynthetic capacities, which did not significantly differ between the age classes in HL or LL treatment and between treatments. On the other hand, high growth irradiance resulted in a greater photochemical yield, photochemical quenching, apparent electron transport rate and inducible non-photochemical quenching in needles formed in the current season. In previous year needles, however, only inducible NPQ was enhanced by high irradiance with other parameters remaining identical among treatments. To test sensitivity to photoinhibition, at the end of the summer plants from the three irradiance levels were transferred to a HL situation and F v/F M was determined over the following 18 days. Sensitivity to photoinhibition was negatively related to growth irradiance and previous year needles were less photoinhibited than current year needles. Thus, differences in acclimation ability between needle age classes were most pronounced at the level of anatomy and light reactions of photosynthesis, both of which showed almost no plasticity in previous year needles but were considerably modified by irradiance in current year needles.
Keywords: Acclimation to irradiance; Photoinhibition; Sun/shade leaves; Taxus baccata

Ribulose-1,5-bisphosphate carboxylase/oxygenase from thermophilic cyanobacterium Thermosynechococcus elongatus by Beata Gubernator; Rafal Bartoszewski; Jaroslaw Kroliczewski; Guenter Wildner; Andrzej Szczepaniak (101-109).
Ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco) can be divided into two branches: the “red-like type” of marine algae and the “green-like type” of cyanobacteria, green algae, and higher plants. We found that the “green-like type” rubisco from the thermophilic cyanobacterium Thermosynechococcus elongatus has an almost 2-fold higher specificity factor compared with rubiscos of mesophilic cyanobacteria, reaching the values of higher plants, and simultaneously revealing an improvement in enzyme thermostability. The difference in the activation energies at the transition stages between the oxygenase and carboxylase reactions for Thermosynechococcus elongatus rubisco is very close to that of Galdieria partita and significantly higher than that of spinach. This is the first characterization of a “green-like type” rubisco from thermophilic organism.
Keywords: Rubisco; Specificity factor; Thermostability; Thermophilic cyanobacteria

Aquafluo 2007: chlorophyll fluorescence in aquatic sciences, an international conference held in Nové Hrady by Ondrej Prasil; David J. Suggett; John J. Cullen; Marcel Babin; Govindjee (111-115).