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The hybridization of double-stranded regions of pre-mRNA from mouse Ehrlich ascites carcinoma cells, rabbit bone marrow cells and primary culture of rabbit kidney cells with an excess of total poly(A)+-mRNA of mouse or rabbit globin mRNA respectively was studied. The hybrids were detected as RNAase-stable acid precipitable material or by adsorbtion of the hybrid complexes of poly(U)-sepharose. The sizes of the hybrid complementary sequences and their thermal stability were estimated.
To meet the growing demand for agricultural products, optimizing photosynthesis is a promising strategy to improve crop yields. Phenotypic variance in photosynthesis has been observed within or between species. To explore the potential of integrating photosynthetic parameters into crop breeding programs, we explored the genetic variation in photosynthesis by assessing photosynthesis-related parameters across plant development in 631 barley recombinant inbred lines (RILs) from eight HvDRR subpopulations under field conditions. The genetic complexity of these parameters was resolved by analyses of bi-parental and multi-parental quantitative trait loci (QTLs). Finally, we examined the merit of integrating photosynthesis-related parameters in genomic prediction of yield and its components. Significant genotypic variations of the photosynthesis-related parameters were found among the RILs, with their heritability ranging from 0.38 to 0.54. The multiple QTLs and dynamic QTLs for photosynthesis observed across different developmental stages underlined the complexity of the genetics of photosynthesis in barley. The considerably higher percentage of phenotypic variance explained for genomic prediction than multi-parental QTL analysis illustrates that the photosynthesis-related parameters are inherited in a more complex way than classical agronomic traits. Notably, the prediction ability for yield was increased by integrating the photosynthesis-related parameters of some developmental stages into genomic prediction models. Thus, our results suggest a novel perspective on increasing the efficiency of crop breeding programs by integrating photosynthesis-related parameters into prediction models.
Glycerate was found to effect photosynthetic O2 evolution in wheat chloroplasts by its conversion to triose phosphate and by influencing the rate of photosynthesis through the reductive pentose phosphate pathway. In the absence of bicarbonate, the photosynthetic O2 evolution with glycerate was low (10 to 25 mumol mg chlorophyll-1 h-1), and only about 15% of the rate of bicarbonate-dependent O2 evolution under optimum conditions. This corresponds to a rate of glycerate conversion to triose phosphate of 20 to 50 mumol mg chlorophyll-1 h-1, which appears sufficient to accommodate flux through the glycolate pathway in vivo. Pi was required for this glycerate-dependent O2 evolution; rates remained relatively constant between 0.1 and 40 mM Pi, and proceeded with little lag upon illumination (less than 0.5 min). Evidence for O2 evolution due to glycerate conversion to triose phosphate could be conclusively demonstrated by addition of glycolaldehyde, an inhibitor of the regenerative phase of photosynthesis, which prevents CO2 fixation. The effect of glycerate on photosynthesis in the presence of bicarbonate was determined by measuring both photosynthetic O2 evolution and 14CO2 fixation at varying Pi concentrations. Low concentrations of glycerate (micro- to millimolar levels) prevented inhibition of photosynthesis by Pi. With 1 mM bicarbonate and pH 8.2, which is favorable for glycolate synthesis, maximum rates of photosynthesis were obtained at low Pi (25 microM), whereas strong inhibition of photosynthesis occurred at only 0.2 mM Pi. Addition of glycerate relieved the inhibition of photosynthesis by Pi, indicating the possible importance of glycerate metabolism in the chloroplast under photorespiratory conditions. The initiation of photosynthesis by glycerate at inhibitory Pi levels occurred with little reduction in the ratio of CO2 fixed/O2 evolved, and the main effect of glycerate was on carbon assimilation. While the basis for the beneficial effect of glycerate on CO2 assimilation under moderate to high Pi levels is uncertain, it may increase the concentration of 3-phosphoglycerate (PGA) in the chloroplast, and thus make conditions more favorable for induction of photosynthesis and reduction of PGA to triose phosphate.
