The photosynthetic apparatus of Prochlorococcus: Insights through comparative genomics

Within the vast oceanic gyres, a significant fraction of the total chlorophyll belongs to the light-harvesting antenna systems of a single genus, Prochlorococcus. This organism, discovered only about 10 years ago, is an extremely small, Chl b-containing cyanobacterium that sometimes constitutes up to 50% of the photosynthetic biomass in the oceans. Various Prochlorococcus strains are known to have significantly different conditions for optimal growth and survival. Strains which dominate the surface waters, for example, have an irradiance optimum for photosynthesis of 200 μmol photons m⁻² s⁻¹, whereas those that dominate the deeper waters photosynthesize optimally at 30–50 μmol photons m⁻² s⁻¹. These high and low light adapted ‘ecotypes’ are very closely related — less than 3% divergent in their 16S rRNA sequences — inviting speculation as to what features of their photosynthetic mechanisms might account for the differences in photosynthetic performance. Here, we compare information obtained from the complete genome sequences of two Prochlorococcus strains, with special emphasis on genes for the photosynthetic apparatus. These two strains, Prochlorococcus MED4 and MIT 9313, are representatives of high- and low-light adapted ecotypes, characterized by their low or high Chl b/a ratio, respectively. Both genomes appear to be significantly smaller (1700 and 2400 kbp) than those of other cyanobacteria, and the low-light-adapted strain has significantly more genes than its high light counterpart. In keeping with their comparative light-dependent physiologies, MED4 has many more genes encoding putative high-light-inducible proteins (HLIP) and photolyases to repair UV-induced DNA damage, whereas MIT 9313 possesses more genes associated with the photosynthetic apparatus. These include two pcb genes encoding Chl-binding proteins and a second copy of the gene psbA, encoding the Photosystem II reaction center protein D1. In addition, MIT 9313 contains a gene cluster to produce chromophorylated phycoerythrin. The latter represents an intermediate form between the phycobiliproteins of non-Chl b containing cyanobacteria and an extremely modified β phycoerythrin as the sole derivative of phycobiliproteins still present in MED4. Intriguing features found in both Prochlorococcus strains include a gene cluster for Rubisco and carboxysomal proteins that is likely of non-cyanobacterial origin and two genes for a putative and β lycopene cyclase, respectively, explaining how Prochlorococcus may synthesize the α branch of carotenoids that are common in green organisms but not in other cyanobacteria. This revised version was published online in June 2006 with corrections to the Cover Date.     

Partial sequence of ribulose-1,5-bisphosphate carboxylase/oxygenase and the phylogeny of Prochloron and Prochlorococcus (Prochlorales)

The prochlorophytes, oxygenic photosynthetic prokaryotes having no phycobiliprotein but possessing chlorophylls a and b, have been proposed to have a common ancestry with green chloroplasts, yet this is still controversal. We report here that partial sequence comparisons of the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase, including sequence data from two prochlorophytes, Prochlorococcus and Prochloron, indicate that Prochlorococcus is more closely related to a photosynthetic bacterium, Chromatium vinosum (-purple bacteria), than to cyanobacteria, while Prochloron is closely related to the prochlorophyte Prochlorothrix and to cyanobacteria. The molecular phylogenetic tree indicates that a common ancestor of Prochlorococcus and -purple bacteria branched off from the land plant lineage earlier than Prochloron, Prochlorothrix, and cyanobacteria.Correspondence to: A. Shimada     

The development of the photosynthetic apparatus and energy transduction in malate-limited phototrophic cultures of Rhodobacter capsulatus

