Seasonal changes in photosystem II organisation and pigment composition in Pinus sylvestris

Conifers of the boreal zone encounter considerable combined stress of low temperature and high light during winter, when photosynthetic consumption of excitation energy is blocked. In the evergreen Pinus sylvestris L. these stresses coincided with major seasonal changes in photosystem II (PSII) organisation and pigment composition. The earliest changes occurred in September, before any freezing stress, with initial losses of chlorophyll, the D1-protein of the PSII reaction centre and of PSII light-harvesting-complex (LHC II) proteins. In October there was a transient increase in F₀, resulting from detachment of the light-harvesting antennae as reaction centres lost D1. The D1-protein content eventually decreased to 90%, reaching a minimum by December, but PSII photochemical efficiency [variable fluorescence (F_v)/maximum fluorescence (F_m)] did not reach the winter minimum until mid-February. The carotenoid composition varied seasonally with a twofold increase in lutein and the carotenoids of the xanthophyll cycle during winter, while the epoxidation state of the xanthophylls decreased from 0.9 to 0.1 from October to January. The loss of chlorophyll was complete by October and during winter much of the remaining chlorophyll was reorganised in aggregates of specific polypeptide composition, which apparently efficiently quench excitation energy through non-radiative dissipation. The timing of the autumn and winter changes indicated that xanthophyll de-epoxidation correlates with winter quenching of chlorophyll fluorescence while the drop in photochemical efficiency relates more to loss of D1-protein. In April and May recovery of the photochemistry of PSII, protein synthesis, pigment rearrangements and zeaxanthin epoxidation occurred concomitantly. Indoor recovery of photosynthesis in winter-stressed branches under favourable conditions was completed within 3 d, with rapid increases in F₀, the epoxidation state of the xanthophylls and in light-harvesting polypeptides, followed by recovery of D1-protein content and F_v/F_m, all without net increase in chlorophyll. The fall and winter reorganisation allow Pinus sylvestris to maintain a large stock of chlorophyll in a quenched, photoprotected state, allowing rapid recovery of photosynthesis in spring.Abbreviations Elips early light-induced proteins - EPS epoxidation state - F₀ instantaneous fluorescence - F_m maximum fluorescence - F_v variable fluorescence - LHC II light-harvesting complex of PSII - LiDS lithium dodecyl sulfate This research was supported by the Swedish Natural Science Research Council. We wish to thank Dr. Adrian Clarke¹ (Department of Plant Physiology, University of Umeå, Sweden) for advice on electrophoresis, valuable discussion and providing antibodies. Dr. Stefan Jansson¹ and Dr. Torill Hundal (Department for Biochemistry, University of Stockholm, Sweden) provided antibodies. Jan Karlsson¹ helped with the HPLC, Dr. Marianna Krol gave advice on green gels and Dr. Vaughan Hurry (Cooperative Research Centre for Plant Sciences, Australian National University, Canberra, Australia) provided valuable discussion.     

Effects of desiccation on the excitation energy distribution from phycoerythrin to the two photosystems in the red alga Porphyra perforata

Low temperature (77°K) fluorescence emission and excitation spectra were recorded for wet and desiccated thalli of Porphyra perforata . The photosystem I (F730) and photosystem II (F695) fluorescence emission kinetics during photosystem II trap closure were also recorded at 77°K. Desiccation induced a lowering of the fluorescence yield over the whole emission spectrum but the decrease was most pronounced for the photosystem II fluorescence bands, F688 and F695. It was shown that the desiccation-induced changes of the phycoerythrin sensitized emission spectrum were due to 1) a decrease in the fluorescence yield of the photosystem I antenna, 2) an even stronger decrease in the fluorescence of photosystem II, which was mediated by an increased spillover (k_T(II→I)) of excitation to photosystem I and an increase in the absorption cross section, α, for photosystem I. We hypothesize that the increase of both k_T(II→I) and α are part of a mechanism by which the desiccation-tolerant, high light exposed, Porphyra can avoid photodynamic damage to photosystem II, when photosynthesis becomes inhibited as a result of desiccation during periods of low tide.     

Contributions to the orchid flora of Thailand IX

In continuation of earlier papers in this series, published in the now discontinued Botanisk Tidskrift Vol. 65–72, 1969–1977, additions and corrections to earlier papers on East Asiatic orchids are supplied. Seven new species are proposed, of which five from neighboring countries, and further seven new records for Thailand are listed. The five species alien to Thailand may be expected to be found also in Thailand. Some nomenclatural changes and new synonyms are proposed. An attempt is made to clarify taxonomical and nomenclatural problems on some entities in the Rhopalanthe section of Dendrobium.     

