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1.
Factors concerning the chloroplast disposition in bundle sheathcells were investigated in finger millet (Eleusine coracanaGaertn.), and NAD malic enzyme type C4 plant with the centripetalarrangement of bundle sheath chloroplasts. Segments were cutfrom immature regions of emerging leaves in which the centripetalarrangement of bundle sheath chloroplasts had not yet been established.The leaf segments were floated on solutions with or withoutreagents. Sections were made of the segments at time intervalsand the distribution of bundle sheath chloroplasts was observedby light microscopy. The bundle sheath chloroplasts migratedto the vascular bundle and established a centripetal arrangementby 12-16 h in control solutions. Auxins, cycloheximide and cytochalasinB inhibited the disposition of bundle sheath chloroplasts whilechloramphenicol and colchicine had no effect. The inhibitoryeffect of auxins appeared only at early stages of chloroplastmigration while cycloheximide and cytochalasin B were effectiveeven at later stages. Cessation of elongation growth, cytoplasmicprotein synthesis and microfilaments seemed to be associatedwith the centripetal disposition of bundle sheath chloroplasts.Copyright1993, 1999 Academic Press Bundle sheath chloroplast, C4 plant, chloroplast orientation, Eleusine coracana, finger millet  相似文献   

2.
Mitochondria and chloroplasts are structurally associated inthe bundle sheath cells of Portulaca oleracea L., an NAD malicenzyme type C4 plant. These associations occur in some restrictedregions where the mitochondrial cristae extend inwards. Exposureof plants to 1.0 µ11–1 SO2 for 3 h induced shrinkageof mitochondria of the bundle sheath cells, which further visualizedthe structural association between the organelles. C4 plant, chloroplast, mitochondrion, Portulaca oleracea, sulphur dioxide  相似文献   

3.
In C4 plants, bundle sheath (BS) chloroplasts are arranged inthe centripetal position or in the centrifugal position, althoughmesophyll (M) chloroplasts are evenly distributed along cellmembranes. To examine the molecular mechanism for the intracellulardisposition of these chloroplasts, we observed the distributionof actin filaments in BS and M cells of the C4 plants fingermillet (Eleusine coracana) and maize (Zea mays) using immunofluorescence.Fine actin filaments encircled chloroplasts in both cell types,and an actin network was observed adjacent to plasma membranes.The intracellular disposition of both chloroplasts in fingermillet was disrupted by centrifugal force but recovered within2 h in the dark. Actin filaments remained associated with chloroplastsduring recovery. We also examined the effects of inhibitorson the rearrangement of chloroplasts. Inhibitors of actin polymerization,myosin-based activities and cytosolic protein synthesis blockedmigration of chloroplasts. In contrast, a microtubule-depolymerizingdrug had no effect. These results show that C4 plants possessa mechanism for keeping chloroplasts in the home position whichis dependent on the actomyosin system and cytosolic proteinsynthesis but not tubulin or light.  相似文献   

4.
Light and electron microscopic observations of the leaf tissueof Panicum milioides showed that the bundle sheath cells containeda substantial number of chloroplasts and other organelles. Theradial arrangement of chlorenchymatous bundle sheath cells,designated as Kranz leaf anatomy, has been considered to bespecific to C4 plants. However, photosynthetic 14CO2 fixationand 14CO2 pulse-and-chase experiments revealed that the reductivepentosephosphate pathway was the main route operating in leavesof P. milioides. The interveinal distance of the leaves wasintermediate between C3and C4Gramineae species. These resultsindicate that P. milioides is a natural plant species havingchracteristics intermediate between C3 and C4 types. (Received March 6, 1975; )  相似文献   

