Red Light Pulse Research Articles

Using the temperature-dependent photovoltage to investigate porous silicon/silicon structures

Structures based on porous silicon por-Si/p-Si, both freshly prepared by chemical etching and aged, exhibit a temperature-dependent photovoltage at high levels of electron-hole pair generation by pulse trains of red and white light. These structures are investigated by measuring this photovoltage, which is shown to consist of two components: a photovoltage generated in p-Si, and an oppositely directed photovoltage that appears in por-Si, characterized by trapping of nonequilibrium holes at the surface of por-Si nanocrystals during the period of illumination by the first pulse of white light. For aged structures capture of electrons in the oxide of the por-Si is also observed. The concentration of interface electronic states and electron traps at the interface of p-Si with por-Si is determined by measuring the photovoltage induced by pulses of red light.

Functional interaction of cryptochrome 1 and phytochrome D

Arabidopsis thaliana wild-type and single, double and triple mutants lacking phytochrome A (phyA-201), phytochrome B (phyB-5), phytochrome D (phyD-1), phytochrome E (phyE-1), cryptochrome 1 (hy4-2.23n) and cryptochrome 2 (fha-1) were used to study the photoreceptor signal-transduction network. The inhibition of hypocotyl elongation was analysed using pulses of red light preceded by a pre-irradiation of white light. The interactions of phyA, phyB and cry1 have been studied in a series of previous papers. Here we focus on the signal transduction initiated by phyD. We observed that phyD can partly substitute for the loss of phyB. Specifically, in the phyB background, red pulses were only effective if both cry1 and phyD were present. The response to red pulses, enabled by the pre-irradiation of white light, was completely reversible by far-red light. Loss of reversibility occurred with an apparent half-life of 2 h, similar to the half-life of 3 h observed for the effect mediated by phyB. Furthermore, we could show that the response to an end-of-day far-red pulse in phyB depends on both phyD and cry1. In contrast to phyD, a functional interaction of phyE and cry1 could not be detected in Arabidopsis seedlings.

Phytochromes and gene expression: Ni, M., Tepperman, J.M. and Quail, P.H. (1999) Binding of phytochrome B to its nuclear signalling partner PIF3 is reversibly induced by light, Nature 400, 781–784

One of the most keenly researched topics in plant biology is how plants sense their local light environment. The authors of this paper have analysed the interaction between phytochrome B and the nuclear-localized phytochrome-interacting factor 3 (PIF3), a putative transcriptional regulator. The assay system relied on the binding of radiolabelled domains of phytochrome B to matrix-immobilized PIF3. Full-length phytochrome B binds to PIF3 only after photoconversion to its active (Pfr) form by a red-light pulse. A subsequent far-red pulse results in reconversion to its inactive form and rapid dissociation from PIF3. Individually, the N-terminal chromophore binding domain and C-terminal dimerization domain show relatively weak binding to PIF3, and the two appear to act synergistically to determine the strength of binding. These results further extend the phytochrome signalling pathway from the cytoplasm to the nucleus and demonstrate the potential to link photoactivation to gene expression.

The effect of light on the level of acetylcholine in seedlings of the wild-type and phytochrome mutants of tomato (Lycopersicon esculentum Mill.)

Applying the method of pyrolysis coupled with gas chromatography (PYR-GC) the content of endogenous acetylcholine (ACh) was investigated in the extracts obtained from tomato (Lycopersicon esculentum Mill.). Seven-day-old seedlings of wild type (WT) and phytochrome mutants au (aurea), hp (high pigment), fri (far-red light insensitive) and tri (temporarily red light insensitive) were studied. In the analyzed material the presence of choline and acetylcholine was discovered. The highest content of ACh (381 mmole/g of fresh weight) was found in tomato cotyledons, whereas the lowest amount (162 nmole/g of fresh weight) in roots. The level of ACh in the plants grown under the continuous light was higher than in etiolated ones. However, no considerable differences in the concentrations of ACh in au and tri seedlings grown under the continuous light and in darkness were observed. The irradiation of etiolated seedlings of wild type with red light was accompanied by the increase of endogenous level of ACh. The pulse of far-red light applied directly after red light reversed this stimulating effect. A similar effect of both light wavelengths on the content of ACh was also found in the case of the tri mutant. On the other hand, in the case of fri mutant, pulse of red light caused the drop in the content of ACh, whereas far-red applied after red light caused visible increase in the level of the investigated substance. In tissues of au mutant no effect of red and far-red lights on the concentration of ACh was established.

