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1.
Summary Individual leaves of eastern cottonwood ( Populus deltoides Bartr.), representing an ontogenetic series from leaf plastochron index (LPI) 3.0 to 8.0, were fed 14CO 2 and harvested after 2–24 h. Importing leaves from LPI-1.0 through 8.0 on each plant were sectioned into 9 parts, and each part was quantitatively assayed for 14C activity. The highest level of 14C import was by leaves from LPI 1.0 to 3.0, irrespective of source-leaf age. 14C was translocated preferentially to either the right or left lamina-half depending on the position of the importing leaf in the phyllotactic sequence and its stage of development. For example, import was high when the importing leaf and the source leaf had two vascular bundles in common, moderately high with one bundle in common, and low with no bundles in common. The distribution of 14C within young importing leaves was highest in the lamina tip and decreased toward the base. With increasing leaf age, incorporation declined in the lamina tip and increased in the base.It may be concluded that each cottonwood leaf progresses through a continuum of importing and exporting stages as its lamina expands. The photosynthate imported by a given leaf is compartmentalized, with different exporting leaves supplying photosynthate to rather restricted regions of the lamina. Such localization within the importing leaf depends on its vascular connections with each of the exporting leaves, and these are predictable from a knowledge of the phyllotaxy.Plant Physiologists. 相似文献
2.
Phloem unloading in developing leaves of Beta vulgaris L. (`Klein E' multigerm) occurred from successively higher order branches of veins as leaves matured. Phloem unloading was studied in autoradiographs of leaf samples taken at various times during the arrival of a pulse of 14C-labeled photoassimilate. Extension of mass flow of sieve element contents into leaf vein branches was determined from the high level of radiolabel in veins soon after first arrival of the pulse. Rapid entry, indicative of mass flow through open sieve pores, occurred down to the fourth division of veins in young, importing leaves and to the fifth or terminal branch in importing regions near the zone of transition from sink to source. The rate of unloading decreased with leaf age, as evidenced by the increased time required for the vein-mesophyll demarcation to become obscured. The rate of import per unit leaf area, measured by steady state labeling with 14CO 2 also decreased as a leaf matured. The decline in import appeared to result from progressive changes that increased resistance to unloading of sieve elements and eventually terminated phloem unloading. 相似文献
3.
Summary Individual leaves of eastern cottonwood ( Populus deltoides), representing an ontogenetic series from leaf plastochron index 0.0 to 8.0, were fed 14CO 2 photosynthetically and then harvested at times ranging from 15 to 1440 min. The lamina of each fed leaf was sectioned from tip to base into 5 parts, and each part was quantitatively assayed for 14C activity. In young leaves, the percentage of the total 14C fixed (expressed in dpm/mg of dry leaf tissue) was high in the lamina tip and decreased almost linearly toward the base. With increasing leaf age, the percentage of 14C fixed decreased in the lamina tip and increased in the base. The relative activity in mature leaves was almost uniform throughout the lamina. No differences were detected in the 14C distribution patterns within leaves over the time series.On the basis of the data presented and of anatomical observations of developing cottonwood leaves, the hypothesis that the precociously mature lamina tip may provide photosynthates to the still-expanding lamina base was shown to be invalid. It is concluded that bidirectional transport in a developing cottonwood leaf results from simultaneous import to the immature basal region and export from the mature tip. 相似文献
4.
Leaf excision greatly affected the actual levels of 14C-assimilates in laminas and petioles of primary bean leaves ( Phaseolus vulgaris L.) following a transport period. However, it did not affect the percentage of starch in the insoluble residue; starch decreased from 20% of the insoluble residue after exposure to 14CO 2 to 3% after 5 hr in both attached and detached leaves. The transition from import to export of attached and detached leaves was at the same stage, i.e., when the cotyledons were 63 to 85% depleted. The composition of the 14C-assimilates in importing leaves was different from that in exporting leaves. In the former, only 5% of the soluble label was free sugar, while 74% was free sugar in the latter. The failure of importing leaves to export was not due to the labeled substances being nontransferable. Extracts from importing leaves applied to exporting leaves were exported; these extracts were high in amino acids and organic acids but low in free sugar. However, exporting leaves exposed to 14CO 2 appeared to export sugars more readily than amino acids. Cotyledon excision did not delay transition of leaves from import to export. Actually, excision seemed to enhance slightly the transition of the primary leaves from import to export. 相似文献
5.
