Calcium requirement of phytochrome-mediated fern-spore germination: No direct phytochrome-calcium interaction in the phytochrome-initiated transduction chain

The decision to germinate is regulated by divergent molecular networks in spores and seeds

Dispersal is a key step in land plant life cycles, usually via formation of spores or seeds. Regulation of spore- or seed-germination allows control over the timing of transition from one generation to the next, enabling plant dispersal. A combination of environmental and genetic factors determines when seed germination occurs. Endogenous hormones mediate this decision in response to the environment. Less is known about how spore germination is controlled in earlier-evolving nonseed plants. Here, we present an in-depth analysis of the environmental and hormonal regulation of spore germination in the model bryophyte Physcomitrella patens (Aphanoregma patens). Our data suggest that the environmental signals regulating germination are conserved, but also that downstream hormone integration pathways mediating these responses in seeds were acquired after the evolution of the bryophyte lineage. Moreover, the role of abscisic acid and diterpenes (gibberellins) in germination assumed much greater importance as land plant evolution progressed. We conclude that the endogenous hormone signalling networks mediating germination in response to the environment may have evolved independently in spores and seeds. This paves the way for future research about how the mechanisms of plant dispersal on land evolved.

Sexual propagation of Pteris vittata L. influenced by pH, calcium, and temperature

We aimed to optimize germination and growth conditions of the arsenic hyperaccumulating fern, Pteris vittata L. Pot experiments were carried out to investigate the effects of soil pH, soil calcium (Ca) concentration, and temperature on the sexual propagation of P. vittata. At 25 degrees C, germination was both accelerated and increased by high soil pH and Ca concentration. Spores of P. vittata did not germinate on medium with a pH of 4.6. Amending strongly acid soils with 27.5 or 40 micromol/g Ca(OH)2 significantly improved the growth rate during both the germination phase and the gametophyte phase. Amending strongly acid soils with NaOH (55 micromol/g) promoted germination, but did not affect subsequent growth. Among the different temperature, germination and growth rates were higher at 25 degrees C than at 20 degrees C or 30 degrees C. The distribution of P. vittata in China might be influenced by its requirement for high pH and high Ca concentration in the soil and appropriate growth temperature to complete sexual propagation. These results provided important information for improving breeding conditions of P. vitatta and will be helpful for extending the range of areas in which P. vittata can be used for phytoremediation.

Effect of calcium on dark adaptation in Phycomyces phototropism

Adaptation processes enable phototropism of Phycomyces to operate over a 10-decade range of blue-light intensity (1 nW m-2-10 W m-2). To investigate the influence of calcium on dark adaptation, the phototropic latency method was employed with the modification that sporangiophores were temporarily immersed in solutions containing CaCl2 or LaCl3. Following such treatment, the time course of bending was found to have two components with distinct latencies and bending rates. After immersion in darkness for 30 min in LaCl3 solution or 1 h in a solution of CaCl2, MgCl2, or the calcium chelator EGTA, each sporangiophore was adapted to a blue light beam (1 W m-2) for 45 min by rotation around its vertical axis. Cessation of rotation defined the onset of the phototropic stimulus, at which time the intensity was reduced by as much as 10(3)-fold. For a 10(2)-fold reduction (to 10(-2) W m-2), immersion in CaCl2 (10-100 microM) reduces the latency 13 min for the early bending component and 18 min for the late component, whereas treatment with the calcium-channel blocker lanthanum (0.1-11 microM LaCl3) increases the latency 12 min for the early component and 13 min for the late component. EGTA (10 microM) also had an inhibitory effect, increasing the latency of the first and the second components by 7 and 10 min, respectively. In experiments performed similarly, but without the light adaptation treatment after immersion, no differences between calcium-treated and control sporangiophores were found. The bending rates of both components show only a weak dependence on calcium.(ABSTRACT TRUNCATED AT 250 WORDS)

Phytochrome-mediated germination and early development in spores of Dryopteris filix-mas L.: phase-specific and non phase-specific inhibition by staurosporine

The alkaloid staurosporine, currently known as the most potent inhibitor of protein kinase C, PKC, was tested for its ability to inhibit phytochrome-mediated spore germination in Dryopteris filix-mas L., evaluated by the induction of chlorophyll synthesis. Approximately half-maximal inhibition was obtained at a concentration of 10(-5) M. This effect of staurosporine was phase-specific and was found during the same period in which the presence of extracellular calcium is necessary for realization of the light signal. Furthermore, the ability of staurosporine to prevent progression of a germinated spore into early gametophyte development, evaluated by the accumulation of chlorophyll, was examined. Again, staurosporine (10(-5) M) significantly diminished chlorophyll accumulation, determined quantitatively in vivo by single-cell measurements, in a non-phase specific way. The fact that the phase-specific inhibitory effect of staurosporine in preventing germination was coincident with the phase-specific requirement of Ca2+ suggests that both Ca2+ and staurosporine affect the same step in the signal-transduction chain. A phosphorylation event catalysed by PKC or any Ca2+ -dependent protein kinase is proposed as the target of staurosporine and Ca2+.

Determination of cytoplasmic calcium concentration in Dryopteris spores : A developmentally non-disruptive technique for loading of the calcium indicator fura-2

Germination of Dryopteris spores is mediated by the physiologically active, far-red-absorbing form of phytochrome, Pfr, and external Ca(2+) is necessary for the transduction of the light signal. Because knowledge about the cytoplasmic calcium ion concentration, [Ca(2+)]i, is of great importance for understanding the role of calcium during signal transduction, this value was measured using fura-2 in fern spores undergoing the normal developmental progression into germination. Fura-2 was loaded into the spores by electroporation, which does not disrupt the normal process of germination. The intensity of the fluorescence emission of the loaded fura-2 was analysed by a microspectrophotometric assay of single spores, and successful loading could be obtained by the application of ten electrical pulses (field strength 7.5 kV · cm(-1), half-life (time constant) 230 μs). Fura-2 was alternately excited by light of wavelengths 355 and 385 nm through an inverted fluorescence microscope, and the emitted fura-2 fluorescence was collected by a silicon-intensified video camera. The cytoplasmic calcium ion concentration was calculated from the ratio of the camera output obtained for both wavelengths and displayed by a pseudo-color technique. Spores responded to changes of the extracellular Ca(2+) concentration, and this observation is considered as evidence that fura-2 is loaded into the cytoplasm. The substitution of a low external [Ca(2+)] (1 mM ethyleneglycol-bis(2-aminoethyl-ether) {ie166-01},N'-tetraacetic acid (EGTA)) by 1 mM CaCl2 caused a fast increase of [Ca(2+)]i from approx. 50 nM to above 500 nM. In contrast, the subsequent substitution of CaCl2 by EGTA decreased [Ca(2+)]i again below 100 nM within 0.5 h. Furthermore, the application of ionomycin could initiate a change in [Ca2+]i according to the Ca(2+) gradient established between the extracellular medium and cytoplasm. In spores sown on a Ca(2+)-free medium, [Ca(2+)]i, analysed in a buffer containing EGTA, was found to be around 50 nM during the first days of cultivation, independent of the irradiation protocol. However, if spores were grown in darkness on a Ca(2+)-containing medium and analysed in EGTA, [Ca(2+)]i was significantly higher (≧ 500 nM). In red-light-irradiated spores, [Ca(2+)]i was found to decrease with increasing time after irradiation, and was determined to be less than 100 nM when analysis was done 44 h after germination was initiated by the light treatment.