Ion antagonism in phytochrome-mediated calcium-dependent germination of turions of Spirodela polyrhiza (L.) Schleiden

The light-dependent germination response of turions (resting fronds) is mediated by phytochrome and requires the presence of Ca2+ in the medium (K.-J. Appenroth and H. Augsten, 1990, Photochem. Photobiol. 52: 61–65). The Ca2+ requirement of germination is apparent only in the presence of exogenous Mg2+. A competitive ion antagonism was demonstrated between Ca2+ and Mg2+ in this physiological response; Mg2+ could also be replaced by Ba2+ or Sr2+. Without exog-enous Mg2+, a Ca2+ concentration as low as 0.9 μM fulfilled the Ca2+ requirement. This type of ion antagonism resembled the competitive Ca/Mg interaction reported previously for calcium-binding proteins. The physiological response was blocked by inhibitors of Ca2+ uptake (verapamil, La3+). It was concluded that uptake of Ca2+ from the external medium is an essential step in the phytochrome-mediated germination of turions. The results are in agreement with the assumption that the uptake of Ca2+ is blocked at the side of entry by other alkaline earth ions. Treatment of turions with Mg2+ (1 mM) for 24 h at varying times after the red light pulse in otherwise virtually Ca2+-free KNO3 solution resulted in a response similar to a Ca2+ step-down treatment. This is in agreement with the assumption that the Ca2+- and the Mg2+-sensitive periods coincide. The ion interaction described here represents the first photophysiological example in plants of an antagonistic effect between Ca2+ and Mg2+ similar to that which occurs in vitro with calmodulin.

Regulation of phytochrome B signaling by phytochrome A and FHY1 in Arabidopsis thaliana.

Phytochrome A (phyA) and phytochrome B (phyB) share the control of many processes but little is known about mutual signaling regulation. Here, we report on the interactions between phyA and phyB in the control of the activity of an Lhcb1*2 gene fused to a reporter, hypocotyl growth and cotyledon unfolding in etiolated Arabidopsis thaliana. The very-low fluence responses (VLFR) induced by pulsed far-red light and the high-irradiance responses (HIR) observed under continuous far-red light were absent in the phyA and phyA phyB mutants, normal in the phyB mutant, and reduced in the fhy1 mutant that is defective in phyA signaling. VLFR were also impaired in Columbia compared to Landsberg erecta. The low-fluence responses (LFR) induced by red-light pulses and reversed by subsequent far-red light pulses were small in the wild type, absent in phyB and phyA phyB mutants but strong in the phyA and fhy1 mutants. This indicates a negative effect of phyA and FHY1 on phyB-mediated responses. However, a pre-treatment with continuous far-red light enhanced the LFR induced by a subsequent red-light pulse. This enhancement was absent in phyA, phyB, or phyA phyB and partial in fhy1. The levels of phyB were not affected by the phyA or fhy1 mutations or by far-red light pre-treatments. We conclude that phyA acting in the VLFR mode (i.e. under light pulses) is antagonistic to phyB signaling whereas phyA acting in the HIR mode (i.e. under continuous far-red light) operates synergistically with phyB signaling, and that both types of interaction require FHY1.

Control of hypocotyl elongation in Arabidopsis thaliana by photoreceptor interaction.