Microautoradiography was used to follow the translocation pathways of 14C-labeled photosynthate from mature source leaves, through the stem, to immature sink leaves three nodes above. Translocation occurred in specific bundles of the midveins and petioles of both the source and sink leaves and in the interjacent internodes. When each of six major veins in the lamina of an exporting leaf was independently spot-fed 14CO 2, label was exported through specific bundles in the petiole associated with that vein. When the whole lamina of a mature source leaf was fed 14CO 2, export occurred through all bundles of the lamina, but acropetal export in the stem was confined to bundles serving certain immature sink leaves. Cross-transfer occurred within the stem via phloem bridges. Leaves approaching maturity translocated photosynthate bidirectionally in adjacent subsidiary bundles of the petiole. That is, petiolar bundles serving the lamina apex were exporting unlabeled photosynthate while those serving the lamina base were simultaneously importing labeled photosynthate. The petioles and midveins of maturing leaves were strong sinks for photosynthate, which was diverted from the export front to differentiating structural tissues. The data support the idea of bidirectional transport in adjacent bundles of the petiole and possibly in adjacent sieve tubes within an individual bundle.Abbreviations C
central leaf trace
- L
left leaf trace
- LPI
leaf plastochron index
- R
right leaf trace 相似文献
6.
A search for source leaf sucrose pools that differed in their relation to export was carried out in photosynthesizing leaves of Beta vulgaris L. The time course of depletion of [ 14C]sucrose in a leaf in unlabeled CO 2 following steady state labeling provided evidence for two distinct sucrose pools. After the start of the light period, leaf blade sucrose remained constant although it exchanged between the two pools. Newly synthesized sucrose destined for export passed through one pool more rapidly than through the other. All of the leaf blade sucrose appeared to exchange with export sucrose. Modeling and regression analysis of [ 14C]sucrose data provided a means for estimating the size of the two pools. From 20 to 40% of the sucrose was calculated to be present in the pool that provided the less direct path to export; this was likely vacuolar sucrose. The remainder of the sucrose in the blade was probably in the cytoplasm and veins. Added amounts of leaf blade sucrose, produced in response to elevated CO 2, appeared to be stored mainly in the vacuolar compartment. 相似文献
7.
Changes in growth parameters and 14CO 2 and [U- 14C]-sucrose incorporation into the primary metabolic pools and essential oil were investigated in leaves and stems of M. spicata treated with etherel and gibberellic acid (GA). Compared to the control, GA and etherel treatments induced significant phenotypic
changes and a decrease in chlorophyll content, CO 2 exchange rate, and stomatal conductance. Treatment with etherel led to increased total incorporation of 14CO 2 into the leaves wheras total incorporation from 14C sucrose was decreased. When 14CO 2 was fed, the incorporation into the ethanol soluble fraction, sugars, organic acids, and essential oil was significantly
higher in etherel treated leaves than in the control. However, [U- 14C]-sucrose feeding led to decreased label incorporation in the ethanol-soluble fraction, sugars, organic acids, and essential
oils compared to the control. When 14CO 2 was fed to GA treated leaves, label incorporation in ethanol-insoluble fraction, sugars, and oils was significantly higher
than in the control. In contrast, when [U- 14C]-sucrose was fed the incorporation in the ethanol soluble fraction, sugars, organic acids, and oil was significantly lower
than in the control. Hence the hormone treatment induces a differential utilization of precursors for oil biosynthesis and
accumulation and differences in partitioning of label between leaf and stem. Etherel and GA influence the partitioning of
primary photosynthetic metabolites and thus modify plant growth and essential oil accumulation.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
8.
Mature leaves of a variegated cultivar of Coleus blumei Benth. with a green border and central albino region constitute a source-sink system suitable for studies on assimilate partitioning. Leaves treated with 14CO 2 on a small part of the intact green border export assimilate via the shortest path into the stem. Leaves with all but a small lobe of the green border removed show different partitioning of labeled assimilates when the leaf is exposed to 14CO 2 (Fisher and Eschrich, 1985): The whole albino region of the leaf is supplied but no tracer is exported into the stem. When the green border is completely removed, 14CO 2-treatment of the albino region leads to the fixation of CO 2, obviously by PEP carboxylase, as indicated by the occurrence of labeled malate. Results show that the albino region of the variegated leaf constitutes a potential sink when deprived of its green border. In addition, CO 2-fixation by PEP carboxylase in albino tissue seems to indicate a common capacity of leaves which is normally masked by photosynthesis. The difference of assimilate partitioning between leaves with intact and leaves with partly removed green borders demonstrates that the unlabeled assimilates control the movement of labeled assimilates. 相似文献
9.
