Translocation Of Photosynthates Research Articles

The rolC promoter of Agrobacterium rhizogenes Ri plasmid is activated by sucrose in transgenic tobacco plants.

The 5'-upstream region of the rolC gene of the Ri plasmid is expressed specifically in phloem cells of transgenic higher plants. In this study, we demonstrated that the rolC promoter is activated by sucrose in phloem cells of transgenic tobacco seedlings bearing rolC promoter-uidA chimeric fusion gene. Since the rolC promoter is not activated by sorbitol, sucrose metabolism rather than osmotic pressure exerted by the disaccharide may be responsible for induction. Thus, experiments using 5'-upstream deletion mutants, internal deletion mutants, and chimeric constructs with a heterologous promoter (-90 region of the cauliflower mosaic virus 35S promoter) were conducted to define the region of the rolC promoter involved in sucrose activation. The results indicated that a cis-acting sucrose responsive region of the rolC promoter is located between -135 and -94 bp with respect to the transcription initiation site. In phloem cells, high concentrations of sucrose are encountered owing to ongoing translocation of photosynthates from source to sink tissues. Therefore, sucrose as a signal molecule may regulate the phloem-specific expression of the rolC promoter.

Dry Matter Production, Yield, and Allocation of Carbon‐14 Assimilates by Wheat as Affected by Nitrogen Source and Salinity

AbstractWheat (Triticum aestivum L.) growth is affected by both salinity and the type of N fed to the plants. The objective of this research was to determine the effect of salinity applied at different stages of the life cycle of wheat plants supplied with either NH4 or NO3 on growth, yield, and translocation of photosynthates. Plants were grown in sand culture irrigated with nutrient solution until maturity. The nutrient solution contained 4 mM N, either as (NH4)2SO4 or Ca(NO3)2. Salinity (60 mM NaCl) was applied to the nutrient solution at 19, 70, and 92 d after sowing. Some of the plants received 14CO2 pulses 100 d after sowing, and 14C distribution in each plant part was determined 24 h later. Dry biomass production and grain yield were reduced when salinity was applied 19 d after sowing (beginning of the vegetative stage), whereas no effect of NaCl was observed when salinity was applied later. Ammonium‐fed plants always produced more tillers and spikes than NO3‐fed plants. Total grain yield was similar with plants growing in either N form. Nitrate‐treated plants produced fewer, but heavier, spikes due to a larger number of grains per spike than NH4‐fed plants. Ammonium‐fed plants showed a preferential allocation of 14C‐assimilates to young developing tillers. Nitrate‐fed plants, under similar conditions, allocated assimilates preferentially to grain. Salinity enhanced translocation of assimilates to the spikes when plants were grown with NO3.

Comparison of Osmotic Adjustment Responses to Water and Temperature Stresses in Spring Wheat and Sudangrass

This study explores the mechanisms of osmotic adjustment by comparing the growth of spring wheat and sudangrass, which exhibit different degrees of osmotic adjustment, under soil water and temperature stresses. Leaf water potential (ψ 1), osmotic potential (π), and rate of leaf area growth of spring wheat and sudangrass seedlings were measured at combinations of five soil water potentials, from -0·03 to -0·25 MPa, and six root temperatures, from 14 to 36°C. Spring wheat exhibit little osmotic adjustment. The leaf osmotic potential was not affected by either soil water or root temperature stress. Osmotic potential of sudangrass decreased in parallel with the decreasing leaf water potential as a result of osmotic adjustment. As soil water potential decreased from -0·03 to -0·25 MPa, the rates of growth and photosynthesis of spring wheat both decreased by about 30%. For sudangrass with the same range of soil water potential, the photosynthesis rate decreased by only 10% while the leaf area growth rate decreased by 49%. We introduce a dimensionless index (R) to quantify the degree to which environmental stresses alter the balance between production of photosynthates and their use for growth. The index, R, is equal to 1 when stress reduces growth and photosynthesis by the same degree, i.e. the balance between production and consumption of photosynthate is not disturbed. R is smaller than 1 when growth is reduced more than photosynthesis. R was equal to 1 for spring wheat where there was no osmotic adjustment. For sudangrass, R decreased from 1 to 0·25 as osmotic potential decreased from -1·10 to -1·63 MPa. These findings lead to the hypothesis that osmotic adjustment could result from an imbalance between production, consumption and translocation of photosynthates under stressed conditions.

