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At least 253 records · Page 14Linked to original sources
PubMed2006

Effects of carbohydrate accumulation on photosynthesis differ between sink and source leaves of Phaseolus vulgaris L.

Accumulation of non-structural carbohydrate in leaves represses photosynthesis. However, the extent of repression should be different between sink leaves (sugar consumers) and source leaves (sugar exporters). We investigated the effects of carbohydrate accumulation on photosynthesis in the primary leaves of bean (Phaseolus vulgaris L.) during leaf expansion. To increase the carbohydrate content of the leaves, we supplied 20 mM sucrose solution to the roots for 5 d (sugar treatment). Plants supplied only with water and nutrients were used as controls. The carbohydrate contents, which are the sum of glucose, sucrose and starch, of the sugar-treated leaves were 1.5-3 times of those of the control leaves at all developmental stages. In the young sink leaves, the photosynthetic rate at saturating light and at an ambient CO2 concentration (A360) did not differ between the sugar-treated and control leaves. The A360 of sugar-treated source leaves gradually decreased relative to the control source leaves with leaf expansion. The initial slope of the A-Ci (CO2 concentration in the intercellular space) curve, and the Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) content per leaf area showed trends similar to that of A360. Differences in Amax between the treatments were slightly smaller than those in A360. These results indicate that the effect of carbohydrate accumulation on photosynthesis is significant in the source leaves, but not in the young sink leaves, and that the decrease in Rubisco content was the main cause of the carbohydrate repression of photosynthesis.

Apoproteins↗
PubMed2002

Short-term light and leaf photosynthetic dynamics affect estimates of daily understory photosynthesis in four tree species.

Instantaneous measurements of photosynthesis are often implicitly or explicitly scaled to longer time frames to provide an understanding of plant performance in a given environment. For plants growing in a forest understory, results from photosynthetic light response curves in conjunction with diurnal light data are frequently extrapolated to daily photosynthesis (A(day)), ignoring dynamic photosynthetic responses to light. In this study, we evaluated the importance of two factors on A(day) estimates: dynamic physiological responses to photosynthetic photon flux density (PPFD); and time-resolution of the PPFD data used for modeling. We used a dynamic photosynthesis model to investigate how these factors interact with species-specific photosynthetic traits, forest type, and sky conditions to affect the accuracy of A(day) predictions. Increasing time-averaging of PPFD significantly increased the relative overestimation of A(day) similarly for all study species because of the nonlinear response of photosynthesis to PPFD (15% with 5-min PPFD means). Depending on the light environment characteristics and species-specific dynamic responses to PPFD, understory tree A(day) can be overestimated by 6-42% for the study species by ignoring these dynamics. Although these overestimates decrease under cloudy conditions where direct sunlight and consequently understory sunfleck radiation is reduced, they are still significant. Within a species, overestimation of A(day) as a result of ignoring dynamic responses was highly dependent on daily sunfleck PPFD and the frequency and irradiance of sunflecks. Overall, large overestimates of A(day) in understory trees may cause misleading inferences concerning species growth and competition in forest understories with < 2% full sunlight. We conclude that comparisons of A(day) among co-occurring understory species in deep shade will be enhanced by consideration of sunflecks by using high-resolution PPFD data and understanding the physiological responses to sunfleck variation.

Acer↗
PubMed2003

Leaf senescence and late-season net photosynthesis of sun and shade leaves of overstory sweetgum (Liquidambar styraciflua) grown in elevated and ambient carbon dioxide concentrations.

We examined the effects of elevated CO2 concentration ([CO2]) on leaf demography, late-season photosynthesis and leaf N resorption of overstory sweetgum (Liquidambar styraciflua L.) trees in the Duke Forest Free Air CO2 Enrichment (FACE) experiment. Sun and shade leaves were subdivided into early leaves (formed in the overwintering bud) and late leaves (formed during the growing season). Overall, we found that leaf-level net photosynthetic rates were enhanced by atmospheric CO2 enrichment throughout the season until early November; however, sun leaves showed a greater response to atmospheric CO2 enrichment than shade leaves. Elevated [CO2] did not affect leaf longevity, emergence date or abscission date of sun leaves or shade leaves. Leaf number and leaf area per shoot were unaffected by CO2 treatment. A simple shoot photosynthesis model indicated that elevated [CO2] stimulated photosynthesis by 60% in sun shoots, but by only 3% in shade shoots. Whole-shoot photosynthetic rate was more than 12 times greater in sun shoots than in shade shoots. In senescent leaves, elevated [CO2] did not affect residual leaf nitrogen, and nitrogen resorption was largely unaffected by atmospheric CO2 enrichment, except for a small decrease in shade leaves. Overall, elevated [CO2] had little effect on the number of leaves per shoot at any time during the season and, therefore, did not change seasonal carbon gain by extending or shortening the growing season. Stimulation of carbon gain by atmospheric CO2 enrichment in sweetgum trees growing in the Duke Forest FACE experiment was the result of a strong stimulation of photosynthesis throughout the growing season.

