Flower Induction In Pharbitis Nil Research Articles

The role of light in the plants world

This article describes the differences in how people and plants perceive light. This is important in some artificial light applications. In particular, it concerns the horticulture area, in which LED lighting is increasingly used. There is a misunderstanding of the specifics of the environment in this area. As a result, even experienced lighting professionals design greenhouse lamps in the same way as for people. This article describes the negative consequences of this approach. Full Text: PDF ReferencesA. R. Young, J. Claveau, and A.B. Rossi, Ultraviolet radiation and the skin: Photobiology and sunscreen photoprotection, Jurnal of the American Academy of Dermatology, vol. 76, p. 100-109, Mar. 2017. CrossRef S. Pashiardis, S.A. Kalogirou, and A. Pelengaris, Characteristics of Photosynthetic Active Radiation (PAR) Through Statistical Analysis at Larnaca, SM Journal of Biometrics & Biostatistics, p. 1-16, Jun. 2017. CrossRef W. Bommel, Interior Lighting: Visual Mechanism. Springer Nature Switzerland AG., p. 3-23, 2019. CrossRef L.T. Sharpe, A. Jagla, and W. Jägle, A luminous efficiency function, V*(λ), for daylight adaptation, Journal of Vision, vol. 5, no. 11, p. 948-968, Apr. 2012. CrossRef I. Fryc, and E. Czech, Application of optical fibers and CCD array for measurement of luminance distribution, Proceedings of SPIE, vol. 5064, p. 18-21, Apr. 2003. CrossRef I. Fryc, Design issue of novel type of an illuminance meter photometric head, Jurnal of Modern Optics, vol. 56, no. 33, p. 1504-1508, Jul. 2009. CrossRef I. Fryc, and P. Tabaka, The influence of different photometric observers on luxmeter accuracy for LEDs and FLs lamps measurements, Optica Applicata, vol. 49(2), p. 345-354, Jul. 2019. CrossRef M. Liu, Y. Yan, Q. Xue, and L. Gong, The research and analysis of factors affecting Critical Flicker Frequency, 6th Int. Conference on Applied Human Factors and Ergonomics, Las Vegas, 2015. CrossRef W. Wojtkowski, SEPIC converter for high power LED lighting, Przeglad Elektrotechniczny, vol. 86, no. 10, p. 260-263, 2010. DirectLink W. Wojtkowski, Step-up converters for power LED power supply, Przeglad Elektrotechniczny, vol. 87, no. 4, p. 71-72, 2011. DirectLink Y. Berkovich, and all, LED crop illumination inside space greenhouses, in Reach, vol. 6, Elsevier, p. 11-24, 2017. CrossRef C.M. Campillo, R. Fortes and M.H. Prieto, Solar Radiation Effect on Crop Production, Mar. 2012 CrossRef I. Ashdown, Photometry and Photosynthesis: From Photometry to PPFD., Nov. 2015 DirectLink K.J. McCree, The Action Spectrum, Abasorptance and Quantum Yield of Photosynthesis in Crop Plants, Agricultural Meteorology, vol. 9, 191-216, Oct. 1970. CrossRef OSRAM Opto Semiconductors, Horticulture Lighting with LEDs, Nov. 2016 CrossRef Standard DIN 5031-10 Optical radiation physics and illuminating engineering. CrossRef EconoLux Indastries Ltd., What Light do Plants Need, Hong Kong, 2016. CrossRef M.B. Ali, L. Khandaker, and S. Oba, Comparative study on functional components, antioxidant activity and color parameters of selected leafy vegetables as affected by photoperiods, J Food Agric Environ, vol. 7, p. 392-398, 2009. CrossRef A. Szmidt-Jaworska, K. Jaworski, A. Tretyn, and J. Kopcewicz, The involvement of cyclic GMP in the photoperiodic flower induction of Pharbitis nil, Jurnal of Plant Physiology, vol. 161, p. 277-284, 2004. CrossRef A. Szmidt-Jaworska, K. Jaworski, and J. Kopcewicz, The Involvement of Cyclic ADPR in Photoperiodic Flower Induction of Pharbitis nil, Jurnal of Plant Growth Regulation, vol. 25, p. 233-244, Sep. 2006. CrossRef A. Szmidt-Jaworska, K. Jaworski, A. Zienkiewicz, M. Lenartowska, and J. Kopcewicz, Guanylyl cyclase activity during photoperiodic flower induction in Pharbitis nil, Jurnal of Plant Growth Regulation, vol. 57, p. 173-184, 2009. CrossRef Light Laboratory Inc., Goniophotometer Test Report HLG ELITE lamps. CrossRef U.J. Błaszczak, D.A. Aziz, L. Gryko, Influence of the spectral composition of LED lighting system on plants cultivation in a darkroom, Proceedings of SPIE, vol. 10445, p. 1-9, 2017. CrossRef