共生藻の光合成と光合成産物の宿主への移行

共生藻の光合成と光合成産物の宿主への移行

TRANSLOCATION AND USE OF 14C-LABELED PHOTOSYNTHATES FROM SENESCING `CARIGNANE' GRAPEVINE LEAVES AND THEIR STORAGE IN OTHER PARTS OF THE PLANT

The extent of translocation of 14C-labeled photosynthates from the senescent leaf to the parent vine before leaf abscission and the short-term effects of premature leaf removal on the carbohydrate balance of the vine were studied by using autoradiography and trapping 14CO2 respired from the treated leaf. The treated leaf abscissed 1.5 days after administering the label. The plant was harvested after natural leaf abscission. The radioactivity recovered from the plant, excluding the treated leaf, was 20% of the input. Radioactivity was detected in the roots, trunk, shoot, and leaves. Most of the radioactivity remained in the trunk and the young and old roots. The implications of premature leaf removal by mechanical harvesting on the carbohydrate balance of the vine are discussed.

14CO2 Assimilation and Translocation of 14C‐Photosynthates by Different Parts of Indian Mustard (Brassica juncea L.)

AbstractThe role of leaves, stem and reproductive parts in 14CO2 fixation and subsequent photosynthate translocation was studied in Indian mustard (Brassica juncea L.) at three growth stages. The data indicated that leaves, stem and pods are important sources of photosynthates for seed filling. At bud emergence stage leaves are the principle site of 14CO2, fixation. The contribution of leaves declines at subsequent stages, where as the contribution of pod walls increased from bud emergence stage to ripening stage. The contribution of the stem remains more or less constant at all three growth stages studied. Although stem can fix 14CO2, at bud emergence and flowering stages it imported 14C‐photosynthates from leaves. However, stem exported photosynthates during subsequent growth stages.

MOLECULAR CLONING OF cDNA-ENCODING SORBITOL-6-PHOSPHATE DEHYDROGENASE FROM APPLE

Sorbitol plays a important role in the translocation of photosynthate in apple. Sorbitol-6-phosphate dehydrogenase (S6PDH, is the key enzyme regulating sorbitol biosynthesis. The cloning of functional gene like S6PDH provides the potential to elucidate the mechanism of production and translocation of sugar in the Rosaceae family and to manipulate endogenous sorbitol production in horticultural crops. Poly(A)+RNA was prepared from apple seedlings and cDNA library constructed in an expression vector was screened by the loquat-S6PDH antibody prepared by Hirai (Natl. Res. Inst. Veg. Ornam. Plants & Tea, Japan). The cloned cDNA contained an open reading frame of 930 base pairs encoding a sequence of 310 amino acids. Identification of the cDNA was accomplished by expression of active enzyme in Escherichia coli harboring the cDNA and by the presence of a partial amino acid sequence identical to that found in the purified enzyme. Northern blot analysis showed the expression of S6PDH gene in apple seedlings.

Carbohydrate dynamics in mature Pinuselliottii var. elliottii trees

Starch is the main carbohydrate storage form in conifers and is derived from the translocation of photosynthate (soluble sugars) in the phloem. We examined seasonal patterns in concentrations of both carbohydrate forms in the needles, twigs and branches, stems, and coarse and fine roots of mature Pinuselliottii Engelm. var. elliottii trees in a north Florida plantation. Starch showed marked and similar seasonality in all the tissues, with maxima in the late winter near the time of the inception of new growth in the spring. Sugars showed little seasonality, except in the fine roots. Repeated fertilization had little effect on either sugar or starch concentrations in all tissues. Using published biomass data from these same stands, we estimated that coarse roots store more than half of the starch in these stands over the year, with foliage and fine roots storing less than 5%.

Evidence for a plasma membrane proton pump in phloem cells of higher plants

Metabolic energy is required for the loading of sucrose into the phloem and translocation of sugars throughout the plant. The proton electrochemical gradient generated by a plasma membrane proton pump (H(+)-ATPase) is thought to provide energy for these processes. The plasma membrane H(+)-ATPase is encoded by a multigene family in Arabidopsis thaliana. Here we characterize the expression of isoform AHA3 (Arabidopsis H(+)-ATPase isoform 3). The AHA3 mRNA start site was mapped and 464 bp of the putative upstream regulatory region sequenced. A translational fusion of AHA3 to the beta-glucuronidase (GUS) reporter gene was constructed and used to generate transgenic Nicotiana and Arabidopsis plants. Using a histochemical stain, expression of the AHA3/GUS fusion was found predominantly in phloem cells of leaves, stems, roots, and flowers. Biochemical measurements of GUS activity in pith and vascular explants confirmed the histochemical localization. Our results support the hypothesis that a proton pump is present in phloem cells, possibly providing energy to drive plasma membrane cotransport systems required for phloem loading and translocation of photosynthates. In addition to AHA3/GUS expression in phloem, expression was observed in pollen and regions of the ovule, tissues whose physiological functions correlate with a requirement for high levels of solute transport.