Panicum milioides, a naturally occurring species with C4-like Kranz leaf anatomy, is intermediate between C3 and C4 plants with respect to photo-respiration and the associated oxygen inhibition of photosynthesis. This paper presents direct evidence for a limited degree of C4 photosynthesis in this C3-C4 intermediate species based on: (a) the appearance of 24% of the total 14C fixed following 4 s photosynthesis in 14CO2-air by excised leaves in malate and aspartate and the complete transfer of label from the C4 acids to Calvin cycle intermediates within a 15 s chase in 12CO2-air; (b) pyruvate- or alanine-enhanced light-dependent CO2 fixation and pyruvate stimulation ote- or alanine-enhanced light-dependent CO2 fixation and pyruvate stimulation of oxaloacetate- or 3-phosphoglycerate-dependent O2 evolution by illuminated mesophyll protoplasts, but not bundle sheath strands; and (c) NAD-malic enzyme-dependent decarboxylation of C4 acids at the C-4 carboxyl position, C4 acid-dependent O2 evolution, and 14CO2 donation from (4-14C)C4 acids to Calvin cycle intermediates during photosynthesis by bundle sheath strands, but not mesophyll protoplasts. However, P. milloides differs from C4 plants in that the activity of the C4 cycle enzymes is only 15 to 30% of a C4 Panicum species and the Calvin cycle and phosphoenolpyruvate carboxylase are present in both cell types. From these and related studies (Rathnam, C.K.M. and Chollet, R. (1979) Arch. Biochem. Biophys. 193, 346-354; (1978) Biochem. Biophys. Res. Commun. 85, 801-808) we conclude that reduced photorespiration in P. milioides is due to a limited degree of NAD-malic enzyme-type C4 photosynthesis permitting an increase in pCO2 at the site of bundle sheath, but not mesophyll, ribulose-bisphosphate carboxylase-oxygenase.
Anabaena inaequalis was sensitive to nickel ion in the order of decreasing sensitivity of growth, photosynthesis, and acetylene reduction. At a culture density of 9 x 10(4) cells per millilitre, growth after 12 days was completely inhibited by 0.125 ppm (microgram/mL) Ni2+. Nickel caused the increase of both the lag phase of growth and the culture doubling time, and caused the retardation phase to be sooner. Photosynthesis and acetylene reduction were completely inhibited by 10 and 20 ppm Ni2+, respectively, at a cell concentration of 1.3 x 10(6) cells per millilitre. Preincubation for 24 h in the presence of nickel ion significantly increased the sensitivity of photosynthesis and acetylene reduction. Under these conditions acetylene reduction was more sensitive than photosynthesis. Nickel ion reduced culture growth by 35% at a level of 0.05 ppm and inhibited that culture's acetylene-reducing ability by 29% while leaving photosynthesis unaffected. Nickel caused some damage to filament apical cells and induced pigment bleaching in aged cultures. Nickel toxicity was proposed to be due to poisoning of intracellular enzyme systems by nickel ions.
Previous reviews of the effects of temperature on in vivo photosynthesis have mainly concerned the effects of temperature on light saturated rates. The quantum yield of photosynthesis (phi), as a measure of light limited photosynthesis, has generally been regarded as temperature insensitive. At temperatures close to the minima and maxima at which plants can sustain photosynthetic CO2 assimilation, light may damage the photosynthetic apparatus, an effect termed photoinhibition. A constant feature of photoinhibition is a reduction in phi. In maize, chilling-dependent photoinhibition reduces both phi and the light saturated rate of CO2 assimilation (Asat) and of O2 evolution. Analysis of recovery of CO2 uptake in these leaves suggests that whilst Asat recovers in a few hours, phi may not be fully restored for days. Examination of mature crop canopies shows that only a small proportion of the leaves are likely to become light saturated and then only for part of the day. The relative significance of temperature-induced changes in Asat and phi have also been tested in canopy models of maize crop photosynthesis. These suggest that whilst changes in either parameter will have similar effects on total canopy photosynthesis on the sunniest days of the year, for an average summer's day changes in phi will be of far greater importance. Consideration is therefore given to the factors associated with thylakoid membranes that may determine temperature-induced decreases in phi. Chilling of maize leaves under high light levels reduces the quantum yield of PSII and whole chain electron transport in concert with a decrease in the capacity of isolated thylakoids to bind atrazine, which is indicative of a loss or damage to the QB protein. Besides such classical symptoms of photoinhibition of PSII, chilling also induces the accumulation of a 31 kDa polypeptide in the thylakoids of maize leaves. This polypeptide fractionates with the light-harvesting chlorophyll a/b protein complex (LHCII) and has been tentatively identified as an unprocessed precursor of CP29 since it binds chlorophyll and is immunologically related to CP29. Accumulation of the 31 kDa polypeptide is associated with a modification in the energetics of LHCII, which may result in a decrease in excitation energy from LHCII to PSII and contribute to a decrease in phi. Examination is also made of how stress-induced modifications of interactions between PSII complexes, functioning of the cyt b6/f complex, the permeability of the thylakoid membrane to protons and the activity of the coupling factor may contribute to decreases in phi.
