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1

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Pathways of assimilation and transfer of fixed nitrogen in coralloid roots of cycad-Nostoc symbioses (1988)

Pate, J. S. ; Lindblad, P. ; Atkins, C. A.

Springer

Planta 176 (1988), S. 461-471

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ISSN: 1432-2048

Keywords: Carbon dioxide fixation ; Citrulline ; Coralloid roots ; Cycads (nitrogen fixation) ; Nitrogen fixation ; Nitrogen transport ; Nostoc

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Freshly detached coralloid roots of several cycad species were found to bleed spontaneously from xylem, permitting identification of products of nitrogen transfer from symbiotic organ to host. Structural features relevant to the export of fixed N were described for Macrozamia riedlei (Fisch. ex Gaud.) Gardn. the principal species studied. Citrulline (Cit), glutamine (Gln) and glutamic acid (Glu), the latter usually in a lesser amount, were the principal translocated solutes in Macrozamia (5 spp.), Encephalartos (4 spp.) and Lepidozamia (1 sp.), while Gln and a smaller amount of Glu, but no Cit were present in xylem sap of Bowenia (1 sp.),and Cycas (2 spp.). Time-course studies of 15N enrichment of the different tissue zones and the xylem sap of 15N2-pulse-fed coralloid roots of M. riedlei showed earlier 15N incorporation into Gln than into Cit, and a subsequent net decline in the 15N of Gln of the coralloid-root tissues, whereas Cit labeling continued to increase in inner cortex and stele and in the xylem sap. Hydrolysis of the 15N-labeled Cit and Gln consistently demonstrated much more intense labeling of the respective carbamyl and amide groups than of the other N-atoms. Coralloid roots of M. riedlei pulse-fed 14CO2 in darkness showed 14C labeling of aspartic acid (Asp) and Cit in all tissue zones and of Cit of xylem bleeding sap. Lateral roots and uninfected apogeotropic roots of M. riedlei and M. moorei also incorporated 14CO2 into Cit. The 14C of Cit was restricted to the carbamyl-C. Comparable 15N2 and CO2-feeding studies on corallid roots of Cycas revoluta showed Gln to be the dominant product of N2 fixation, with Asp and alanine as other major 14C-labeled amino compounds, but a total absence of Cit in labeled or unlabeled form.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00397652

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2

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The extrafloral nectaries of cowpea (Vigna unguiculata (L.) Walp): I. Morphology, anatomy and fine structure (1985)

Kuo, J. ; Pate, J. S.

Springer

Planta 166 (1985), S. 15-27

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ISSN: 1432-2048

Keywords: Nectary ; extrafloral ; Vigna (nectaries)

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract The cowpea bears two distinctive types of extrafloral nectaries. One, on the stipels of trifoliolate leaves, consists of a loosely demarcated abaxial area (1–2 mm diameter) of widely-spaced trichomes (papillae) borne on a stomata-free epidermis, and lacking a specific vascular supply. Each trichome has up to eight apical (head) cells, two to four intermediate cells, and a single large stalk cell. The secretory faces of the apical cells bear wall ingrowths and an easily detached cuticle. The wall separating the stalk cell and the underlying epidermal cell(s) has a mean plamodesmatal frequency of 25/μm2. The second type of nectary consists of a large elliptical mound of tissue (short and long axes about 2 mm and 4 mm) formed between a pair of flowers on an inflorescence stalk. It comprises four to eight cone-shaped subnits of secretory tissue, each with a circular secretory orifice and an individual supply of phloem, but not of xylem. Cells of the secretory tissue of the nectary subunits separate as they mature, and nectar flows to the orifice through the resulting intercellular spaces. Intact secretory cells and cellular debris are extruded into the nectar. Some of the sieve elements terminating in the inner secretory tissue exhibit open sieve pores. Each mature secretory cell contains many small (2 μm diameter) spherical protein bodies and one to three large (up to 2–3 μm diameter 15 μm long), paracrystalline bodies. These inclusions are absent or not fully developed in inner, less mature regions of the secretory tissue. Mechanisms of secretion are proposed for the two classes of nectary, including estimates of flux of sugar into the trichomes of the stipel nectary.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00397381

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3

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The extrafloral nectaries of cowpea (Vigna unguiculata (L.) Walp.) II. Nectar composition, origin of nectar solutes, and nectary functioning (1985)

Pate, J. S. ; Peoples, M. B. ; Storer, P. J. ; [et al.]