The effects of infection of root systems by Plasmodiophora brassicae on the translocation of 14C-labelled assimilates from the first and third leaves of cabbage seedlings were investigated. During the early phases of Plasmodium development, there were small differences in the distribution patterns of 14C-labelled assimilate between healthy and infected seedlings. At the end of growth of plasmodia and during resting spore formation, both first and third leaves exported more assimilates than corresponding leaves of healthy seedlings. When the infected roots were dissected into various regions after exposure of the fed leaves to 14CO 2, more assimilate accumulated in the club root region than in any other part. 相似文献
10.
Partitioning of current photosynthates towards primary metabolites and its simultaneous incorporation in leaf alkaloids was investigated in developing leaves of medicinally important Catharanthus roseus. Of the total 14CO 2 assimilated, the leaves at positions 1–6 fixed 8, 22, 25, 19, 13, and 8 %, respectively, and stem 3 %. Leaf fresh mass, chlorophyll content, and CO 2 exchange rate increased up to the third leaf. The total alkaloid content was highest in young actively growing leaves, which declined with age. Total 14C fixed and its content in ethanol soluble fraction increased up to the third leaf and then declined. The 14C content in primary metabolites such as sugars and organic acids was also highest in the 3 rd leaf. The utilization of 14C assimilates into alkaloids was maximum in youngest leaf which declined with leaf age. Hence the capacity to synthesize alkaloids was highest in young growing leaves and metabolites from photosynthetic pathway were most efficiently utilized and incorporated into alkaloid biosynthetic pathway by young growing leaves. 相似文献
11.
Roots of Vitis vinifera L., were treated with benzyladenine when the plant shoots were 38 cm long. Seventy-two hours after benzyladenine treatment, apical or basal leaves on separate shoots were exposed to 14CO 2. Control shoots received 14CO 2 but no benzyladenine. Application of benzyladenine directed 14C-photosynthate to roots, but a small amount of radioactivity was detected in the shoot tip when 14CO 2 was administered to an apical leaf. Distribution of radioactivity among the sugar, organic acid, and amino acid fractions was altered by benzyladenine treatment. In all parts of plants with roots treated with benzyladenine and apical leaf fed 14CO 2, the percentage of the total label in the sugar fraction comprised of fructose was generally more than twice that in control plants. 相似文献
12.
Glucose metabolism of healthy and tobacco mosaic virus-infected leaf-discs of Nicotiana tabocum L. var. Xanthi showing local-necrotic lesions was investigated using glucose- 14C. Local lesion formation following inoculation with tobacco mosaic virus resulted in enhanced glucose metabolism reflected by an increased rate of release of 14CO 2 from glucose-U- 14C and greater incorporation of 14C into all cell fractions. When specifically labelled glucose was fed to healthy and tobacco mosaic virus infected leaves, the C 6/C 1 ratio (rate of release of 14CO 2 from glucose-6- 14C/rate of release of 14CO 2 from glucose-l- 14C) was similar for healthy and virus-infected leaves. The C 6/C 1 ratios recorded from 0.30 to 0.50 indicate that both the glycolytic and pentose phosphate pathways participate in glucose catobolism in healthy and virus-infected leaves. Although the C 6/C 1 ratio was the same as that of the healthy leaf the rate of release of 14CO 2 from glucose-6- 14C and glucose-1- 14C was greatly increased in the virus-infected leaf. The increased glucose catabolism occurs by both glycolytic and pentose phosphate pathways in the virus-infected leaf. 相似文献
13.
A spring wheat crop was grown at ambient and elevated (550 μmol mol ?1) CO 2 concentrations under free-air CO 2 enrichment (FACE) in the field. Four experimental blocks, each comprising 21-m-diameter FACE and control experimental areas, were used. CO 2 elevation was maintained day and night from crop emergence to final grain harvest. This experiment provided a unique opportunity to examine the hypothesis that CO 2 elevation in the field would lead to acclimatory changes within the photosynthetic apparatus under open field conditions and lo assess whether acclimation was affected by crop developmental stage, leaf ontogeny and leaf age. Change in the photosynthetic apparatus was assessed by measuring changes in the composition of total leaf and thylakoid polypeptides separated by SDS-PAGE. For leaves at completion of emergence of the blade, growth at the elevated CO 2 concentration had no apparent effect on the amount of any of the major proteins of the photosynthetic apparatus regardless of the leaf examined. Leaf 5 on the main stem was in full sunlight at emergence, but then became shaded progressively as 3–4 further leaves formed above with continued development of the crop. By 35 d following completion of blade emergence, leaf 5 was in shade. At this point, the chlorophyll alb ratio had declined by 26% both in plants grown at the control CO 2 concentration and in those grown at the elevated CO 2 concentration, which is indicative of shade acclimation. The ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) content declined by 45% in the control leaves, but by 60% in the leaves grown at the elevated CO 2 concentration. The light- harvesting complex of photosystcm II (LHCII) and the chlorophyll content showed no decrease and no difference between treatments, indicating that the decrease in Rubisco was not an effect of earlier senescence in the leaves at the elevated CO 2 concentration. Following completion of the emergence of the flag-leaf blade, the elevated-CO 2 treatment inhibited the further accumulation of Rubisco which was apparent in control leaves over the subsequent 14 d. From this point onwards, the flag leaves from both treatments showed a loss of Rubisco, which was far more pronounced in the elevated-CO 2 treatment, so that by 36 d the Rubisco content of these leaves was just 70% of that of the controls and by 52 d it was only 20%. At 36 d, there was no decline in chlorophyll, LHCII or the chloroplast ATPase coupling factor (CFI) in the elevated CO 2 concentration treatment relative to the control. By 52 d, all of these proteins showed a significant decline relative to the control. This indicates that the decreased concentration of Rubisco at this final stage probably reflected earlier senescence in the elevated-CO 2 treatment, but that this was preceded by a CO 2-concentration-dependent decline in Rubisco. 相似文献
14.
