Photosynthesis Research (v.127, #3)
Remembering Jeanette Snyder Brown (1925–2014) by Winslow R. Briggs; Govindjee (287-293).
Jeanette Snyder Brown (universally called Jan) was associated with the Department of Plant Biology, Carnegie Institution for Science (until recently Carnegie Institution of Washington) over a period of 37 years. Jan has left a scientific legacy of extensive publications concerned with photosynthetic pigments and their organization, and a historic collection of portraits of scientists who were prominent during her long tenure in the Department of Plant Biology. This legacy will stand for many years to come.
Keywords: Photographs of scientists; Photosynthetic pigments; Spectral forms of Chlorophyll a; Stacy French
Photosynthetic use of inorganic carbon in deep-water kelps from the Strait of Gibraltar by María Jesús García-Sánchez; Antonio Delgado-Huertas; José Antonio Fernández; Antonio Flores-Moya (295-305).
Mechanisms of inorganic carbon assimilation were investigated in the four deep-water kelps inhabiting sea bottoms at the Strait of Gibraltar; these species are distributed at different depths (Saccorhiza polysiches at shallower waters, followed by Laminaria ochroleuca, then Phyllariopsis brevipes and, at the deepest bottoms, Phyllariopsis purpurascens). To elucidate the capacity to use HCO3 − as a source of inorganic carbon for photosynthesis in the kelps, different experimental approaches were used. Specifically, we measured the irradiance-saturated gross photosynthetic rate versus pH at a constant dissolved inorganic carbon (DIC) concentration of 2 mM, the irradiance-saturated apparent photosynthesis (APS) rate versus DIC, the total and the extracellular carbonic anhydrase (CAext), the observed and the theoretical photosynthetic rates supported by the spontaneous dehydration of HCO3 − to CO2, and the δ13C signature in tissues of the algae. While S. polyschides and L. ochroleuca showed photosynthetic activity at pH 9.5 (around 1.0 µmol O2 m−2 s−1), the activity was close to zero in both species of Phyllariopsis. The APS versus DIC was almost saturated for the DIC values of natural seawater (2 mM) in S. polyschides and L. ochroleuca, but the relationship was linear in P. brevipes and P. purpurascens. The four species showed total and CAext activities but the inhibition of the CAext originated the observed photosynthetic rates at pH 8.0 to be similar to the theoretical rates that could be supported by the spontaneous dehydration of HCO3 −. The isotopic 13C signatures ranged from −17.40 ± 1.81 to −21.11 ± 1.73 ‰ in the four species. Additionally, the δ13C signature was also measured in the deep-water Laminaria rodriguezii growing at 60–80 m, showing even a more negative value of −26.49 ± 1.25 ‰. All these results suggest that the four kelps can use HCO3 − as external carbon source for photosynthesis mainly by the action of external CAext, but they also suggest that the species inhabiting shallower waters show a higher capacity than the smaller kelps living in deeper waters. In fact, the photosynthesis in the two Phyllariopsis species could be accomplished by the spontaneous dehydration of HCO3 − to CO2. These differences in the capacity to use HCO3 − in photosynthesis among species could be important considering the increasing levels of atmospheric CO2 predicted for the near future.
Keywords: Carbonic anhydrase; CO2 concentration mechanism; Kelps; HCO3 − ; Laminaria ochroleuca ; Phyllariopsis brevipes ; Phyllariopsis purpurascens ; Saccorhiza polyschides ; δ13C
Multiple roles of oxygen in the photoinactivation and dynamic repair of Photosystem II in spinach leaves by Da-Yong Fan; Zi-Piao Ye; Shi-Chang Wang; Wah Soon Chow (307-319).
Oxygen effects have long been ambiguous: exacerbating, being indifferent to, or ameliorating the net photoinactivation of Photosystem II (PS II). We scrutinized the time course of PS II photoinactivation (characterized by rate coefficient k i) in the absence of repair, or when recovery (characterized by k r) occurred simultaneously in CO2 ± O2. Oxygen exacerbated photoinactivation per se, but alleviated it by mediating the utilization of electrons. With repair permitted, the gradual net loss of functional PS II during illumination of leaves was better described phenomenologically by introducing τ, the time for an initial k r to decrease by half. At 1500 μmol photons m−2 s−1, oxygen decreased the initial k r but increased τ. Similarly, at even higher irradiance in air, there was a further decrease in the initial k r and increase in τ. These observations are consistent with an empirical model that (1) oxygen increased k i via oxidative stress but decreased it by mediating the utilization of electrons; and (2) reactive oxygen species stimulated the degradation of photodamaged D1 protein in PS II (characterized by k d), but inhibited the de novo synthesis of D1 (characterized by k s), and that the balance between these effects determines the net effect of O2 on PS II functionality.
