Chloroplast Membrane Components Research Articles

Online CO2 and H2 O oxygen isotope fractionation allows estimation of mesophyll conductance in C4 plants, and reveals that mesophyll conductance decreases as leaves age in both C4 and C3 plants.

Mesophyll conductance significantly, and variably, limits photosynthesis but we currently have no reliable method of measurement for C4 plants. An online oxygen isotope technique was developed to allow quantification of mesophyll conductance in C4 plants and to provide an alternative estimate in C3 plants. The technique is compared to an established carbon isotope method in three C3 species. Mesophyll conductance of C4 species was similar to that in the C3 species measured, and declined in both C4 and C3 species as leaves aged from fully expanded to senescing. In cotton leaves, simultaneous measurement of carbon and oxygen isotope discrimination allowed the partitioning of total conductance to the chloroplasts into cell wall and plasma membrane versus chloroplast membrane components, if CO2 was assumed to be isotopically equilibrated with cytosolic water, and the partitioning remained stable with leaf age. The oxygen isotope technique allowed estimation of mesophyll conductance in C4 plants and, when combined with well-established carbon isotope techniques, may provide additional information on mesophyll conductance in C3 plants.

Dynamics of protein and polar lipid recruitment during lipid droplet assembly in Chlamydomonas reinhardtii.

In plants, neutral lipids are frequently synthesized and stored in seed tissues, where the assembly of lipid droplets (LDs) coincides with the accumulation of triacylglycerols (TAGs). In addition, photosynthetic, vegetative cells can form cytosolic LDs and much less information is known about the makeup and biogenesis of these LDs. Here we focus on Chlamydomonas reinhardtii as a reference model for LDs in a photosynthetic cell, because in this unicellular green alga LD dynamics can be readily manipulated by nitrogen availability. Nitrogen deprivation leads to cellular quiescence during which cell divisions cease and TAGs accumulate. The major lipid droplet protein (MLDP) forms a proteinaceous coat surrounding mature LDs. Reducing the amount of MLDP affects LD size and number, TAG breakdown and timely progression out of cellular quiescence following nitrogen resupply. Depending on nitrogen availability, MLDP recruits different proteins to LDs, tubulins in particular. Conversely, depolymerization of microtubules drastically alters the association of MLDP with LDs. LDs also contain select chloroplast envelope membrane proteins hinting at an origin of LDs, at least in part, from chloroplast membranes. Moreover, LD surface lipids are rich in de novo synthesized fatty acids, and are mainly composed of galactolipids which are typical components of chloroplast membranes. The composition of the LD membrane is altered in the absence of MLDP. Collectively, our results suggest a mechanism for LD formation in C.reinhardtii involving chloroplast envelope membranes by which specific proteins are recruited to LDs and a specialized polar lipid monolayer surrounding the LD is formed.

Can Enhanced CO2 Help to Mitigate the Global Warming Impact in the Tropical Coffee Plant?

Coffee crop has been predicted to become threatened by future climate changes and global warming conditions. Still, the effective biological impact of enhanced air [CO2] and temperature on this plant remain to be fully elucidated, as only recently this subject has begun to be studied for coffee (1,2). Therefore, this work aims at linking coffee physiological and biochemical responses to such environmental changes, using the photosynthetic metabolism as probe of the plant tolerance. Potted plants from Coffea arabica L. cv. Icatu (an important cultivated genotype) were grown for 1 year under controlled conditions (temperature, RH, irradiance, photoperiod), at 380 or 700μLCO2L-1 air, without nutrient, water and root space limitations (2). Temperature was then gradually increased (0.5°C/day) from 25/20°C (day/night) up to 42/34°C. Photosynthetic functioning was assessed at 25/20°C, 31/25°C, 37/30°C and 42/34°C through: leaf gas exchanges (net photosynthesis, stomatal conductance, photosynthetic capacity), fluorescence parameters (photochemical efficiency of the photosystem (PS) II), thylakoid electron transport rates involving PSI and II, activities of RuBisCO and RuB5PK. The impact on lipid components of chloroplast membranes and respiratory enzymes (NADH-MDH, PK) was also evaluated. Globally, the results showed a higher metabolic performance in the plants grown under enhanced [CO2] and to a marginal impact until 37°C, configuring a much higher tolerance to high temperature than suggested by classical works for C. arabica plants. Only at 42°C the tolerance limit was exceeded, as shown by significant impacts in most parameters (particularly at enzymes level), although the high [CO2] plants usually preserved a better performance. If available, results from a large transcriptomics approach (RNAseq) will be presented in order unravel global and integrated plant responses. Our findings showed that the enhanced growth [CO2] promoted the preservation of the photosynthetic functional status at high temperatures (37 and 42°C) in the coffee plant, what is quite relevant in a context of predicted climate changes and global warming scenarios.

