Abstract: Further study on the localization of abscisic acid (ABA) has been undertaken at the ultrastructural level in Chenopodium polyspermum L. Axillary-bud-bearing nodes on the main axis were fixed with soluble 1-(3-dimethylaminopropyl)-3 ethyl carbodiimide, then postfixed with paraformaldehyde and embedded in Lowicryl K4M at-20° C. Ultrathin sections mounted on grids were successively incubated with rabbit anti-ABA antibodies and with gold-labelled goat anti-rabbit anti-bodies (40 nm particle size). Control sections treated with preimmune rabbit serum and ABA-preabsorbed antibodies were devoid of label. The background staining was very low with this technique. Quantitative analysis of the immunolabelling showed that two main sites of ABA accumulation could be defined: first, plastids in cortical cells and vascular parenchyma cells associated with sieve elements and xylem vessels; second, the cell cytoplasm and nucleus in the axillary bud tip and in procambial strands. In vascular bundles, the cambial cells showed no immunoreactivity. These observations support the hypothesis for the cytoplasmic synthesis of ABA which is subsequently trapped in plastids as cells mature.

Abstract: The properties and composition of bundle sheath and mesophyll thylakoids from maize leaves are compared. This was possible because of the isolation of large amounts of purified material obtained by enzymatic digestion of mechanically disrupted leaves. Bundle sheath thylakoids from mature leaves, lack the chlorophyll-proteins and polypeptides associated with the reaction centre of photosystem II. They do, however, contain significant amounts of LHCII, which transfers excitation energy to photosystem I. LHCII isolated from bundle sheath thylakoids had a different freeze-fracture ultrastructure and a different polypeptide composition from LHCII isolated from mesophyll thylakoids, indicating a differential expression of the LHCII gene family in mesophyll and bundle sheath cells of maize leaves.

Abstract: Primary leaf segments from 8-day-old dark-grown, and from 4- and 8-day-old light-grown seedlings of Zea mays L. cv. Fronica, were treated with 10-bM benzyladenine (BA) in the dark for 14 h. The segments were then studied after an exposure to light for 14 h. Photosynthetic activity (O2 evolution and CO2 fixation) and chlorophyll accumulation were stimulated by BA in dark-grown leaf segments with etioplastids in the earliest stage of development. In these segments BA stimulated the activities of ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39), phosphoenolpyruvate carboxylase (EC 4.1.1.31), NADP+-malic enzyme (EC 1.1.1.40) and pyruvate, orthophosphate dikinase (EC 2.7.9.1). In segments taken from 4- and 8-day light-grown seedlings, BA did not enhance the photosynthetic activity nor the chlorophyll accumulation. The activity of the enzymes mentioned above, was significantly enhanced by the BA-treatment. BA mainly affected grana stacking in mesophyll cell chloroplasts in primary leaf segments taken from 3- to 5-day light-grown seedlings. Stroma thylakoid development was stimulated only in leaf segments from 3-day-old plants. At the same time BA accelerated grana loss in chloroplasts of bundle sheath cells, a typical phenomenon of development in such chloroplasts. Stroma thylakoid length in these chloroplasts increased by a BA treatment in segments from 3- and 4-day light-grown plants. A significantly higher number of chloroplasts was only observed with segments taken from 8-day light-grown seedlings and treated with BA. The etiochloroplast number in segments taken from 8-day etiolated plants was significantly higher in BA-treated segments after 26 h illumination. In etiochloroplasts from both mesophyll and bundle sheath cells, BA enhanced grana stacking after illumination for 4 h or more, whereas stroma membrane length was significantly higher only after 26 h light. It is concluded that the effects of BA depend on the developmental stage. BA accelerates the development of mesophyll and bundle sheath cell (etio)chloroplasts, but does not affect the ultrastructure of mature chloroplasts.

