Photosynthesis Research (v.108, #1)

Desiccation of the resurrection plant Haberlea rhodopensis at high temperature by Gergana Mihailova; Snejana Petkova; Claudia Büchel; Katya Georgieva (5-13).
Haberlea rhodopensis plants, growing under low irradiance in their natural habitat, were desiccated to air-dry state at a similar light intensity (about 30 μmol m−2 s−1) under optimal (23/20°C, day/night) or high (38/30°C) temperature. Dehydration of plants at high temperature increased the rate of water loss threefold and had a more detrimental effect than either drought or high temperature alone. Water deficit decreased the photochemical activity of PSII and PSI and the rate of photosynthetic oxygen evolution, and these effects were stronger when desiccation was carried out at 38°C. Some reduction in the amount of the main PSI and PSII proteins was observed especially in severely desiccated Haberlea leaves. The results clearly showed that desiccation of the homoiochlorophyllous poikilohydric plant Haberlea rhodopensis at high temperature had more damaging effects than desiccation at optimal temperature and in addition recovery was slower. Increased thermal energy dissipation together with higher proline and carotenoid content in the course of desiccation at 38°C compared to desiccation at 23°C probably helped in overcoming the stress.
Keywords: Chlorophyll fluorescence; Desiccation-tolerant plant; Photosynthesis; Thylakoid membrane proteins

Increase in the activity of fructose-1,6-bisphosphatase in cytosol affects sugar partitioning and increases the lateral shoots in tobacco plants at elevated CO2 levels by Masahiro Tamoi; Yoshie Hiramatsu; Shigeki Nedachi; Kumi Otori; Noriaki Tanabe; Takanori Maruta; Shigeru Shigeoka (15-23).
We generated transgenic tobacco plants with high levels of fructose-1,6-bisphosphatase expressing cyanobacterialfructose-1,6-/sedoheptulose-1,7-bisphosphatase in the cytosol. At ambient CO2 levels (360 ppm), growth, photosynthetic activity, and fresh weight were unchanged but the sucrose/hexose/starch ratio was slightly altered in the transgenic plants compared with wild-type plants. At elevated CO2 levels (1200 ppm), lateral shoot, leaf number, and fresh weight were significantly increased in the transgenic plants. Photosynthetic activity was also increased. Hexose accumulated in the upper leaves in the wild-type plants, while sucrose and starch accumulated in the lower leaves and lateral shoots in the transgenic plants. These findings suggest that cytosolic fructose-1,6-bisphosphatase contributes to the efficient conversion of hexose into sucrose, and that the change in carbon partitioning affects photosynthetic capacity and morphogenesis at elevated CO2 levels.
Keywords: Branching; The Calvin cycle; Fructose-1; 6-Bisphosphatase; Photosynthesis; Sucrose biosynthesis; Transgenic plants

Structure of PSI, PSII and antennae complexes from yellow-green alga Xanthonema debile by Zdenko Gardian; Josef Tichý; František Vácha (25-32).
Photosynthetic carbon fixation by Chromophytes is one of the significant components of a carbon cycle on the Earth. Their photosynthetic apparatus is different in pigment composition from that of green plants and algae. In this work we report structural maps of photosystem I, photosystem II and light harvesting antenna complexes isolated from a soil chromophytic alga Xanthonema debile (class Xanthophyceae). Electron microscopy of negatively stained preparations followed by single particle analysis revealed that the overall structure of Xanthophytes’ PSI and PSII complexes is similar to that known from higher plants or algae. Averaged top-view projections of Xanthophytes’ light harvesting antenna complexes (XLH) showed two groups of particles. Smaller ones that correspond to a trimeric form of XLH, bigger particles resemble higher oligomeric form of XLH.
Keywords: Photosynthesis; Chromophytes; Xanthonema debile ; Photosystem I; Photosystem II; FCP; Electron microscopy

One-step isolation and biochemical characterization of a highly active plant PSII monomeric core by Cristina Pagliano; Fabiana Chimirri; Guido Saracco; Francesco Marsano; James Barber (33-46).
We describe a one-step detergent solubilization protocol for isolating a highly active form of Photosystem II (PSII) from Pisum sativum L. Detailed characterization of the preparation showed that the complex was a monomer having no light harvesting proteins attached. This core reaction centre complex had, however, a range of low molecular mass intrinsic proteins as well as the chlorophyll binding proteins CP43 and CP47 and the reaction centre proteins D1 and D2. Of particular note was the presence of a stoichiometric level of PsbW, a low molecular weight protein not present in PSII of cyanobacteria. Despite the high oxygen evolution rate, the core complex did not retain the PsbQ extrinsic protein although there was close to a full complement of PsbO and PsbR and partial level of PsbP. However, reconstitution of PsbP and PsbPQ was possible. The presence of PsbP in absence of LHCII and other chlorophyll a/b binding proteins confirms that LHCII proteins are not a strict requirement for the assembly of this extrinsic polypeptide to the PSII core in contrast with the conclusion of Caffarri et al. (2009).
Keywords: Photosystem II; Monomer; Pisum sativum ; PsbP; Oxygen evolving activity

