Parenchyma Sheath Cells Research Articles

Two new petrified gymnosperms with solenoid piths from the Pedra de Fogo Formation, Permian of Maranhão, Brazil

Solenoid piths are formed by systems of secretory ducts or canals, and they are relatively common in petrified gymnosperms from the Permian of Gondwana. We described herein two new taxa, Polycanaloxylon merlottii gen. et sp. nov. and Europoxylon garapensis sp. nov., from the Pedra de Fogo Formation (Cisuralian), northeastern Brazil. In both species the pith is non-septate and solenoid, primary xylem bundles have endarch maturation, rays are short and uniseriate, pits on the radial walls of tracheids are commonly uni to biseriate, cross-field pitting is cupressoid and wood is pycnoxylic. Whereas P. merlottii has a solenoid pith with a parenchyma sheath and sclerenchyma cells, E. garapensis is distinguished by a pith that only has secretory canals and parenchyma cells. In addition to expanding the distribution area of a typical Euramerican taxon into Parnaíba Basin, the report of Europoxylon reinforces a connection between these areas in the Late Pennsylvanian, thus enabling the dispersion of floristic elements. Solenoid forms are especially common in Kungurian sedimentary deposits of southern Brazil, and possibly India. However, since the occurrence of them seems to be linked to specific habitats, it should be proven that such environments are indeed contemporaneous in order to use these stems as a tool for relative dating in Gondwanan localities.

Intracellular position of mitochondria and chloroplasts in bundle sheath and mesophyll cells of C3 grasses in relation to photorespiratory CO2 loss

In C3 plants, photosynthetic efficiency is reduced by photorespiration. A part of CO2 fixed during photosynthesis in chloroplasts is lost from mitochondria during photorespiration by decarboxylation of glycine by glycine decarboxylase (GDC). Thus, the intracellular position of mitochondria in photosynthetic cells is critical to the rate of photorespiratory CO2 loss. We investigated the intracellular position of mitochondria in parenchyma sheath (PS) and mesophyll cells of 10 C3 grasses from 3 subfamilies (Ehrhartoideae, Panicoideae, and Pooideae) by immunostaining for GDC and light and electron microscopic observation. Immunostaining suggested that many mitochondria were located in the inner half of PS cells and on the vacuole side of chloroplasts in mesophyll cells. Organelle quantification showed that 62–75% of PS mitochondria were located in the inner half of cells, and 62–78% of PS chloroplasts were in the outer half. In mesophyll cells, 61–92% of mitochondria were positioned on the vacuole side of chloroplasts and stromules. In PS cells, such location would reduce the loss of photorespiratory CO2 by lengthening the path of CO2 diffusion and allow more efficient fixation of CO2 from intercellular spaces. In mesophyll cells, it would facilitate scavenging by chloroplasts of photorespiratory CO2 released from mitochondria. Our data suggest that the PS cells of C3 grasses have already acquired an initial structure leading to proto-Kranz and further C3–C4 intermediate anatomy. We also found that in the Pooideae, organelle positioning in PS cells on the phloem side resembles that in mesophyll cells.

Cocksfoot mottle sobemovirus establishes infection through the phloem

Cocksfoot mottle virus (CfMV) localization in oat plants was analyzed during three weeks post infection by immunohistochemical staining to follow its spread through different tissues. In early stages of infection, the virus was first detectable in phloem parenchyma and bundle sheath cells of inoculated leaves. Bundle sheath and phloem parenchyma were also the cell types where the virus was first detected in stems and systemic leaves of infected plants. In later stages of infection, CfMV spread also into the mesophyll surrounding vascular bundles and was seldom detected in xylem parenchyma of inoculated leaves. In systemic leaves, CfMV was not detected from xylem. Moreover, sometimes it was found from phloem only. In straw and roots, CfMV was detected both from phloem and xylem. According to our observations, CfMV predominantly moves through phloem, which makes the systemic movement of CfMV different from that of another monocot-infecting sobemovirus, Rice yellow mottle virus (RYMV).

