RuBP Carboxylase Activity Research Articles

Effects of Chronic Doses of Ozone on Loblolly Pine: Photosynthetic Characteristics in the Third Growing Season

Abstract Gas exchange characteristics of loblolly pine seedlings were measured in the third growing season of ozone fumigations to determine the effects of long-term ozone exposure on photosynthetic capacity. Light and CO2 response curves indicated significant decreases of 21% and 27%, respectively, in light-saturated and CO2-saturated photosynthetic capacities at 2 x ambient ozone (92 ppb 12-hr seasonal mean) compared to charcoal-faltered (CF) air, approximately 0.5 x ambient ozone (29 ppb 12-hr seasonal mean). Differences in the response curves suggest changes in light-harvesting and biochemical efficiencies as well as changes in the activity of RuBP Carboxylase and the regeneration rate of RuBP. Chlorophyll and carotenoid conditions per unit leaf area were decreased at the high ozone treatment in older flushes. Stomatal resistance limited photosynthesis by about 29% in both CF and 2 x ambient ozone treated plants, suggesting that chronic ozone exposure did not affect stomatal control in loblolly pine. For. Sci. 35(3):745-755.

Activity and activation state of ribulose-1,5-bisphosphate carboxylase of spruce trees with varying degrees of damage relative to the occurrence of novel forest decline

The aim was to determine whether a reduced carboxylation efficiency in needles of damaged spruce trees (Picea abies), is derived from a direct impairment of the ribulose-1,5-bisphosphate carboxylase (RuBP carboxylase) or there is an indirect inhibition of the RuBP carboxylase. In 1985, 1986 and 1987 measurements of RuBP carboxylase activity were carried out at three locations. Trees of different ages and degrees of damage were examined. RuBP carboxylase was assayed using both a rapid extraction method to determine the initial activity and an in vitro test after total activation to determine the total activity. The activation state was calculated as the ratio of initial activity to total activity.Within three vegetation periods the total activity in needles of damaged and apparently healthy or slightly damaged spruce trees indicated no definite difference in the annual average. On the other hand, in damaged needles a continued decline of the actual activation of RuBP carboxylase was established. The observation of continued depression of the activation state of the enzyme in needles of damaged spruce trees can possibly be due to a reduced photosynthetic electron transport rate.The measurements of the soluble protein content indicate a tendency to increased amounts in the needles of damaged trees. In accordance, a considerable increase of the activity of some enzymes like glutamine synthethase, phosphoenol-pyruvate carboxylase, and catalase could be noticed. However, there is no clear connection between the RuBP carboxylase and the content of soluble proteins.

Photosynthesis and nitrogen relationships in leaves of C3 plants.

The photosynthetic capacity of leaves is related to the nitrogen content primarily bacause the proteins of the Calvin cycle and thylakoids represent the majority of leaf nitrogen. To a first approximation, thylakoid nitrogen is proportional to the chlorophyll content (50 mol thylakoid N mol-1 Chl). Within species there are strong linear relationships between nitrogen and both RuBP carboxylase and chlorophyll. With increasing nitrogen per unit leaf area, the proportion of total leaf nitrogen in the thylakoids remains the same while the proportion in soluble protein increases. In many species, growth under lower irradiance greatly increases the partitioning of nitrogen into chlorophyll and the thylakoids, while the electron transport capacity per unit of chlorophyll declines. If growth irradiance influences the relationship between photosynthetic capacity and nitrogen content, predicting nitrogen distribution between leaves in a canopy becomes more complicated. When both photosynthetic capacity and leaf nitrogen content are expressed on the basis of leaf area, considerable variation in the photosynthetic capacity for a given leaf nitrogen content is found between species. The variation reflects different strategies of nitrogen partitioning, the electron transport capacity per unit of chlorophyll and the specific activity of RuBP carboxylase. Survival in certain environments clearly does not require maximising photosynthetic capacity for a given leaf nitrogen content. Species that flourish in the shade partition relatively more nitrogen into the thylakoids, although this is associated with lower photosynthetic capacity per unit of nitrogen.