Lineage-Specific Transcriptional Profiles of Symbiodinium spp. Unaltered by Heat Stress in a Coral Host

Dinoflagellates of the genus Symbiodinium form an endosymbiosis with reef building corals, in which photosynthetically derived nutrients comprise the majority of the coral energy budget. An extraordinary amount of functional and genetic diversity is contained within the coral-associated Symbiodinium, with some phylotypes (i.e., genotypic groupings), conferring enhanced stress tolerance to host corals. Recent advances in DNA sequencing technologies have enabled transcriptome-wide profiling of the stress response of the cnidarian coral host; however, a comprehensive understanding of the molecular response to stress of coral-associated Symbiodinium, as well as differences among physiologically susceptible and tolerant types, remains largely unexplored. Here, we examine the transcriptome-wide response to heat stress via RNA-Seq of two types of Symbiodinium, the putatively thermotolerant type D2 and the more susceptible type C3K, resident within the same coral host species, Acropora hyacinthus. Contrary to previous findings with coral hosts, we find no detectable change in gene expression across the dinoflagellate transcriptome after 3 days of elevated thermal exposure, despite physical evidence of symbiosis breakdown. However, hundreds of genes identified as orthologs between the C and D types exhibited significant expression differences within treatments (i.e., attributable solely to type, not heat exposure). These include many genes related to known thermotolerance mechanisms including heat shock proteins and chloroplast membrane components. Additionally, both the between-treatment similarities and between-type differences remained pervasive after 12-18 months of common garden acclimation and in mixed Symbiodinium assemblages within the same coral host colony.

Molecular and cellular mechanisms of neutral lipid accumulation in diatom following nitrogen deprivation

BackgroundNitrogen limitation can induce neutral lipid accumulation in microalgae, as well as inhibiting their growth. Therefore, to obtain cultures with both high biomass and high lipid contents, and explore the lipid accumulation mechanisms, we implemented nitrogen deprivation in a model diatom Phaeodactylum tricornutum at late exponential phase.ResultsNeutral lipid contents per cell subsequently increased 2.4-fold, both the number and total volume of oil bodies increased markedly, and cell density rose slightly. Transcriptional profile analyzed by RNA-Seq showed that expression levels of 1213 genes (including key carbon fixation, TCA cycle, glycerolipid metabolism and nitrogen assimilation genes) increased, with a false discovery rate cut-off of 0.001, under N deprivation. However, most light harvesting complex genes were down-regulated, extensive degradation of chloroplast membranes was observed under an electron microscope, and photosynthetic efficiency declined. Further identification of lipid classes showed that levels of MGDG and DGDG, the main lipid components of chloroplast membranes, dramatically decreased and triacylglycerol (TAG) levels significantly rose, indicating that intracellular membrane remodeling substantially contributed to the neutral lipid accumulation.ConclusionsOur findings shed light on the molecular mechanisms of neutral lipid accumulation and the key genes involved in lipid metabolism in diatoms. They also provide indications of possible strategies for improving microalgal biodiesel production.