In order to test the interaction of different phytochromes and blue-light receptors, etiolated seedlings of wild-type Arabidopsis thaliana (L.) Heynh., a phytochrome (phy) B-overexpressor line (ABO), and the photoreceptor mutants phyA-201, phyB-5, hy4-2.23n, fha-1, phyA-201/phyB-5, and phyA-201/hy4-2.23n were exposed to red and far-red light pulses after various preirradiations. The responsiveness to the inductive red pulses is primarily mediated by phyB which is rather stable in its far-red-absorbing form as demonstrated by a very slow loss of reversibility. Without preirradiation the red pulses had an impact on hypocotyl elongation only in PHYA mutants but not in the wild type. This indicates a suppression of phyB function by the presence of phyA. Preirradiation with either far-red or blue light resulted in an inhibition of hypocotyl elongation by red pulses in the wild type. Responsiveness amplification by far-red light is mediated by phyA and disappears slowly in the dark. The extent of responsiveness amplification by blue light was identical in the wild type and in the absence of phyA, or the cryptochromes cryl (hy4-2.23n) or cry2 (fha-1). Therefore, we conclude that stimulation of phyB by blue light preirradiation is either mediated by an additional still-unidentified blue-light-absorbing pigment or that phyA, cry1 and cry2 substitute for each other completely. Both blue and red preirradiation established responsiveness to red pulses in phyA-201/phyB-5 double mutants. These results demonstrate that inhibition of hypocotyl elongation by red pulses is not only mediated by phyB but also by a phytochrome(s) other than phyA and phyB.

Study of evolution of active volume in irradiated silicon detectors

Light pulses emitted by a red (670 nm) Light Emitting Diode (LED) have been used to study the charge collection properties of non-irradiated and irradiated n-type silicon detectors. The advantages of red LED light pulses, compared to low-range alpha particles, are the availability of an external trigger and a very shallow distribution of the created e–h pairs (<10 μm). These features, combined with the use of a fast current amplifier and a 2.5 Gs/s sampling oscilloscope, allow the study of the evolution of the electric field in irradiated detectors. Evidence of a sensitive region on both sides of the detector has been observed. The model of the diode that depletes from the n + junction side after conductivity-type inversion is discussed and the electric field distribution in the inverted detector is presented. A first evaluation of the strength of the electric field in the undepleted bulk of the detector is proposed.

Phytochrome-dependent modulation and re-induction of growth of the first rhizoid in Dryopteris paleacea Sw

Phytochrome-dependent growth in Dryopteris paleacea Sw. was investigated in young, developing gametophytes with respect to formation and differentiation of rhizoids. Under continuous red light (Rc), the first rhizoids grew synchronously by tip elongation at a constant rate of 240 μm · d−1 until formation and outgrowth of the second rhizoid. Cessation of growth of the first rhizoids and outgrowth of the second rhizoids showed a correlation in time assumed to be mediated by intercellular signaling. The first rhizoids showed two modes of response to actinic irradiations: (i) modulation of rhizoid growth, and (ii) re-induction of growth in non-growing rhizoids. In the former, the promotory effect of actinic irradiations on rhizoids pre-cultured under Rc determined both the time for which rhizoids continued to grow after transfer into darkness and the final rhizoid length. In the latter, re-induced growth was studied using non-growing rhizoids which were obtained after irradiation with a far-red light (FR) pulse at the end of the pre-culture in Rc and transfer into darkness for 3 d to stop growth. Re-induction of growth occurred with a lag phase of 36 to 48 h after formation of the FR-absorbing form of phytochrome (Pfr) by a red light (R) pulse. From the incomplete R/FR reversibility it is evident that, here, coupling of Pfr to signal transduction is possible within minutes. Re-induction of growth possesses the advantage that the effect of actinic irradiations can be studied as an all-or-none response at the level of single gametophytes in future experiments. The present results clearly indicate that the developmental stage of the whole gametophyte, i.e. temporal and spatial patterns undergone during development, affects the regulation of rhizoid growth by the external factor light.

Analysis of photocontrol of aspartate kinase in barley (Hordeum vulgare L.) seedlings.