Abstract: The distribution of the glycolytic enzymes, phosphofructokinase, aldolase, triosephosphate isomerase, phosphoglycerate kinase, pyruvate kinase, and the oxidative pentose phosphate pathway enzymes, glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, was determined in the leaf tissues of two C3-plants, pea and leek, and two C4-plants, maize and sorghum. All enzymes examined were found in epidermal tissue. In pea, maize, and sorghum leaves, the specific activities of these enzymes were usually higher in the nonphotosynthetic epidermal tissue than in the photosynthetic tissues of the leaves. In leek leaves, which were etiolated, specific activities were similar in both epidermal and mesophyll tissue. The distribution of the rate limiting enzymes of glycolysis and the oxidative pentose phosphate pathways probably reflects the capacity of each tissue to generate NADH, NADPH, and ATP from the oxidation of glucose. This capacity appears to be greater in leaf tissues unable to generate reducing equivalents and ATP by photosynthesis, that is, in epidermal tissues and etiolated mesophyll tissue.

Abstract: Photosystem I reaction centers were isolated from mesophyll and bundle-sheath chloroplasts of the C4 maize plant. Both preparations were found to be free of chlorophyll b and to have the same spectral properties and chlorophyll/P700 ratio as photosystem I reaction centers isolated from C3 plants. Photosystem I reaction centers from both mesophyll and bundle sheath were found to consist of six subunits with apparent molecular masses of about 70 kDa, 20 kDa, 17 kDa, 16 kDa, 10 kDa and 8 kDa, corresponding to photosystem I reaction center subunits I, II, IV, V, VI and VII of spinach, as tested by their immunological cross-reactivity with antibody raised against the respective spinach subunits. No cross-reactivity was found with antibodies raised against subunit III of spinach, either in whole thylakoids or purified reaction centers of both bundle-sheath and mesophyll chloroplasts. It is concluded that photosystem I reaction centers of bundle-sheath and mesophyll thylakoids of maize are identical and lack the polypeptide corresponding to subunit III present in all C3 plants so far tested.

Abstract: The tissue and subcellular distribution of prephenate aminotransferase, an enzyme of the shikimate pathway, was investigated in protoplasts from leaves of Sorghum bicolor. Activity was detected in purified epidermal and mesophyll protoplasts, and in bundle sheath strands. After fractionation of mesophyll and epidermal protoplasts by differential centrifugation, 92% of the total prephenate aminotransferase activity was detected in the plastid fraction.

Abstract: A procedure was developed to obtain intact and purified mitochondria from mesophyll and bundle sheath tissues of Zea mays L. cv. I.N.R.A. 180, an NADP+-malic enzyme type C4 plant. There was little cross-contamination between the two mitochondrial fractions. Both types of mitochondria oxidized NADH, succinate and malate with respiratory control. In mesophyll mitochondria malate oxidation was highly sensitive to KCN (85–90% inhibition of first state 3) and showed good respiratory control. In bundle sheath mitochondria malate oxidation was less sensitive to cyanide (75-80% inhibition) and showed poor respiratory control. Malate and NADH appeared to be the best substrates for respiratory activity. Mesophyil mitochondria could not oxidize glycine, whereas bundle sheath mitochondria could. The results indicate that mesophyll and bundle sheath mitochondria of Zea mays are differentiated, not only with respect to the decarboxylation of malate but also with respect to the decarboxylation phase of photorespiration.

Abstract: Guttating leaf teeth of Potentilla palustris plants from Wisconsin, USA, were cleared or processed for plastic sectioning or scanning electron microscopy Anatomical features include: 1) long slender hydathode area occupying most of the tooth, 2) adaxial pad of small, flat epidermal cells with 50 or more sunken water pores about the size of ordinary abaxial stomates, 3) three converged bundles that extend distally, where their tracheary files are separated by intervening files of xylem parenchyma cells with sinuous walls, 4) adaxial mass of small, loosely arranged epithem cells above the xylem, 5) one slender phloem strand that extends only about a third of the way into the hydathode, and 6) bundle sheath extending distally only abaxially and along the flanks of the hydathode Potentilla hydathodes differ significantly from non-guttating ones described earlier in Physocarpus (Rosaceae)

Abstract: In current year needles of diseased Picea abies the radial walls of the bundle sheath were found in a state of partial delignification, while the cells were filled with granular, heavily fluorescent substances which absorbed UV light at 280 nm. The same symptoms were observed after fumigation of healthy young plants with 0.3 ppm SO2 for 20 days. Findings may bear relevance to disturbances in water transport from the vascular system towards the evaporating surfaces of the needle.