Characterization of the main lipid components of chloroplast membranes and cold induced changes in Coffea spp.

Low temperatures affect many plant physiological and biochemical components, amongst them the lipid phase of membranes. The present work aimed to characterize the lipid composition of chloroplast membranes of three Coffea genotypes, representing three agronomic valuable species ( Coffea arabica cv. Icatu, Coffea canephora cv. Conilon clone 02 and Coffea dewevrei), under adequate environmental conditions and to relate its cold tolerance ability to the adjustments triggered during a gradual temperature decrease, after chilling exposure and upon a recovery period. Under adequate temperature (25/20 °C, day/night) the lipid composition of chloroplast membranes was fairly similar amongst the genotypes concerning the total fatty acid (TFA) content and individual FAs (both globally or within the classes), suggesting a close lipid composition amongst Coffea species, which can be considered as “C18:3” plants. Under cold exposure and subsequent recovery the genotypes undergo adjustments, some of them with acclimation potential. The genotypes displayed some ability to increase lipid synthesis, increasing their FA content. However, under cold exposure (even at 4 °C), Icatu and C. dewevrei plants performed qualitative adjustments, including preferential synthesis of phospholipids (especially PG) instead of galactolipids and increases in the unsaturation degree of DGDG and phospholipid classes (PG, PC and PI). Clone 02 maintained almost all lipid characteristics, what explains its higher cold sensitivity. Furthermore, differences that contribute to explain contrasting cold sensitivity in Icatu (more tolerant) and C. dewevrei emerged when analyzing PA content (taken as a stress metabolite) and the FA composition within MGDG and PG classes. C. dewevrei presented the higher increase, absolute value and relative weight of PA, while Icatu was the solely genotype to show a rise in the unsaturation degree of MGDG and PG, displaying as well the highest DBI values for these classes. We conclude that lipid qualitative and quantitative adjustments constitute a flexible mechanism that decisively contributes to cold acclimation in Coffea spp., working in tandem with others that minimize oxidative stress damages.

Impact of UV-B irradiation on photosynthetic performance and chloroplast membrane components in Oryza sativa L.

The impact of UV-B radiation on photosynthetic related parameters was studied in Oryza sativa L. cv. Safari plants, after an UV-B irradiation performed 1 h per day for 7 days (between 8 and 14 days after germination) with a ten narrow-band ( λ 311 nm) that resulted in a total biological effective UV-B (UVB BE) of 2.975 kJ m −2 day −1 and a total of 20.825 kJ m −2. Gas exchange measurements were severely affected, showing reductions higher than 80% in net photosynthesis ( P n), stomatal conductance and photosynthetic capacity ( A max), 1 day after the end of the 7-days UV-B treatment. Similarly, several fluorescence parameters ( F o, F v/ F m, F v ′ / F m ′ , ϕ e, q P and q E) and thylakoid electron transport (involving both photosystems) were also severely reduced. Concomitantly, a decline of xanthophylls, carotenes, Chl a, Chl ( a + b) and Chl ( a/ b) values was accompanied by the increase of the lipoperoxidation level in chloroplast membranes, altogether reflecting a loss of protection against oxidative stress. Seven days after of the end of UV-B treatment, most fluorescence parameters recovered, but in P n, A max, thylakoid electron transport rates, Chl a and lipid classes, as well as the level of lipoperoxidation, the impacts were even stronger than immediately after the end of stress, denoting a clear loss of performance of photosynthetic structures. However, only a moderate impact on total lipids was observed, accompanied by some changes in the relative weight of the major chloroplast membrane lipid classes, with emphasis on the decrease of MGDG and the increase of phospholipids. That suggested an ability to de novo lipid synthesis allowing qualitative changes in the lipid matrix. Notably, the leaves developed after the end of UV-B irradiation showed a much lower impact, with significantly decreased values only in P n and g s, rises in several fluorescence parameters, thylakoid electron transport, photosynthetic pigments (xanthophylls and chls) and DEPS, while lipid classes presented values close to control. The results showed a global impact of UV-B in the photosynthetic structures and performance in irradiated leaves, but revealed also a low impairment extent in the leaves entirely developed after the end of the irradiation, reflecting a remarkable recovery of the plant after the end of stress, what could constitute an advantage under occasional UV-B exposure events in this vital worldwide staple food crop.