Ultrastructural changes during early infection of Vigna unguiculata and Phaseolus vulgaris leaves by Xanthomonas axonopodis pv. phaseoli and an unexpected association between chloroplast and mitochondrion

Common bacterial blight, caused by Xanthomonas axonopodis pv. phaseoli, is an important disease affecting beans causing considerable yield losses in many producing areas. Our aim was to investigate Xap–beans interactions in the first 48 h after infection analyzing structurally relevant changes by electron microscopy. Scanning electron microscopy analysis demonstrated morphological changes on leaf surfaces of both species. Transmission electron microscopy showed different types of chloroplast structural disorganization in both parenchyma and bundle sheath cells of Vigna unguiculata which were only observed in parenchyma cells of Phaseolus vulgaris. Additionally, we report an unexpected physical association between the chloroplasts and mitochondria observed only to P. vulgaris-infected plants.

Extracellular Matrix in Early Stages of Direct Somatic Embryogenesis in Leaves of Drosera spathulata

Leaves from mature in vitro grown plants of Drosera spathulata Labill. regenerated new plantlets on solid induction medium in light. Especially vascular sheath parenchyma cells located close to basal part of tentacule showed high embryogenic potential. Proembryoids arrising from the tentacule base part were visible by scanning electron microscopy. Their surface cells were linked and covered with thin external, fibrilar network representing an extracellular matrix (ECM). Proembryogenic surface cells were later connected by coarse strands of fibrils. Young protoderm was formed arround globular embryoids and its cells were characterized by “brain-like” surface structure. However, the surface of fully developed protodermal cells was practicaly smooth and cells were stick to each other very tightly in torpedo and cotyledonary shaped embryoids. The presence of ECM was typical only for somatic proembryos and globular embryos. The ECM network was never observed on the surface of heart and torpedo shaped embryos.

Cellular compartmentation of ammonium assimilation in rice and barley

This review describes immunolocalization studies of the tissue and cellular location of glutamine synthetase (GS; EC 6.3.1.2) and glutamate synthase (Fd GOGAT; EC 1.4.7.1 and NADH-GOGAT; EC 1.4.1.14) proteins in roots and leaves of rice (Oryza sativa L.) and barley (Hordeum vulgare L.). In rice, cytosolic GS (GS1) protein was distributed homogeneously through all cells of the root. NADH GOGAT protein was strongly induced and its cellular location altered by ammonium treatment, becoming concentrated within the epidermal and exodermal cells. Fd GOGAT protein location changed with root development, from a widespread distribution in young cells to becoming concentrated within the central cylinder as cells matured. Plastid GS protein was barely detectable in rice roots, but was the major isoform in leaves, being present in the mesophyll and parenchyma sheath cells. GS1 was specific to the vascular bundle, as was NADH GOGAT, whereas Fd GOGAT was primarily found in mesophyll cells. In barley roots, GS1 protein was found in the cortical and vascular parenchyma and its concentration was highest in N-deficient seedlings. Plastid GS protein was detected in both cortical and vascular cells, where different plastid forms, containing different concentrations of GS protein, were identified. In barley leaves, GS2 protein was detected in the mesophyll chloroplasts and GS1 was found in the mesophyll and vascular cells. N nutrition strongly influenced this distribution, with a marked increase in GS1 concentration in the vascular cells in response to nitrate and ammonium, and an increase in mesophyll GS2 concentration in nitrate-grown seedlings. Fd GOGAT protein was found in both the mesophyll and vascular plastids. These localization studies show that the GS/GOGAT cycle is highly compartmentalized at both the subcellular and cellular levels. Reasons for this compartmentation, and the roles of each isoform, are discussed.