Phyto‐ and necromass above and below ground in a fen

Few investigations deal with the subterranean phytomass in fens (minerotrophic peatlands), their results differing widely. This study was carried out in a “rich fen” in central Sweden, and involved excavation of peat monoliths, depth‐sectioning and hand‐sorting as to species, type of organ, and living or dead condition. The below‐ground living phytomass was large, over 4 kg m−2 in each of two sample plots, being no <97–96% in the dominants, Carex limosa and C. lasiocarpa, 89% on average in Menyanthes trifoliata, and c. 93% for all species. Carex limosa had its rhizome maximum slightly higher than C. lasiocarpa, but a greater part of its roots penetrated deeper. For Menyanthes, also net annual production above and below ground was estimated. The subterranean phytomass decreased with depth, but living roots were found even at 42 cm. The recognizable necromass did not decrease with depth. These recent constituents would render a very unequal age to the peat. The imbalance between the small green aerial phytomass and the much greater subterranean phytomass was emphasized. It could be related to a relatively very great translocation of photosynthates from above to below ground, and/or to longevity of below‐ground organs, the latter at least in Menyanthes.

Potential contribution of carbon by microphytic crusts in pinyon-juniper woodlands

Abstract We examined the possibility that microphytic crusts (terrestrial algae, cyanobacteria, lichens, and mosses) contribute organ carbon fixed in photosynthesis directly to the soil ecosystem. Microphytic crusts and their underlying soils were collected from pinyon‐juniper woodlands in the fall and in spring. Samples of these crusts were exposed to 14 CO2‐labeled atmosphere. In general, a downward translocation of photosynthate over time from the crust was demonstrated by an increase in 14C content in the soils beneath the crusts. Following a 30‐min exposure to labeled atmosphere, the crusts accumulated as much as 55 × 103 disintegrations per minute (dpm) for a 0.1‐mL subsample volume (in the spring), leveling off about 25 × 103 dpm 10 and 21 days later. The crusts respired from 34 to 36% of the initial fixed carbon. The underlying soils accumulated significant 14C (relative to background) in both fall and spring samples. The source of this increase in 14C radiation in the soil is attributable to carb...

The effect of resource integration on fitness related traits in a clonal dune perennial, Hydrocotyle bonariensis.

The costs and benefits of resource integration in Hydrocotyle bonariensis were examined by comparing severed and intact clones grown across multiple resource gradients. Basipetal movement of water, nitrogen and photosynthates was demonstrated to occur between two rhizome branch systems interconnecting hundreds of ramets within a clone. Hydrocotyle clones of this size and larger have been shown to span highly patchy and unpredictable resource conditions in coastal dune environments. The extensive movement of water and nitrogen to portions of a clone deficient in these resources, resulted in a significant net benefit to the clone in terms of fitness-related traits: total biomass, ramet proliferation and seed production. The translocation of photosynthates across light gradients allowed for sexual reproduction and clonal expansion in the shade although this incurred a net cost to the clone in terms of ramet and seed production.

The effect of water status and season on the incorporation of 14CO2 and [14C]‐acetate into resin and rubber fractions in guayule

The effects of drought stress and season on both allocation of photosynthates to stems and leaves and potential for stem rubber synthesis were studied in guayule (Parthenium argentatum Gray USDA line 11604). Two‐year‐old plants grown under field conditions in the Negev desert of Israel were subjected to different irrigation regimes, and water status was assessed by measuring the relative water content (RWC). Undetached plant tips were exposed to a 1 h pulse of 14CO2, followed by a 24 h chase. 14C fixed and translocated to different plants parts and notably 14C incorporation into rubber and resin fractions was determined. The potential of detached branch slices to incorporate [14C]‐acetate into rubber was also studied. A higher percentage of fixed 14C was translocated from shoot tips in winter (28–30%) than in summer (15–18%). The percentage of [14C]‐acctate incorporated into the rubber fraction by stem slices was maximal in winter (20%) and minimal in summer (3–5%) in both cases in the absence of drought stress. In summer the translocation of photosynthates into stems was inversely related to plant RWC, dropping from 18% three days after irrigation to 3% 14 days later, and the potential of stems to synthesise rubber was high under drought conditions and low in well irrigated plants.