Microhabitat variation in the hydrothermal vent mussel, Bathymodiolus thermophilus, at the Rose Garden vent on the Galapagos Rift

Clumps of Bathymodiolus thermophilus were collected from three discrete areas at the ‘Rose Garden’ site on the Galapagos Rift using the deep submersible Alvin. Two mussel collections were made from the central Riftia mass, an area associated with very active venting, and three other collections were of two different peripheral mussel clumps. Before collection the clumps were extensively photographed and the water at two of the ‘microhabitats’ was analysed in situ for oxygen silica, sulfide and temperature. Sulfide levels of up to 300 μM were recorded at the central collection site, while the highest sulfide level recorded at the peripheral site assayed was 35 μM. Levels of RuBP carboxylase activity in the gills were significantly higher in mussels collected from the central ‘Riftia site’ than in either peripheral site. ATP sulfurylase was significantly higher in the gills of mussels from the central clump than in one of the peripheral clump collections. The chemical composition (% water, protein, carbohydrate, lipid and ash) and stable carbon isotope ratios (δ13C) of the mussels showed the same trends, with highest lipid and carbohydrate and the lowest water content and δ13C in the central site mussels. Similarly, the mussels from the central site were significantly depleted in stable nitrogen (δ15N) when compared with the peripheral site mussels. Variations between sites and tissues of the same animal may be indicative of differential utilization of inorganic or dissolved molecular nitrogen sources. The condition index (CI = soft tissue dry mass / internal shell volume) was similar for all animals collected at Rose Garden. The presence of a commensal polychaete, Branchipolynoe symmytilida, in the mantle cavity of the mussels was also correlated with the collection site, with the highest incidence of occurrence in the central clump.

Influence of Benzyladenine on Leaf Senescence and Photosynthesis in Sunflower (Helianthus annuus L.)

AbstractThe effect of foliar application of benzyladenine on sunflower leaf senescence, photosynthesis, RuBP carboxylase activity and diffusion resistance was investigated. A considerable drop in photosynthetic rate and rise in diffusion resistance were noted dunng the seed filling period. Benzyladenine application maintained the chlorophyll content and chlorophyll a : b ratio at higher level, enhanced RuBP carboxylase activity and net photosynthesis in both upper and lower leaves. A lower level of diffusion resistance was also observed by benzyladenine application during seed filling period. The results suggested that application of benzyladenine at 30, 60 and 90 days after sowing could help to maintain photosynthesis and assimilate supply to the developing seeds of sunflower.

Photosynthetic light acclimation in fully developed leaves of the juvenile and adult life phases of Hedera helix

The aim of this study was to investigate the extent to which fully developed leaves of Hedera helix L. are capable of acclimating to new light conditions and how this ability is determined by the life phase of the plant. To this end juvenile and adult plants were transferred from a low (L) to a moderately high (H) light regime and vice versa and changes of photosynthetic gas exchange, RuBP carboxylase (EC 4.1.1.39) activity and specific anatomy were monitored in leaves that were fully developed prior to the transfer.Immediately after transfer from L to H there was a decrease in the rate of net photosynthesis (Fn). This photoinhibition was particularly pronounced in leaves of the adult life phase. Fn recovered after 10 to 20 days at H, and 40 to 65 days after transfer the rate exceeded that of control plants by about 20% in leaves of the adult life phase and by about 50% in leaves of the juvenile life phase. If H plants were transferred to L, Fn had declined only slightly after 30 to 40 days and regained its initial level within a few days, when the plants were returned to the original high light regime.The increased rates of Fn per unit leaf area in leaves transferred from L to H were associated with higher light levels necessary to saturate Fn, higher carboxylation efficiencies, higher contents of soluble protein and higher activities of RuBP carboxylase, whereas the quantum yield did not change. Although fully differentiated before transfer, the leaves had formed a further cell layer in the palisade parenchyma. Related to leaf volume there was no increase in Fn.Our results indicate that in the adult life phase of ivy phenotypie light acclimation occurs mainly during leaf development, whereas in juvenile plants fully expanded leaves still possess a rather wide modulativc acclimation plasticity.

Changes in Some Photosynthetic and Photorespiratory Properties in Barley Leaves after Treatment with Jasmonic Acid

The influence of jasmonic acid (JA) on photosynthesis, dark respiration, photorespiration, and the activities of ribulose bisphosphate carboxylase/oxygenase (RuBPCO) and phosphoenolpyruvate carboxylase in 7-day-old barley seedlings ( Hordeum vulgare L., var. Alfa) was investigated. Plants treated with JA showed a decrease of the rate of photosynthetic CO 2 fixation and the activity of RuBP carboxylase. The rate of dark respiration was increased two-fold, of photorespiration increased about 70 %, and the CO 2 -compensation point increased about 20 %. Stomatal resistance increased about 70 % over control plants. As a result of the inhibition of the carboxylase activity of RuBPCO, the carboxylase/oxygenase ratio decreased.