The ecological hazard of artificial lighting in greenhouses

This article draws attention to the shortcomings of modern lighting systems used in greenhouses. Its content focuses on the negative effects of mismatches between the photosynthetic needs of plants and the parameters of artificial light sources. Greenhouse lamps designers often do not have the knowledge of biological cultivation dependencies. Therefore, their cooperation with specialists of plant physiology and gardeners is indispensable. This is important because it can affect the consumer quality of vegetables. Full Text: PDF ReferencesM.Kucharczyk, I.Gąsak, Ecological effects of light pollution , III International Conference on Scientific and Technical TRANSEIA, Krynica Zdrój, Poland, 6-8 December 2017. DirectLink T. H. Goldsmith, What Birds See, Scientific American Inc. (2006), CrossRef E.J. Gerl, M.R. Morris, The Causes and Consequences of Color Vision, Springer Science + Business Media, LLC, 2008. CrossRef K. Jaworski, A. Szmidt-Jaworska, J. Kopcewicz, Two calcium dependent protein kinases are differently regulated by light and have different activity patterns during seedling growth in Pharbitis nil, open access at Springerlink.com, Journal: 10725, Article: 9609, 2011. CrossRef K. Jaworski, A. Pawełek, J. Kopcewicz, A. Szmidt-Jaworska, The calcium-dependent protein kinase (PnCDPK1) is involved in Pharbitis nil flowering, Journal of Plant Physiology 169 p. 1578-1585, 2012. CrossRef A. Szmidt-Jaworska, K. Jaworski, J. Kopcewicz, Effect of light on soluble guanylyl cyclase activity in Pharbitis nil seedlings, Journal of Photochemistry and Photobiology B: Biology 93 p. 9-15, 2008. CrossRef Horticulture Lighting Group, Goniophotometer Test Report of the ELITE ECO lamp CrossRef K. Marra, E. P. LaRochelle, M. S. Chapman, P. J. Hoopes, K. Lukovits, E. V. Maytin, T. Hasan, B. W. Pogue, Comparison of Blue and White Lamp Light with Sunlight for Daylight‐Mediated, 5‐ALA Photodynamic Therapy, in vivo, Wiley Online Library, 16 April 2018 CrossRef M. Gilewski, The Ecological Harmfulness of RGB LED Light, International Conference on Energy, Power, Electrical and Environmental Engineering : EPEEE 2018, DEStech Publications, Wuhan, Hong Kong, September 27-28, 2018. CrossRef K. J. McCree, The Action Spectrum, Absorptance and Quantum Yield of Photosynthesis in Crop Plants, Agricultural Meteorology, Elsevier Publishing Company, 9 p. 191-216 , 1972. CrossRef EconoLux Indastries Ltd., What Light do Plants Need, Hong Kong CrossRef I. Ashdown, Photometry and Photosynthesis: From Photometry to PPFD, SunTracker Technologies Ltd CrossRef OSRAM Opto Semiconductors, Horticulture Lighting with LEDs, OS SSL | NR AW CH, November 2016 CrossRef M. Mottus, M. Sulev, F. Baret, R. Lopez-Lozano, A. Reinart, Photosynthetically Active Radiation: Measurement and Modeling CrossRef Heliospectra AB, Full Flexibility ELIXIA grow ligh CrossRef Heliospectra AB, Full Flexibility ELIXIA grow light CrossRef A. Szmidt-Jaworska1, K. Jaworski1, A. Tretyn, J. Kopcewicz, The involvement of cyclic GMP in the photoperiodic flower induction of Pharbitis nil, J. Plant Physiol. 161. p. 277-284, 2004. CrossRef A. Szmidt-Jaworska, K. Jaworski, J. Kopcewicz, The Involvement of Cyclic ADPR in Photoperiodic Flower Induction of Pharbitis nil, J Plant Growth Regul 25: p. 233-244, 2006. CrossRef A. Szmidt-Jaworska, K. Jaworski, A. Zienkiewicz, M. Lenartowska, J. Kopcewicz, Guanylyl cyclase activity during photoperiodic flower induction in Pharbitis nil, Plant Growth Regul 57: p. 173-184, 2009. CrossRef U.J. Błaszczak, D.A. Aziz, L. Gryko, Influence of the spectral composition of LED lighting system on plants cultivation in a darkroom, Proceedings of SPIE, vol. 10445, (2017) 1-9. CrossRef L. Gryko, U. Blaszczak, A.S. Zajac, Colorimetric characterization of the tunable LED-based light source at the output of the homogenizing rod, Proceedings of SPIE, vol. 10808, 2018. CrossRef I.Fryc, T. Dimitrova-Grekow, An automated system for evaluation of the quality of light sources, 6th IEEE Lighting Conference of the Visegrad Countries : LUMEN V4, Karpacz, September 13-16, 2016. CrossRef J. Kusznier, M. Zajkowski, L. Budzynski, D. Tyniecki, Ring optical mixer for LED with truncated surfaces, Proceedings of SPIE, vol. 10325, 2017. CrossRef W. Wojtkowski, LED Power Supply with Thermal Protection for Automotive Application, 7th Lighting Conference of the Visegrad Countries : LUMEN V4, Třebíč, September 18-20, 2018. CrossRef W. Wojtkowski, Constant Frequency Operation of the Parallel Loaded Resonant DC/DC Converter for Power LED Lighting, International Conference on Energy, Power, Electrical and Environmental Engineering : EPEEE 2018, DEStech Publications, Wuhan, Hong Kong, September 27-28, 2018. CrossRef Pashiardis S, Kalogirou SA and Pelengaris A. Characteristics of Photosynthetic Active Radiation (PAR) Through Statistical Analysis at Larnaca, Cyprus. SM J Biometrics Biostat. 2(2): 1009, 2017. DirectLink R. Inger, J. Bennie, T. W. Davies, K. J. Gaston, Potential Biological and Ecological Effects of Flickering Artificial Light, PLoS One, vol. 9(5) (2014) PMC4038456 CrossRef C. Dong, Y. Fu, G. Liu, H. Liu, "Growth, photosynthetic characteristics, antioxidant capacity and biomass yield and quality of wheat (Triticum aestivum L.) exposed to LED light sources with different spectra combinations", J Agron Crop Sci, vol. 200, p. 219-230, 2014. CrossRef