Chlorophyll and nitrogen contents were highest in leaves of middle position, similarly as photosynthetic efficiency represented by 14C fixation (maxima in leaf 5 from the top). All the leaves lost 14C after 2 weeks of 14CO 2 exposure. However, the reduction in radioactivity was less in young upper leaves than in the mature lower leaves. Leaves exported 14C-photosynthates to stem both above and below the exposed leaf. Very little radioactivity was recovered from the seeds of plants in which only first or second leaves were exposed to 14CO 2 implying thereby that the carbon contribution of first two leaves to seed filling was negligible. The contribution of leaves to seed filling increased with the leaf position up to the sixth leaf from the top and after the seventh leaf their contribution to seed filling declined gradually. 相似文献
15.
Light (about 3,000 foot-candles) neither increased nor decreased the sink strength of young, rapidly expanding leaves of Phaseolus vulgaris L. cv. Black Valentine, as measured by the comparative rates of import of 14C-labeled photosynthates by sink leaves in the light versus dark in short term experiments. Although irradiated sink leaves accumulated more 14C activity, the difference was fully accounted for by photosynthetic reabsorption of respiratory CO 2 derived from substrates translocated to the sink leaves. Maximum sink strength was attained when the sink leaf reached 7 to 8 cm2 in area (9 to 10% of its fully expanded size). Thereafter sink strength declined rapidly and asymptotically to a near zero value at about 45% final area. During this period, however, the rapid decline in translocation was offset by a rapid rise in the photosynthetic rate of the sink leaf, maintaining a near constant relative rate of dry weight increase until the sink leaf had expanded to about 17% of its final area. Although the increasing photosynthetic capacity was associated with a decreasing import capacity, suggesting that the rate of translocation to the sink leaf was controlled by the developing capacity of the sink leaf for photosynthesis, it was not possible to vary the total (true) translocation rate to the sink leaf by varying the photosynthetic rate of the sink leaf in short term light-dark experiments. Despite a high ratio of source to sink in these experiments, no evidence accrued that translocation into young bean leaves was ever sink-limited. 相似文献
16.
Summary The capacity of a growing leaf blade of Cucurbita pepo L. to import 14C-labelled photoassimilate is lost in a basipetal direction. Import into the lamina tip stops when the blade is 10% expanded. Development of the leaf progresses linearly with time and the lamina base stops importing when the blade is 45% expanded. Export capacity also develops basipetally and follows immediately the loss of import capacity, at least in the lamina base. The small amount of material initially exported from the leaf tip is redistributed to the still-importing leaf base, delaying export from the lamina until the blade is 35% expanded. Loss of import capacity by the petiole is both basipetal and dorsoventral. The proximal, adaxial portion of the petiole is the last region to cease importing 14C. Leaves of Beta vulgaris L. and Nicotiana tabacum L. also lose import capacity in a basipetal direction. 相似文献
17.