Photosynthetic enzyme activities in lemongrass cultivated in temperate climates

Abstract Phosphoenolpyruvate carboxylase and RuBP carboxylase activities and Δ 13 C values were measured in lemongrass. The values obtained range among those typical of C 4 plants. The glycolate oxidase activity can be correlated to the usual low C 4 photorespiratory levels. The high chlorophyll a/b ratio is also consistent with a high efficiency photosynthesis. It is evident that Cymbopogon citratus , even though cultivated in climates colder than those of its origin, may possess a C 4 photosynthetic mechanism.

CO2 fixation in halobacteria

Seven strains of extremely halophilic bacteria (Halobacterium spp., Halococcus spp., and Haloarcula sp.) fixed CO2 under light and dark conditions. Light enhanced CO2 fixation in Halobacterium halobium but inhibited it in Halobacterium volcanii and Haloarcula strain GN-1. Propionate stimulated 14CO2 incorporation in some strains, but inhibited it in others. Semi-starvation in basal salts plus glycerol induced enhanced CO2 fixation rates. 14CO2 fixation in semi-starved cells was stimulated by NH 4 + or pyruvate and inhibited by succinate and acetate in most strains. No possible reductant was found. In cell-free extracts of H. halobium, NH 4 + but not propionate stimulated 14CO2 fixation. No RuBP carboxylase activity was detected. The main 14C-labeled α-keto acid detected after a 2-min incubation with 14CO2 and pyruvate was pyruvate. Little or no α-ketobutyrate was detected among the early products of propionate-stimulated CO2 fixation. Glycine was the major amino acid synthesized during a 2-min incubation with NH 4 + , propionate, and 14CO2. Propionate-stimulated CO2 fixation was sensitive to trimethoprim and insensitive to avidin. A novel pathway for non-reductive CO2 fixation involving a glycine synthase reaction with CO2, NH 4 + , and a methyl carbon derived from the β-carbon cleavage of propionate is tentatively proposed.

Seasonal Patterns of Photosynthetic Traits in Early Maturing Maize

AbstractA biochemical approach to maize breeding must be based on an exact knowledge about changes of relevant traits with ontogenetic stage. In 1983 seasonal patterns of net assimilation rate (NAR), chlorophyll and carotenoids contents, and of activities of RuBP carboxylase, PEP carboxylase and NADP malate dehydrogenase were recorded for two early maturing maize cultivars. For all traits the general trends were similar for both cultivars throughout the growing season but short term fluctuations were less synchronized after anthesis. About 75% of the maximum green leaf area was expanded within 20 days around middle of July. Specific seasonal patterns were observed for all traits. Before anthesis values were maximum for NAR in late June and in early July, for enzyme activities at the end of June and for pigment contents at the beginning of July. First decreases occurred for all traits before anthesis, further decreases were observed for PEP carboxylase in August and for chlorophyll content in September. Marked temporary declines coincided for NAR and pigment contents with a cold spell end of June and for these traits and RuBP carboxylase activity with anthesis. Evidence was scarce that any of the photosynthetic traits reflected the photosynthetic efficience of the two cultivars for a long stretch of time.

Variation of RuBP carboxylase activity among anther‐derived plants of Solanum phureja

The effect of genotype and ploidy on RuBP carboxylase (EC 4.1.1.39) activity, chlorophyll content, leaf area, chloroplast ultrastructure and not photosynthesis among monoploid. diploid and tetraploid anther‐derived plants of Solanum phureja Juz, and Buk. was studied. Within the monoploid group, RuBP carboxylase activity and concentration displayed a significant genotypic effect. For the diploids, variation among genotypes was significant for total protein content and maximum specific activity of RuBP carboxylase, and among the tetraploids for net photosynthesis and specific leaf weight. Ploidy effect was evident regarding net photosynthesis, leaf area and chlorophyll content. The different ploidy groups among the anther‐derived plants surpassed the anther donor plant for all characteristics except maximum activity of RuBP carboxylase and net photosynthesis. For the latter only the tetra‐ploid group was superior to the anther source plant. However, a monoploid genotype with an increase of 9% in maximum activity of RuBP carboxylase over the anther‐donor plant was identified. Segregation of trails rind differential gene expression together with possible mutations during androgenesis are discussed as sources of variation.