Incubation of prolamellar bodies (PLB) in high-salt media leads to changes in PLB structure and properties of their protochlorophyllide oxidoreductase–protochlorophyllide (PORPChlide) complex. The paracrystalline organisation typical of PLB is disrupted and NADPH dissociates from photoconvertible PORPChlide, with absorption maxima at 640 and 650 nm (PORPChlide 640/650 ), and a non-photoconvertible form, with absorption maxima at 635 nm (PORPChlide 635 ), is formed. These effects are strongly dependent on the valence of the cation of the perturbing salt, indicating that they involve surface double layers effects. They are also influenced by the nature of the anion and by high concentrations of non-electrolytes, suggesting the involvement of surface hydration effects. The structural changes are largely, if not entirely, independent of the presence of excess NADPH. Changes to the PORPChlide complex, however, are strongly inhibited by excess NADPH suggesting that the two sets of changes may not be causally linked. As long as the disruption is not too great, the structural changes seen on incubation of PLB in high salt media lacking excess NADPH are reversed on removal of the high salt perturbation. This reversal is independent of the presence or absence of added NADPH. Reformation of photoconvertible PORPChlide, however, requires the presence of NADPH. The reformation of paracrystalline PLB in the absence of NADPH strongly indicates that preservation of PLB structure, in isolated PLB preparations at least, is independent of the presence or absence of PORPChlide 650 .
Keywords: Protochlorophyllide oxidoreductase; Prolamellar body; Protochlorophyllide; Chlorophyllide; Cubic membrane

The operation of photosynthetic energy-dissipating processes is commonly characterized by measuring the light response of the nonphotochemical quenching (NPQ) of chlorophyll fluorescence, or NPQ versus E curves. This study proposes a mathematical model for the quantitative description of the generic NPQ versus E curve. The model is an adaptation of the Hill equation and is based on the close dependence of NPQ on the xanthophyll cycle (XC). The model was tested on NPQ versus E curves measured in the plant Arabidopsis thaliana and the diatom Nitzschia palea, representing the two main types of XC, the violaxanthin–antheraxanthin–zeaxanthin (VAZ) type and the diadinoxanthin–diatoxanthin (DD–DT) type, respectively. The model was also fitted to a large number of published light curves, covering the widest possible range of XC types, taxa, growth conditions, and experimental protocol of curve generation. The model provided a very good fit to experimental and published data, coping with the large variability in curve characteristics. The model was further used to quantitatively compare the light responses of NPQ and of PSII electron transport rate, ETR, through the use of indices combining parameters of the models describing the two types of light–response curves. Their application to experimental and published data showed a systematic large delay of the buildup of NPQ relatively to the saturation of photochemistry. It was found that when ETR reaches saturation, NPQ is on average still below one fifth of its maximum attainable level, which is only reached at irradiances about three times higher. It was also found that organisms having the DD–DT type of XC appeared to be able to start operating the XC at lower irradiances than those of the VAZ type.
Keywords: Chlorophyll fluorescence; Modelling; Nonphotochemical quenching; Photoacclimation; Photoprotection; Xanthophyll cycle

We investigated the effects of limiting (1.96 × 10−9 mol l−1 total Cu, corresponding to pCu 14.8; where pCu = −log [Cu2+]) and toxic Cu concentrations up to 8.0 × 10−5 mol l−1 total Cu (equivalent to pCu 9.5) on growth rates and photosynthetic activity of exponentially grown Phaeocystis cordata, using batch and semi-continuous cultures. With pulse amplitude modulated (PAM) fluorometry, we determined the photochemical response of P. cordata to the various Cu levels, and showed contrasting results for the batch and semi-continuous cultures. Although maximum photosystem II (PSII) quantum yield (ΦM) was optimal and constant in the semi-continuous P. cordata, the batch cultures showed a significant decrease in ΦM with culture age (0–72 h). The EC50 for the batch cultures was higher (2.0 × 10−10 mol l−1, pCu9.7), than that for the semi-continuous cultures (6.3 × 10−11 mol l−1, pCu10.2). The semi-continuous cultures exhibited a systematic and linear decrease in ΦM as Cu levels increased (for [Cu2+] < 1.0 × 10−12 mol l−1, pCu12.0), however, no effect of high Cu was observed on their operational PSII quantum yield (Φ′M). Similarly, semi-continuous cultures exhibited a significant decrease in ΦM, but not in Φ′M, because of low-Cu levels. Thus, Cu toxicity and Cu limitation damage the PSII reaction centers, but not the processes downstream of PSII. Quenching mechanisms (NPQ and Q n) were lower under high Cu relative to the controls, suggesting that toxic Cu impairs photo-protective mechanisms. PAM fluorometry is a sensitive tool for detecting minor physiological variations. However, culturing techniques (batch vs. semi-continuous) and sampling time might account for literature discrepancies on the effects of Cu on PSII. Semi-continuous culturing might be the most adequate technique to investigate Cu effects on PSII photochemistry.
Keywords: Phaeocystis cordata ; Photosynthesis; Copper; Chlorophyll fluorescence; Phytoplankton