Cellular compartmentation of ammonium assimilation in rice and barley

This review describes immunolocalization studies of the tissue and cellular location of glutamine synthetase (GS; EC 6.3.1.2) and glutamate synthase (Fd GOGAT; EC 1.4.7.1 and NADH-GOGAT; EC 1.4.1.14) proteins in roots and leaves of rice (Oryza sativa L.) and barley (Hordeum vulgare L.). In rice, cytosolic GS (GS1) protein was distributed homogeneously through all cells of the root. NADH GOGAT protein was strongly induced and its cellular location altered by ammonium treatment, becoming concentrated within the epidermal and exodermal cells. Fd GOGAT protein location changed with root development, from a widespread distribution in young cells to becoming concentrated within the central cylinder as cells matured. Plastid GS protein was barely detectable in rice roots, but was the major isoform in leaves, being present in the mesophyll and parenchyma sheath cells. GS1 was specific to the vascular bundle, as was NADH GOGAT, whereas Fd GOGAT was primarily found in mesophyll cells. In barley roots, GS1 protein was found in the cortical and vascular parenchyma and its concentration was highest in N-deficient seedlings. Plastid GS protein was detected in both cortical and vascular cells, where different plastid forms, containing different concentrations of GS protein, were identified. In barley leaves, GS2 protein was detected in the mesophyll chloroplasts and GS1 was found in the mesophyll and vascular cells. N nutrition strongly influenced this distribution, with a marked increase in GS1 concentration in the vascular cells in response to nitrate and ammonium, and an increase in mesophyll GS2 concentration in nitrate-grown seedlings. Fd GOGAT protein was found in both the mesophyll and vascular plastids. These localization studies show that the GS/GOGAT cycle is highly compartmentalized at both the subcellular and cellular levels. Reasons for this compartmentation, and the roles of each isoform, are discussed.

Bundle Sheath Cells are Responsible for Direct Root Regeneration from Leaf Explants of Helianthus occidentalis L.

Summary Direct root organogenesis from isolated leaf explants of Helianthus occidentalis L. was induced using MS culture media supplemented with (x-naphthalene acetic acid (NAA) and benzyladenine (BA). The highest numbers of roots were formed de novo from bundle sheath cells located around leaf veins when explants were cultured on induction medium supplemented with 2.7 pmol/L NAA and 0.44 pmol/L BA. The structural events accompanying reactivation and division of competent bundle sheath cells and cells derived from them were investigated employing light, transmission and scanning electron microscopy in time course experiments. Vein parenchyma and bundle sheath cells located around leaf veins started to divide first after 2 days of culture. Vein parenchyma cells, however, ceased their divisions by day 5, while reactivated bundle sheath cells produced cambium-like cells. These later cells gave origin to circular meristematic tissue, and subsequently to root primordia. Root primordia appeared after 7 days and regenerated roots emerged from leaf explants after 15 days of culture. Ultrastructure of reactivated regeneration competent cells is described and is compared with other examples of regeneration in vitro.

Immunocytochemical localization of enzymes involved in the C3 and C4 pathways in the photosynthetic cells of an amphibious sedge, Eleocharis vivipara

Eleocharis vivipara link, an amphibious leafless sedge, develops traits of C4 photosynthesis and Kranz anatomy in the terrestrial form but develops C3-like traits with non-Kranz anatomy when submerged. The cellular localization of C3 and C4 enzymes in the photosynthetic cells of the two forms was investigated by immunogold labeling and electron microscopy. The terrestrial form has mesophyll cells and three kinds of bundle sheath cell, namely, parenchyma sheath cells, non-chlorophyllous mestome sheath cells, and Kranz cells. Phosphoenol-pyruvate carboxylase (PEPCase) was present in the cytosol of both the mesophyll cells and the parenchyma sheath cells, with higher-density labeling in the latter, but not in the Kranz cells. Pyruvate, Pi dikinase (PPDK) was found at high levels in the chloroplasts of both the mesophyll cells and the parenchyma sheath cells with some-what stronger labeling in the latter. This enzyme was also absent from the Kranz cells. Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) was found in the chloroplasts of all types of photosynthetic cell, but labeling was significantly less intense in the parenchyma sheath cells than in other types of cell. The submerged form also has three types of photosynthetic cell, as well as non-chlorophyllous mestome sheath cells, but it lacks the traits of Kranz anatomy as a consequence of modification of the cells. Rubisco was densely distributed in the chloroplasts of all the photosynthetic cells. However, PEPCase and PPDK were found in both the mesophyll cells and the parenchyma sheath cells but at lower levels than in the terrestrial form. These data reveal that the terrestrial form has a unique pattern of cellular localization of C3 and C4 enzymes, and they suggest that this pattern and the changes in the extent of accumulation of the various enzymes are the main factors responsible for the difference in photosynthetic traits between the two forms.