There is continuing controversy over whether a degree of C 4 photosynthetic metabolism exists in ears of C 3 cereals. In this context, CO 2 exchange and the initial products of photosynthesis were examined in flag leaf blades and various ear parts of two durum wheat ( Triticum durum Desf.) and two six-rowed barley ( Hordeum vulgare L.) cultivars. Three weeks after anthesis, the CO 2 compensation concentration at 210 mmol mol ?1 O 2 in durum wheat and barley ear parts was similar to or greater than that in flag leaves. The O 2 dependence of the CO 2 compensation concentration in durum wheat ear parts, as well as in the flag leaf blade, was linear, as expected for C 3 photosynthesis. In a complementary experiment, intact and attached ears and flag leaf blades of barley and durum wheat were radio-labelled with 14CO 2 during a 10s pulse, and the initial products of fixation were studied in various parts of the ears (awns, glumes, inner bracts and grains) and in the flag leaf blade. All tissues assimilated CO 2 mainly by the Calvin (C 3) cycle, with little fixation of 14CO 2 into the C 4 acids malate and aspartate (about 10% or less). These collective data support the conclusion that in the ear parts of these C 3 cereals C 4 photosynthetic metabolism is nil. 相似文献
18.
An advanced radiogasometric method for the study of plant leaf CO 2 exchange is presented. The method enables determination of the rates of CO 2 fixation, photorespiration and respiration in the light under steady‐state photosynthesis and discrimination between primary and stored photosynthates as substrates of photorespiratory and respiratory decarboxylations. The method is based on the analysis of the time curves of 14CO 2 evolution from labeled primary and stored photosynthates in leaves previously exposed to 14CO 2. The molar rates of different decarboxylation reactions are calculated from the initial slopes of the curves taking into account the specific radioactivity of CO 2 fed to leaves and/or evolved from leaves. To estimate the contribution of primary and stored photosynthates, the measurements of 14CO 2 evolution are performed after feeding plant leaves for different periods with 14CO 2. Photorespiration and respiration are distinguished on the basis of data obtained from measurements of 14CO 2 evolution under normal (210 ml l −1) and low (15 ml l −1) concentrations of oxygen. A principally new method for the determination of the rate of intracellular refixation of respiratory CO 2 has been developed. The method is based on the measurements of 14CO 2 evolution from leaves into the medium of very high concentrations (30 ml l −1) of 12CO 2, where the probability of refixation of 14CO 2 evolved inside the cell is close to zero. The results obtained were comparable with the data derived from parallel refixation measurements by means of gasometric methods. As an example of application, the data on CO 2 exchange in leaves of two contrasting groups of C 3‐species, differing in the ability of starch accumulation, are presented. 相似文献
19.
Chlorophyll fluorescence and internal patterns of 14CO 2 fixation were measured in sun and shade leaves of spinach after treatment with various light intensities. When sun leaves were irradiated with 2000μmol m ?2 s ?1 for 2h, FV/ FM decreased by about 15%, but 14CO 2 fixation was unaffected, whereas shade leaves exhibited a 21% decrease in Fv/ FM and a 25% decrease in 14CO 2 fixation. Irradiation of sun and shade leaves with 4000μmol m ?1 for 4 h decreased F V/ FM by 30% in sun leaves and 40% in shade leaves, while total 14CO 2 fixation decreased by 41% in sun leaves and 55% in shade leaves. After light treatment, gradients of CO 2 fixation across leaves were determined by measuring 14CO 2 fixed in paradermal leaf sections after a 10s pulse of 14CO 2. Gradients of 14CO 2 fixation in control sun and shade leaves were identified when expressed on a relative basis and normalized for leaf depth. Treatment of leaves with 2000 μmol PAR m ?2 s ?1 for 2h did not after patterns of carbon fixation across sun leaves, but slightly altered the pattern in shade leaves. In contrast, treatment of sun and shade leaves with 4000μmol m ?2 s ?1 for 4h decreased carbon fixation more in the palisade mesophyll cells than in the spongy mesophyll cells of sun and shade leaves, and fixation in medial tissue of shade leaves was dramatically decreased compared to the adaxial and abaxial tissue. The interaction between leaf anatomy and biochemical parameters involved in tolerance to photoinhibition in spinach is discussed. 相似文献
20.
When single leaves attached at a given node were allowed to carry on photosynthesis in 14CO 2 for 30 min, younger plants showed a higher proportion of upward translocation than did older plants. Downward translocation of 14C-photosynthate was stimulated by ATP pre-treatment of the translocating leaf, while upward translocation was not affected by ATP. A similar phenomenon was observed in the translocation of 14C-sucrose infiltrated into a leaf with or without ATP. Downward translocation of photosynthate was inhibited by DNP pre-treatment of a fed leaf. Upward translocation, however, was not affected by DNP. Thirty min after infiltration of 14C-glucose into a leaf, almost all the 14C translocated upwards was found to be in the form of glucose, while a great part of the 14C translocated downwards was in the form of sucrose. In the case of translocation of infiltrated 14C-sucrose, 14C found both above and below the fed leaf was mainly in the form of sucrose. 相似文献
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