Springer

Planta 166 (1985), S. 28-38

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ISSN: 1432-2048

Keywords: Nectary, extrafloral ; Vigna (nectaries)

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Nectar was collected from the extrafloral nectaries of leaf stipels and inflorescence stalks, and phloem sap from cryopunctured fruits of cowpea plants. Daily sugar losses as nectar were equivalent to only 0.1–2% of the plant's current net photosynthate, and were maximal in the fourth week after anthesis. Sucrose:glucose:fructose weight ratios of nectar varied from 1.5:1:1 to 0.5:1:1, whereas over 95% of phloem-sap sugar was sucrose. [14C]Sucrose fed to leaves was translocated as such to nectaries, where it was partly inverted to [14C]glucose and [14C]fructose prior to or during nectar secretion. Invertase (EC 3.2.1.26) activity was demonstrated for inflorescence-stalk nectar but not stipel nectar. The nectar invertase was largely associated with secretory cells that are extruded into the nectar during nectary functioning, and was active only after osmotic disruption of these cells upon dilution of the nectar. The nectar invertase functioned optimally (phloem-sap sucrose as substrate) at pH 5.5, with a starting sucrose concentration of 15% (w/v). Stipel nectar was much lower in amino compounds relative to sugars (0.08–0.17 mg g-1 total sugar) than inflorescence nectar (22–30 mg g-1) or phloem sap (81–162 mg g-1). The two classes of nectar and phloem sap also differed noticeably in their complements of organic acids. Xylem feeding to leaves of a range of 14C-labelled nitrogenous solutes resulted in these substrates and their metabolic products appearing in fruit-phloem sap and adjacent inflorescence-stalk nectar. 14C-labelled asparagine, valine and histidine transferred freely into phloem and appeared still largely as such in nectar. 14C-labelled glycine, serine, arginine and aspartic acid showed limited direct access to phloem and nectar, although labelled metabolic products were transferred and secreted. The ureide allantoin was present in phloem, but absent from both types of nectar. Models of nectary functioning are proposed.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00397382

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4

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Evaluation of N2-fixation and nitrogen economy of a maize/cowpea intercrop system using15N dilution methods (1987)

Ofori, Francis ; Pate, J. S. ; Stern, W. R.

Springer

Plant and soil 102 (1987), S. 149-160

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ISSN: 1573-5036

Keywords: cowpea ; intercropping ; maize ; 15N methods ; N economy ; N2-fixation

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract Yields of above ground biomass and total N were determined in summer-grown maize and cowpea as sole crops or intercrops, with or without supplementary N fertilizer (25 kg N ha−1, urea) at an irrigated site in Waroona, Western Australia over the period 1982–1985. Good agreement was obtained between estimates of N2 fixation of sole or intercrop cowpea (1984/85 season) based on the15N natural abundance and15N fertilizer dilution techniques, both in the field and in a glasshouse pot study. Field-grown cowpea was estimated to have received 53–69% of its N supply from N2-fixation, with N2-fixation onlyslightly affected by intercropping or N fertilizer application. Proportional reliance on N2-fixation of cowpea in glasshouse culture was lower (36–66%) than in the field study and more affected by applied N. Budgets for N were drawn up for the field intercrops, based on above-ground seed yields, return of crop residues, inputs of fixed N and fertilizer N. No account was taken of possible losses of N through volatilization, denitrification and leaching or gains of N in the soil from root biomass. N2-fixation was estimated tobe 59 kg N ha−1 in the plots receiving no fertilizer N, and 73 kg N ha−1 in plots receiving 25 kg N ha−1 as urea. Comparable fixation by sole cowpea was higher (87 and 82 kg N ha−1 respectively) but this advantage was outweighed by greater land use efficiency by the intercrop than sole crops.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02370697

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5

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Ultrastructure of the haustorial interface and apoplastic continuum between host and the root hemiparasiteOlax phyllanthi (Labill.) R. Br. (Olacaceae) (1989)

Kuo, J. ; Pate, J. S. ; Davidson, N. J.

Springer

Protoplasma 150 (1989), S. 27-39

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ISSN: 1615-6102

Keywords: Root hemiparasite ; Olax ; Host-parasite interface ultrastructure ; Apoplastic tracers ; Transport pathway ; Water: solute uptake

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary Structural features of haustorial interface parenchyma of the root hemiparasiteOlax phyllanthi are described. Walls contacting host xylem are thickened non-uniformly with polysaccharides, not lignin, and show only a thin protective wall layer when abutting pits in walls of host xylem vessels or tracheids. Lateral walls of interface parenchyma exhibit an expanded middle layer of open fibrillar appearance, sometimes with, but mostly lacking adjoining layers of dense wall material. Free ribosomes and rough endoplasmic reticulum are prominent and occasional wall ingrowths present. Experiments involving transpirational feeding of the apoplast tracers lanthanum nitrate or uranyl acetate to host roots cut below haustorial connections, indicate effective apoplastic transfer from host to parasite root via the haustorium. Deposits of the tracers suggest a major pathway for water flow through host xylem pits, across the thin protective wall layer, and thence into the haustorium via the electronopaque regions of the terminal and lateral walls of the contact parenchyma. Graniferous tracheary elements and walls of parenchyma cells of the body of the haustorium appear to participate in tracer flow as do walls of cortical cells, stele parenchyma and xylem conducting elements of the parasite root, suggesting that both vascular and non-vascular routes are involved in extracytoplasmic transfer of xylem sap from host to parasite. The Casparian strip of the endodermis and the suberin lamella of the exodermis of theOlax root act as barriers to flow within the system.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01352918

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