Aspartate kinase (AK) activity is regulated by light. The activity was more in light exposed barley seedlings than those grown in the dark. The light effect was manifested even with small exposures of 5 min duration and red light was more effective than white light in this respect. The effect of 5 min red light could be reversed by a 5 min pulse of far-red light indicating the involvement of phytochrome in this response. The phytochrome is also involved in long term light effects (24 hr exposures with white light). Ca++ takes part in the signal transduction pathway for this light response. Western blot analysis using antibodies raised against the purified lysine- and threonine-sensitive AK isoenzymes from spinach leaves showed no cross reaction with the antibodies to the threonine-sensitive AK in the dark and 5 min far-red light exposed seedlings. But the protein band was detected in the white and red lights. Northern blot analysis of seedlings grown under dark and exposed to white, red and far-red lights and probed with the gene encoding aspartokinase-homoserine dehydrogenase (AKHSD) protein indicated that the gene was differentially expressed. In dark grown seedlings, AKHSD transcript was in low concentration as compared to white light where the transcript concentration was high. A 5 min red light pulse increased the transcript concentration significantly in contrast to 5 min far-red light. The transcript concentration was reduced when 5 min red light was followed by a 5 min far-red light pulse. The AK activity in dark-raised seedlings is attributed to the presence of only one isoenzyme that is sensitive to lysine but insensitive to Ca++ and calmodulin (CAM). In both white and red light exposed seedlings, three isoenzymes of AK were detected. Two of these were sensitive to threonine while one was sensitive to lysine. Both of the threonine sensitive isoenzymes were activated by Ca++ and CAM. Also one of these isoenzymes seems to be located and synthesized in chloroplasts because its synthesis was completely inhibited by chloramphenicol but not by cycloheximide.

Different Regulation of β-amylase and Starch Phosphorylase by Light in Dormant and Non-Dormant Turions of Spirodela polyrhiza

Summary The influence of single red light pulses and of continuous red light on the activity of two enzymes, i.e. β-amylase (EC 3.2.1.2) and starch phosphorylase (EC 2.4.1.1), was investigated in dormant and non-dormant turions of Spirodela polyrhiza. The activity of β-amylase was induced by continuous red light but not by red light pulses in dormant turions. In non-dormant turions, however, the activity of β-amylase following a single red light pulse was two times higher than after continuous red light. This high effectiveness of a single red light pulse, as compared with continuous red, represents a novel mode of regulation of enzyme activity by light. It is suggested that a low fluence response of phytochrome is abolished by a high irradiance response elicited by continuous red light. The light-induced increase in the activity of β-amylase is due to de novo synthesis of the enzyme as shown by Western blot analysis using polyclonal antibodies raised against β-amylase from Spirodela polyrhiza. The presence of light-activable precursor was excluded by showing that cysteine added to the extraction medium did not influence the activity of β-amylase. In contrast, the activity of starch phosphorylase was induced by continuous red light in dormant turions but decreased in non-dormant turions. During the cold after-ripening treatment turions qualitatively changed their response to light, becoming light-insensitive when partly after-ripened (21 days). In all instances, a red light pulse was ineffective in inducing starch phosphorylase. Isoforms of β-amylase and starch phosphorylase were separated by non-denaturating PAGE. No special induction by light of any specific isoform of β-amylase and starch phosphorylase was found in turions. Since both enzymatic activities and their regulation by light do not correlate with the breakdown of starch, we conclude that they are not directly involved in the regulation of starch degradation in turions.

Photoregulated expression of the PsPK3 and PsPK5 genes in pea seedlings.