Carbon Dioxide↗
PubMed2004

Use of modeled photosynthesis and decomposition to describe tree growth at the northern tree line.

Growth of subarctic Scots pine (Pinus sylvestris L.) trees was investigated by a combination of process-based models and dendroecological approaches. Tree ring width indices were strongly autocorrelated and correlated with simulated photosynthetic production of the previous year and with organic matter N mineralization of the current year. An autoregressive model, with photosynthesis and N mineralization as external inputs, explained growth of the trees well. However, relationships for the period 1950-1992 differed significantly from relationships for the period 1876-1949; the slope of the regression of tree ring width index and photosynthesis was lower for the 1950-1992 period. Also, the autocorrelation structure of the data changed. First-order autocorrelation decreased and second-order autocorrelation increased from the earlier to the later period. This means that growth is becoming less sensitive to variations in photosynthetic production, whereas the relationships between growth and N mineralization are remaining fairly constant. We postulate that, although photosynthesis has increased in response to increasing CO2 concentrations, tree growth rate cannot parallel the increase in photosynthesis because potential growth rate is limited directly by temperature.

Carbon Dioxide↗
PubMed2005

Localized ozone fumigation system for studying ozone effects on photosynthesis, respiration, electron transport rate and isoprene emission in field-grown Mediterranean oak species.

We used a localized ozone (O3) fumigation (LOF) system to study acute and short-term O(3) effects on physiological leaf traits. The LOF system enabled investigation of primary and secondary metabolic responses of similarly and differently aged leaves on the same plant to three different O3 concentrations ([O3]), unconfounded by other influences on O3 sensitivity, such as genetic, meteorological and soil factors. To simulate the diurnal cycle of O3 formation, current-year and 1-year-old Quercus ilex (L.) and Quercus pubescens (L.) leaves were fumigated with O3 at different positions (and hence, different leaf ages) on the same branch over three consecutive days. The LOF system supplied a high [O3] (300+/-50 ppb) on leaves appressed to the vents, and an intermediate, super-ambient [O3] (varying between 120 and 280 ppb) on leaves less than 30 cm from the vent. Leaves more than 60 cm from the O3 vent were exposed to an [O3] comparable with the ambient concentration, with a 100 ppb peak during the hottest hours of the day. Only leaves exposed to the high [O3] were affected by the 3-day treatment, confirming that Mediterranean oak are tolerant to ambient and super-ambient [O3], but may be damaged by acute exposure to high [O3]. Stomatal and mesophyll conductance and photosynthesis were all reduced immediately after fumigation with high [O3], but recovered to control values within 72 h. Both the intercellular and chloroplast CO2 concentrations ([CO2]) remained constant throughout the experiment. Thus, although treatment with a high [O3] may have induced stomatal closure and consequent down-regulation of photosynthesis, we found no evidence that photosynthesis was limited by low [CO2] at the site of fixation. One-year-old leaves of Q. ilex were much less sensitive to O3 than current-year leaves, suggesting that the low stomatal conductance observed in aging leaves limited O3 uptake. No similar effect of leaf age was found in Q. pubescens. Dark respiration decreased during the treatment period, but a similar decrease was observed in leaves exposed to low [O3], and therefore may not be an effect of O3 treatment. Light respiration, on the other hand, was mostly constant in ozone-treated leaves and increased only in leaves in which photosynthesis was temporarily inhibited by high [O3], preventing them from acting as strong sinks that recycle respiratory CO2 in the leaves. There was no evidence of photochemical damage in Q. ilex leaves, whereas Q. pubescens leaves exposed to a high [O3] showed limited photochemical damage, but recovered rapidly. Biochemical markers were affected by the high [O3], indicating accumulation of reactive oxygen species (ROS) and increased denaturation of lipid membranes, followed by activation of isoprene biosynthesis in Q. pubescens leaves. We speculate that the high isoprene emissions helped quench ROS and normalize membrane stability in leaves recovering from O3 stress.