5.
Chloroplast photorelocation movement is extensively studied in C3 but not C4 plants. C4 plants have two types of photosynthetic cells: mesophyll and bundle sheath cells. Mesophyll chloroplasts are randomly distributed along cell walls, whereas bundle sheath chloroplasts are located close to the vascular tissues or mesophyll cells depending on the plant species. The cell-specific C4 chloroplast arrangement is established during cell maturation, and is maintained throughout the life of the cell. However, only mesophyll chloroplasts can change their positions in response to environmental stresses. The migration pattern is unique to C4 plants and differs from that of C3 chloroplasts. in this mini-review, we highlight the cell-specific disposition of chloroplasts in C4 plants and discuss the possible physiological significances.Key words: abscisic acid, aggregative movement, avoidance movement, blue light, bundle sheath cell, C4 plant, chloroplast, cytoskeleton, environmental stress, mesophyll cellChloroplasts can change their intracellular positions to optimize photosynthetic activity and/or reduce photodamage occurring in response to light irradiation. On treating with high-intensity light, the chloroplasts move away from the light to minimize photodamage (avoidance response). Meanwhile, on irradiating with low-intensity light, they move toward the light source to maximize photosynthesis (accumulation response). These chloroplast-photorelocation movements are observed in a wide variety of plant species from green algae to seed plants,13 although little attention has been paid to C4 plants. There is a report stating that monocotyledonous C4 plants showed changes in the light transmission of leaves in response to blue light,4 although the direction of migration of the chloroplasts is not described.C4 plants have two types of photosynthetic cells: mesophyll (M) cells and bundle sheath (BS) cells, which have numerous well-developed chloroplasts. BS cells surround the vascular tissues, while M cells encircle the cylinders of the BS cells (Fig. 1). The C4 dicarboxylate cycle of photosynthetic carbon assimilation is distributed between the two cell types, and acts as a CO2 pump to concentrate CO2 in the BS chloroplasts.5,6 C4 plants are divided into three subtypes on the basis of decarboxylating enzymes: NADP-malic enzyme (ME), NAD-ME and phosphoenolpyruvate carboxykinase. Although the M chloroplasts of all C4 species are randomly distributed along the cell walls, BS chloroplasts are located either in a centripetal (close to the vascular tissue) or in a centrifugal (close to M cells) position, depending on the species (Fig. 1A).7 Thus, C4 M and BS cells have different systems for chloroplast positioning: an M cell-specific system for dispersing chloroplasts and a BS cell-specific system for holding chloroplasts in a centripetal or centrifugal disposition.Open in a separate windowFigure 1The intracellular arrangement of chloroplasts in finger millet (Eleusine coracana), an NAD-ME-type C4 plant. (A) Light micrograph of a transverse section of a leaf blade from a control plant. Bundle sheath (BS) cells surround the vascular tissues, while mesophyll (M) cells encircle the cylinders of the BS cells. BS chloroplasts are well developed, and are located in a centripetal position, whereas M chloroplasts are randomly distributed along the cell walls. B, bundle sheath cell; M, mesophyll cell; V, vascular bundle. (B) Transverse section of a leaf blade from a drought-stressed plant. Most M chloroplasts are aggregatively distributed toward the BS side, while the centripetal arrangement of BS chloroplasts is unchanged. (C and D) Transverse sections of leaf segments irradiated with blue light of intensity 500 µmol m−2 s−1 with or without 30 µM ABA for 8 h (C and D, respectively). The adaxial side of each leaf section (upper side in the photograph) was illuminated. In the absence of ABA, M chloroplasts exhibited avoidance movement on the illuminated side and aggregative movement on the opposite side. In the presence of ABA, aggregative movement was observed on both sides. Scale bars = 50 µm.  相似文献   

6.
The relationship between leaf anatomy, ultrastructure and carbondiscrimination was investigated in leaves of two F1hybrids (F1-1and F1-2) between two different types of the grassPanicum [anNAD-malic enzyme (ME) C4species], which differ in bundle sheathultrastructure. The female parent was Kabulabula grass, whichhas centrifugal chloroplasts in bundle sheath cells and is designatedan NAD-ME(F) species, while the male parent was Makarikari grass,which has centripetal chloroplasts in the bundle sheath cellsand is designated an NAD-ME(P) species. Suberin lamellae arepresent in Kabulabula grass but are lacking in Makarikari grass.Both F1hybrids had the same chromosome number (2n =36) as theparents but exhibited both univalent (about 45%) and bivalent(about 55%) chromosome pairing which was the major basis forthe identification of F1hybrids. In F1-1, elongated bundle sheathcell chloroplasts are arranged mainly in a centripetal position,similar to those in the male parent, Makarikari grass. In contrast,most of the bundle sheath cells in F1-2 are packed with starch-containingchloroplasts, although in some cells chloroplasts tended tobe centripetally arranged. In both F1hybrids, suberin lamellaewere found in the bundle sheath cell walls, similar to the femaleparent, Kabulabula grass. The 13C values of both F1hybrids were-11.4 to -11.7, almost the same as those of Kabulabula grass(-11.4), but significantly higher than those of Makarikari grass(-12.7). These results indicate that the chloroplast orientationin the bundle sheath cells and the presence of suberin lamellaeare not obligatorily linked in their expression and suggestthat suberin lamellae may play an important role in discriminationagainst13C. Panicum ; NAD-malic enzyme species; hybrid; chloroplast position; 13C discrimination; suberin lamellae  相似文献   