Response of wheat growth and CO2 assimilation to altering root-zone temperature

Wheat plants (Triticum aestivum L. var. Chisholm) grown at an air temperature of 23 °C and a root-zone temperature of 3 °C exhibited a significant reduction in shoot and root dry weight and leaf area compared with plants grown at a root-zone temperature of 23 °C. This reduction was correlated with a significantly lower CO2 assimilation rate that was associated with lower leaf conductance, lower internal CO2 concentration, and more negative water potential. Low CO2 assimilation rate was also associated with high starch and total soluble sugar levels in the shoot, less translocation of photosynthate, and possibly less sink demand. Leaf chlorophyll concentration was not affected by altering the root-zone temperature, whereas water use efficiency of plants grown at a root-zone temperature of 3 °C was as much as 1.5 times higher as those grown at 23 °C. Key words: carbohydrate, chlorophyll, photosynthate partitioning, leaf conductance, water potential, water use efficiency.

Photosynthetic Carbon Production and Use by Developing Cotton Leaves and Bolls

Understanding the photosynthetic C contribution of leaves to vegetative and reproductive processes is important in defining yield productivity. However, the morphological complexity of the cotton (Gossypium hirsutum L.) canopy has proven a significant barrier to establishing specific yield relationships. Therefore, a 2‐yr study examined the developmental sequences of C production and utilization by leaves and bolls within the crop canopy. Photosynthesis of sympodial leaves reached a maximum just prior to anthesis of the subtended flower and thereafter declined throughout the boll‐filling period. Carbon budgets for individual sympodial leaves and their subtended bolls at mainstem Nodes 8, 10, and 12 indicated that C production was seldom synchronized with C utilization. Carbon import requirements for the first three fruiting positions at mainstem Node 10 were 50,37, and 21%, respectively. Bolls at mainstem Node 8 collectively required >60% import of C to sustain growth during the season. Only at mainstem Node 12 were leaves capable of supplying the total C needs of their subtended bolls. Carbon deficiencies at mainstem Nodes 8 and 10 suggested that substantial translocation of photosynthate from adjacent leaves and leaves outside the mainstem node was necessary. This was confirmed through short‐term studies of l4C‐assimilate movement from leaves to developing cotton bolls. Breeding goals for improved C production by leaves were simulated to evaluate avenues for increased yields through crop genetics. These simulations indicated an advantage of increased leaf longevity in the maintenance of C production.

Photosynthetic Response of Wheat to Soil Water Deficits in the Tropics

AbstractThe changes in photosynthetic rate and translocation of photosynthates in winter wheat (Triticum Aestivum L.) grown in lysimeters were studied, in response to periodic soil water deficit during late tillering and flowering stages. Soil water deficits were imposed to previously nonstressed plants during late tillering and flowering states. Timing of irrigation was scheduled according to the ratio between irrigation water applied and cumulative pan evaporation (IW/CPE) of 0.75 (low deficit), and 0.5 (moderate deficit), as well as by suspending irrigations after crown root initiation stage (severe deficit). To determine the rate of photosynthesis, a short radioactive pulse of 14CO2 with 300 ppm concentration was given to second leaf from the top at tillering, and to the flag leaf at flowering stages for 20 second exposure time. The translocation of photosynthates was estimated by scanning 14C activity in different plant parts. In late tillering the midday Photosynthetic rate (PR) was significantly 3 mg CO2 dm−2 h−1 lower under low water deficit (WD1) than under zero water deficit (WD0). Under higher stress conditions, soil water acted as a limiting factor to keep the rate from rising above 13.2 during stress at late tillering (WD2), 14.5 flowering (WD4), and 10.0 mg CO2 dm−2 h−1 for stress at both the growth stages (WD5), respectively. The difference in daily accumulated photosynthesis (8 h), between stressed and nonstressed were 15, 40, 42, and 77 mg CO2 dm−2 h−1 respectively at WD1 WD2, WD4, and WD5. The retention of 14C in flag leaf decreased considerably after 24 hours of exposure time when the labelled assimilates were translocated in bulk to the ear head. Under stressed condition a general trend was observed for upward translocation of assimilates towards the ear, even from the stem and root. The percent 14C activity observed in ear after 24 hours was greatest in severely stressed plants. The photosynthetic rate is reasonable predicted by midday LDR and surface moisture.