Structural characterization of photosynthetic cells in an amphibious sedge, Eleocharis vivipara, in relation to C3 and C4 metabolism

Eleocharis vivipara Link is a unique amphibious leafless sedge. The terrestrial form has Kranz anatomy and the biochemical traits of C4 plants while the submerged form develops structural and biochemical traits similar to those of C3 plants. The structural features of the culms, which are the photosynthetic organs, of the two forms were examined and compared. The culms of the terrestrial form have mesophyll cells and three bundle sheaths which consist of three kinds of cell, namely, the innermost Kranz cells that contain large numbers of organelles, the middle mestome sheath cells that lack chloroplasts, and the outermost parenchyma sheath cells that contain chloroplasts. The culms of the submerged form had a tendency towards reduction in numbers and size of Kranz cells and vascular bundles, as compared to the terrestrial form, and they had spherical mesophyll cells that were tightly packed without intercellular spaces inside the epidermis. The submerged form had a higher ratio of cross-sectional area of mesophyll cells plus parenchyma sheath cells to that of Kranz cells than the terrestrial form. The difference was mainly due to a decrease in the number and the size of the Kranz cells and to a marked increase in the size of the mesophyll cells and the parenchyma sheath cells in the submerged form, as compared to the terrestrial form. The Kranz cells of the terrestrial form had basically the structural characteristics of plants of the NAD-malic enzyme type, with the exception of the intracellular location of organelles. The Kranz cells of the submerged form included only a few organelles, and the percentage of organelles partitioned to the Kranz cells was significantly smaller in the submerged form than in the terrestrial form. In addition, the size of chloroplasts of the Kranz cells was 60–70% of that of the terrestrial form. These structural differences between the two forms may be related to the functional differences in their mechanisms of photosynthesis.

Direct somatic embryogenesis in leaves ofCichorium

Leaves from 2-month-old in vitro grown plantlets of a clone ofCichorium placed in agitated liquid induction medium at 35°C in the dark produce embryoids after 5 days of culture, without synchronization. Vascular sheath parenchyma cells react first, but every mesophyll cell is potentially embryogenic. Single cells show an early patchy callosic wall and undergo dedifferentiation. With SEM the cells of those proembryoids just emerging through the epidermis are seen to be linked by a fibrillar network, the nature of which is discussed. Four FITC-labelled lectins were tested; only DBA shows embryogenic specificity.

Mechanisms of chloride partitioning in the leaves of salt‐stressed Sorghum bicolor L.

Chloride transport in sheath and blade tissue and the cellular distribution of Cl‐ were investigated in an attempt to determine the physiological basis of the preferential accumulation of Cl‐ in sheaths of salt‐stressed sorghum (Sorghum bicolor L.). Import and export of 36Cl‐ in leaf sheaths and blades of intact sorghum were followed over a 2 week period. X‐ray microanalysis of frozen‐hydrated bulk tissue samples was used to determine the accumulation of Cl‐ and other elements in the vacuoles of sheath and blade cells.Sheath tissue accumulated Cl‐ despite a relatively high Cl‐ turnover rate. Chloride was shown to accumulate in most cell types of the sheath, particularly in adaxial epidermal cells. After an initial increase in the concentration of Cl‐, blade tissue regulated Cl‐ levels within certain limits. Chloride levels in blades were greater in the abaxial and adaxial epidermal cells than in other cell types. The epidermal cells of blades accumulated Cl‐ to approximately the same concentration as sheath epidermal cells. The Cl‐ concentration in the photosynthetically active mesophyll and bundle sheath cells, however, remained low.Thus, the partitioning of Cl‐ previously observed in the leaves of salinized sorghum apparently results from the ability of bundle sheath and mesophyll cells to maintain concentrations of Cl‐ at lower levels than do epidermal cells. In addition, the relatively large sheath parenchyma cells tend to serve as reservoirs for the storage of Cl‐.