The question was studied whether limited availability of the carbon source controls the development of the photosynthetic apparatus in Rhodobacter capsulatus. The organisms were grown phototrophically in a chemostat limited by malate as the sole source of reducing equivalents and carbon. The incident light-energy flux, representing the only energy source, was kept constant. Steady state levels of protein and dry weight of cells as well as molar growth yield coefficients (Y) decreased with increasing dilution rate (D, representing the growth rate, ) up to about D=0.14 h^-1. At higher D-values biomass levels as well as Y stayed largely constant. The specific rate of malate consumption leading to biomass production increased linearly while the rate representative of processes other than conversion of carbon into biomass increased almost exponentially with . Specific bacteriochlorophyll (Bchl) contents of cells as well as the specific rate of Bchl synthesis were rather low at low D-values. They increased as D was increased. Light energy fluxes required to half-maximally saturate proton extrusion by whole cells decreased when D was increased up to 0.1 h^-1; at higher D-values, however, they reached constancy. Maximal rates of proton extrusion as well as of photophosphorylation calculated on a Bchl basis decreased when D was increased up to 0.14 h^-1 and reached constancy at higher D-values. The results suggest that the availability of the growth limiting substrate controls the formation of the photosynthetic apparatus and, consequently, its functional properties including the efficiency of light-energy transduction. A relationship is assumed between malate conversion into biomass, i.e. Y-values, and the efficiency of light-energy transduction.Abbreviations ALA 5-aminoleyulinic acid - Bchl bacteriochlorophyll - D dilution rate [h^-1] - R Rhodobacter - Y molar growth yield coefficient - growth rate [h^-1]     

Effects of pre-storage conditions on storage of in vitro cultures of Nephrolepis exaltata (L.) Schott and Cordyline fruticosa (L.) A. Chev.

In vitro cultures of Nephrolepis exaltata and Cordyline fruticosa were stored at 5°, 9° or 13°C, at a low irradiance (3–5 mol m^–2 s^–1) or in darkness. Prior to storage the cultures were subjected to 18°, 21°, 24° or 27°C and 15, 30 or 45 mol m^–2 s^–1 in a factorial combination.The optimal storage conditions for Nephrolepis were 9°C in complete darkness. These cultures were still transferable to a peat/perlite mixture at the end of the experimental period of 36 months.The optimal storage conditions for Cordyline were 13°C and a low light level (±3–5 mol m^-2 s^-1). When the pre-storage conditions were normal growth room conditions (24°C and 30 mol m^-2 s^-1), in vitro cultures could be stored for 18 months. With the most favourable pre-storage treatment (18°C and 15 mol m^-2 s^-1) some cultures still had green shoots after 36 months of storage, but did not survive transfer to peat/perlite.Pre-conditioning before storage was most favourable for Nephrolepis, and not that important, but still favourable, for Cordyline. There was an interaction between pre-storage temperature and pre-storage irradiance. For both species a high irradiance level was less favourable than a low irradiance level when combined with high growth room temperatures.Abbreviations BA 6-benzyladenine - IAA indole-3-acetic acid - NOA 2-naphthoxyacetic acid     

Fidelity of conjugation in Saccharomyces cerevisiae.

Summary An efficient method for the production of synchronous zygotes in Saccharomyces cerevisiae is described. Cells were synchronised under defined conditions in either an a, mixed culture or by incubation of each mating type in cell-free medium in which cells of the opposite mating type had been grown. Synchronised cells were allowed to fuse under defined conditions on filter membranes. This method was used to test the fidelity of conjugation in S. cerevisiae. Under conditions where cells of a or mating type were in contact with up to 6 cells of each of two strains of opposite mating type, less than 1 multiple mating in 10⁴ diploid matings occurred. It is concluded that in sexual conjugation in S. cerevisiae some process distinct from cell contact restricts cell fusion to paired combinations of conjugant cells.     