Metabolism of Oxamide (Slow-Release Nitrogen Fertilizer) in Rice Plant

Metabolism of oxamide-carbon in rice plant was investigated by a trace experiment using 14C labelled oxamide. 14C activity in the rice plant fed with 14C -oxamide was detected in evolving CO2, organic acid, amino acid, amide, sugar, protein, and starch. Of these metabolites, the activity was higher in oxalate followed by CO2. Metabolism of oxamide was markedly influenced by the pre-treatment with oxamide, which induced the operation of the system controlling oxamide metabolism in rice plant. In successive cultures with only water after treatment with oxamide, the level of oxalate decreased mainly and the decrease corresponded to the increase of evolving CO2. These evidences suggest that oxamide was metabolized to oxalate with subsequent CO2 evolution. One part of the evolving CO2 was found to be incorporated into the TCA cycle by the activity of PEP carboxylase mainly in roots, and another part into the Calvin cycle by the activity of RuBP carboxylase mainly in shoots. Therefore, it was considered that or...

Temperature adaptation of RuBP carboxylase: kinetic properties in marine Antarctic diatoms

Colonization of cold waters by unicellular algae, which are ectothermic organisms, is made possible by the evolutionary development of molecular mechanisms which allow photosynthesis at low temperatures. The apparent activation energy ( E a), Michaelis-Menten constant [ K m(RuBP)], V/K m ratios, temperature, and pH optima of d-ribulose 1,5-bisphosphate carboxylase (RuBP carboxylase) were investigated in three species of Antarctic diatoms, Corethron criophilum Castracane, Nitzschia turgiduloïdes (Hasle), N. kerguelensis O'Meara, and in two temperate species, Skeletonema costatum (Greville) Cleve and Phaeodactylum tricornutum Bohlin. The optimum of activity occurred at the same pH (8.0) for the temperate and Antarctic species. E a values corresponding to these species are the same (≈17 kcal·mol −1). We obtained a minimum K m value at a culture temperature of 4.5°C for the Antarctic species and 20°C for the temperate ones. This minimum K m value (60 μM) is of the same order of magnitude as values found in terrestrial plants. These results suggest the occurrence of mechanisms for the maintenance and regulation of RuBP carboxylase activity in Antarctic diatoms at low temperatures.

In vivo regulation of form I ribulose 1,5-bisphosphate carboxylase/ oxygenase from Rhodopseudomonas sphaeroides

When autotrophically grown cells of Rhodopseudomonas (Rhodobacter) sphaeroides were supplied with an organic carbon source, the activity of ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBPC/O) decreased 30 to 60%. The extent of inactivation varied depending on the level of derepression of form I and form II RuBPC/O, and on the nature of the organic carbon source, pyruvate being the most effective. Raising the concentration of CO 2 in the gas phase of autotrophic cultures brought about a similar loss of RuBPC/O activity. Immunological assays of form I and form II RuBPC/O proteins indicated that the synthesis of both enzymes had been repressed. Moreover, it is demonstrated that the observed loss of RuBP carboxylase activity was due to inactivation of the form I enzyme; the form II RuBPC/O was not affected. The isolated inactivated form I RuBPC/O exhibited a fivefold lower specific activity compared to the active form I enzyme. The inactivation was accompanied by changes in the properties as well as the structure of the form I enzyme. In autotrophic cells, form I RuBPC/O appeared to be associated with a phosphate-containing compound that decreased the enzyme's relative mobility in nondenaturing gels and increased its density in sucrose gradients. Form I RuBPC/O was released from an apparent complex or aggregate upon in vivo inactivation and/or after in vitro heat treatment. The inactive form I enzyme was found to reactivate in vitro by a slow reaction that was accelerated by heat treatment. However, experiments showed no evidence for in vivo reactivation after cells were reexposed to autotrophic conditions (1.5% CO 2 in H 2). All these data indicate that R. sphaeroides RuBPC/O activity is controlled at the transcriptional and post-transcriptional levels, through regulatory systems that repress the synthesis of form I and form II RuBPC/O and inactivate the predominant form (form I) when the carbon source no longer becomes limiting for growth.