Photosynthesis, the use of light energy in the conversion of CO2 and inorganic nutrients into plant material, is the ultimate source of the food protein necessary to man's existence. Given certain assumptions, the overall maximal theoretical photosynthetic efficiency of agricultural plants can be calculated. Actual measured maximal growth rates of plants are equivalent to efficiency levels well below that theoretical maximum. In air, C4 plants can some closer to the theoretical value than C3 plants, perhaps because C4 plants avoid the occurrence of measurable photorespiration and oxygen inhibition of photosynthesis. Alfalfa, a C3 legume, is an extremely productive protein source. Its protein yield per acre can surpass that of commonly grown C4 crops (corn, sorghum) and C3 seed crops (soybean, wheat, rice). Alfalfa leaf protein is of high nutritional quality and can apparently be used directly in the human diet, eliminating the protein loss involved in animal production. Plant protein productivity can be raised as part of an increase in overall crop yield. The growth of plants in atmospheres with elevated CO2 levels can result in increased yields. In C3 plants this is due, at least in part, to the suppression of photorespiration and oxygen inhibition of photosynthesis. We have investigated the effect of CO2 concentration on alfalfa photosynthetic metabolism. Our results support the contention that alfalfa productivity can be increased by an environment of elevated CO2. A second approach toward increased plant protein productivity is through regulation of carbon flow during photosynthesis so as to increase portein production relative to that of other plant constituents. In particular, we have investigated whether ammonia (the form in which plants first incorporate nitrogen) can act to regulate leaf carbon metabolism. Our results indicate that NH4+, in part through stimulation of pyruvate kinase, brings about increased production of amino acids at the expense of sucrose production in alfalfa. The effect may be of considerable importance in the regulation of green leaf protein synthesis.
Photosynthesis in a Phormidium species which forms dense conical-shaped structures in thermal springs is strongly inhibited by aeration but is stimulated by sulfide and other agents (cysteine, thioglycolate, sulfite) which lower the oxidation-reduction potential. The compact structures which this alga forms in nature may restrict oxygen penetration from the enviroment so that the anaerobic or microaerophilic conditions necessary ofr photosynthesis can develop. The alga may be defective in a regulatory mechanism that controls the reoxidation of reduced pyridine nucleotides formed during photosynthesis. It is suggested that other mat-forming and benthic blue-green algae may also prefer anaerobib conditions for growth and photosynthesis.
There is no evolutionary continuity between photochemical abiosynthesis and bacterial photosynthesis. Rather, the photosynthetic bacteria are descendants of fermenters that did not use light. Photosynthesis and respiration, both using electron flow coupled with phosphorylation, have a common origin ('conversion hypothesis'), but photosynthesis came first. Anaerobic (nitrate or sulphate) respiration cannot have preceded photosynthesis as neither nitrate nor sulphate existed on the early earth. Sulphate was made first by photosynthetic sulphur bacteria. Nitrate arose even later, namely, in the aerobic biosphere produced by the blue-green algae, the first 'phytotrophs'. Photophosphorylation may have originated through the combination with membrane function of substrate level phosphorylation in reactionsand function of substrate level phosphorylation in reactions of photoproducts. Cyclic photophosphorylation arose while the biosphere was still reducing. It was supplemented later by processes for the light-based production of reducing power (NADH), ATP-powered electron flow, and subsequently light-powered electron flow with ATP production (noncyclic photophosphoryaltion). These later processes served the assimilation of CO2.