Possible role of cyclic AMP in the synthesis of chlorophyll in Chlorella fusca

The intracellular concentration of cAMP in the green alga Chlorella fusca was in the range of 2 · 10^-9 to 10^-8 moles/g dry weight and was strongly dependent on the growth conditions. The cAMP level was high with high light intensity, low nitrate or glucose concentration. Intracellular cAMP increased only by factor of 2 when high amounts (up to 10^-3 M) of cAMP were added to the medium. Most of the given cAMP was converted to 5-AMP.Addition of cAMP had little effect on the chlorophyll content of the cells, only at 10^-6 M some enhancement in photoautotrophic cultures was observed. On the other hand high amounts of cAMP in the medium increased the growth rate. DBcAMP^* showed a positive effect on chlorophyll synthesis and growth rate at much lower concentrations compared to cAMP.Stimulation effects of exogenous cAMP on the synthesis of chlorophyll were also observed in mixotrophic cultures with a high glucose/nitrate ratio, conditions where chlorophyll synthesis is repressed. Similar to autotrophic conditions DBcAMP was more effective than cAMP.These data indicate that cAMP may act in a system controlling the chlorophyll content of the cells in response to nutrients or light.Abbreviation DBcAMP^* N⁶-2-O-dibutyryl-adenosine-35-monophosphate     

Salinity studies with drought-resistant species of Sporobolus

Summary Dry matter productivity under saline conditions was compared in 5 desiccation-tolerant resurrection grasses and one desiccation sensitive species, all in the genus Sporobolus. S. stapfianus was the most salt tolerant, requiring 215 mole NaCl m^-3 to reduce shoot dry matter increments to 50% of increments in plants not treated with salt. (This was comparable to published values for the salt tolerant grass Diplachne fusca.) S. lampranthus was salt sensitive, requiring 35 mol m^-3 for 50% control yields. S. festivus, S. aff. Fimbriatus, and the deisccation sensitive S.pyramidalis was moderately tolerant (150–170 mol m^-3). The moderate salt resistance of S. aff. fimbriatus was attributed mainly to exclusion of NaCl by roots. Salt export through leaf surfaces was a minor factor. Half of the leaf mesophyll cells survived 50 min immersion in 200 mol NaCl m^-3. Plants of S. aff. fimbriatus and S. pyramidalis tolerated a broad range of soil pH. Plants of 4 desiccation tolerant Sporobolus species survived air-dryness following 3 weeks pretreatment with salinities up to 200 mol m^-3     

On the use of Avena protoplasts to study chloroplast development

Different methods were tested to isolate protoplasts from etiolated, partially greened, and light-grown leaves of Avena sativa. Preparations with high yields and high photosynthetic capacities (time of illumination 4 h) were obtained when small transverse leaf segments were incubated for 2 h at 30°C in 2% cellulysin (Calbiochem), 0.6 M mannitol, and 0.5% bovine serum albumin (BSA) at pH 5.6, without shaking. As measured by light-dependent O₂ evolution or fixation of labeled bicarbonate, protoplasts exhibited rates of up to 124 mol per mg of chlorophyll per h at 20°C and saturating bicarbonate, which were nearly identical to those found with intact leaves. The assay conditions necessary for this activity were 0.6 M sorbitol, 50 mM N-2-hydroxy-ethylpiperazine-N-2-ethane sulfonic acid (pH 7.6), and 10 mM NaHCO₃. If plastids were isolated from these protoplasts, sorbitol was 0.45 M, including 10 mM ethylenediaminetetraacetate (EDTA). under these conditions, rates of photosynthesis were up to 125 (light-grown) and 71 (6 h illuminated) mol O₂ evolved or ¹⁴CO₂ fixed per mg of chlorophyll per h, compared to 3.5 mol·mg chl^-1·h^-1 obtained with mechanically isolated plastids. With this system, CO₂-dependent O₂ evolution was already detected after 3 h of illumination of etiolated tissue, but could only be observed at pH values between 7.6 and 8.6, in the presence of EDTA. At lower pH (7.3) or at pH 7.6 in the absence of EDTA, light-dependent O₂ evolution up to 24 h of greening was only measurable with 3-phosphoglycerate as the substrate. The possible effects of EDTA in this respect as well as the advantages of using protoplasts or plastids isolated from protoplasts for developmental studies are discussed.Abbreviations BSA bovine serum albumin - EDTA ethylenediamine tetraacetic acid - HEPES N-2-hydroxyethyl-piperazine-N-2-ethane-sulphonic acid - MES 2(N-morpholino) ethane sulphonic acid - PGA 3-phosphoglycerate     

ATP is required for K+ active transport in the archaebacterium Haloferax volcanii