Mono- and digalactosyldiacylglycerol composition of dinoflagellates. I. Peridinin-containing taxa

Two glycolipids, monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG), are components of chloroplast membranes. This study addresses the lack of information regarding the major intact forms of these glycolipids in photosynthetic dinoflagellates through the use of a full-scan positive-ion electrospray ionization/mass spectrometry (ESI/MS) survey of MGDG and DGDG in 35 peridinin-containing taxa from the class Dinophyceae. Further analysis using positive-ion electrospray ionization/mass spectrometry/mass spectrometry (ESI/MS/MS) was performed to determine the positional distribution of fatty acids associated with MGDG and DGDG. The dinoflagellates examined were divided into two clusters based on the forms of MGDG and DGDG present. The first possessed 18:5/18:4 MGDG (sn-1/sn-2), 18:5/18:5 MGDG, 18:4/18:4 DGDG, and 18:5/18:4 DGDG as major forms, and the second possessed 20:5/18:4 MGDG, 20:5/18:5 MGDG, 20:5/18:4 DGDG, and 20:5/18:5 DGDG as major forms. The differentiation between C18/C18 and C20/C18 glycolipids indicates differing biosynthetic pathways, as well as a possible evolutionary divergence between the two dinoflagellate clusters.

Developmental regulation and spatial expression of a plastidial fatty acid desaturase from Olea europaea

Trienoic fatty acids are major components of chloroplast membranes and are also precursors of the oxylipins, such as methyl jasmonate, that play important roles in signal transduction pathways relating to plant development and responses to stress. A cDNA encoding a plastidial ω-3 fatty acid desaturase responsible for trienoic formation has been isolated from a library made from ripening fruits of Olea europaea L. The predicted protein contains 436 amino acid residues including a consensus chloroplast specific transit peptide. Alignment with other desaturase sequences showed strong homology with the plastidial ω-3 desaturases fad7 and fad8. Since fad8 is only expressed at low temperatures and the olive fruit were developing at > 20 °C, it is concluded that the isolated cDNA is most likely to be derived from fad7. Northern hybridisation showed a transient expression of the putative fad7 gene at early stages of drupe (5–7 WAF) and mesocarp (16–19 WAF) development. In situ hybridisation showed particularly prominent expression in the palisade and vascular tissue of young leaves, the embryo sac and transmitting tissue of the carpel, and the tapetum, pollen grains and vascular tissue of anthers. The distinctive spatial, temporal and environmental regulation of the putative fad7 gene is consistent with major roles, not only in thylakoid membrane formation, but also in the provision of α-linolenate-derived signalling molecules that are particularly important in plant tissues involved in transportation and reproduction.

Isolation and characterization of an Arabidopsis mutant deficient in the thylakoid lipid digalactosyl diacylglycerol.

The galactolipids monogalactosyl and digalactosyl diacylglycerol occur in all higher plants and are the predominant lipid components of chloroplast membranes. They are thought to be of major importance to chloroplast morphology and physiology, although direct experimental evidence is still lacking. The enzymes responsible for final assembly of galactolipids are associated with the envelope membranes of plastids, and their biochemical analysis has been notoriously difficult. Therefore, we have chosen a genetic approach to study the biosynthesis and function of galactolipids in higher plants. We isolated a mutant of Arabidopsis that is deficient in digalactosyl diacylglycerol by directly screening a mutagenized M2 population for individuals with altered leaf lipid composition. This mutant carries a recessive nuclear mutation at a single locus designated dgd1. Backcrossed mutants show stunted growth, pale green leaf color, reduced photosynthetic capability, and altered thylakoid membrane ultrastructure.

