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Evidence for two pathways of phloem loading (1994)

Eschrich, Walter ; Fromm, Jörg

Oxford, UK : Blackwell Publishing Ltd

Physiologia plantarum 90 (1994), S. 0

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ISSN: 1399-3054

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: The minor veins of small leaf discs, punched out of mature leaves and incubated in 14C-sucrose solution, appear labeled in macro- and microautoradiographs. Discs with a labeled vein pattern and with labeled sieve tubes in microautoradiographs were found in Beta vulgaris, Vicia faba, Gomphrena globosa and Antirrhinum majus. However, in several other plant species, minor veins appeared unlabeled in macroautoradiographs when the discs were incubated in 14C-sucrose. Mesophyll cells (Acer pseudoplatanus, Juglans regia, Fagia, sylvatica, Syringa vulgaris, Laburnum anagyroides), bundle-sheath cells of major veins (Salix viminalis, Robinia pseudoacacia, Commelina communis) or epidermal layers (Ginkgo biloba, Chlorophytum comosum) appeared labeled. Lack of radioactivity in sieve tubes of this latter group was confirmed by microauto-radiography. Using 14C-glucose instead of 14C-sucrose, leaf discs of Beta vulgaris showed no labeled vein pattern and in microautoradiographs the sieve tubes appeared unlabeled. In view of the by-pass phloem loading, this study provides evidence for two pathways of phloem loading.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1399-3054.1994.tb02526.x

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Growth, membrane potential and endogenous ion currents of willow (Salix viminalis) roots are all affected by abscisic acid and spermine (1997)

Fromm, Jörg ; Meyer, Andreas J. ; Weisenseel, Manfred H.

Oxford, UK : Blackwell Publishing Ltd

Physiologia plantarum 99 (1997), S. 0

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ISSN: 1399-3054

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: Growth measurements of hormone-treated roots from willow cuttings were combined with electrophysiological recordings to study hormone-induced changes in membrane potential and in endogenous ion currents. The mean growth rate of roots was 10 ± 2 μm min−1 in regular nutrient solution. It increased to 13 ± 2 μm min+1 after application of spermine and decreased to 0.07 ± 0.01 μm min−1 after treatment with abscisic acid (ABA). Transient depolarizations were elicited in root cortex cells by spermine, while ABA caused a transient hyperpolarization. All changes in membrane potential were accompanied by transient responses of the endogenous current. These responses suggest that first anions, then cations leave the root during spermine-induced depolarizations. From the changes of the endogenous current an apparent efflux of anions (presumably Cl−) and cations (presumably K+) of 200 to 700 pmol cm−2 per depolarization was calculated.To further investigate a possible relation between endogenous ion currents, growth and the growth regulators ABA and spermine, long-lasting extracellular vibrating-probe measurements were performed. Control roots showed an inward current of about 1.5 μA cm−2 at the apical elongation zone and an outward current with a maximum density of 1.3 μA cm−2 at the central and basal elongation zone. The addition of ABA and spermine (final concentration 0.1 mM) to the bathing medium affected the endogenous current in opposite ways: ABA caused a reduction of inward and outward current, while spermine stimulated both. Since protons are a major component of the endogenous current, and sucrose can be taken up by root cells from the apoplast via symport with H+, a role of the endogenous current in growth regulation is indicated.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1399-3054.1997.tb05353.x

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Control of phloem unloading by action potentials in Mimosa (1991)

Fromm, Jörg

Oxford, UK : Blackwell Publishing Ltd

Physiologia plantarum 83 (1991), S. 0

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ISSN: 1399-3054

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: In the sensitive plant, Mimosa pudica, action potentials arise when the leaves are touched and they trigger a sudden decrease in turgor of the pulvinar motor cells, which causes the leaf to close. These potentials may travel through the phloem and they appear to influence pulvinar phloem unloading after stimulation. Mature leaves were exposed to 14CO2 and phloem translocation was observed by autoradiography. In unstimulated pulvini, labeled photoassimilates were restricted to the phloem. However, after stimulation, the 14C-label appeared to be concentrated in the extensor region of the motor cortex. Since stimulation elicits an action potential, it is suggested that it also triggers phloem unloading of sucrose in the pulvini.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1399-3054.1991.tb00130.x

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