The effect of ammonium and nitrate on CO2 assimilation, RuBP and PEP carboxylase activity and dry matter production in wheat

Photosynthetic(14)CO2 assimilation, ribulose 1, 5-bisphosphate carboxylase (RuBPC), phosphoenol pyruvate carboxylase (PEPC) and dry matter (DM) production were examined in wheat under varying levels and forms of nitrogen.(14)CO2 assimilation increased gradually after germination reaching a peak value at anthesis, followed by a sharp decline. A similar pattern was observed for both the carboxylases, RuBPC and PEPC activities. Increase in nitrogen levels, in general, brought about a significant increase over the control (zero-nitrogen) in(14)CO2 assimilation, RuBPC, PEPC activities and DM production. There were no significant differences in RuBPC activity and(14)CO2 assimilation with respect to the forms of nitrogen. Significantly higher PEPC activity and DM was observed in plants supplied with nitrate-nitrogen (NO3-N), as compared to those supplied with ammonium-nitrogen (NH4-N). The significance of PEPC activity in C3 photosynthesis is discussed in relation to DM distribution.

The state of activation of ribulose-1,5-bisphosphate carboxylase in wheat leaves

In light and in darkness, exposure of leaf segments to CO2-free atmospheres caused a marked reduction in extractable RuBP carboxylase activity. By contrast, darkness caused a relatively small decrease in carboxylase activity in extracts from leaf segments kept in air containing CO2. Recovery of carboxylase activity in leaves during illumination in air after exposure to CO2-free conditions paralleled recovery of capacity for photosynthesis; in darkness recovery of carboxylase activity in leaves was slower than in the light. Extracts from leaves exposed to CO2-free conditions recovered activity when provided with CO2 and Mg(2+); there were clearly, however, substances in the extracts that modified the activity achieved and caused anomalous decreases and increases with time after extraction. Studies of the effect of orthophosphate on the activity of purified wheat carboxylase in vitro were consistent with the view that many of the effects observed on the activity of crude leaf extracts were due to orthophosphate content.

Effects of abscisic acid on photosynthesis in whole leaves: changes in CO2 assimilation, levels of carbon-reduction-cycle intermediates, and activity of ribulose-1,5-bisphosphate carboxylase

Addition of abscisic acid (ABA) to the transpiration stream of leaves of Xanthium strumarium caused stomatal closure and, simultaneously, an independent reduction of CO2 assimilation. An attempt was made to identify the site of inhibition that had occurred, presumably, in the path of photosynthetic carbon reduction. Leaves were supplied with ABA. When inhibition of photosynthesis was fully expressed, the partial pressure of CO2 in the intercellular spaces was adjusted to the level that had occurred before ABA had been applied and before stomata had closed. Then the leaf was rapidly frozen, and pool sizes of carbon-reduction-cycle intermediates were determined. Comparison with samples from control leaves showed that the decline in the rate of assimilation was associated with decreases of the levels of 3-phosphoglycerate, triose phosphates, fructose-1,6-bisphosphate, and hexose phosphates. In contrast, the pool size ofribulose-1,5-bisphosphate (RuBP) remained unchanged or even increased. Similar results were obtained with leaves of Zea mays, in which the levels of all measured intermediates, including malate and pyruvate, declined after application of ABA; the level of RuBP rose. In other experiments with leaves of X. strumarium, rates of CO2 assimilation were lowered by reductions in the partial pressure of CO2 in the ambient air. Relationships between assimilation rates of CO2 and metabolite levels were similar to those determined after applications of ABA at constant partial pressure of CO2. Because the uptake of CO2 decreased in ABA-treated leaves in spite of continued availability of CO2 and RuBP, we concluded that application of ABA caused an inhibition of the carboxylation of RuBP in both, the C3 species, X. strumarium, and the C4 species, Z. mays. However, the RuBP-carboxylase activity of rapidly prepared extracts of ABA-treated leaves was as high as that of control leaves. The substance or the process which, after application of ABA, interferes with the carboxylation of RuBP remains unknown.