A receptor component of the chloroplast protein translocation machinery.

The chloroplast outer envelope protein OEP86 functions as a receptor in precursor protein translocation into chloroplasts. Sequence analysis suggests that the precursor of OEP86 is directed to the chloroplast outer envelope by a cleavable, negatively charged, and unusually long amino-terminal peptide. This presequence is unlike other potential targeting signals and suggests the existence of another membrane insertion pathway. Insertion of precursor OEP86 required the hydrolysis of adenosine triphosphate and the existence of surface exposed chloroplast membrane components, and it was not competed by another precursor protein destined for the internal plastid compartments.

Structural characteristics of thylakoid membranes of Arabidopsis mutants deficient in lipid fatty acid desaturation

The ultrastructure of thylakoid membranes from Arabidopsis thaliana wild-type, JB67 and LK3 fatty acid desaturation deficient mutants was studied by thin-section and freeze-fracture electron microscopy. There was a decrease in the amount of the appressed and non-appressed membranes in JB67 and LK3 Arabidopsis mutants when compared to the wild type, resulting in a reduction in the length of photosynthetic membrane per plastid. The results from freeze-fracture showed a decrease in size and a marked increase in packing density of membrane-associated particles on the exo- and endoplasmic fracture faces of the mutants. In addition, areas of the appressed membranes of the mutants contained particles in regular arrays under conditions where no such arrays were observed in wild-type thylakoid membranes. These observations suggest, that the decreased level of lipid fatty acid unsaturation affects the ability of the lipid matrix to mediate the assembly of chloroplast membrane components. The role of polyunsaturated membrane lipids is considered in terms of their ability to promote functional oligomeric assemblies of components of the photosynthetic apparatus.

Observations on Components of Photosystem II During the Greening of Select Mutants of Scenedesmus

The formation of photosystem II of the photosynthetic apparatus was studied in five different developmental mutants of the green alga, Scenedesmus obliquus . These strains are characterized by their ability to synthesize chlorophyll only in the light and by specific differences in their photosystem II (PS-II) capacity and composition when fully developed. Cells from mutants C-2A, LF1-YI-RVT1 and WT-LHC 1 -Y3 form a functional PS-II upon transfer from darkness into light whereas those of strains C-2A-10 and LF1-Y1 do not develop PS-II activity under any conditions. Analysis of a variety of chloroplast reactions with the latter two strains showed that they lack the PS-II reaction center only minimally. 35 S labeling during light-induced chloroplast development revealed that only C-2A-10 and LF1-Y1 failed to develop the normal D1 protein (32 kDa polypeptide In LF1-Y1, only the unprocessed form (34 kDa) of this protein was synthesized and, as was noted for the original mutant LF-1, is inactive as a PS-II reaction center component. During development of C-2A-10, which appears to be pleiotropic in its PS-II deficiency, this protein is not synthesized and the PS-II core antenna polypeptides (the 48 and 44 kDA polypeptides) and a 14.5 kDa polypeptide also appear to be synthesized in lesser amounts or not to be synthesized at all. No other changes in PS-II chloroplast membrane components were noted in these studies, which would implicate other polypeptides in PS-II function of Scenedesmus .