The distribution of plasmodesmata in the phloem ofHevea brasiliensis in relation to laticifer loading

Cell to cell connections, including plasmodesmata and perforations, were examined in the non-conducting secondary phloem ofHevea brasiliensis. Samples were taken from trunks of numerous trees, from several clones, and prepared for thin sectioning and transmission or scanning electron microscopy and as optical sections for fluorescence microscopy. Numerous plasmodesmata were found clustered in primary pit-fields between the ray and axial parenchyma cells. Between the laticifers and adjacent parenchyma sheath cells, structures corresponding to functional plasmodesmata were not observed. But some unusual structural features were occasionally seen in these walls. These observations are discussed in relation to the possible function of the cell types, and to the loss of latex on the tapping ofHevea. It is suggested that the loading of the laticifer might first require a symplastic pathway for the transport of metabolites, at the end of which the assimilates must enter the apoplast. A transmembrane active transport system then transfers the metabolites in the laticifer. The presumable role of parenchyma cells in the loading of laticifers is emphasized.

Water pathways in wheat leaves. III. The passage of the mestome sheath and the function of the suberised lamellae

The fluorochrome sulphorhodamine G, when present in the transpiration stream in wheat leaves, passes rapidly out of the veins and produces fluorescence in the mesophyll and epidermal cell walls. The path of movement of the dye out of the tracherary elements and across the mestome sheath to the parenchyma sheath cells was followed by rapid freezing, freeze‐subsitution, dry embedding in resin, sectioning and epifluorescence microscopy. The sulphorhodamine solution was visible in tracheary elements, and, where it had passed out of the tracheary elements, strongly fluorescent in some of the cell walls. The patterns of wall fluorescence are used to chart the movements of water from the xylem through some of the radial walls of mestome sheath cells near the xylem to the free space of the mesophyll. The suberised lamellae of the mestome sheath cells must form an incomplete barrier near the xylem to permit passage of the dye. A hypothesis is formulated that the function of the suberised lamellae is to keep separate the oppositely directed fluxes of water and assimilates through the sheath. It is further proposed that the function of pits in living cells is a similar insulation of the symplastic traffic from the wayward waters of the apoplast.

Ultrastructure of the Small Vascular Bundles and Transfer Pathways for Photosynthate in the Leaves of Rice Plant

The ultrastructure of small vascular bundles of the 8th leaf blades in rice seedlings was examined with the electron microscope. 1. In the parenchyma sheath cells the chloroplasts have a centrifugal position, whereas the mitochondria have a centripetal position. The phloem is bounded by a single layer of thick-walled parenchyma cells, which differentiate into the mestome sheath cells in the upper leaves. The thick-walled parenchyma cells have the plastids with starch granules, mitochondria and dictyosomes. The suberized lamellae are not detected in the walls of these sheath cells. 2. The protophloem sieve elements and companion cells locatcd abaxially within the vascular bundles show an apparent degeneration in the expanded leaf, but the degeneraion is not observed in the elongating zone of the folded leaf. Thus, the protophloem may degencrate during the leaf emergence and ceases to function after leaf expansion. 3. Late-formcd metaphloem sieve elements are narrow and thickwalled, but the associated companion cells are wider than the sieve elements. The metaphloem sieve elements have the P-type plastids and a small amount of mitochondria and endoplasmic reticulum. The rnetaphloem companion cells contain many mitochondria and endoplasmic reticulum, and often contain osmiophilic globules. Ultrastructural features of the metaphloem parenchyma cells are the same as the companion cells. 4. The distribution of plasmodesmata in transections of the small vascular bundles has been determined. The plasmodesmata occur in the outer and inner tangential walls of the parenchyma sheath cells. The late-formed metaphloem companion cells are connected by numerous plasmodesmata with adjacent parenchyma cells of the metaphloem and metaxylem, and also with the thick-walled parenchyma cells respectively. The companion cell and the sieve element are connected by plasmodcsmata which are branched on the companion cell side. The data support the view that photosynthate moves through a symplastic pathway from mesophyll to the metaphloem sievc elements. The following pathways are suggested.[table]