The Archaebacterium Haloferax volcanii concentrates K⁺ up to 3.6 M. This creates a very large K⁺ ion gradient of between 500- to 1,000-fold across the cell membrane. H. volcanii cells can be partially depleted of their internal K⁺ but the residual K⁺ concentration cannot be lowered below 1.5 M. In these conditions, the cells retain the ability to take up potassium from the medium and to restore a high internal K⁺ concentration (3 to 3.2 M) via an energy dependent, active transport mechanism with a K _m of between 1 to 2 mM. The driving force for K⁺ transport has been explored. Internal K⁺ concentration is not in equilibrium with m suggesting that K⁺ transport cannot be accounted for by a passive uniport process. A requirement for ATP has been found. Indeed, the depletion of the ATP pool by arsenate or the inhibition of ATP synthesis by N,N-dicyclohexylcarbodiimide inhibits by 100% K⁺ transport even though membrane potential m is maintained under these conditions. By contrast, the necessity of a m for K⁺ accumulation has not yet been clearly demonstrated. K⁺ transport in H. volcanii can be compared with K⁺ transport via the Trk system in Escherichia coli.Abbreviations CCCP Carbonylcyanide m-chlorophenyl-hydrazone - DCCD N,N-dicyclohexylcarbodiimide - MES 2-[N-morpholino] ethane sulfonic acid - MOPS 3-[N-morpholino] propane sulfonic acid - TRIS Tris (hydroxymethyl) aminomethane - TPP tetraphenyl phosphonium     

Induction of budding on chloronemata and caulonemata of the moss,Physcomitrella patens,using isopentenyladenine

The bud-inducing effect of the cytokinin N⁶-(²-isopentenyl)-adenine (i⁶-Ade) was examined in the moss Physcomitrella patens growing in liquid culture. Under these conditions, buds could be induced on chloronemata as well as on caulonemata. By application of i⁶-Ade, bud-formation was accelerated in both types of tissue. The number of buds, their size and their site of development were dependent on the concentration of the cytokinin in the range of 10^-7 M to 10^-5 M. Moreover, the percentage of caulonema cells increased with a cytokinin concentration of 10^-5 M. These results indicate that chloronema cells may also function as target cells for exogenous cytokinins. The composition of proteins from caulonemata and chloronemata of two different species (P. patens and Funaria hygrometrica), grown on solid medium were compared. No differences could be detected between the protein patterns of caulonemata and chloronemata of the same species while between the two species the differences were obvious.Abbreviations i⁶-Ade N⁶-(²-isopentenyladenine) - Da dalton - SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis     

Iron uptake by leaf mesophyll cells: The role of the plasma membrane-bound ferric-chelate reductase

The uptake of ⁵⁹Fe from FeCl₃, ferric (Fe³⁺) citrate (FeCitr) and Fe³⁺-EDTA (FeEDTA) was studied in leaf mesophyll of Vigna unguiculata (L.) Walp. Uptake rates decreased in the order FeCl₃>FeCitrFeEDTA, and uptake depended on an obligatory reduction step of Fe³⁺ to Fe²⁺, after which the ion could be taken up independently of the chelator, citrate. Uptake was strongly increased by photosynthetically active light (>630 nm), and kinetic analysis revealed saturation kinetics with a K _m (FeCitr) of 80–110 M. In the presence of an external Fe²⁺ scavenger, bathophenanthroline disulfonate, the mesophyll also reduced external FeCitr with a K _m of approx. 50–60 M. The reduction rates for FeCitr were five-to eightfold higher than necessary for uptake. Purified plasma membranes from leaves revealed an NADH-dependent FeCitr- and FeEDTA-reductase activity, which had a pH optimum of 6.5–6.8 and a K _m of approx. 20 M for NADH. Under anaerobic conditions, a K _m of 130–170 M for ferric chelates was obtained, while in the presence of oxygen a K _m (FeCitr) of approx. 100 M was found. It is concluded that the leaf plasma membrane provides a ferric-chelate-reductase activity, which plays a crucial role in iron uptake of leaf cells. Under in-vivo conditions, however, reactive oxygen species or strong (blue) light may also contribute to the obligatory reduction of Fe³⁺ prior to uptake.Abbreviations BPDS bathophenanthroline disulfonate - DCMU 3-(3,4 dichlorophenyl)-1,1-dimethyl urea - FCR ferricchelate reductase - FeCitr Fe³⁺-citrate - FeEDTA Fe³⁺-EDTA - PM plasma membrane This work was supported by the SCIENCE program of the European Community (contract no. SC1000344; P.R.M.). We wish to thank P. Siersma and C. Winter for their cooperation at the Central Isotope Laboratory of the Biological Centre of the University of Groningen.     