Interference by Herbicidal Inhibitors of Electron Transport with Phosphorylation and Permeability Properties of Chloroplast Membranes

Many herbicides inhibit chloroplast electron transport by interfering with a proteinaceous component of the Qв complex located in the appressed granal membrane. Certain of these herbicides, designated inhibitory uncouplers, also interfere with photophosphorylation and affect other chloroplast-mediated responses, some of which involve components located in the nonappressed granal membrane. The inhibitory uncouplers can be divided into dinoseb (phenolic) types which contain dissociable protons and dicryl (acylanilide) types which are nonionic. The dinoseb types can function as protonophores and shuttle protons across the thylakoid membrane at low concentrations and can alter the integrity of semipermeable membranes at higher concentrations. However, the dicryl types only alter the integrity of the membranes. The inhibitory uncouplers, but not the DCMU-types of electron transport inhibitors: stimulated electron trans- port from DPIPH2 to methyl viologen; inhibited valifiomycin-induced swelling of intact chloroplasts; increased the permeability of the chloroplast envelope to K+ in the absence of an ionophore; prevented energization of the thylakoid membrane by PS I; and increased the permeability of phosphatidyl choline liposomes to protons. Chlorination response patterns obtained with isomers of N-phenyl-2-methylpentanamides in the above reactions, in general, were similar for interference with the Qв complex, i.e., in all assays, dichlorination in the 3,4 or 3,5 positions was associated with maximum inhibitory potency, whereas substitution in an ortho position decreased inhibitory activity. With a series of 1-alkyl-3-(α,α,α-trifluoro-m-tolyl)ureas, maximum inhibition of electron transport was obtained with the butyl derivative, whereas maximum responses for uncoupling and membrane disturbances were obtained with the hexyl or octyl derivatives. Some of the interferences produced by inhibitory uncouplers may result from interactions with the lipoidal components of chloroplast membranes.

Correlation of structure and function of chloroplast membranes at the supramolecular level

Freeze-fracture electron microscopy has revealed that different size classes of intramembrane particles of chloroplast membranes are nonrandomly distributed between appressed grana and nonappressed stroma membrane regions. It is now generally assumed that thylakoid membranes contain five major functional complexes, each of which can give rise to an intramembrane particle of a defined size. These are the photosystem II complex, the photosystem I complex, the cytochrome f/b6 complex, the chlorophyll a/b light-harvesting complex, and the CF0 -CF1 ATP synthetase complex. By mapping the distribution of the different categories of intramembrane particles, information on the lateral organization of functional membrane units of thylakoid membranes can be determined. In this review, we present a brief summary of the evidence supporting the correlation of specific categories of intramembrane particles with known biochemical entities. In addition, we discuss studies showing that ions and phosphorylation of the membrane adhesion factor, the chlorophyll a/b light-harvesting complex, can affect the lateral organization of chloroplast membrane components and thereby regulate membrane function.

Changes in fatty acids and glycerolipids of tobacco leaves during air-curing.

Changes in the lipid components of tobacco leaves during air-curing were investigated. In the air-curing system the contents of total fatty acids and linolenic acid decreased markedly. Digalactosyldiglyceride, monogalactosyldiglyceride, sulfoquinovosyldiglyceride and phosphatidylglycerol, which are components of chloroplast membranes, were degraded almost completely during the process. Phosphatidylethanolamine, phosphatidylserine, phosphatidylcholine (PC) and phosphatidylinositol (PI) were relatively resistant to the degradation process during the yellowing stage, but they also decreased markedly thereafter. PC and PI remained until the final drying stage, although their contents were low. In most polar lipids a considerable decrease was observed in the ratio of linolenic acid. Free fatty acid content increased gradually.

Participation of ?-carotene in reactivation of PSI of heptane-extracted spinach chloroplasts