Keywords: Oxygen effects; Photoinactivation; Photoinhibition; Photosystem II; Recovery from photoinactivation; Reactive oxygen species
Metabolic engineering of Dunaliella salina for production of ketocarotenoids by N. Anila; Daris P. Simon; Arun Chandrashekar; G. A. Ravishankar; R. Sarada (321-333).
Dunaliella is a commercially important marine alga producing high amount of β-carotene. The use of Dunaliella as a potential transgenic system for the production of recombinant proteins has been recently recognized. The present study reports for the first time the metabolic engineering of carotenoid biosynthesis in Dunaliella salina for ketocarotenoid production. The pathway modification included the introduction of a bkt gene from H. pluvialis encoding β-carotene ketolase (4,4′β-oxygenase) along with chloroplast targeting for the production of ketocarotenoids. The bkt under the control of Dunaliella Rubisco smaller subunit promoter along with its transit peptide sequence was introduced into the alga through standardized Agrobacterium-mediated transformation procedure. The selected transformants were confirmed using GFP and GUS expression, PCR and southern blot analysis. A notable upregulation of the endogenous hydroxylase level of transformants was observed where the BKT expression was higher in nutrient-limiting conditions. Carotenoid analysis of the transformants through HPLC and MS analysis showed the presence of astaxanthin and canthaxanthin with maximum content of 3.5 and 1.9 µg/g DW, respectively. The present study reports the feasibility of using D. salina for the production of ketocarotenoids including astaxanthin.
Keywords: Dunaliella ; Carotenoids; Astaxanthin; Metabolic engineering
Synthesis of chlorophyll-c derivatives by modifying natural chlorophyll-a by Meiyun Xu; Yusuke Kinoshita; Shogo Matsubara; Hitoshi Tamiaki (335-345).
Chlorophyll-a (Chl-a) was extracted from cyanobacterial cells and modified to methyl pyropheophorbide-a. The 3-vinyl-chlorin was transformed to zinc complex of the corresponding 3-acetyl-porphyrin. The zinc porphyrin was oxidized to give cis-7,8- and 17,18-dihydroxy-chlorins as well cis-7,8-cis-17,18-tetrahydroxybacteriochlorin. After zinc-demetallation, the isolated cis-7,8- and 17,18-diols were reduced at the 3-acetyl group and triply dehydrated under acidic conditions to afford two regioisomeric 3-vinyl-porphyrins, methyl divinyl-pyroprotopheophorbide-a possessing the 8-vinyl group and 17-propionate residue (one of the divinyl-protoChl-a derivatives) and methyl pyropheophorbide-c 1 possessing the 8-ethyl group and 17-acrylate residue (one of the Chl-c 1 derivatives), respectively. The resulting 7,8,17,18-tetrol was reduced and then acidically treated, giving five-fold dehydrated free base porphyrin, methyl pyropheophorbide-c 2 possessing the 3,8-divinyl groups and 17-acrylate residue (one of the Chl-c 2 derivatives). The visible absorption and fluorescence emission spectra of the three semi-synthetic 3-vinyl-porphyrins in dichloromethane were compared with those of the corresponding 8-ethyl-porphyrin bearing the 17-propionate residue, methyl pyroprotopheophorbide-a (one of the protoChl-a derivatives). The Soret and Qy absorption maxima were shifted to longer wavelengths with an increase of π-conjugation in a molecule: protoChl-a (8-CH2CH3/17-CH2CH2COOCH3) < divinyl-protoChl-a (8-CH=CH2/17-CH2CH2COOCH3) < Chl-c 1 (8-CH2CH3/17-CH=CHCOOCH3) < Chl-c 2 derivatives (8-CH=CH2/17-CH=CHCOOCH3). The 171,172-dehydrogenation broadened the absorption bands. The emission maxima were bathochromically shifted in the same order. The reaction mechanism of the present dehydration indicates that the biosynthetic pathway of Chls-c would include the hydroxylation of the 17-propionate reside at the 171-position and successive dehydration to the 17-acrylate residue.
Keywords: Acrylate residue; Biosynthetic pathway; Fluorescence emission spectrum; Light-harvesting antenna pigment; Substitution effect; Visible absorption spectrum
Marine phototrophic consortia transfer electrons to electrodes in response to reductive stress by Libertus Darus; Pablo Ledezma; Jürg Keller; Stefano Freguia (347-354).