7.
Salsola arbusculiformis is identified as a C3–C4intermediatespecies based on anatomical, biochemical and physiological characteristics.This is the first report of a naturally occurring intermediatespecies in the Chenopodiaceae, the family with the largest numberof C4species amongst the dicots. In the genus Salsola, mostspecies have Salsoloid anatomy with Kranz type bundle sheathcells and C4photosynthesis, while a few species have Sympegmoidanatomy and were found to have non-Kranz type bundle sheathcells and C3photosynthesis. In the cylindrical leaves of C4Salsolawith Salsoloid type anatomy, there is a continuous layer ofdistinct, chlorenchymatous Kranz type bundle sheath cells surroundedby a single layer of mesophyll cells; whereas species with Sympegmoidtype anatomy have an indistinct bundle sheath with few chloroplastsand multiple layers of chlorenchymatous mesophyll cells. However,S. arbusculiformis has intermediate anatomical features. Whileit has two-to-three layers of mesophyll cells, characteristicof Sympegmoid anatomy, it has distinctive, Kranz-like bundlesheath cells with numerous chloroplasts and mitochondria. Measurementsof its CO2compensation point and CO2response of photosynthesisshow S. arbusculiformis functions as an intermediate specieswith reduced levels of photorespiration. The primary means ofreducing photorespiration is suggested to be by refixing photorespiredCO2in bundle sheath cells, since analysis of photosyntheticenzymes (activity and immunolocalization) and14CO2labellingof initial fixation products suggests minimal operation of aC4cycle. Copyright 2001 Annals of Botany Company Immunolocalization, photosynthetic enzymes, C3–C4intermediate, C4-plants, leaf anatomy, Chenopodiaceae, Salsola arbusculiformis  相似文献   

8.
Mitochondria were isolated from mesophyll protoplasts and bundlesheath protoplasts or strands which were obtained by enzymaticdigestion of six C4 species: Zea mays, Sorghum bicolor, Panicummiliaceum, Panicum capillare, Panicum maximum and Chloris gayana,representative of three C4 types. Photorespiratory glycine oxidationand related enzyme activities of mesophyll and bundle sheathmitochondria were compared. Mesophyll mitochondria showed good P/O ratios with malate andsuccinate as substrate but lacked the ability to oxidize glycine.On the other hand, mitochondria isolated from bundle sheathprotoplasts of P. miliaceum and bundle sheath strands of Z.mays possessed glycine oxidation activity similar to that ofmitochondria from C3 plant leaves. The two enzymes involvedin glycine metabolism in mitochondria, serine hydroxymethyltransferaseand glycine decarboxylase, were also assayed in the mitochondriaof the two cell types. The activities of the two enzymes inbundle sheath mitochondria were in the range found in C3 mitochondria.In contrast, the activities in mesophyll mitochondria were eithernot detectable or far lower than those in bundle sheath mitochondriaand ascribed to contaminating bundle sheath mitochondria. The present results indicate the deficiency of a complete glycineoxidation system in mesophyll mitochondria and also a differentiationbetween mesophyll and bundle sheath cells of C4 plants withrespect to the photorespiratory activities of the mitochondria. (Received June 8, 1983; Accepted August 29, 1983)  相似文献   

9.
The influence of varying light intensity and quality on thecarbon labelling patterns in Rumex vesicarius (a C3 plant),Setaria italica (a malate-formingC4 plant), and Amaranthus paniculatus(an aspartate-forming C4 plant) was studied. In A. paniculatusand B. vesicarius blue light decreased the transfer of radioactivityto sugars and starch but in S. italica only slightly decreasedradioactivity in sugar phosphates, sucrose, and insolubles.Negligible transfer was observed from the C4 acids to sugarphosphates, sucrose, and starch under dim blue-green and blue-yellowlights in S. italica and A. paniculatus. Blue light favouredthe formation of malate, aspartate, and alanine in all threeplants. The differential effect of blue and red light suggesteda variation in the mechanisms of C4-photosynthesis in Setariaand Amaranthus. Leaves of S. italica and A. paniculatus were allowed to photosynthesizein 14CO2 for 5 s and then the distribution of the labelled productsbetween the mesophyll and the bundle sheath cells was determinedduring subsequent photosynthesis in 12CO2. Malate and aspartatewhich appeared initially in the mesophyll layer moved rapidlyinto the bundle sheath cells. Phosphoglyceric acid originatingin the bundle sheath moved swiftly to the mesophyll layer. Sugarphosphates were recovered from both the mesophyll and the bundlesheath cells. Most of the starch was found in the bundle sheathcells while sucrose and alanine were localized in the mesophyllcells.  相似文献   