Ethylene, auxin, and abscisic acid interactions in the control of photoperiodic flower induction in Pharbitis nil

Interactions between indole-3-acetic acid (IAA), abscisic acid (ABA), and ethylene (ET) in the photoperiodic flower induction of a short-day (SD) plant Pharbitis nil were investigated. It was shown that both IAA and ABA applied just before and during the first half of the 16-h-long inductive night inhibited flower induction in P. nil. Ethylene is also thought to be a strong flowering inhibitor of SD plants but only when it is applied in the second half of the inductive night. The application of IAA just before the inductive night decreased the content of endogenous ABA in cotyledons only during the first half of the inductive night. Additionally, the application of 2-aminoethoxyvinylglycine (AVG) — an ethylene biosynthesis inhibitor — partially reversed the inhibitory effect of IAA and ABA on flowering. The results suggest that the mechanisms of P. nil flower inhibition by IAA and ABA might be independent. However, both the hormones influenced ethylene production which directly inhibited flowering. We also show that ABA applied on the cotyledons of P. nil seedlings just before the inductive night caused a clear increase in the expression of PnACS1 and PnACS2 genes (encoding enzymes involved in ethylene biosynthesis) from the first hours after its application. The transcripts of PnACO1 and PnACO3 genes were also increased but their maximal values were shifted in relation to the PnACS1 and PnACS2. The data presented here strongly support the idea that both IAA and ABA inhibit P. nil flowering through the modulation of ethylene biosynthesis.