Intracellular structures of Puccinia Poarum on its alternate hosts

A morphological and quantitative comparison has been made of the development of intracellular structures of the heteroecious rust, Puccinia poarum , in tissues of its pycnial-aecial host, Tussilago farfara and of its uredinial-telial host, Poapratensis . The relatively unspecialized intracellular hyphae of pycnial-aecial pustules differ from haustoria of uredinial-telial stages in their greater length, more irregular growth with occasional septation, and in their lack of a clear neck region or recognizable haustorium mother cell. Intracellular structures of P. poarum were found in epidermal, mesophyll and bundle sheath cells of both hosts, occurring in greater concentration in the bundle sheath than in the mesophyll. In Tussilago , infection of the vascular tissue was demonstrated. The frequency of penetration of mesophyll cells by haustoria in Poa was greater than that by intracellular hyphae in Tussilago . The volume of haustoria present in cells of the different types of infected tissue in Poa leaves was inversely related to host cell size, being highest in bundle sheath parenchyma cells and lowest in the epidermis. Haustoria in mesophyll cells increased in size and complexity throughout successive sub-stages of uredinial and telial development. The effects of infection of P. poarum on host tissue included reduced growth of Tussilago mesophyll cells adjacent to pycnia, increased volume of nuclei in infected cells of both hosts and a typically close association between nuclei of infected Poa cells and haustoria. These differences between monokaryotic intracellular hyphae and dikaryotic haustoria in growth habit, frequency of penetration of host cells, association with host nuclei and ability to infect vascular tissue suggest that the alternating phases of the rust life-cycle differ in their nutrition and physiology, requiring two types of intracellular structure.

Fragmentation of Cotton Bract and a Technique for Detecting Bract in Cotton Dust1

AbstractBract fragments are thought to be a major component of the respirable dust generated during the processing of cotton (Gossypium sp.) lint in textile mills. Byssinosis is an occupational disease affecting susceptible textile workers exposed to respirable dust. Procedures designed to reduce mill dust require that the dust components be identified. The cotton bract is a candidate component. The objectives of this study were (A) to determine if changes occur in the friability and structure of bract during postanthesis development and (B) to develop a tracer technique suitable for following the micronization of this plant part. Whole bracts were collected from greenhouse‐grown cotton, ‘Tamcot SP21’. Bract friability was determined by placing whole bracts in porcelain jars and abrading these plants with porcelain cylinders for ½‐hour on a roller mill. Whole anthesis bracts were broken apart to the extent that 6% of their weight was collected in a particle size fraction < 250 μm. By contrast, in bracts collected from 20 to 120 days postanthesis there was a trend toward a greater percent of the bract to be broken apart to a particle size of < 250 μm by the same procedure. Observation of tissue sections prepared from bracts showed that this change in friability was associated with an increased number of lignified bundle sheath parenchyma cells and tracheary elements in bract veins. Other anatomical changes accompanying bract senescence included significant decreases in epidermal, mesophyll, and lamina thickness at or shortly after the time of capsule dehiscence. Four fluorescent dyes and two fluorescent brightening agents were applied separately in aqueous solution to cotton bract and leaf trash. Colour Index Basic Yellow 37 was found to be the most suitable dyeing agent. Two‐ to 10‐μm diameter particles obtained from the pulverized remains of dyed bract were distinguished from undyed bract particles of the same size by observation with an epifluorescence microscope using a 334‐ to 365‐nm exciter beam at a magnification of 625 ✕. Significant differences in friability of dyed and undyed bract were not observed by roller mill tests. It is reasonable to conclude that these tracer procedures will identify the bract component in respirable cotton mill dust.