A carotenoid requirement for photosystem I activity in spinach chloroplasts using extraction-reconstitution technique has been investigated. The transfer of electron from N,N,N',N'-tetramethyl-p-phenylene diamine through the chloroplast photosystem to methyl viologen dye or to NADP(+) was used as an assay of photosystem I activity. Extraction of lyophilized spinach chloroplasts with heptane at near 0°C removed almost all β-carotene and reduced photochemical activities associated with photosystem I to a low level (about 15% of the original activity). Reconstitution of the extracted chloroplasts with β-carotene completely restored photosystem I activity. The maximum rate of methyl viologen photoreduction in reconstituted chloroplasts occurred at an β-carotene/chlorophyll molar ratio of 0.5. Cyclic phosphorylation mediated by phenazine methosulphate was partially restored. Xanthophylls (lutein, neoxanthin, violaxanthin), as components of chloroplast membranes, were not able to replace β-carotene in reconstitution of chloroplasts and had essentially no effect on restoring photoreactions. On the basis of the P700/total chlorophyll ratio it can be assumed that extraction of lyophilized chloroplasts with heptane do not affect photosystem I reaction centre. Therefore it is possible that β-carotene, removed during heptane extraction and belonging mainly to the antenna pigment pool of photosystem I, is effective in the restoration of photosystem I activity.

Coloured Components of Chloroplast Membranes as Intrinsic Membrane Probes for Monitoring the Development of Heat Injury in Intact Tissues

Assays for heat injury in intact leaves were investigated by heating leaf tissue at a rate of 1°C per minute and recording changes in chlorophyll fluorescence; chlorophyll absorbance; light-induced absorbance change at 518 nm of the bulk chloroplast pigments (chlorophylls and carotenoids); and photooxidation of chloroplast cytochrome-554 (cytochrome f ). Leaves of the golden passionfruit (Passiflora edulis forma flavicarpa were used as the experimental material. Heat injury to the chloroplast thylakoid membranes began above 35°C as evidenced by abnormal changes in chlorophyll fluorescence and absorbance and inactivation of chloroplast membrane activities. Chlorophyll fluorescence increased and chlorophyll absorbance decreased above 35°C and the increase and decrease, respectively, were greatest at 52°C. The measurements made on intact leaf tissue together with assays of photosystem 2 activity in isolated chloroplasts indicated the relative thermostabilities of several chloroplast membrane activities. Inactivation of photosystem 2 activity linked to oxygen evolution appeared to be associated with membrane changes occurring between 35 and 44°C. The 518-nm absorbance changes indicated that energy-dependent proton pumping and associated reactions were inactivated between 44 and 48°C. Photosystem-1-mediated photooxidation of cytochrome-554 became inactivated between 48 and 52°C. These studies demonstrate that chlorophylls, carotenoids and cytochrome f may be used as intrinsic membrane probes for monitoring the development of heat injury in the chloroplast membrane system. The absorbance and fluorescence changes that these compounds undergo upon heating provide a basis for reliable and rapid methods applicable to intact tissue for determining heat sensitivity in green plants.

Influence of S-Ethyl Dipropylthiocarbamate on Growth, Chlorophyll and Carotenoid Production and Chloroplast Ultrastructure of Germinating Polytrichum commune Spores

Influence of S-Ethyl Dipropylthiocarbamate on Growth, Chlorophyll and Carotenoid Production and Chloroplast Ultrastructure of Germinating Polytrichum commune Spores

Regulation of ferredoxin-catalyzed photosynthetic phosphorylations.

Under aerobic conditions that are likely to prevail in chloroplasts in vivo, the optimal concentration of ferredoxin for cyclic photophosphorylation was found to be equal to that required for NADP reduction and about one-tenth of that needed for cyclic photophosphorylation under anaerobic conditions. In the presence of ferredoxin and NADP, cyclic photophosphorylation operated concurrently with noncyclic photophosphorylation, producing an ATP: NADPH ratio of about 1.5. The effective operation of ferredoxin-catalyzed cyclic photophosphorylation by itself required a curtailment of the electron flow from water which was accomplished experimentally by the use of either an inhibitor or far-red monochromatic light. An unexpected discovery was that the operation of cyclic photophosphorylation by itself was also regulated by a back reaction of NADPH and ferredoxin with two components of chloroplast membranes, component C550 and cytochrome b559. The significance of these findings to photosynthesis in vivo is discussed.