Prostaglandin F2a inhibition of epinephrine stimulated cyclic AMP and progesterone production by rat corpora lutea of various ages

Epinephrine can mimic the stimulatory effects of LH in vitro on cyclic AMP (cAMP) and progesterone production by isolated rat corpora lutea. The aim of the present study was to test whether the effects of epinephrine in vitro on the rat corpus luteum, as with LH, can be inhibited by prostaglandin F_2a (PGF_2a. The stimulatory effect of epinephrine on tissue levels of cAMP in 1-day-old corpora lutea was not inhibited by PGF₂. A dose-dependent inhibition by PGF_2a (0.5–50 μM) was seen for 3-day-old corpora lutea and this inhibition could not be overcome by higher concentrations of epinephrine (0.165–165 μM). The stimulation by epinephrine on progesterone production was inhibited by PGF_2a (5 μM) in 3- and 5-day-old, but not in 1-day-old corpora lutea. Thus, PGF_2a can inhibit the stimulatory effect of epinephrine in 3- and 5-day-old corpora lutea, but not in the newly formed corpora lutea (1-day-old) and PGF_2a shows in this respect the same agedependent inhibitory pattern as in relation to LH stimulation.     

Photoinhibition of photosynthesis represents a mechanism for the long-term regulation of photosystem II

The obligate shade plant, Tradescantia albiflora Kunth grown at 50 mol photons · m^–2 s^–1 and Pisum sativum L. acclimated to two photon fluence rates, 50 and 300 mol · m^–2 · s^–1, were exposed to photoinhibitory light conditions of 1700 mol · m^–2 · s^–1 for 4 h at 22° C. Photosynthesis was assayed by measurement of CO₂-saturated O₂ evolution, and photosystem II (PSII) was assayed using modulated chlorophyll fluorescence and flash-yield determinations of functional reaction centres. Tradescantia was most sensitive to photoinhibition, while pea grown at 300 mol · m^–2 · s^–1 was most resistant, with pea grown at 50 mol · m^–2 · s^–1 showing an intermediate sensitivity. A very good correlation was found between the decrease of functional PSII reaction centres and both the inhibition of photosynthesis and PSII photochemistry. Photoinhibition caused a decline in the maximum quantum yield for PSII electron transport as determined by the product of photochemical quenching (q_p) and the yield of open PSII reaction centres as given by the steady-state fluorescence ratio, F_vF_m, according to Genty et al. (1989, Biochim. Biophys. Acta 990, 81–92). The decrease in the quantum yield for PSII electron transport was fully accounted for by a decrease in F_vF_m, since q_p at a given photon fluence rate was similar for photoinhibited and noninhibited plants. Under lightsaturating conditions, the quantum yield of PSII electron transport was similar in photoinhibited and noninhibited plants. The data give support for the view that photoinhibition of the reaction centres of PSII represents a stable, long-term, down-regulation of photochemistry, which occurs in plants under sustained high-light conditions, and replaces part of the regulation usually exerted by the transthylakoid pH gradient. Furthermore, by investigating the susceptibility of differently lightacclimated sun and shade species to photoinhibition in relation to q_p, i.e. the fraction of open-to-closed PSII reaction centres, we also show that irrespective of light acclimation, plants become susceptible to photoinhibition when the majority of their PSII reaction centres are still open (i.e. primary quinone acceptor oxidized). Photoinhibition appears to be an unavoidable consequence of PSII function when light causes sustained closure of more than 40% of PSII reaction centres.Abbreviations F_o and F_o minimal fluorescence when all PSII reaction centres are open in darkness and steady-state light, respectively - F_m and F_m maximal fluorescence when all PSII reaction centres are closed in darkand light-acclimated leaves, respectively - F_v variable fluorescence - (F_m-F_o) under steady-state light con-ditions - F_s steady-state fluorescence in light - Q_A the primary,stable quinone acceptor of PSII - q_Ne non-photochemical quench-ing of fluorescence due to high energy state - (pH); q_Ni non-photochemical quenching of fluorescence due to photoinhibition - q_p photochemical quenching of fluorescence To whom correspondence should be addressedThis work was supported by the Swedish Natural Science Research Council (G.Ö.) and the award of a National Research Fellowship to J.M.A and W.S.C. We thank Dr. Paul Kriedemann, Division of Forestry and Forest Products, CSIRO, Canberra, Australia, for helpful discussions.     