Butadienes↗
PubMed2006

Modeling photosynthesis in olive leaves under drought conditions.

We quantified parameters for a model of leaf-level photosynthesis for olive, and tested the model against an independent dataset. Specific temperature-dependence parameters of the model for olive leaves were measured, as well as the relationship of the model parameters with area-based leaf nitrogen (N) content. The effect of soil water deficit on leaf photosynthesis was examined by applying two irrigation treatments to 29-year-old trees growing in a plantation: drip irrigation sufficient to meet the crop water requirements (I) and dry-farming (D). In both treatments, leaves had a higher photosynthetic capacity in April than in August. In August, photosynthetic capacity was lower in D trees than in I trees. Leaf photosynthetic capacity was linearly and positively related to leaf N content on an area basis (N(a)) and to leaf mass per unit area (LMA), and the regression slope varied with irrigation treatment. The seasonal reduction in N(a) was used in the model to predict photosynthesis under drought conditions. Olive leaves showed a clear limitation of photosynthesis by triose phosphate utilization (TPU) even at 40 degrees C, and the data suggest that olive invests fewer resources in TPU than other species. The seasonal decrease in photosynthetic capacity moderated the stomatal limitation to carbon dioxide (CO(2)) fixation as soil water deficit increased. Further, it enabled leaves to operate close to the transition point between photosynthetic limitation due to RuBP carboxylation capacity and that due to RuBP regeneration capacity, and resulted in a near constant value of internal CO(2) concentration from April to August. Under well watered conditions, N-use efficiency of the olive leaves was enhanced at the expense of reduced water-use efficiency.

Climate↗
PubMed1998

Manganous ions suppress photosynthesis gene expression in Rhodobacter sphaeroides.

The effect of manganous ions [Mn(II)] and ferrous ions [Fe(II)] on expression of photosynthesis genes in Rhodobacter sphaeroides was investigated. The presence of Mn(II) during phototrophic (anaerobic) and chemotrophic (aerobic) growth of R. sphaeroides caused a decrease in the amount of bacteriochlorophyll and carotenoid pigments which were synthesized and this was associated mainly with a decrease in the level of light-harvesting complex II. Mn(II) was shown to cause a decrease in expression of the puc operon, which encodes the polypeptides of light-harvesting complex II. Expression of the puc operon is controlled by the central repressor of photosynthesis gene expression, PpsR. In a ppsR mutant there was no effect of Mn(II) on photosynthesis gene expression. It is concluded that Mn(II) may act as a corepressor in the action of PpsR or act via an as yet uncharacterized protein that interacts with PpsR. In contrast to the effects of Mn(II), Fe(II) was required for high levels of photosynthesis gene expression. This requirement for Fe(II) was shown to be related to the regulation of hemA, a gene under the control of the transcriptional regulator, FnrL. Mn(II) did not affect FnrL-dependent gene expression.

Cations, Divalent↗
PubMed2006

Photosynthesis, productivity, and yield of maize are not affected by open-air elevation of CO2 concentration in the absence of drought.

While increasing temperatures and altered soil moisture arising from climate change in the next 50 years are projected to decrease yield of food crops, elevated CO2 concentration ([CO2]) is predicted to enhance yield and offset these detrimental factors. However, C4 photosynthesis is usually saturated at current [CO2] and theoretically should not be stimulated under elevated [CO2]. Nevertheless, some controlled environment studies have reported direct stimulation of C4 photosynthesis and productivity, as well as physiological acclimation, under elevated [CO2]. To test if these effects occur in the open air and within the Corn Belt, maize (Zea mays) was grown in ambient [CO2] (376 micromol mol(-1)) and elevated [CO2] (550 micromol mol(-1)) using Free-Air Concentration Enrichment technology. The 2004 season had ideal growing conditions in which the crop did not experience water stress. In the absence of water stress, growth at elevated [CO2] did not stimulate photosynthesis, biomass, or yield. Nor was there any CO2 effect on the activity of key photosynthetic enzymes, or metabolic markers of carbon and nitrogen status. Stomatal conductance was lower (-34%) and soil moisture was higher (up to 31%), consistent with reduced crop water use. The results provide unique field evidence that photosynthesis and production of maize may be unaffected by rising [CO2] in the absence of drought. This suggests that rising [CO2] may not provide the full dividend to North American maize production anticipated in projections of future global food supply.