The effect of exogenous acetylcholine and other cholinergic agents on photoperiodic flower induction of Pharbitis nil

Exogenous acetylcholine (ACh), acetylcholinesterase (AChE) inhibitors, as well as agonists and antagonists of ACh receptors applied on the cotyledons of 5-day-old seedlings of <em>Pharbitis nil</em> during a 16-hour long inductive night or during a 12-hour long subinductive night, do not essentially influence the flower bud formation. Also the application of above mentioned substances to the seedlings growing under the conditions of 72 hours of darkness, 24 hours of light and then 24 hours of darkness does not influence in an essential way flowering of <em>P. nil</em>. On the other hand, applying these substances on the cotyledons of <em>P. nil</em> during 24-hour-long inductive night, preceded by 72 hours of darkness and then 24 hours of light of lowered intensity finished by 15-minute-long impulse of far red light which inhibit flowering, caused the reversion of the effect of far red light irradiation and stimulated the flowering. The obtained results suggest that endogenous system ACh/AChE could participate in the mechanism of a phytochrome controlled flowering of short day plants.

Cross talk between phytohormones in the regulation of flower induction in Pharbitis nil

Application of gibberellic acid (GA3) on the cotyledons of 5-d-old Pharbitis nil reversed the inhibitory effect of both abscisic acid (ABA) and ethylene on flowering. Application of GA3 slightly decreased ethylene production and did not affect the endogenous ABA content in the cotyledons during the night. However, it reversed the stimulating effect of ABA on ethylene production.

Cross talk between phytohormones in the regulation of flower induction in Pharbitis nil

Cross talk between phytohormones in the regulation of flower induction in Pharbitis nil

Involvement of aba in flower induction of Pharbitis nil

<p>Flowering of plants is controlled by hormones among which both stimulators and inhibitors are present. The role of abscisic acid (ABA) in flower induction of the short day plant <em>Pharbitis nil</em> was shown in our experiments through exogenous applications and endogenous level determination of the hormone in cotyledons of seedlings grown under special light conditions.</p><p>The application of ABA to cotyledons or shoot apices during the first half of a 24-h long inductive night inhibits flowering. The same compound applied towards the end of or after a 14-h long subinductive night increases the number of flower buds produced by these plants.</p><p>Exposing <em>P. nil</em> seedlings at the beginning of a 24-h long inductive night to far red light (FR) decreases the level of endogenous abscisic acid in cotyledons and leads to flower inhibition. However, a pulse of red light (R) reversing the inhibitory effect of far red light on the flowering of <em>P. nil</em> increases the ABA content.</p><p>The results obtained confirm previous observations that ABA may play a dual and an important role in the regulation of floral bud formation in <em>P. nil</em>. The flowering occurs when the level of endogenous abscisic acid is low at the beginning and is high toward the end of the inductive night.</p>

Guanylyl cyclase activity during photoperiodic flower induction in Pharbitis nil

It is known that the level of cGMP is modulated in plant cells in response to a number of stimuli but intracellular events dependent on cGMP metabolism are not clear. Guanylyl cyclases (GCs) are enzymes which are responsible for synthesis of cGMP in eukaryotic and prokaryotic cells. To collect evidence for the participation of cGMP in light signal transduction we isolated enzyme with guanylyl cyclase activity from Pharbitis nil and analysed its level and activity during photoperiodic flower induction. Soluble proteins were isolated from seedlings of a model short-day plant P. nil, partly purified and identified by in vivo and in vitro enzyme assay. In green plants enzyme activity amounted to 484 nmol cGMP/min/mg protein, whereas in etiolated plants it was three times lower (158 nmol cGMP/min/mg protein). Analyse cyclase consists of a single polypeptide of Mr 40 kDa. In order to determine if changes in guanylyl cyclase activity occurred in response to a long, inductive night, we measured enzyme activity in 4-h intervals and observed its increase at 4, 8 and 16 h of darkness. This pattern also fits well with changes in the endogenous cGMP level during a 16 h long flower inductive night. Immunocytochemical analysis confirmed these observations and revealed that changes in the GC level during light/dark conditions appeared. During 16 h long inductive night the strongest signal was observed in cotyledons after 4 and 16 h of the darkness. A high level of fluorescence was generally distributed in mesophyll, however, it was also observed in guard cells. Staining was apparently absent in the veins and cotyledon body. Furthermore, the location inside the cell was analysed. The protein was immunolocalized preferentially in the cytosol, chloroplasts and peroxysomes. Taken together, these data demonstrate in Pharbitis nil the presence of an enzyme which is able to convert GTP to cGMP. Because its level and activity are affected by light we believe that GC/cGMP play a substantial role in light/dark dependent process in plants, such as photoperiodic flower induction.