Leaf vascular architecture in the atypical C4 NADP – malic enzyme grass Arundinella hirta

Leaf anatomy, particularly vascular organization, of the grass species Arundinella hirta is atypical for a C4 NADP – malic enzyme species. Most conspicuously, interveinal distances are large, more similar to those of C3 than C4 species. When the longitudinal files of the bundle-sheath-like distinctive cells are included with vein counts, interveinal distance falls within the range for the C4 NADP – malic enzyme biochemical type. A quantitative analysis of the lengths of distinctive cell files shows that ca. 22% lack any contact with transverse veins or other vascular tissue. This reinforces the idea that the functional significance of typical C4 anatomy is the spatial relationship between bundle sheath tissue and mesophyll. While the general features of blade and sheath vascular architecture of A. hirta are shared with other C3 and C4 grass species, the wide vein spacing potentially creates limitations on the rate of loading photosynthate into vein phloem that are not experienced by other C4 species. Measurements of phloem cross-sectional area per vein and total phloem cross-sectional area give no indication of a constriction in conductive capacity within the leaf blade or sheath. These observations provide an essential background for studies of short- and long-distance translocation of 14C-labelled photosynthate in this atypical species.

Potato Leafhopper (Homoptera: Cicadellidae) Feeding Disruption of Phloem Translocation in Alfalfa

Histological and artificial injury (leafhopper injury simulation) studies of potato leafhopper, Empoasca fabae (Harris), injury to alfalfa, Medicago sativa L., have suggested that leafhopper feeding disrupts photosynthate translocation. To test directly for this disruption, we compared the distribution of radioactive, CO2-derived photosynthate in leafhopper-injured and healthy (uninjured) alfalfa stems. Exposure to two adult potato leafhoppers, confined for 3 d on the top 10 cm of alfalfa stems, reduced the upward flow of labeled translocate to the stem tips 300-fold and produced an accumulation of assimilates in the lower stem 2.4 times that of uninjured stems. Similar disruptions of translocation were achieved by caging two leafhopper adults for > 6 h to the fourth internodes of stems. Stem exposure for these shorter durations resulted in a 3.7-fold decrease in tagged photosynthate at the tips of injured stems. Also, twice as much tagged translocate was found at the leafhopper-exposed site compared with the same internode of uninjured stems. No evidence of recovery by alfalfa from such phloem disruption, resulting from a 6 or 12 h exposure to two adult leafhoppers, was found 4 d after leafhopper removal.

Yield Loss in Sweet Corn in Response to Defoliation or Infection by Exserohilum turcicum

Abstract Net CO2 assimilation was reduced in sites of infection by Exserohilum turcicum in leaves of Seneca 60 sweet corn before lesions appeared. In leaf tissue adjacent to infected areas, there was an early small increase in CO2 assimilation followed by a gradual decline to nearly 0 net CO2 exchange by 7 days after inoculation. Translocation of photosynthates in to disease lesions from healthy tissue distal to the lesions was observed within 1 h after exposure of 1.2–cm2 areas of the leaf blade to 14CO2. No translocation from lesions to healthy leaf tissue was observed. The effects of defoliation at specific leaf positions on yield of sweet corn plants were accurately simulated by a model in which yield is expressed as a function of healthy leaf area absorption of incident insolation. Removal of leaves from the bottom third of the plants caused no yield loss, whereas removal of leaves above the ear caused significant losses. The model underes, timated the yield loss caused by infection by E. turcicum by approximately 22 %. The observed effects of infection by E. turcicum on photosynthetic efficiency in leaf tissue adjacent to lesions and on translocation of photosynthates into lesion from distal parts of the leaf show that the effect of northern leaf blight on yield is greater than can be accounted for by the direct loss of healthy leaf area through necrosis within disease lesions.

Ammonia Gas Temporarily Interrupts Translocation of 11C Photosynthate in Sunflower

Experiments are reported where it is shown that loading into veins and translocation in phloem is inhibited by treatment of leaves and stems with small amounts of ammonia gas