Agriculture↗
PubMed2006

Species having C4 single-cell-type photosynthesis in the Chenopodiaceae family evolved a photosynthetic phosphoenolpyruvate carboxylase like that of Kranz-type C4 species.

Spatial and temporal regulation of phosphoenolpyruvate carboxylase (PEPC) is critical to the function of C(4) photosynthesis. The photosynthetic isoform of PEPC in the cytosol of mesophyll cells in Kranz-type C(4) photosynthesis has distinctive kinetic and regulatory properties. Some species in the Chenopodiaceae family perform C(4) photosynthesis without Kranz anatomy by spatial separation of initial fixation of atmospheric CO(2) via PEPC from C(4) acid decarboxylation and CO(2) donation to Rubisco within individual chlorenchyma cells. We studied molecular and functional features of PEPC in two single-cell functioning C(4) species (Bienertia sinuspersici, Suaeda aralocaspica) as compared to Kranz type (Haloxylon persicum, Salsola richteri, Suaeda eltonica) and C(3) (Suaeda linifolia) chenopods. It was found that PEPC from both types of C(4) chenopods displays higher specific activity than that of the C(3) species and shows kinetic and regulatory characteristics similar to those of C(4) species in other families in that they are subject to light/dark regulation by phosphorylation and display differential malate sensitivity. Also, the deduced amino acid sequence from leaf cDNA indicates that the single-cell functioning C(4) species possesses a Kranz-type C(4) isoform with a Ser in the amino terminal. A phylogeny of PEPC shows that isoforms in the two single-cell functioning C(4) species are in a clade with the C(3) and Kranz C(4) Suaeda spp. with high sequence homology. Overall, this study indicates that B. sinuspersici and S. aralocaspica have a C(4)-type PEPC similar to that in Kranz C(4) plants, which likely is required for effective function of C(4) photosynthesis.

Amino Acid Sequence↗
PubMed2001

Effect of solar ultraviolet-B radiation during springtime ozone depletion on photosynthesis and biomass production of Antarctic vascular plants.

We assessed the influence of springtime solar UV-B radiation that was naturally enhanced during several days due to ozone depletion on biomass production and photosynthesis of vascular plants along the Antarctic Peninsula. Naturally growing plants of Colobanthus quitensis (Kunth) Bartl. and Deschampsia antarctica Desv. were potted and grown under filters that absorbed or transmitted most solar UV-B. Plants exposed to solar UV-B from mid-October to early January produced 11% to 22% less total, as well as above ground biomass, and 24% to 31% less total leaf area. These growth reductions did not appear to be associated with reductions in photosynthesis per se: Although rates of photosynthetic O(2) evolution were reduced on a chlorophyll and a dry-mass basis, on a leaf area basis they were not affected by UV-B exposure. Leaves on plants exposed to UV-B were denser, probably thicker, and had higher concentrations of photosynthetic and UV-B absorbing pigments. We suspect that the development of thicker leaves containing more photosynthetic and screening pigments allowed these plants to maintain their photosynthetic rates per unit leaf area. Exposure to UV-B led to reductions in quantum yield of photosystem II, based on fluorescence measurements of adaxial leaf surfaces, and we suspect that UV-B impaired photosynthesis in the upper mesophyll of leaves. Because the ratio of variable to maximal fluorescence, as well as the initial slope of the photosynthetic light response, were unaffected by UV-B exposure, we suggest that impairments in photosynthesis in the upper mesophyll were associated with light-independent enzymatic, rather than photosystem II, limitations.

Antarctic Regions↗
PubMed1966

Monochromatic light saturation curves for photosynthesis in Chlorella.

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.

Eukaryota↗
PubMed2001

A small decrease of plastid transketolase activity in antisense tobacco transformants has dramatic effects on photosynthesis and phenylpropanoid metabolism.