10.
Cultivars of cassava, Manihot esculenta Crantz, were studiedto determine the mechanism of photosynthetic carbon assimilationin this species. The results, contrary to recent reports, indicatethat cassava is a C3 plant based on a number of physiologicaland biochemical photosynthetic characteristics. The CO2 compensationpoints among 10 cassava cultivars ranged from 55 to 62 µlliter–1, which was typical for C3 plants including castorbean, a member of the same family (Euphorbiaceae). The initialproducts of photosynthesis in cassava are C3-like; the activitiesof several key C4 enzymes in cassava are low and similar tothose of C3 plants. Data on the rates of photosynthesis perunit of leaf area and the photosynthetic response of cassavato CO2 is also consistent with C3 photosynthesis. Cassava hasa distinctive chlorenchymatous vascular bundle sheath locatedbelow a single layer of palisade cells. Unlike C3-C4 intermediatesand C4 species, the bundle sheaths of cassava are not surroundedby mesophyll cells. The bundle sheath cells which occur at highfrequency in cassava may function in both photosynthesis andtransport of photosynthates in the leaf. (Received July 31, 1990; Accepted September 25, 1990)  相似文献   

11.
  • C4 plants supply concentrated CO2 to bundle sheath (BS) cells, improving photosynthetic efficiency by suppressing photorespiration. Mesophyll chloroplasts in C4 plants are redistributed toward the sides of the BS cells (aggregative movement) in response to environmental stresses under light. Although this chloroplast movement is common in C4 plants, the significance and mechanisms underlying the aggregative movement remain unknown.
  • Under environmental stresses, such as drought and salt, CO2 uptake from the atmosphere is suppressed by closing stomata to prevent water loss. We hypothesized that CO2 limitation may induce the chloroplast aggregative movement. In this study, the mesophyll chloroplast arrangement in a leaf of finger millet, an NAD-malic enzyme type C4 plant, was examined under different CO2 concentrations and light conditions.
  • CO2 limitation around the leaves promoted the aggregative movement, but the aggregative movement was not suppressed, even at the higher CO2 concentration than in the atmosphere, under high intensity blue light. In addition, mesophyll chloroplasts did not change their arrangement under darkness or red light.
  • From these results, it can be concluded that CO2 limitation is not a direct inducer of the aggregative movement but would be a promoting factor of the movement under high intensity blue light.
  相似文献   

12.
Bundle sheath protoplasts (BSP) were isolated and purified fromfour C4 species of the phosphoenolpyruvate (PEP) carboxykinasetype (Panicum maximum, P. texanum, Chloris gayana and Eriochloaborumensis), and cell organellses were separated from the BSPextract by differential centrifugation or sucrose density gradientcentrifugation. Separation of the organelles was ascertainedby the distribution of marker enzymes for chloroplasts, mitochondria,peroxisomes and cytoplasm. Contrary to the previous report [Rathnamand Edwards (1975) Arch. Biochem. Biophys. 171: 214], the distributionof PEP carboxykinase in BSP of P. maximum was the same as thatof UDP-glucose pyrophosphorylase, a marker for cytoplasm, andPEP carboxykinase activity was not recovered in the intact chloroplasts.The same results were obtained with P. texanum, C. gayana andE. borumensis. Therefore, we conclude that PEP carboxykinase is exclusivelylocalized in the cytoplasm of bundle sheath cells of C4 plants. (Received July 23, 1983; Accepted October 17, 1983)  相似文献   