The PsPK3 and PsPK5 genes of the garden pea encode protein-serine/threonine kinases whose catalytic domains are closely related to known signal transducing kinases from animals and fungi. The PsPK3 polypeptide is predicted to be located in the nucleus, whereas PsPK5 is a homologue of NPH1, the probable blue light receptor for phototropism from Arabidopsis. We found previously that when etiolated pea seedlings are illuminated with continuous white light, PsPK3 and PsPK5 transcript levels within apical buds decline substantially, reaching their minimum levels within one day of exposure to light. The role of light in regulating the expression of the PsPK3 and PsPK5 genes was investigated further. To gain insight into the rapidity with which expression changes, 6-day old, dark-grown pea seedlings were transferred to continuous white light, and PsPK3 and PsPK5 RNA levels monitored over the ensuing 24 h. While transcripts from the RbcS gene family increase, the PsPK3 and PsPK5 mRNAs decline rapidly to their minimum levels. PsPK5 mRNA declines 10-fold in ca. 2 h, whereas PsPK3 mRNA declines 4-fold in ca. 8 h. We used single pulses of light to elucidate which photoreceptor triggers the negative regulation of PsPK3 and PsPK5 gene expression. To assess phytochrome involvement, etiolated seedlings were treated with single pulses of red light, red followed by far-red light, or far-red light alone. RbcS induction by a red light pulse is reversible with a subsequent far-red light pulse, clearly showing that phytochrome mediates its induction. Likewise, RbcS expression is induced with a single pulse of blue light or a dichromatic pulse of red+blue light. However, none of these pulses trigger the PsPK3 and PsPK5 mRNA levels to decline. Given the lack of effectiveness of light pulses, etiolated seedlings were transferred to continuous light of three different qualities to determine the spectral sensitivity of PsPK3 and PsPK5 gene expression. Exposure to continuous red, continuous far-red, or continuous blue light causes the PsPK3 and PsPK5 mRNAs to decline and transcripts from the RbcS and Cab gene families to increase. One likely explanation is that phytochrome A mediates the responses of these genes to continuous far-red light. The effectiveness of continuous red light and blue light in triggering the reduction in PsPK3 and PsPK5 mRNA levels and the increase in RbcS and Cab mRNAs may imply the participation of additional phytochromes and/or cryptochromes. Thus, the PsPK3 and PsPK5 genes exhibit responsiveness to continuous light, but a lack of responsiveness to single light pulses that is unusual, and perhaps unique, among light-regulated genes.

Photoinduction of Spore Germination in Marchantia polymorpha L. is Mediated by Photosynthesis

The effects of light on spore germination (protrusion of protonemata) in the liverwort Marchantia polymorpha L. were examined. Spore germination was found to be light dependent and light irradiation for 10 h or longer was necessary. Test using specific wavelengths showed that the entire spectrum from near UV to red light was effective, red light being the most effective. Spore germination could be induced by intermittent irradiation with 15-min red light pulses given every 1 or 2 h for 24 h. The effect of intermittent red light was not reversed by subsequent or simultaneous far-red light irradiation. However, spore germination was inhibited by the photosynthesis inhibitor DCMU (100 fiM). Complete inhibition of spore germination was found when DCMU was given during the light period. When DCMU was applied during the dark periods, only a slight reduction of germination rate was observed. Further, it was found that Chi formed in the spores during imbibition in darkness. Light sensitivity increased at nearly the same rate as the appearance of Chi. Moreover, spore germination was induced in total darkness by the addition of glucose to the medium. These results clearly indicate that photosynthesis mediates the photoinduction of spore germination in Marchantia polymorpha.

Slow Degradation of Hydrogenated Amorphous Silicon Photoconductivity Under Pulsed Illumination

AbstractWe degraded hydrogenated amorphous silicon (a-Si:H) using red light pulses of 32 microseconds to 2 milliseconds. These metastable photoconductivity degradations were compared to degradation with continuous light of the same intensity and same exposure time. For a given integrated exposure time we observe higher degraded photoconductivities (by up to 40 %) as we shorten the pulses. For example, to obtain the same amount of degradation with 120 microsecond pulses as with continuous illumination, the integrated sample exposure time must be doubled. Experiments were conducted to exclude thermal effects. Our result cannot be explained with a simple recombination-driven degradation mechanism, because electron and hole populations rise and fall to steady-state values in only a few microseconds. We conclude that carrier recombination creates a more proximate precursor to metastable degradation of a-Si:H. When illumination begins, this precursor's density rises more slowly than the density of photocarriers and therefore degradation is delayed.