Transketolase (TK) catalyzes reactions in the Calvin cycle and the oxidative pentose phosphate pathway (OPPP) and produces erythrose-4-phosphate, which is a precursor for the shikimate pathway leading to phenylpropanoid metabolism. To investigate the consequences of decreased TK expression for primary and secondary metabolism, we transformed tobacco with a construct containing an antisense TK sequence. The results were as follows: (1) a 20 to 40% reduction of TK activity inhibited ribulose-1,5-bisphosphate regeneration and photosynthesis. The inhibition of photosynthesis became greater as irradiance increased across the range experienced in growth conditions (170 to 700 micromol m(-2) sec(-1)). TK almost completely limited the maximum rate of photosynthesis in saturating light and saturating CO(2). (2) Decreased expression of TK led to a preferential decrease of sugars, whereas starch remained high until photosynthesis was strongly inhibited. One of the substrates of TK (fructose-6-phosphate) is the starting point for starch synthesis, and one of the products (erythrose-4-phosphate) inhibits phosphoglucose isomerase, which catalyzes the first reaction leading to starch. (3) A 20 to 50% decrease of TK activity led to decreased levels of aromatic amino acids and decreased levels of the intermediates (caffeic acid and hydroxycinnamic acids) and products (chlorogenic acid, tocopherol, and lignin) of phenylpropanoid metabolism. (4) There was local loss of chlorophyll and carotene on the midrib when TK activity was inhibited by >50%, spreading onto minor veins and lamina in severely affected transformants. (5) OPPP activity was not strongly inhibited by decreased TK activity. These results identify TK activity as an important determinant of photosynthetic and phenylpropanoid metabolism and show that the provision of precursors by primary metabolism colimits flux into the shikimate pathway and phenylpropanoid metabolism.

Antisense Elements (Genetics)↗
PubMed1992

Conservation of the photosynthesis gene cluster in Rhodospirillum centenum.

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.

Bacteriochlorophylls↗
PubMed2006

Interactions between the effects of atmospheric CO2 content and P nutrition on photosynthesis in white lupin (Lupinus albus L.).

Phosphorus (P) is a major factor limiting the response of carbon acquisition of plants and ecosystems to increasing atmospheric CO2 content. An important consideration, however, is the effect of P deficiency at the low atmospheric CO2 content common in recent geological history, because plants adapted to these conditions may also be limited in their ability to respond to further increases in CO2 content. To ascertain the effects of low P on various components of photosynthesis, white lupin (Lupinus albus L.) was grown hydroponically at 200, 400 and 750 micromol mol(-1) CO2, under sufficient and deficient P supply (250 and 0.69 microM P, respectively). Increasing growth CO2 content increased photosynthesis only under sufficient growth P. Ribulose 1,5-biphosphate carboxylase/oxygenase (Rubisco) content and activation state were not reduced to the same degree as the net CO2 assimilation rate (A), and the in vivo rate of electron transport was sufficient to support photosynthesis in all cases. The rate of triose phosphate use did not appear limiting either, because all the treatments continued to respond positively to a drop in oxygen levels. We conclude that, at ambient and elevated CO2 content, photosynthesis in low-P plants appears limited by the rate of ribulose biphosphate (RuBP) regeneration, probably through inhibition of the Calvin cycle. This failure of P-deficient plants to respond to rising CO2 content above 200 micromol mol(-1) indicates that P status already imposes a widespread restriction in plant responses to increases in CO2 content from the pre-industrial level to current values.

Atmosphere↗
PubMed2006

Functional dynamics of plant growth and photosynthesis--from steady-state to dynamics--from homogeneity to heterogeneity.

Plants are much more dynamic than we usually expect them to be. This dynamic behaviour is of paramount importance for their performance under natural conditions, when resources are distributed heterogeneously in space and time. However, plants are not only the cue ball of their physical and chemical environment. Endogenous rhythms and networks controlling photosynthesis and growth buffer plant processes from external fluctuations. This review highlights recent evidence of the importance of dynamic temporal and spatial organization of photosynthesis and of growth in leaves and roots. These central processes for plant performance differ strongly in their dependence on environmental impact and endogenous properties, respectively. Growth involves a wealth of processes ranging from the supply of resources from external and internal sources to the growth processes themselves. In contrast, photosynthesis can only take place when light and CO2 are present and thus clearly requires 'input from the environment'. Nevertheless, growth and photosynthesis are connected to each other via mechanisms that are still not fully understood. Recent advances in imaging technology have provided new insights into the dynamics of plant-environment interactions. Such processes do not only play a crucial role in understanding stress response of plants under extreme environmental conditions. Dynamics of plants under modest growth conditions rise from endogenous mechanisms as well as exogenous impact too. It is thus an important task for future research to identify how dynamic external conditions interact with plant-internal signalling networks to optimize plant behaviour in real time and to understand how plants have adapted to characteristic spatial and temporal properties of the resources from their environment, on which they depend on.