13.
Intact chloroplasts were isolated from mesophyll and bundlesheath protoplasts of a C4 plant, Panicum miliaceum L., to measurethe uptake of [1-14C]pyruvate into their sorbitol-impermeablespaces at 4?C by the silicone oil filtering centrifugation method.When incubated in the dark, both chloroplasts showed similarslow kinetics of pyruvate uptake, and the equilibrium internalconcentrations were almost equal to the external levels. Whenincubated in the light, only mesophyll chloroplasts showed remarkableenhancement of the uptake, the internal concentration reaching10–30 times of the external level after 5 min incubation.The initial uptake rate of the mesophyll chloroplasts was enhancedabout ten fold by light and was saturated with increasing pyruvateconcentration; Km and Vmax were 0.2–0.4 mM and 20–40µmol(mg Chl)–1 h–1, respectively. The lightenhancement was abolished by DCMU and uncoupling reagents suchas carbonylcyanide-m-chlorophenylhydrazone and nigericin. Theseresults indicate the existence of a light-dependent pyruvatetransport system in the envelope of mesophyll chloroplasts ofP. miliaceum. The uptake activity of mesophyll chloroplastsboth in the light and the dark was inhibited by sulfhydryl reagentssuch as mersalyl and p-chloromercuriphenylsulfonate, but thebundle sheath activity was insensitive to the reagents. Thesefindings are further evidence for the differentiation of mesophylland bundle sheath chloroplasts of a C4 plant with respect tometabolite transport. (Received July 3, 1986; Accepted October 8, 1986)  相似文献   

14.
Light microscopic observation of leaf blades of Panicum dichotomiflorumshowed that a mestome sheath was present and chloroplasts inbundle sheath cells were in the centrifugal position. However,a sharp pattern of post-illumination CO2 burst was observedin less than 30 sec after the extinction of light. Among threeC4-acid decarboxylating enzymes, only the activity of NAD-malicenzyme was high. These results indicate that P. dichotomiflorumis a NAD-malic enzyme type species having centrifugal chloroplastsin bundle sheath cells and the sharp pattern of post-illuminationCO2 burst is closely correlated with the C4-acid decarboxylationsystem through NAD-malic enzyme 1This research was supported by a grant from the Ministry ofAgriculture, Forestry and Fishery (GEP55-II-1-7). (Received August 18, 1980; )  相似文献   

15.
Maize seedlings were grown in pots either with or without preconditionedseeds of the parasitic weed, Striga hermonthica. After between4 and 8 weeks, net photosynthesis in the leaves of maize plantsinfected with Striga decreased compared to leaves of uninfectedcontrol plants. The activities of four enzymes of photosyntheticmetabolism were, however, little affected by infection. A pulse-chaseexperiment using 14CO2 showed that C4 acids were the main earlyproducts of assimilation even when the rate of photosynthesiswas much decreased by infection, but more radio-activity appearedin glycine and serine than in leaves of healthy maize plants.Leaves of infected maize required longer to reach a steady rateof photosynthesis upon enclosure in a leaf chamber than leavesof uninfected plants after similar treatment. Electron microscopy of transverse sections of the leaves ofinfected maize indicated that the cell walls in the bundle sheathand vascular tissue were less robust than in leaves of healthyplants. The results suggest that infection with Striga causesan increase in the permeability of cell walls in the bundlesheath, leakage of CO2 from the bundle sheath cells and decreasedeffectiveness of C4 photosynthesis in host leaves. Key words: Zea mays, Striga hermonthica, photosynthesis, photorespiration, enzyme activity  相似文献   

16.
Light microscopic observation of leaf blades of Panicum dichotomiflorumshowed that a mestome sheath was present and chloroplasts inbundle sheath cells were in the centrifugal position. However,a sharp pattern of post-illumination CO2 burst was observedin less than 30 sec after the extinction of light. Among threeC4-acid decarboxylating enzymes, only the activity of NAD-malicenzyme was high. These results indicate that P. dichotomiflorumis a NAD-malic enzyme type species having centrifugal chloroplastsin bundle sheath cells and the sharp pattern of post-illuminationCO2 burst is closely correlated with the C4-acid decarboxylationsystem through NAD-malic enzyme 1This research was supported by a grant from the Ministry ofAgriculture, Forestry and Fishery (GEP55-II-1-7). (Received August 18, 1980; )  相似文献   

17.
Enzymes of the C4, C3 pathway and photorespiration have beenanalyzed for P. hians and P. milioides, which have chlorenchymatousbundle sheath cells in the leaves. On whole leaf extracts thelevels of PEP carboxylase are relatively low compared to C4species, RuDP carboxylase is typical of C3 species, and enzymesof photorespiratory metabolism appear somewhat intermediatebetween C3 and C4. Substantial levels of PEP carboxylase, RuDPcarboxylase, and photorespiratory enzymes were found in bothmesophyll and bundle sheath cells. Low levels of C4-acid decarboxylatingenzymes may limit the capacity for C4 photosynthesis in P. hiansand P. milioides. The results on enzyme activity and distributionbetween mesophyll and bundle sheath cells are consistent withCO2 fixation via C3 pathway in these two species. 1 This research was supported by the College of Agriculturaland Life Sciences, University of Wisconsin, Madison; and bythe University of Wisconsin Research Committee with funds fromthe Wisconsin Alumni Research Foundation; and by the NationalScience Foundation Grant BMS 74-09611. (Received September 16, 1975; )  相似文献   