The quantum requirement of green cells for CO2 fixation has been evaluated and discussed in view of the recent discovery of photorespiration and of multiple biochemical pathways for photosynthetic CO2 fixation. The reported quantum requirement of algae generally is near 9 quanta per CO2 fixed. It is suggested that the high CO2 concentrations and low O2 concentrations used for these algae experiments would have completely suppressed photorespiration and, therefore, the minimum number of quanta required to fix 1 CO2 molecule was correctly determined in these experiments. With higher plant leaves, when measurements are made under physiological environments, quantum requirements range from about 12 to 20 quanta per CO2 fixed. It is suggested that these physiological quantum requirements are higher because photorespiration is functional in these leaves and that photorespiration requires energy. The energy requirement of photorespiration was derived using biochemical models of leaf photosynthesis combining photorespiration with specific biochemical pathways for CO2 fixation. The calculated physiological quantum requirements for C3, C4 and CAM plant photosynthesis are 13, 15 and 17 respectively. The literature values on quantum requirements correspond well with these biochemical models of net photosynthesis. However, it was concluded that the biochemical models fail to give a complete description of photosynthesis in plants using the C4-dicarboxylic acid cycle.
The transcripts of nuclear genes for the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcS), chlorophyll a/b-binding protein (cab), and extrinsic 33-kDa protein involved in photosystem II water oxidation (woxA) were not detectable in the white wild cultured cells of sycamore (Acer pseudoplatanus), in contrast to their high levels in the sibling green mutant cells and the constitutive expression of actin genes (act) in both cell types. We have examined the template activities of nuclear DNAs using the HeLa cell in vitro transcription system. All of the three photosynthesis genes from the green cell line and act from both cell types were well transcribed in vitro, but these photosynthesis genes from the white cell line were not, indicating that the transcriptional regulation is ascribable to DNA templates. Digestion of nuclear DNA with methyl-sensitive and -insensitive isoschizomeric endonucleases and the subsequent Southern hybridization showed that each gene has the identical recognition sites of restriction enzymes in the green and white cell lines, but some of the sites were methylated only in the photosynthesis genes in the white cells. There was observed a clear inverse relationship between the level of expressed transcripts and the extent of DNA methylation. Thus, it is inferred that the selective methylation of DNA is a likely mechanism for suppressing transcription of nuclear genes for photosynthesis in the nonphotosynthetic plant cells.
We used a small oxygen electrode and a grating monochromator of 10 mmu half-band width to determine light-saturation curves of photosynthesis for films of Chlorella pyrenoidosa no more than 1 cell thick. All curves were referenced to the lightsaturated rate observed in 5 mw/cm(2) of 680 mmu. To a close approximation (+/- 2%) the light-saturated rate was independent of wavelength over the region in which light intensity was sufficient to make the test (450-705 mmu). At wavelengths of high absorption we obtained intensities sufficient to cause photoinhibition. As a measure of photoinhibition we used the breakpoint, the lowest intensity at which rate of photosynthesis decreased with time. In general, the saturated rate was slightly lower and the estimated breakpoint was considerably lower at wavelengths of high absorption. Maximum rate of absorption of quanta at the breakpoint was highest in the far-red (>/= 700 mmu), lower and relatively constant in the near-red (630-680 mmu), and lowest in the blue. At 435 and 450 mmu the breakpoint occurred below saturation. We attribute small deviations in maximum rate of photosynthesis to effects of photoinhibition. Independence of wavelength observed for the light-saturated rate is consistent with models of photosynthesis in which maximum rate is limited by the same dark reaction at all wavelengths.
Intraspecies and intergenus complementation analysis were utilized to demonstrate that photosynthesis genes are clustered in distantly related purple photosynthetic bacteria. Specifically, we show that the linkage order for genes involved in bacteriochlorophyll and carotenoid biosynthesis in Rhodospirillum centenum are arranged essentially as in Rhodobacter capsulatus and Rhodobacter sphaeroides. In addition, the location and relative distance observed between the puf and puh operons which encode for light harvesting and reaction-centre structural genes are also conserved between these species. Conservation of the photosynthesis gene cluster implies either that there are structural or regulatory constraints that limit rearrangement of the photosynthesis gene cluster or that there may have been lateral transfer of the photosynthesis gene cluster among different species of phototrophic bacteria.