Abstract: The vascular anatomy of seven genera of Magnoliaceae:Elmerrillia, Liriodendron, Magnolia, Manglietia, Michelia, Paramichelia andTalauma, was examined Based on the primary vascular bundles, and not on the protoxylem courses, the vasculature was reconstructed The vasculature was observed ontogenetically throughout the axes in both the flowers and vegetative shoots to determine the fundamental plan of the vascular systems, including the cortical and outer cortical vascular systems in the flowers Each cortical strand, which was previously treated as a single strand, was found to consist of several collateral bundles arranged concentrically The central, cortical and outer cortical vascular systems in the flowers are homologous and show parastichous patterns The primary vascular system in the vegetative shoots is likewise arranged in a parastichous pattern, although it was previously considered to have a non-parastichous pattern

Abstract: In maize leaves nitrogen (N)-deprivation induced a significant decline of chlorophyl and total N contents. On the contrary, sulphur (S) content increased with N-deprivation. The activities of ATP-sulphurylase and O-acetylserine sulphydrylase also decreased with N-deprivation, but ATP-sulphurylase activity was more sensitive than O-acetylserine sulphydrylase activity to N-deficiency both in whole leaf extracts and in isolated leaf cells. Finally, N-deprivation induced higher changes in activity of the two enzymes in mesophyll protoplasts than in bundle sheath strands.

Abstract: (a) Support in Plants 1. Unicellular plants (algae and fungi) have: (i) firm cell walls of cellulose (algae) or fungal cellulose and chitin in fungi; (ii) cell turgor, due to osmotic pressure on cell walls, which gives rigidity and support (see Fig. 6.3 and section 6.1(f)). 2. Multicellular flowering plants have: (i) cell walls; (ii) cell turgor; (iii) supporting tissue, i.e. collenchyma, sclerenchyma and vascular bundles in primary unthickened stems (lignified tissue is found in sclerenchyma and secondary thickening or wood of trees and shrubs: see Fig. 3.2, section 8.1(f), and Fig. 8.7; (iv) climbing plants, e.g. honeysuckle and runner bean, have twining stems; vine and sweet pea have tendrils; and blackberry has prickles.

Abstract: Thin sections of malva (Malva sp.) leaves collected in the field and showing mottle and vein-clearing symptoms were examined by electron microscopy. Cytoplasmic inclusions typical of potyvirus and consisting of pinwheels, laminated aggregates, and scrolls were readily observed. In addition, rhabdoviruslike particles were also seen in the perinuclear space of phloem parenchyma cells and within membranous sacs scattered throughout the cytoplasm of other vascular bundle cells. Occasionally rhabdoparticles could be found embedded in an amorphous electron-dense body located within the cell vacuole. The rhabdovirus particles, approximately 75 × 300 nm, were bound by a membrane with outer projections and had an inner core displaying cross striations. The cytoplasm of infected mesophyll cells had chloroplasts containing large amorphous inclusion bodies and had extensive membranous tubules that were frequently associated with the potyvirus inclusions. These ultrastructural aspects, the size of the particles, and t...

Abstract: A method is described which allows the visual demonstration of the vascular system of the receme of fava beans (Vicia faba L.). 150 recemes of plants of various breeding populations were investigated. It was possible to show the structure of the entire vascular system characteristic of faba bens. The existence of a system of completely independent vascular bundles (IVS), which according to GATES et al. (1983) might avoid the competition between flowers within a receme is though to be improbable.

Abstract: Virus particles of isometric shape with a diameter of 26 nm were found in the sieve tubes and accompanying phloem cells in ultrathin sections prepared from the nerves of white mustard (Sinapis alba L.) leaves and roots infected with the beet mild yellowing virus (BMYV). BMYV particles were much more frequent in the roots ofSinapis alba plants. Isometric particles were not found in the leaves and roots of healthy mustard plants.