18.
K. W. Hilu 《Genetics》1988,118(1):163-167
Finger millet (Eleusine corocana subsp. coracana), an important cereal in East Africa and India, is a tetraploid species with unknown genomic components. A recent cytogenetic study confirmed the direct origin of this millet from the tetraploid E. coracana subsp. africana but questioned Eleusine indica as a genomic donor. Chloroplast (ct) DNA sequence analysis using restriction fragment pattern was used to examine the phylogenetic relationships between E. coracana subsp. coracana (domesticated finger millet), E. coracana subspecies africana (wild finger millet), and E. indica. Eleusine tristachya was included since it is the only other annual diploid species in the genus with a basic chromosome number of x = 9 like finger millet. Eight of the ten restriction endonucleases used had 16 to over 30 restriction sites per genome and were informative. E. coracana subsp. coracana and subsp. africana and E. indica were identical in all the restriction sites surveyed, while the ct genome of E. tristachya differed consistently by at least one mutational event for each restriction enzyme surveyed. This random survey of the ct genomes of these species points out E. indica as one of the genome donors (maternal genome donor) of domesticated finger millet contrary to a previous cytogenetic study. The data also substantiate E. coracana subsp. africana as the progenitor of domesticated finger millet. The disparity between the cytogenetic and the molecular approaches is discussed in light of the problems associated with chromosome pairing and polyploidy.  相似文献   

19.
In C(4) plants, mesophyll (M) chloroplasts are randomly distributed along the cell walls, whereas bundle sheath chloroplasts are located in either a centripetal or centrifugal position. It was reported previously that only M chloroplasts aggregatively redistribute to the bundle sheath side in response to extremely strong light or environmental stresses. The aggregative movement of M chloroplasts is also induced in a light-dependent fashion upon incubation with abscisic acid (ABA). The involvement of reactive oxygen species (ROS) and red/blue light in the aggregative movement of M chloroplasts are examined here in two distinct subtypes of C(4) plants, finger millet and maize. Exogenously applied hydrogen peroxide or ROS scavengers could not change the response patterns of M chloroplast movement to light and ABA. Blue light irradiation essentially induced the rearrangement of M chloroplasts along the sides of anticlinal walls, parallel to the direction of the incident light, which is analogous to the avoidance movement of C(3) chloroplasts. In the presence of ABA, most of the M chloroplasts showed the aggregative movement in response to blue light but not red light. Together these results suggest that ROS are not involved in signal transduction for the aggregative movement, and ABA can shift the blue light-induced avoidance movement of C(4)-M chloroplasts to the aggregative movement.  相似文献   

20.
Trifolium alpinum L. is a high-quality alpine forage plant growingspontaneously from 1900 to 2800 m above sea level and is widelydistributed in Piedmont and the Valle d'Aosta (Italy), whereit can reach population frequencies of 90 per cent. Yields weredetermined on forage harvested in the Valle dell'Orco (Piedmont)and were comparable to cultivated clovers from higher latitudes;yields decreased progressively as the elevation increased. Thechemical and nutritional characteristics of the forage, thoughcomparable to clovers cultivated in the Po valley (Italy), were,however, more constant. The structure of the leaf lamina asrelated to elevation was investigated using light microscopy,TEM and SEM. This is complemented by data on chlorophyll concentration,succulence, specific leaf weight and area. At all elevationsT. alpinum lacks, apart from bundle sheath cell chloroplastsin a centrifugal arrangement, the structural characteristicsof C4 plants. The chlorophyll a:b ratio (less than four) istypical of a C2 plant. Succulence indices (S and Sm) were verylow, making CAM pathway photosynthesis unlikely. Unusual anddifficult to interpret structures included: small functionalchloroplasts in both the epidermises, stomata present almostexclusively in the upper epidermis and mitochondria enveloped(or enclosed) by chloroplasts. It was observed that, as theelevation increases, populations are selected which are well-adaptedfor gas exchange (increase in specific leaf area, stomatal densityand intercellular spaces) and characterized by a decrease inthe grana thylacoid:integrana thylacoid ratio (consistent withthe increase in the chlorophyll a:b ratio), the per cent water,Sm and the specific leaf weight. Trifolium alpinum L., alpine trefoil, leaf structures, photosynthesis, yield, elevation, C2, C4  相似文献   

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