Characterization of cDNAs encoding CuZn-superoxide dismutases in Scots pine

A Scots pine (Pinus sylvestris L.) cDNA library was screened with two heterologous cDNA probes (P31 and T10) encoding cytosolic and chloroplastic superoxide dismutases (SOD) from tomato. Several positive clones for cytosolic and chloroplastic superoxide dismutases were isolated, subcloned, mapped and sequenced. One of the cDNA clones (PS3) had a full-length open reading frame of 465 bp corresponding to 154 amino acid residues and showed approximately 85% homology with the amino acid sequences of angiosperm cytosolic SOD counterparts. Another cDNA clone (PST13) was incomplete, but encoded a putative protein with 93% homology to pea and tomato chloroplastic superoxide dismutase. The derived amino acid sequence from both cDNA clones matched the corresponding N-terminal amino acid sequence of the purified mature SOD isozymes. Northern blot hybridizations showed that, cytosolic and chloroplastic CuZn-SOD are expressed at different levels in Scots pine organs. Sequence data and Southern blot hybridization confirm that CuZn-SODs in Scots pine belong to a multigene family. The results are discussed in relation to earlier observations of CuZn-SODs in plants.     

The role of glutamine synthetase in the regulation of nitrogenase activity (“switch off” effect) in Rhodospirillum rubrum

We have studied the changes in the activities of both nitrogenase (switch off) and glutamine synthetase in Rhodospirillum rubrum upon addition of ammonium ions or glutamine to nitrogen fixing cultures. Both activities decrease drastically and return in a parallel manner when added ammonia is metabolized. The decrease in glutamine synthetase activity does not seem to be primarily due to adenylylation of the enzyme. Addition of glutamine to cells starved for nitrogen results in inactivation of glutamine synthetase but nitrogenase is only partially switched off.Abbreviations CeMe₃NBr Cetyltrimethylammonium bromide - Hepes N-2-hydroxyethyl-piperazine-N-2 sulfonic acid - MSO methionine-D,L-sulfoximine - Tea-Dmg triethanol amine-3,3-dimethylglutaric acid     

The Thyrotropic Cell in the Atlantic Salmon,Salmo salar

The thyrotropin (TSH) producing cells are distributed in the rostral and proximal pars distalis. This cell type is the smallest and most infrequent cell of the adenohypophysis. Its cytology is similar to the smallest gonadotropic (GTH) cells although the two cell types can be separated by the size of the small secretory granules (diameter less than 200 nm) in the TSH cells. In presmolts and smolts the cells are more numerous than in parr and adult salmon and have cytological features indicating an increased activity. This was also the case after intraperitoneal injections of synthetic TRH. Antisera to carp GTH and salmon GTH cross-reacted with both the GTH and the TSH cells. Anti-human TSH cross-reacted only with the TSH cells which confirms the assumption of antigenic similarity between human and fish TSH.     

Solubilization and spectral characteristics of chlorophyll-protein complexes isolated from the thermophilic blue-green alga Synechococcus lividus

The thermophilic blue-green alga Synechococcus lividus was grown at 38 and 55°C. The reaction center chlorophyll-protein complexes (CP) of Photosystem (PS I) and PS II, CP a_I and CP a_II, were isolated by sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis at 4°C. SDS solubilization of thylakoids was performed in the temperature range 0–65°C. The low-temperature absorption and fluorescence emission spectral properties of the isolated chlorophyll-protein complexes were analyzed. Only traces of CP a_I were solubilized at temperatures below the lipid phase transition temperature. Instead, a minor PS I component, CP a′_I, was obtained that had absorption and fluorescence characteristics similar to those of CP a_I. CP a′_I had a slightly lower mobility than CP a_I in SDS-polyacrylamide gel electrophoresis. The amount of CP a_I in the gel scan profile increased dramatically when solubilization was carried out above the phase transition temperatures, but started to decrease above 60°C. CP a_II, on the other hand, could be efficiently extracted even at 0°C and was stable in the scan profile up to extraction temperatures of 30–40°C. Low-temperature absorption and fluorescence emission spectra were typical for CP a_I and CP a_II and no specific effects of the two growth temperatures on these properties were observed. The phase transition temperature was considered to be critical for the solubilization of CP a_I, either because of the difficulties of SDS (especially as it forms micelles at low temperatures) in penetrating the solidified membrane lipids at temperatures below that of the phase transition or because the CP a_I monomers of the PS I antennae are so strongly bound to each other that they cannot be dissociated by SDS before thermal agitation has reached a certain level that is achieved above the phase transition temperature. We consider both the difficulties in solubilizing CP a_I at sub-transition temperatures and the heat stability of the two complexes as adaptations which enable Synechococcus to grow under extreme high-temperature regimes.