Cyclic GMP stimulates flower induction of Pharbitis nil via its influence on cGMP regulated protein kinase

It was revealed that cGMP is involved in the control of photoperiodic flower induction. Further insight into the signalling function of cGMP is likely to be obtained by analysis of its effectors. Therefore, in the present study, we used various agents that cause changes in cGMP-dependent kinase (PKG) activity and examined their effects on the activity of kinase isolated from Pharbitis nil and flower induction. It was found that exogenous applications of PKG activators (cGMP, 8-pCPT-cGMP, 8-Br-cGMP, 8-pCPT-PET-cGMP) to cotyledons which were exposed to a 12-h-long subinductive night significantly increased flowering response. From among the many antagonists of cGMP-dependent protein kinase Rp-8-Br-PET-cGMPS, Rp-8-pCPT-cGMP and the synthetic heptapeptide inhibitor of PKG were used for our analysis. When Rp-8-Br-PET-cGMPS and Rp-8-pCPT-cGMP were applied during a 16-h-long inductive night, significant reduction in the number of flower buds was observed, whereas synthetic heptapeptide did not change the intensity of flowering. The influence of the analysed chemicals on protein kinase activity was also examined in vitro. With the exception of synthetic heptapeptide, which seems ineffective, the enzyme activity was stimulated by all agonists and significantly reduced by all antagonists. The activity of protein kinase was assayed in P. nil soluble protein fractions from plants grown under flower-inducing and non-inducing conditions. In vitro phosphorylation was slightly greater in the soluble fraction obtained from plants grown under the flower-inducing condition, reaching 1.05 nmol/min/mg protein, when compared to the control 0.81 nmol/min/mg protein. In relation to the results described above, we can conclude that cGMP as a mediator participating in photoperiodic flower induction may govern this process by the phosphorylation mechanism via its influence on cGMP-dependent protein kinase activity.

Ethylene and ABA interactions in the regulation of flower induction in Pharbitis nil

Hormones are included in the essential elements that control the induction of flowering. Ethylene is thought to be a strong inhibitor of flowering in short day plants (SDPs), whereas the involvement of abscisic acid (ABA) in the regulation of flowering of plants is not well understood. The dual role of ABA in the photoperiodic flower induction of the SDP Pharbitis nil and the interaction between ABA and ethylene were examined in the present experiments. Application of ABA on the cotyledons during the inductive 16-h-long night inhibited flowering. However, ABA application on the cotyledons or the shoot apices during the subinductive 12-h-long night resulted in slight stimulation of flowering. Application of ABA also resulted in enhanced ethylene production. Whereas nordihydroguaiaretic acid (NDGA) - an ABA biosynthesis inhibitor - applied on the cotyledons of 5-d-old seedlings during the inductive night inhibited both the formation of axillary and of terminal flower buds, application of 2-aminoethoxyvinylglycine (AVG) and 2,5-norbornadiene (NBD) - inhibitors of ethylene action - reversed the inhibitory effect of ABA on flowering. ABA levels in the cotyledons of seedlings exposed to a 16-h-long inductive night markedly increased. Such an effect was not observed when the inductive night was interrupted with a 15-min-long red light pulse or when seedlings were treated at the same time with gaseous ethylene during the dark period. Lower levels of ABA were observed in seedlings treated with NDGA during the inductive night. These results may suggest that ABA plays an important role in the photoperiodic induction of flowering in P. nil seedlings, and that the inhibitory effect of ethylene on P. nil flowering inhibition may depend on its influence on the ABA level. A reversal of the inhibitory effect of ethylene on flower induction through a simultaneous treatment of induced seedlings with both ethylene and ABA strongly supports this hypothesis.