Adaptation, Physiological↗
PubMed2005

Aerobic anoxygenic photosynthesis genes and operons in uncultured bacteria in the Delaware River.

Photosynthesis genes and operons of aerobic anoxygenic photosynthetic (AAP) bacteria have been examined in a variety of marine habitats, but genomic information about freshwater AAP bacteria is lacking. The goal of this study was to examine photosynthesis genes of AAP bacteria in the Delaware River. In a fosmid library, we found two clones bearing photosynthesis gene clusters with unique gene content and organization. Both clones contained 37 open reading frames, with most of those genes encoding known AAP bacterial proteins. The genes in one fosmid were most closely related to those of AAP bacteria in the Rhodobacter genus. The genes of the other clone were related to those of freshwater beta-proteobacteria. Both clones contained the acsF gene, which is required for aerobic bacteriochlorophyll synthesis, suggesting that these bacteria are not anaerobes. The beta-proteobacterial fosmid has the puf operon B-A-L-M-C and is the first example of an uncultured bacterium with this operon structure. The alpha-3-proteobacterial fosmid has a rare gene order (Q-B-A-L-M-X), previously observed only in the Rhodobacter genus. Phylogenetic analyses of photosynthesis genes revealed a possible freshwater cluster of AAP beta-proteobacteria. The data from both Delaware River clones suggest there are groups of freshwater or estuarine AAP bacteria distinct from those found in marine environments.

Aerobiosis↗
PubMed2005

Wheat leaf photosynthesis loss due to leaf rust, with respect to lesion development and leaf nitrogen status.

In wheat (Triticum aestivum cv. Soissons) plants grown under three different fertilisation treatments, we quantified the effect of leaf rust (Puccinia triticina) on flag leaf photosynthesis during the whole sporulation period. Bastiaans' model: Y = (1 - x)beta was used to characterize the relationship between relative leaf photosynthesis (Y) and disease severity (x). The evolution of the different types of symptoms induced by the pathogen (sporulating, chlorotic and necrosed tissues) was evaluated using image analysis. The beta-values varied from 2 to 11, 1.4-2, and 0.8-1 during the sporulation period, when considering the proportion of sporulating, sporulating + necrotic, and total diseased area, respectively. Leaf nitrogen (N) content did not change the effect of the disease on host photosynthesis. We concluded that leaf rust has no global effect on the photosynthesis of the symptomless parts of the leaves and that the large range in the quantification of leaf rust effect on the host, which is found in the literature, can be accounted for by considering the different symptom types. We discuss how our results could improve disease assessments and damage prediction in a wheat crop.

Basidiomycota↗
PubMed2005

Gradients of lipid storage, photosynthesis and plastid differentiation in developing soybean seeds.

This study establishes a topographical framework for functional investigations on the regulation of lipid biosynthesis and its interaction with embryo photosynthesis in developing soybean seed. Structural observations, combined with molecular and functional parameters, revealed the gradual transformation of chloroplasts into storage organelles, starting from inner regions going outwards. This is evidenced by electron microscopy, confocal laser scanning microscopy, in situ hybridization and histochemical/biochemical data. As a consequence of plastid differentiation, photosynthesis becomes distributed along a gradient within the developing embryo. Electron transport rate, effective quantum yield and O2 production rate are maximal in the embryo periphery, as documented by imaging pulse-amplitude-modulated fluorescence and O2 release via microsensors. The gradual loss of photosynthetic capacity was accompanied by a similarly gradual accumulation of starch and lipids. Noninvasive nuclear magnetic resonance spectroscopy of mature seeds revealed steep gradients in lipid deposition, with the highest concentrations in inner regions. The inverse relationship between photosynthesis and lipid biosynthesis argues against a direct metabolic involvement of photosynthesis in lipid biosynthesis during the late storage stage, but points to a role for photosynthetic oxygen release. This hypothesis is verified in a companion paper.

Chlorophyll↗