This work studies how extracellular electron transfer (EET) from cyanobacteria-dominated marine microbial biofilms to solid electrodes is affected by the availability of inorganic carbon (Ci). The EET was recorded chronoamperometrically in the form of electrical current by a potentiostat in two identical photo-electrochemical cells using carbon electrodes poised at a potential of +0.6 V versus standard hydrogen electrode under 12/12 h illumination/dark cycles. The Ci was supplied by the addition of NaHCO3 to the medium and/or by sparging CO2 gas. At high Ci conditions, EET from the microbial biofilm to the electrodes was observed only during the dark phase, indicating the occurrence of a form of night-time respiration that can use insoluble electrodes as the terminal electron acceptor. At low or no Ci conditions, however, EET also occurred during illumination suggesting that, in the absence of their natural electron acceptor, some cyanobacteria are able to utilise solid electrodes as an electron sink. This may be a natural survival mechanism for cyanobacteria to maintain redox balance in environments with limiting CO2 and/or high light intensity.
Keywords: Biophotovoltaics; Microbial solar cell; Marine photosynthetic bacteria; Cyanobacteria; Extracellular electron transfer; Excess electron dissipation
Mutations in circularly permuted GTPase family genes AtNOA1/RIF1/SVR10 and BPG2 suppress var2-mediated leaf variegation in Arabidopsis thaliana by Yafei Qi; Jun Zhao; Rui An; Juan Zhang; Shuang Liang; Jingxia Shao; Xiayan Liu; Lijun An; Fei Yu (355-367).
Leaf variegation mutants constitute a unique group of chloroplast development mutants and are ideal genetic materials to dissect the regulation of chloroplast development. We have utilized the Arabidopsis yellow variegated (var2) mutant and genetic suppressor analysis to probe the mechanisms of chloroplast development. Here we report the isolation of a new var2 suppressor locus SUPPRESSOR OF VARIEGATION (SVR10). Genetic mapping and molecular complementation indicated that SVR10 encodes a circularly permuted GTPase that has been reported as Arabidopsis thaliana NITRIC OXIDE ASSOCIATED 1 (AtNOA1) and RESISTANT TO INHIBITION BY FOSMIDOMYCIN 1 (RIF1). Biochemical evidence showed that SVR10/AtNOA1/RIF1 likely localizes to the chloroplast stroma. We further demonstrate that the mutant of a close homologue of SVR10/AtNOA1/RIF1, BRASSINAZOLE INSENSITIVE PALE GREEN 2 (BPG2), can also suppress var2 leaf variegation. Mutants of SVR10 and BPG2 are impaired in photosynthesis and the accumulation of chloroplast proteins. Interestingly, two-dimensional blue native gel analysis showed that mutants of SVR10 and BPG2 display defects in the assembly of thylakoid membrane complexes including reduced levels of major photosynthetic complexes and the abnormal accumulation of a chlorophyll-protein supercomplex containing photosystem I. Taken together, our findings suggest that SVR10 and BPG2 are functionally related with VAR2, likely through their potential roles in regulating chloroplast protein homeostasis, and both SVR10 and BPG2 are required for efficient thylakoid protein complex assembly and photosynthesis.
Keywords: Chloroplast development; Leaf variegation; VAR2; Genetic suppressor; SVR10/AtNOA1/RIF1
Andrew A. Benson: personal recollections by Arthur Nonomura; George Lorimer; Barry Holtz; Victor Vacquier; Karl Y. Biel; Govindjee (369-378).
Andrew A. Benson, one of the greatest and much loved scientists of our century, passed away on January 16, 2015; he was born on September 24, 1917. A grand celebration of his life was held on February 6, 2015, in California. Here, we present one of his photographs and key excerpts from what was said then, and soon thereafter.
Keywords: Benson’s protocol; Path of carbon; Photosynthesis; Radioisotope
Gordon research conference on the dynamics and regulation of photosynthesis: from the origin of bio-catalysis to innovative solar conversion by Govindjee; Arthur R. Grossman; Devaki Bhaya (379-389).
We provide here a news report on the 2015 Gordon Research Conference “Dynamics and regulation of photosynthesis: from the origin of biocatalysis to innovative solar conversion.’’ It was held at Bentley University, Waltham, MA, USA, June 28–July 3, 2015, and offered a mix of traditional and emerging areas that highlighted new directions and methods of analyses. A major innovation was short (1 min) poster highlights that added an exciting dynamic to the interactions. Following the end of the formal sessions, three young scientists (Andrian Gutu, of Harvard University, USA; Alizée Malnoë, of University of California, Berkeley, USA; and Yuval Mazor of Tel Aviv University, Israel) were recognized for their research; they also each received a recent volume of “Advances in photosynthesis and respiration including bioenergy and related processes” from Govindjee. We also provide at the end a brief report on the Gordon Research Seminar that preceded the conference.
Keywords: Petra Fromme; Arthur Grossman; Andrian Gutu; Alizée Malnoë; Yuval Mazor; Fabrice Rappaport