Abstract: Smith, J. A. C. and Nobel, P. S. 1986. Water movement and storage in a desert succulent: anatomy and rehydration kinetics for leaves of Agave deserti.—J. exp. Bot. 37: 1044-1053. Anatomic and kinetic aspects of water storage were investigated for the succulent leaves of the desert CAM plant, Agave deserti. An approximately linear relationship was found between the number of vascular bundles and leaf surface area, both for leaves of different sizes and also along the length of a single leaf. The bundles, which were distributed throughout the leaf cross-section, were separated from each other by about eight water-storage cells. Even though the cell walls of the water-storage ground tissue made up only 2-5% of the cell volume, they provided about 10% of the total cross-sectional area available for water transport radial to the xylem because cell-cell contact in such a direction averaged 25% of the cell surface area. The rehydration kinetics of partially dehydrated leaf segments were resolved into three phases: (1) a relatively rapid movement into the vascular tissue (half-time of 2 min); (2) water movement into storage in the ground tissue (half-time of 59 min); and (3) water movement into the intercellular air spaces (half-time of about 10 h). Using the observed kinetics for water movement into the storage tissue and standard diffusion theory, the bulk-averaged diffusivity of water in the relatively homogeneous ground tissue (flt) was 2 0 x 1U-10 m2 s_1. Using this D, and pathway analysis, most of the water moving from the xylem into storage in the massive leaves of A. deserti apparently occurred from cell to cell across the cell membranes rather than through the cell walls.

Abstract: The present study reports on the biochemical characteristics and enzyme activities associated with photosynthetic carbon metabolism of two genotypes of Pennisetum: P. Americanum 23DB a cultivated form and P. Mollissimum a wild form. Growth analysis, leaf area, protein and starch content, chlorophyll content and dry weight were investigated. All these parameters were higher for P. Mollissimum compared to P. Americanum. Both Pennisetum exhibited the Kranz anatomy: bundle sheath cells surrounded by mesophyll cells. Bundle sheath cells contained specialized chloroplasts which differed from mesophyll plastids by being larger. The isolation of the two photosynthetic tissues with a high degree of integrity allowed determination of the first steps of photosynthetic carbon metabolism and their intratissular distribution. Activities together with the leaf anatomy indicated that both Pennisetum have the C4 pathway of co2 assimilation and belong to the NADP-malic enzyme type. Isolated and purified mesophyll protoplasts and bundle sheath cells obtained by enzymatic digestion of the youngest leaves of the two genotypes allowed study of intratissular and intracellular distribution of some enzyme activities such as: inorganic pyrophosphatase and glutamate oxaloacetate transaminase. Some aspects of regulation on enzymes from mesophyll Pennisetum protoplasts and bundle sheath Pennisetum cells were elucidated. The impact of ATP, ADP, AMP and energy charge on the activities of key enzymes of C4 photosynthetic carbon metabolism in Pennisetum metabolism was investigated. Results, reported here on adenylates and energy charge effects suggested that several additional factors such as variations of substrate, Mg2+ and total adenylates concentrations are surely decisive for the modulation of the Pennisetum enzymes.

Abstract: The cellular distribution of the starch biosynthetic and degradative enzymes in protoplasts prepared from maize leaf mesophyll and bundle sheath cells was investigated. In conformity with the cellular distribution of starch, starch biosynthetic enzymes (soluble starch synthase, ADPglucose pyrophosphorylase, branching enzyme and starch phosphorylase) were exclusively localized in the bundle sheath cells. In contrast, starch degradative enzymes (a-amylase, f-amylase and debranching enzyme) were present in both types of leaf cells. Isolated chloroplasts from bundle sheath cells were shown to contain 100% of the starch biosynthetic enzymes. However, approximately 60% of the activity of degradative enzymes and 67% of the activity of starch phosphorylase was localized in bundle sheath chloroplasts. LEAVES OF PLANT species utilizing C4 photosynthetic metabolism are characterized by Kranz anatomy. Although the relationship of this anatomy to biochemical pathways of carbon assimilation is well understood, many of the basic processes of carbon metabolism have not been completely described. Starch metabolism is one of the critical processes in carbon flow. In C4 species, starch normally accumulates only in the chloroplasts of bundle sheath cells (BSC) and is absent from chloroplasts of mesophyll cells (MC). The overall regulation of light accumulation and dark degradation of starch has not been well established. Possible regulating factors include the ratio of 3-PGA/ Pi (Preiss and Levi, 1979), photosynthetic associated pH changes (Preiss and Levi, 1979) or