A single red-light pulse leads to a block of greening in the high-pigment-1 mutant of tomato

A single pulse of red light (R) given to 4-d-old etiolated high-pigment-1 (hp-1) mutant tomato (Solanum lycopersicum L.) seedlings followed by a 3-d dark period is demonstrated to result in a block of greening in subsequent white light. Wild-type seedlings green normally under this regime. The block of greening in the hp-1 mutant depends on the length of the dark period before and after the R pulse and operates via the low-fluence-response mode of phytochrome action. This block of greening takes place in hp-1 double mutants lacking either phytochrome A or phytochrome B1, but is absent in the hp-1 triple mutant lacking both phytochromes A and B1. These observations enable a screen to be devised for new phytochrome B1 mutants either within the photoreceptor or mutants defective in phytochrome B1-signalling steps which result in loss of capacity to green, by mutagenising the phytochrome A-deficient hp-1, fri double mutant.

A Rapid Method for Measuring Freezing Resistance in Crop Plants

AbstractThe objective of this study was to develop a technique based on chlorophyll fluorescence to assess freezing injury and resistance of leaves. Optimization was done with faba bean leaves and applicability to other crops was examined at winter and spring with types of barley, oats, rape and faba beans. Selected leaves from young hardened beans were subjected to standardized freezing tests with different minimum temperatures (Tmin) and fluorescence was monitored. After a dark period basic fluorescence (FO was induced by 0.2 μmol m−2 s−1 pulsed red light and maximum fluorescence (Fm) was assayed at different light intensities. 1500 μmol m−2 s−1 rendered to give the maximum possible output of Fm and best differentiation of differently damaged leaves by Fn=Fm ‐ FO. Leaf temperature during measurement and during a short storage (± 2 h) should be kept at about 0°C to avoid biases between differently damaged leaves. The measuring spot on the leaf must be standardized since fluorescence response differed at the tip and base of a leaflet, but not between the two leaflets of a faba bean leaf. The applicability of Frr (ratio of Fr of stressed to unstressed leaves) as a measure of resistance was demonstrated by comparison of winter hardiness of cultivars with freezing resistance calculated from the relationship of Fvr and the Tmin used in freezing tests.

Photoreceptors involved in the regulation of nitrate reductase in Spirodela polyrhiza

In green fronds of Spirodela polyrhiza a red-light pulse induces an increase of nitrate reductase (NR) activity. The effect is obtained under optimal assay conditions (absence of Mg 2+), therefore reflecting the NR protein level. The effect of a single red-light pulse is reversible by a subsequent far-red pulse, demonstrating the involvement of the photoreceptor phytochrome. Continuous red light applied for 48 h produces a dramatic increase in NR activity which exceeds 25 times the effect of a single red pulse. The threshold value for the induction of NR in continuous red and blue light is 3 μmol m −2 s −1, which coincides with the light compensation point of photosynthesis. In short-term (20 min) experiments NR is post-translationally activated by photosynthesis, whereas the NR level remains constant. The reduction state of the plastoquinone pool is irrelevant to the signal-transduction chains leading to the changed NR level as well as to post-translational regulation of NR, because blocking the photosynthetic electron transport both before (DCMU) or after (DBMIB) the plastoquinone pool inhibits the induction of NR by light. While it is evident that NR in green fronds of Spirodela polyrhiza is mainly regulated by photosynthesis, the decisive photosynthesis-derived signal is not known.