Promotion of stomatal opening in the grass Anthephora pubescens nees by a range of natural and synthetic cytokinis

Stomatal opening in detached epidermis of Anthephora pubescens Nees incubated in the light and CO₂-free air was enhanced by each of 6 natural and 4 synthetic cytokinis. Apertures were maximal following incubation with 10 mmol m^-3 cytokinin in PIPES buffer for all except N⁶-[ ²-isopentyl] adenine and N⁶-[ ²-sopentyl] adenosine which both opened stomata maximally at 0.1 mmol m^-3. Experiments which were undertaken to optimise the conditions of incubation showed that opening was maximal after 3 h incubation and that while 10 mmol m^-3 kinetin increased the rate of stomatal opening, it did not affect the duration. Exogenous KCl was not needed for opening and light was saturating even at the low level of 140 mol m^-2 s^-1.     

Isolation and characteristics of Thiopedia rosea (neotype)

Four new strains of Thiopedia rosea were isolated in pure culture from blooms of platelet-forming purple sulfur bacteria in the top layers of the anoxic hypolimnia of two freshwater lakes. Individual cells of the new strains as well as of T. rosea strain 4211 were spherical to oval, nonmotile and contained gas vesicles in the central part. The predominant photosynthetic pigments were bacteriochlorophyll a and okenone. All strains were strictly anaerobic and obligately phototrophic. Optimal growth occurred at low light intensities of 100 E · m^-2 s^-1 (tungsten lamp); intensities above 150 E · m^-2 s^-1 inhibited growth completely. Photoautotrophic growth was possible at sulfide concentrations up to 0.6 mM; higher concentrations were inhibitory. Acetate, butyrate and valerate supported photoorganotrophic growth in the presence of bicarbonate and sulfide concentrations below 1 mM. Sulfide was required as a source of cellular sulfur because assimilatory sulfate reduction is lacking. All strains were assigned to the species Thiopedia rosea with strain 4211 as a neotype.Dedicated to Prof. Dr. H. G. Schlegel on the occasion of his 66th birthday     

Use of the GUS gene as a selectable marker for Agrobacterium-mediated transformation of Rubus

A transformation system was established for red raspberry, blackberry and blackberry x raspberry hybrids, utilizing the binary vector system of Agrobacterium tumefaciens. Leaf discs or internodal stem segments were inoculated with Agrobacterium strain LBA4404 containing the binary vectors PBI121.X, which has the -glucuronidase (GUS) marker gene, or Bin 19, which has the neomycin phosphotransferase II (NPT II) gene. Regenerants were produced on media containing MS salts, 20 gl^-1 sucrose, 7 gl^-1 agar, 100 mgl^-1 inositol, 0.5 mgl^-1 nicotinic acid, 0.5 mgl^-1 pyridoxine-HCl, 0.1 mgl^-1 thiamine, and either 0.1 mgl^-1 IBA and 2 mgl^-1 BAP for leaf discs, or 0.2 mgl^-1 BAP and 0.2 mgl^-1 2,4-D for stem segments. Kanamycin sulphate, which was used as a selective agent for the NPT II gene, inhibited organogenesis at 50 mgl^-1 and was therefore unsuitable for use as a selectable marker gene in Rubus. All regenerants were assayed utilizing the fluorogenic assay procedure to determine if the GUS gene had been transferred into the material and could therefore cleave the substrate 4-methyl-umbelliferyl--D-glucuronide. Seven GUS-positive plantlets were obtained which confirmed that this marker gene had been transferred into Rubus. A dot blot assay was carried out on GUS-positive plant material to establish if the NPT II gene had also been transferred to the plant material.     