Abstract: The two C4 Panicum species examined differ in C4 acid decarboxylation type and in developmental origin of bundle sheaths in major veins of their leaf blades In Panicum effusum RBr (NAD-malic enzyme type) both mesophyll (PCA) and chlorenchymatous bundle sheath (PCR) cells are derived from ground meristem In contrast, in Panicum bulbosum HBK (NADPmalic enzyme type), bundle sheath cells are derived from procambium, while mesophyll develops from ground meristem To test the hypothesis that the developmental divergence of bundle sheath and mesophyll cells would occur earlier when these two tissues had different ontogenetic origins (in P bulbosum) than when these tissues had the same origin (in P effusum), the development of major veins in each species was investigated We measured cell length and cross sectional area, plastid and mitochondrial number, plastid area, vacuole area fraction, wall thickness and fraction adjacent to intercellular space using direct and digitizer measurements of transmission electron micrographs of leaf cross sections of successive developmental stages Many of the statistically significant changes in the structural parameters measured occurred late in development of both species The magnitude of developmental change in P effusum PCR cells was sometimes more dramatic, viz changes in cell and PCR plastid area, and in mitochondrion number per cell However, earlier divergence of PCR and PCA length and volume, and wall fraction adjacent to intercellular space in P bulbosum than in P effusum indicates that ontogenetic origin of PCR cells from procambium could determine the timing of at least some developmental events

Abstract: Gradients along the transport pathway from the peduncle to the endosperm cavity were examined during grain filling in wheat. Sieve tube exudate was collected from severed aphid stylets established on the peduncle and rachis and on the vascular bundles in the creases of grains. Phloem exudate could also be collected from broken grain pedicels, and by puncturing the vascular bundle in the grain crease with a needle. Stylets on excised grains persisted exuding, indicating that grain sieve tubes are capable of loading solutes. There was little, if any, discernible gradient in osmolality or solute composition (sucrose, total amino acids) of sieve tube contents along the phloem pathway from the peduncle to the rachis or along the rachis itself. Neither was a gradient detected in osmolality along the sieve tube pathway from the rachis through the rachilla and grain stalk to the crease. Demonstrable solute gradients occurred only across those tissues of the grain crease between the crease sieve tubes and the endosperm cavity, a distance of just 1 millimeter. However, while the sucrose concentration in the sieve tubes was almost tenfold that in the endosperm cavity sap, total amino acids were only threefold higher, and the potassium concentrations of the two were equal. Our observations strongly implicate the movement of assimilates from the sieve tubes and across the crease tissues as important control points in grain filling.

Abstract: Bundle sheath chloroplasts of maize leaves contain about one-fourth as much light-harvesting chlorophyll a/b binding protein of photosystem II (LHCP-II) as do mesophyll chloroplasts. We have determined that this difference is, in part, the result of differential expression of different LHCP-II genes. We have prepared and partially characterized cDNA clones specific for six LHCP-II genes of maize. Transcripts of these six LHCP-II genes are present at vastly different levels and account for about 95% of total LHCP-II mRNAs in bundle sheath and mesophyll cells of illuminated dark-grown maize leaves. Three genes are preferentially expressed in mesophyll cells, and their mRNAs constitute about 54% of the total LHCP-II transcripts in greening (24 hr) maize leaves. Two genes are expressed equally in bundle sheath and mesophyll cells. Most interestingly, the RNA of one gene that contributes about 8% of the total LHCP-II transcripts in leaves greening for 24 hr is present at a much higher level in bundle sheath than in mesophyll cells. Moreover, immunoblot analysis of maize thylakoids reveals at least five sizes of LHCP-II; these also differ from one another in their relative abundance in bundle sheath and mesophyll cells of developing maize leaves.