The expression of light-regulated genes in the high-pigment-1 mutant of tomato

Three light-regulated genes, chlorophyll a/b-binding protein (CAB), ribulose-1,5-bisphosphate carboxylase/oxygenase small subunit, and chalcone synthase (CHS), are demonstrated to be up-regulated in the high-pigment-1 (hp-1) mutant of tomato (Lycopersicon esculentum Mill. ) compared with wild type (WT). However, the pattern of up-regulation of the three genes depends on the light conditions, stage of development, and tissue studied. Compared with WT, the hp-1 mutant showed higher CAB gene expression in the dark after a single red-light pulse and in the pericarp of immature fruits. However, in vegetative tissues of light-grown seedlings and adult plants, CAB mRNA accumulation did not differ between WT and the hp-1 mutant. The ribulose-1,5-bisphosphate carboxylase/oxygenase small subunit mRNA accumulated to a higher level in the hp-1 mutant than WT under all light conditions and tissues studied, whereas CHS gene expression was up-regulated in de-etiolated vegetative hp-1-mutant tissues only. The CAB and CHS genes were shown to be phytochrome regulated and both phytochrome A and B1 play a role in CAB gene expression. These observations support the hypothesis that the HP-1 protein plays a general repressive role in phytochrome signal transduction.

Alteration of division polarity and preprophase band orientation in stomatogenesis by light

We have developed an experimental system in which the irradiation with a red light pulse induces stomatal disorientation in the hypocotyl epidermis ofCucumis sativus L. In this system, the orientation of the division plane in guard mother cells was not defined correctly. Preprophase bands formed in these cells but their orientation was abnormal.

Phytochrome-mediated photocontrol of the germination of the scentless mayweed, Matricaria inodora L., and its sensitization by nitrate and temperature

The emergence of Matricaria inodora ( M. perforata) may poorly respond to modified light exposure during tillage. Therefore, the influence of light, nitrate and temperature on the germination of M. inodora has been studied under laboratory conditions. Germination of a native seed batch levels off around 77% after 7 to 9 days at 20°C, if sown in 0.01 M KNO 3 or NaNO 3 with a daily photoperiod of 14 h weak white light. In 0.01 M NaCl or in bidistilled water germination reaches 48 ± 5%. One saturating red-light pulse, applied 12 h after imbibition in 0.01 M KNO 3, gives only 12 ± 3% germination after 7 days, but 5 daily repeated red-pulses produce 75% germination. Ten twofold daily repeated red-light pulses are equivalently efficient, and if all immediately followed by a saturating far-red pulse, perfect reversibility down to the far-red level of 7 ± 3% germination is found. The dark germination was 1.7 ± 0.7%. A fluence-response curve, elaborated for 10 red-pulses, gives an exponential pattern with half-saturating pulse fluence around 35 J m −2, as indicative of phytochrome photoconversion. The influence of additional temperature pretreatment in darkness was tested, followed by half-saturating red-light pulses every 12 or 24 h. Chilling at 2 °C was ineffective up to 6 days, but slightly sensitizing after 21 days, giving around 30% and 46% germination, respectively. Preincubation for 6 days between 20 and 36 °C was more efficient and led to 58–68% germination at 20 °C. A thermoperiodic pretreatment with daily 12 h at 10 °C and 12 h at 30 °C was most efficient, giving 73 ± 4% germination. For all these pretreatments dark germination never exceeded 3%. Elevated dark germination occurred when water-imbibed achenes, being exposed and dried in red-light of 1 W m −2, have been reimbibed in darkness. If drying in red-light was for 6 h to a water content of 20% and reimbibition was in water or 0.01 M KNO 3, dark germination increased to 22 ± 5% or 40 ± 6%, respectively. This dark germination was far-red reversible down to 5 ± 2% with half-escape time around 5 h. If drying in red-light was for 24 h to reach the storing content of water around 11%, the dark germination after reimbibition in water or 0.01 M KNO 3 was only 4 ± 2% and 13 ± 2%, respectively. All corresponding controls for drying and reimbibition in darkness, for both water and nitrate, never exceeded 1% germination. This means that drying of seed in light — but not in darkness — increases emergence after the next rainfall and that the nitrate ion acts as a sensitizer for preformed P fr and facilitates phytochrome-mediated germination. Thus, for maximum germination of surface exposed M. inodora a thermoperiodic pretreatment, daily repeated light exposures and nitrate are needed. This is typical of the shallow germinating ancestor occurring in coastal ranges, the Sea Mayweed, Tripleurospermum maritimum, and may explain why the emergence of M. inodora is scarcely reduced after lightless tillage.