Accumulation of Cd2+ and Pb2+ in the suspension cultures of Agave amaniensis and Costus speciosus and the determination of the culture's growth and phytosteroid content

Cell suspension cultures of Agave amaniensis and Costus speciosus were grown in media containing Cd^{2 +} up to 25 and 20 mg l^–1, respectively, and Pb²⁺ up to 40 mg l^–1. The cultures hyper-accumulated Cd²⁺ up to 900 and 530 g g^–1 and Pb²⁺ up to 1390 and 1170 g g^–1 dry wt. in their respective biomasses. Increasing Pb²⁺ up to 30 mg l^–1 increased the biomass production and total sitosterol content of Costus speciosus by up to 1.7- and 1.3-fold, respectively.     

Dynamics of the phycotoxin domoic acid: accumulation and excretion in two commercially important bivalves

Batch cultures of the toxigenic diatomNitzschia pungens Grunow f.multiseries Hasle were fed to blue mussels (Mytilus edulis) and deep sea Atlantic scallops (Placopecten magellanicus) to elucidate conditions under which domoic acid (DA) was accumulated and excreted (depurated). Mussels accumulated the toxin to a maximum level of 13 g g^-1, at rates of 0.21 to 3.7 g h^-1 g^-1, dry weight. Accumulation efficiency (the proportion of accumulated DA to estimated net uptake) ranged from 1–5%. The highest filtration rate of 1.71 h^-1 occurred at concentrations of 4–8 × 10⁶ Nitzschia cells 1^-1 with no formation of pseudofeces. Depuration rates between fed and starved mussels over a 2 h test period were the same. The depuration rate of domoic acid was about 17% d^-1 and did not account for the low uptake efficiencies, so it is suggested that most of the DA is lost from mussels in the solution during the feeding process. Domoic acid accumulation in mussels was dependent on the amount of toxin available, which in turn was a function of the density and growth phase of theNitzschia population. Changes in filtration rate withNitzschia concentration and depuration rate with time can account for the DA levels of mussels collected during toxic episodes in Cardigan Bay, Prince Edward Island, Canada in 1988 and 1989.Scallops accumulated DA (0.39–1.3 g h^-1 g^-1, more slowly than mussels, however, accumulation efficiencies ranged from 5–100%. Filtration rates remained relatively low and constant at 0.081 h^-1. Scallops retained domoic acid longer than mussels, a fact which must be considered in the marketing of whole scallops for human consumption.     

Accumulation of alkaloids in plant vacuoles does not involve an ion-trap mechanism

Alkaloid uptake into vacuoles isolated from a Fumaria capreolata L. cell suspension culture was investigated. The uptake is carrier-mediated as shown by its substrate saturation, its sensitivity to metabolic inhibitors and especially by its exclusive preference for the (S)-forms of reticuline and scoulerine while the (R)-enantiomers which do not occur in this plant species were strictly discriminated. The carrier has a high affinity for (S)-reticuline with a K _m=0.3 M. The rate of alkaloid uptake was 6 pmol·h^-1·l^-1 vacuole, and 0.03 mg alkaloid·mg^-1 vacuolar protein were taken up. Transport was stimulated five-to seven-fold by ATP and was inhibited by the ATPase inhibitors N,N-dicyclohexylcarbodiimide and 4-4-diisothiocyanatostilbene-2,2 disulfonic acid, as well as by the protonophore carbonyl cyanide m-chlorophenylhydrazone. A number of alkaloids did not compete with labelled (S)-reticuline for uptake into vacuoles. The uptake system is absolutely specific for alkaloids indigenous to the plant from which the vacuoles were isolated. Slight modifications of the topography of an alkaloid molecule even with full retention of its electrical charge results in its exclusion. Alkaloid efflux was also shown to be mediated by a highly specific energy-dependent carrier. These results contradict the previously proposed ion-trap mechanism for alkaloid accumulation in vacuoles. A highly specific carrier-mediated and energy-dependent proton antiport system for alkaloid uptake and release is postulated.Abbreviations CCCP carbonylcyanide m-chlorophenylhydrazone - DCCD N,N-dicyclohexylcarbodiimide - DIDS 4-4-diisothiocyanatostilbene-2,2 disulfonic acid Dedicated to Professor Harry Beevers, Santa Cruz, on the occasion of his 60^th birthday     