Effect of light on soluble guanylyl cyclase activity in Pharbitis nil seedlings

Cyclic GMP acts as a chemical switch in plant cells to modulate cellular reactions. However, its metabolism has not been extensively explored and is still poorly understood. Previous experiments suggest that an endogenous cGMP system could participate in the mechanism of phytochrome controlled photoperiodic flower induction in Pharbitis nil. In order to gain further information on the role of cGMP, we have begun to study the enzyme of cGMP synthesis. In this article, the presence of the enzyme with guanylyl cyclase (GC) activity in soluble protein fractions of P. nil is reported. A large portion of the enzymatic activity is present in the cotyledons, where enzyme activity amounted to 0.45 pmol cGMP/min/mg protein. The enzyme exhibited a K m 0.5 mM for GTP. A plot of 1/v versus 1/[GTP] was linear and V max was 0.74 pmol cGMP/min/mg protein. It was shown that the anti-sGC antibody recognise a 40 kDa protein. Moreover, the NO-donor, sodium nitroprusside (SNP) and YC-1, as a NO-independent stimulator, enhanced enzyme activity. The NS 2028 (a potent GC inhibitor) treatments provoked a 3-fold reduction of the enzyme activity in comparison to the untreated fractions. Furthermore, the influence of light on GC activity was analysed. It was noted that cGMP level increased in cool white light, and darkness inhibited enzyme activity. Exposure to blue light acts to stimulate cGMP formation, whereas in red light a rapid decrease in GC activity was observed that returned to the high level when far-red light was applied after the red light treatment. The results presented in this work strongly argue that an enzyme with guanylyl cyclase activity is present in P. nil organs and its activity is controlled by light via the photoreceptors-dependent pathways.

Ethylene and IAA interactions in the inhibition of photoperiodic flower induction of Pharbitis nil

It has been shown that both IAA and ethylene application inhibit flower induction in the short-day plant Pharbitis nil. However application of IAA has elevated ethylene production in this plant, as well. Strong enhancement of ethylene production is also correlated with the night-break effect, which completely inhibits flowering. In order to determine what the role of IAA and ethylene is in the photoperiodic flower induction in Pharbitis nil, we measured changes in their levels during inductive and non-inductive photoperiods, and the effects of ethylene biosynthesis and action inhibitors on inhibition of flowering by IAA. Our results have shown that the inhibitory effect of IAA on Pharbitis nil flowering is not physiological but is connected with its effect on ethylene biosynthesis.

The Involvement of Cyclic ADPR in Photoperiodic Flower Induction of Pharbitis nil

Cyclic adenosine diphosphate ribose (cADPR) is a potent endogenous calcium-mobilizing agent synthesized from NAD+ by ADP-ribosyl cyclases described for several animal cells. Pharmacological studies suggest that cADPR is an endogenous modulator of Ca2+-induced Ca2+ release channels. There is also information about the sub-micromolar concentration of cADPR in plant cells. Whether cADPR can act as a Ca2+-mobilizing intracellular messenger in plant tissue is an unresolved question. Despite the obvious importance of monitoring cADPR cellular levels under various physiological conditions in plants, its measurement has been technically difficult and requires specialized reagents. In the present study a widely applicable sensitivity assay for cADPR is described. We show that Pharbitis nil tissue from cotyledons contains a certain cADPR level. To explain the possible roles of this second messenger in photoperiodic flower induction, some physiological experiments were also performed. The exogenous applications of cADPR to Pharbitis nil plants, which were exposed to a 12-h-long subinductive night, significantly increased flowering response. Nevertheless 8-Br-cADPR inhibited flowering when these compounds were applied during a 16-h-long inductive night. The effect of ruthenium red, a calcium channel blocker and ryanodine, a calcium channel stimulator, on the photoperiodic induction of flowering was also studied. Ruthenium red, when applied before and during an inductive 16-h dark period, slightly inhibited flowering, whereas ryanodine, when applied before and during a 12-h long subinductive night, stimulated flower bud formation. We also confirmed evidence that Ca2+ ions are involved in the photoperiodic induction of flowering. Thus, the obtained results may suggest the involvement of cyclic ADPR-activated Ca2+ mobilization in the photoperiodic flower induction process in Pharbitis nil.