Relationships between Inorganic Phosphate and Carbohydrate Content in Flag Leaves of Field Grown Wheat during Senescence

Summary The variations in inorganic phosphate (Pi) and carbohydrates were followed during senescence of wheat flag leaves grown in experimental fields under Mediterranean climate. Different patterns were observed depending on the stage of senescence of the leaves and grain development. The relationships between Pi levels and carbohydrate also changed during the process. During the first stages of senescence, daily variations in Pi were related with changes in the starch/sucrose ratio Pi content also seemed to be related to the loss of RuBP-Carboxylase activity. At later stages of the process, the accumulation of carbohydrates in the leaves coincided with a rapid loss of RuBP-Case activity and photosynthesis but not with a substantial loss of inorganic phosphate of the leaves.

Expression of cyanobacterial and higher-plant ribulose 1,5-bisphosphate carboxylase genes in Escherichia coli

Expression strategies for the synthesis of higher-plant and cyanobacterial RuBP carboxylase genes in Escherichia coli have been developed to facilitate the study of the assembly pathway and properties of the enzyme’s large (L) and small (S) subunit proteins. The genes for the L and S subunits of the RuBP carboxylase of wheat and of a cyanobacterium, Synechococcus 6301 have been cloned into bacteriophage and plasmid vectors such that they are transcribed and translated in E. coli. To date no RuBP carboxylase activity has been detected in extracts prepared from E. coli cells synthesizing the wheat L and S subunits, although both gene products were present and soluble. Sucrose gradient analysis of cell extracts from E. coli synthesizing both L and S demonstrated that the soluble wheat L polypeptide was present as a large protein aggregate that contained no S subunits. With the cloned cyanobacterial genes, RuBP carboxylase activity could be recovered in E. coli cell extracts when the L and S gene products were synthesized from genes present on the same, or separate, replicons. Solubility and sedimentation studies of the cyanobacterial L subunits synthesized in the absence of S showed that the L subunit was soluble and present in E. coli as an L 8 structure. The E. coli extracts containing only the L subunit exhibited no detectable RuBP carboxylase activity. Infection of the E. coli cells containing L subunits with an M13 phage expressing the cyanobacterial S gene led to the assembly of functional RuBP carboxylase in these cells. This demonstrates the essential role of the S subunit in allowing the formation of an active enzyme.

Translocation of fixed carbon from symbiotic bacteria to host tissues in the gutless bivalve Solemya reidi

Solemya reidii (Bernard, 1980) were collected by Van Veen grab near a sewage outfall in California, USA, in spring/early summer of 1984 and 1985. Fixation of carbon dioxide by symbiotic chemoautotrophic bacteria in the gills, followed by translocation of the fixed carbon to symbiontfree tissues of the clam has been demonstrated using NaH14CO3 in two types of experiments. The first approach used the technique of tissue autoradiography to determine the exact sites of fixation of carbon dioxide and subsequent utilization of the fixed carbon compounds. Initial deposition (>95% after 10 min) was in the well defined portion of the gill filaments where the symbiotic bacteria reside. The heaviest redeposition of labeled carbon after a 2 d chase period was in the various glandular tissues of the clams (8 to 38% of the gill level). Levels in two of these glandular tissues decreased after a 5 d chase period, probably due to secretion. Significant labeling of muscle tissue, gonads, and the tips of the gill filaments occurred only after the chase periods. In the second approach, rates of initial carbon fixation by symbiotic bacteria and translocation into clam tissues were determined using pulse-chase experiments followed by dissections and assay of the clam tissues for radioactivity. Freshly caught clams fixed carbon at an average rate of 0.8 μmol CO2 g-1 wet weight h-1. In these fresh clams, 88% of the fixed carbon was found in the gills after 2 min incubation periods, with only 44% remaining in the gills after 1 to 1.7 h incubations. Individuals maintained in the laboratory for 100 d had only 5.8% of the RuBP carboxylase (a diagnostic enzyme for autotrophs) activity in their gills compared to freshly caught clams. After 2 min incubations in NaH14CO3, only 21% of the carbon fixed by the “old” clams was found in their gills, and the rate of incoporation into gill tissue was 5.7% of the rate in fresh individuals. These experiments demonstrate that the symbiotic bacteria fix carbon at a high rate, that a significant portion of the carbon fixed by the symbiotic bacteria (>45%) is translocated to the host, and that the translocated carbon is used by the host.