Rumen Microbial Degradation of Starch‐Containing Bundle Sheath Cells in Warm‐Season Grasses1

Leaf sections of the warm‐season grasses ‘Coastal’ bermudagrass (Cynodon dactylon (L.) Pers.), ‘Pensacola’ bahiagrass (Paspalum notatum Flugge), and ‘Pangola’ digitgrass (Digitaria decumbens Stent.) were evaluated for the ease of rumen microbial degradation of cells with high nutrient contents using electron microscopy. Observations of IKI‐stained sections viewed by light microscopy confirmed those of others in that most starch was found in the chloroplasts of parenchyma bundle sheath cells while little or no starch was seen in mesophyll chloroplasts. Parenchyma sheath cells were less rapidly degraded than mesophyll cells in all species. Observations from transmission electron microscopy revealed that in these warm season grasses starch was undegraded until the thick, laminated wall of the parenchyma sheath was degraded or disrupted by rumen bacteria; starch grains were then degraded. These results indicated that the large amount of potential nutrients in the parenchyma bundle sheath of these warm‐season forages may not be readily available because of slow degradation of the sheath cell wall by rumen bacteria.

Photosynthetic Characteristics of Panicum milioides, a Species with Reduced Photorespiration1

A species (Panicum milioides Nees ex. Trin.), has been found which apparently has a reduced rate of photorespiration compared to other C3 plants. It was found in preliminary studies that the response of net photosynthesis (Pn) to O2 concentration was less for this species than for other C3 plants. Therefore, this work was conducted to characterize for five accessions of P. milioides the CO2 exchange related to photorespiration. Panicum maximum Jacq. (C4), P. laevifolium Htack. (C4), and tall fescue (Festuca arundinacea Schreb. (C3) were included for comparison. Leaf cross‐sections of P. milioides were examined for characteristics known to be related to photosynthetic carbon pathways. 13C/12C ratios were determined on P. milioides tissue.P. milioides photorespired less than tall fescue and more than P. maximum as determined by the three criteria: Pn response to O2, CO2 evolution in the light, and CO2 compensation concentration. The change in Pn for each 1% increase in O2 was from −0.36 to −0.48 mg CO2 dm−2 h−1 for five accessions of P. milioides compared to −0.10, −0.13, and −0.61 mg dm−2 h−1 for P. maximum, P. laevifolium, and tall fescue, respectively. P. milioides evolved an average of 0.85 mg CO2 dm−2 h−1 in the light at 20% O2 compared to 0.02 mg dm−2 h−1 for P. maximum and 2.96 mg dm−2 h−1 for tall fescue. CO2 compensation concentrations determined by a Mylar bag technique were 0.4, 15.8, and 54 ppm for P. maximum, P. milioides, and tall fescue, respectively. Determination of CO2 compensation from Pn response to CO2 gave a similar trend, although actual concentrations were different. P. milioides tissue had δ 13C values of about −25 ‰, characteristic of C3 species. A leaf anatomical study showed that P. milioides had enlarged parenchyma sheath cells with centripetally located chloroplasts and mesophyll cells arranged in a radial manner around the parenchyma sheath. The parenchyma sheath cell walls appeared to be thicker than those of most C3 species. It is concluded that while P. milioides exhibits mostly C3 characteristics, its reduced photorespiration rate and some C4‐like anatomical characteristics indicate a degree of intermediacy between C3 and C4.

Sugarcane mosaic virus infection of seedling roots of Zea mays and Sorghum halepense

Sugarcane mosaic virus (SCMV) multiplication was studied in roots of Zea mays L. (Golden Bantam sweet corn) and Sorghum halepense L. (Johnson grass). Mechanical inoculation of corn roots with SCMV did not result in systemic infection, and SCMV could be recovered from only nine of 1950 inoculated roots. Some virus was detected in roots of young leaf-inoculated seedlings. Attempts to purify SCMV from these roots did not yield detectable virus, while 2 mg virus per 100 g host tissue was obtained from leaf tissue. Ultrastructural changes in systemically infected root tip cells of corn and Johnson grass included pinwheel inclusions in epidermal cells of corn, characteristic of the potato virus Y group. Bundle inclusions were found in bundle sheath parenchyma cells of corn root tips. Bundle inclusions, but not pinwheels, were found throughout the root tips of infected Johnson grass roots. Significant changes in levels of nitrogen and carbohydrate were found in SCMV-infected shoots and roots.