Anabaena inaequalis was sensitive to mercuric ion (Hg2+) in the ppb (nanogram per milliliter) range. Growth was inhibited significantly at concentrations of metal ion as low as 2 ppb, and 100 ppb was required to inhibit photosynthesis and acetylene reduction. Low levels of Hg2+ stimulated acetylene reduction and photosynthesis. The lysis of vegetative cells was the primary action of mercuric ions, resulting in the inhibition of growth, photosynthesis, and nitrogenase activity. There was a linear relationship between numbers of cells and the amount of Hg2+ required to induce culture lysis. Calculated on the basis of equivalent cell numbers, Hg2+ was toxic to A. inaequalis at 0.006, 0.009, and 0.100 micrograms of Hg2+ per 10(5) cells for photosynthesis, growth, and acetylene reduction, respectively.
Potato is one of the four staple food crops in the world. It has a wide range of cultivation, high yield, and high nutritional value. Enhancing the photosynthesis of potato is particularly important as it leads to an increase in the potato yield. The light-harvesting pigment-binding protein complex is very important for plant photosynthesis. We identified 12 Stlhcb gene family members from the potato variety "Atlantic" using transcriptome sequencing and bioinformatics. The proteins encoded by the Stlhcb gene family have between 3358 and 4852 atomic number, a relative molecular weight between 24060.16 and 34624.54 Da, and an isoelectric point between 4.99 and 8.65. The RT-qPCR results showed that the 12 Stlhcb genes were expressed in a tissue-specific and time-dependent fashion under low light. The relative expression of the Stlhcb genes in the leaves was significantly higher than that in the stems and roots, and the relative expression of these genes first increased and then decreased with the prolongation of light exposure time. The Stcp24 gene with the highest expression was cloned, and an expression vector was constructed. A subcellular localization analysis was performed in tobacco and an overexpression experiment was performed in potato using an Agrobacterium-mediated method. The subcellular localization analysis showed that the protein encoded by Stcp24 was located in chloroplasts as expected. Overexpression of Stcp24 in transgenic potato increased the yield of potatoes and the content of chlorophyll a and b; increased the net photosynthetic rate, transpiration rate, stomatal conductance, electron transport efficiency, and semi-saturated light intensity; and promoted photosynthesis and plant growth. This study provides a reference for the study of the function of the potato light-harvesting pigment-binding protein gene family. It lays a foundation for further study of the mechanism of the photosynthesis of potato, improvement of the light energy utilization of potato, and molecular breeding of potato.
We utilized differential plaque hybridization to identify three cDNA clones for transcripts which increase in abundance during the salinity-induced transition from C3 photosynthesis to crassulacean acid metabolism (CAM) in Mesembryanthemum crystallinum. Although there are differences in the abundance of these transcripts in unstressed tissue, steady-state levels of all three increased within 30 h following irrigation with 0.5 M NaCl. One cDNA encodes the cytosolic form of glyceraldehyde-3-phosphate dehydrogenase (D-glyceraldehyde-3-phosphate:NAD+ oxidoreductase (phosphorylating) (NAD-GAPDH], an enzyme involved in the production of phosphoenolpyruvate for CO2 fixation at night and the conversion of pyruvate to storage carbohydrate during the day. Coding region and 3'-noncoding sequence probes were used to examine the expression of NAD-GAPDH transcripts in leaf and root tissue. We show that the gene encoding the NAD-GAPDH cDNA is expressed in both leaf and root tissue during C3 photosynthesis and CAM. NAD-GAPDH transcript levels increase rapidly in leaf (but not in root) tissue during the transition to CAM. Our data indicate that the predominant NAD-GAPDH transcript expressed during C3 photosynthesis and CAM is encoded by a single gene in M crystallinum. These results imply that the transition to CAM in some cases involves an upward readjustment in the level of a gene product expressed during C3 photosynthesis, rather than the expression of a CAM-specific isoform with unique regulatory or kinetic properties.