No abstract

Bacteria represent a substantial fraction of the microorganisms that inhabit leaf surfaces. We collected samples of the moss Funaria hygrometrica (L.) in the field and analysed the epiphytes on the gametophyte by the agar impression method and scanning electron/fluorescence microscopy. On the phylloid surface numerous bacteria were detected, notably in the grooves between adjacent lamina cells. Methanol‐ammonium salts agar surfaces impressed with isolated phylloids of green gametophytes resulted in the growth of methylotrophic colonies. Two Methylobacterium strains (M. mesophilicum and M. sp., isolated from the Funaria phylloids) were found to simulate the well‐known effect of cytokinin application on bud formation in Funaria protonemata. In addition, Methylobacterium inoculation promoted the growth of protonemal filaments. The significance of this novel Methylobacterium‐land plant interaction is discussed.

Methylotrophic bacteria inhabit the surface of plant organs, but the interaction between these microbes and their host cells is largely unknown. Protonemata (gametophytes) of the moss Funaria hygrometrica were cultivated in vitro under axenic conditions and the growth of the protonemal filaments recorded. In the presence of methylobacteria (different strains of Methylobacterium), average cell length and the number of cells per filament were both enhanced. We tested the hypothesis that auxin (indole-3-acetic acid, IAA), secreted by the epiphytic bacteria and taken up by the plant cells, may in part be responsible for this promotion of protonema development. The antiauxin parachlorophenoxyisobutyric acid (PCIB) was used as a tool to analyze the role of IAA and methylobacteria in the regulation of cell growth. In the presence of PCIB, cell elongation and protonema differentiation were both inhibited. This effect was compensated for by the addition of different Methylobacterium strains to the culture medium. Biosynthesis and secretion of IAA by methylobacteria maintained in liquid culture was documented via a colorimetric assay and thin layer chromatography. Our results support the hypothesis that the development of Funaria protonemata is promoted by beneficial phytohormone-producing methylobacteria, which can be classified as phytosymbionts.

The cytokinesis-related callose deposition in cell plates and juvenile cross walls of meristematic cells was investigated in the liverwort Riella helicophylla and seedlings of Arabidopsis thaliana. The b-1,3-glucan callose was detected by its specific staining properties with sirofluor and aniline blue by fluorescence microscopy. The photo-labile calcium antagonist nifedipine (NIF) exerted a specific promotive effect when the substance was exposed to light. The nitroso derivative of photolysed NIF was found to be the active compound which was responsible for the enhancement in callose deposition. The nitroso derivative was isolated after photolysis of NIF by UV light (365 nm) and its structure was verified with 1 H-nuclear magnetic resonance and infrared spectroscopy. The characteristic absorption maximum at 770 nm in dimethyl sulfoxide was employed to determine the concentration of the nitrosopyridine in solutions by use of the molar absorption coefficient of the isolated substance. In addition, the nitro derivative of nifedipine was prepared. This nitropyridine was ineffective with respect to the stimulation of callose deposition in dividing cells. The possible mechanism of this cytotoxic effect and its implications for symplastic growth in meristems is discussed.

The Ca(2+) indicator 7-chlorotetracycline has been shown to bind to a pore complex on both outer surfaces of all non-meristematic cells in the unistratose thallus of Riella ('chlorotetracycline-binding surface region'=CSR; Grotha, 1983, Planta 158, 473-481). Prolonged treatment of the thallus with 7-chlorotetracycline, 5-hydroxytetracycline, verapamil and desmethoxyverapamil induces the deposition of callose at the same region. The influence of various treatments on verapamil-induced CSR-callose was measured in situ by microfluorometry of aniline-blue-stained material. Callose deposition is maximal at 10(-4)M verapamil or 5·10(-5)M desmethoxyverapamil with 2·10(-4)M Ca(2+) or Mg(2+) in the medium. The reaction is completely inhibited at pH 5.5 and is optimal between pH 6.5 and 7.5. The production of CSR-callose is absolutely light-dependent with callose being first visible after 30 min of light. La(3+), ethylene glycol-bis(β-aminoethylether)-N,N,N',N'-tetraacetic acid and amiprophosmethyl, antagonists of Ca(2+) functions, and 2-deoxy-D-glucose suppress the verapamil induction of CSR-callose. Furthermore the ionophores A 23187, valinomycin and monensin effectively block the reaction. The deposition of CSR-callose is diminished at increasing external osmolarity and is abolished at osmotic values that stimulate plasmolysis-callose. Wounding causes the formation of wound-callose but inhibits the induction of CSR-callose in cells of the wound edge. Nifedipine increases or prolongs callose synthesis in cell plates. The Ca(2+)-channel blocker diltiazem is completely ineffective. It is suggested as a working hypothesis that verapamil-induced CSR-callose synthesis is caused by a local change in membrane permeability, possibly as a consequence of the opening of Ca(2+) channels being involved in Golgi-vesicle mediated exocytosis (A. Kramer and H. Lehmann, 1986, Ber. Dtsch. Bot. Ges. 99, 111-121).