Recovery from photoinhibition: effect of light and inhibition of protein synthesis of 32-kD chloroplast protein

Recovery from photoinhibition of photosynthesis in intact Lemna gibba was studied in presence of the protein synthesis inhibitors chloramphenicol and cycloheximide. Exposure to an irradiance of 1000 mol m^-2s^-1 in N₂ for 90 min induced 80% photoinhibition. The plants recovered photosynthesis when transfered to normal irradiances (210 mol m^-2s^-1) and air. Chloramphenicol added to the medium was taken up by the plant and reduced photosynthesis slightly. Recovery from photoinhibition was more inhibited than photosynthesis. Cycloheximide was also taken up by the plants and reduced synthesis of light harvesting chlorophyll protein: however, neither photosynthesis nor recovery were much affected. Synthesis of 32-kD chloroplast protein during recovery was inhibited by chloramphenicol, but not by cycloheximide. Synthesis of 32-kD protein was enhanced by 20–210 mol m^-2s^-1 light. The results support the hypothesis that synthesis of 32-kD protein is important for recovery of photosynthesis after photoinhibition.     

The relationship between turgor pressure and titratable acidity in mesophyll cells of intact leaves of a Crassulacean-acid-metabolism plant,Kalanchoe daigremontiana Hamet et Perr

Day/night changes in turgor pressure (P) and titratable acidity content were investigated in the (Crassulacean-acid-metabolism (CAM) plant Kalanchoe daigremontiana. Measurements of P were made on individual mesophyll cells of intact attached leaves using the pressure-probe technique. Under conditions of high relative humidity, when transpiration rates were minimal, changes in P correlated well with changes in the level of titratable acidity. During the standard 12 h light/12 h dark cycle, maximum turgor pressure (0.15 MPa) occurred at the end of the dark period when the level of titratable acidity was highest (about 300 eq H⁺·g^-1 fresh weight). A close relationship between P and titratable acidity was also seen in leaves exposed to perturbations of the standard light/dark cycle. (The dark period was either prolonged, or else only CO₂-free air was supplied in this period). In plants deprived of irrigation for five weeks, diurnal changes in titratable acidity of the leaves were reduced (H=160 eq H⁺·g^-1 fresh weight) and P increased from essentially zero at the end of the light period to 0.02 MPa at the end of the dark period. Following more severe water stress (experiments were made on leaves which had been detached for five weeks), P was zero throughout day and night, yet small diurnal changes in titratable acidity were still measured. These findings are discussed in relation to a hypothesis by Lüttge et al. 1975 (Plant Physiol. 56,613-616) for the role of P in the regulation of acidification/de-acidification cycles of plants exhibiting CAM.Abbreviations CAM crassulacean acid metabolism - FW fresh weight - P turgor pressure     

Influence of culture conditions on the cell yield and amylases biosynthesis in continuous culture by Schwanniomyces castellii

Schwanniomyces castellii excreted -amylase and amyloglucosidase into the medium in the presence of starch. The biosynthesis and the rate of excretion were influenced by dissolved oxygen (specially for -amylase), pH of the culture and dilution rate. The cell yield observed (0.59) remained constant up to D=0.35h^-1 with starch as substrate. But in the case of growth on glucose, the yield observed was equal to 0.62 up to a dilution rate of D=0.18 h^-1. Beyond this value Y x/s decreased and ethanol was produced. The onset of fermentation dependend partly on the nature of the substrate and not only on the environment in particular on the quantity of dissolved oxygen present.