The involvement of cyclic GMP in the photoperiodic flower induction of Pharbitis nil

The involvement of cGMP in the regulation of the flowering of Pharbitis nil was investigated through exogenous applications of cGMP and chemicals that are able to change the cGMP level and analyses of endogenous cGMP level. Exogenous applications of cGMP and 8-pCPT-cGMP (a cyclic GMP non hydrolyzed analog) to P. nil plants, which were exposed to a 12-h-long subinductive night, significantly increased flowering response. NS-2028 (guanylyl cyclase inhibitor) inhibited flowering when that compound was applied during a 16-h-long inductive night, whereas SNP (guanylyl cyclase activator) increased the flowering when plants were subjected to a 12-h-long subinductive night. The inhibitors of cyclic nucleotides phosphodiesterase (isobutyl-methylxanthine and dipyridamole), which increase the cytosolic cGMP level, promoted the flowering and allowed the length of the dark period necessary for induction of flowering to be reduced. The endogenous cGMP level was also measured after the treatment of P. nil seedlings with those chemicals. Results have clearly shown that compounds that were used in physiological experiments modulated endogenous cGMP level. There was a significant difference in the cyclic GMP level between 16-h-long night conditions and a long night with a night-break. During a long inductive night the oscillation of cGMP was observed with four main peaks in 4, 7, 11, 14 h, whereas a 10 min flash of red light in the middle of the night was able to modify these rhythmical changes in the second half of the long night. These results have shown that there are oscillations in the concentration of cGMP in the night and the biosynthesis and/or deactivation of cGMP is affected by light treatment and therefore it may be involved in the regulation of photoinduction processes in cotyledons. From these combined results, we propose a hypothesis that cGMP is involved in the control of photoperiodic flower induction in Pharbitis nil.

Endogenous alpha-ketol linolenic acid levels in short day-induced cotyledons are closely related to flower induction in Pharbitis nil.

Alpha-ketol linolenic acid [KODA, 9,10-ketol-octadecadienoic acid, that is 9-hydroxy-10-oxo-12(Z),15(Z)-octadecadienoic acid] is a signal compound found in Lemna paucicostata after exposure to stress, such as drought, heat or osmotic stress. KODA reacts with catecholamines to generate products that strongly induce flowering, although KODA itself is inactive [Yokoyama et al. (2000) Plant Cell Physiol. 41: 110; Yamaguchi et al. (2001) Plant Cell Physiol. 42: 1201]. We examined the role of KODA in the flower-induction process of Pharbitis nil (violet). KODA was identified for the first time in seedlings of P. nil grown under a flower-inductive condition (16-h dark exposure), by means of LC-SIM and LC-MS/MS. In addition, the changes in endogenous KODA levels (evaluated after esterification of KODA with 9-anthryldiazomethane) during the flower-inductive phase in short day-induced cotyledons were closely related to flower induction. The KODA concentration sharply increased in seedlings during the last 2 h of a 16-h dark period, while the KODA level showed no significant elevation under continuous light. The increase of KODA level occurred in cotyledonal blades, but not in other parts (petiole, hypocotyls and shoot tip). When the 16-h dark period was interrupted with a 10-min light exposure at the 8th h, flower induction was blocked and KODA level also failed to increase. The degree of elevation of KODA concentration in response to 16-h dark exposure was the highest when the cotyledons had just unfolded, and gradually decreased in seedlings grown under continuous light for longer periods, reaching the basal level at the 3rd day after unfolding. Flower-inducing ability also decreased in a similar manner. These results suggest that KODA may be involved in flower induction in P. nil.

Involvement of signal transduction pathway components in photoperiodic flower induction in Pharbitis nil

Involvement of signal transduction pathway components in photoperiodic flower induction in Pharbitis nil