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The timing of the transition from vegetative to reproductive development is of great fundamental and practical interest. Physiological event is a subject to strict and precise control. Among the environmental factors, the most important is photoperiod defined as the following changes in the light and darkness duration in the daily cycle, while the endogenous control depends on hormones action. Due to the different photoperiodic sensitivity, the plants were divided into long-day plants (LDPs), short-day plants (SDPs), and day-neutral plants (DNPs). Mainly genetic and molecular approaches have led to the identification of various components in the photoperiodic pathway among which the key are photoreceptors necessary for light perception, and elements of the endogenous circadian clock. Moreover, the circadian clock also synchronizes changes in the level of hormones. In Arabidopsis thaliana, as well as in many other LDPs, gibberellins (GAs) promote flowering, whereas in SDPs, GAs do not affect or inhibit this process. The influence of other hormones on flower induction is also dependent on photoperiodic requirements. Numerous studies have shown that ethylene (ET) and jasmonates (JAs) usually inhibit generative development. In the case of abscisic acid (ABA), a dual role in photoperiodic flowering was also recognized. The unclear role of individual hormones in the induction of flowering results from the fact that they interact in many ways. It is indisputable, however, that these small molecules are an important element coordinating the transformations leading to the generative induction of plants. On one hand, photoperiod regulates hormone levels and affects their signal transduction pathways, while on the other hand, the steady balance between hormonal stimulators and inhibitors of flowering determines the activation or inhibition of gene expression associated with generative induction pathways.

The abscission of plant organs is a phytohormone-controlled process. Our study provides new insight into the involvement of gibberellic acid (GA3) in the functioning of the flower abscission zone (AZ) in yellow lupine (Lupinus luteus L.). Physiological studies demonstrated that GA3 stimulated flower abortion. Additionally, this phytohormone was abundantly presented in the AZ cells of naturally abscised flowers, especially in vascular bundles. Interesting interactions among GA3 and other modulators of flower separation were also investigated. GA3 accumulated after treatment with the ethylene (ET) precursor 1-aminocyclopropane-1-carboxylic acid (ACC). Abscisic acid (ABA) treatment did not cause such an effect. Furthermore, the expression of the newly identified LlGA20ox1 and LlGA2ox1 genes encoding 2-oxoglutarate-dependent dioxygenases fluctuated after ACC or ABA treatment which confirmed the existence of regulatory crosstalk. GA3 appears to cooperate with the ET precursor in the regulation of AZ function in L. luteus flowers; however, the presented mechanism is ABA-independent.

This paper presents a comprehensive study on the mechanisms of tree responses to pathogens. We describe natural resistance concerning the presence of different types of barriers protecting plants from invasion and also give them strength after a pathogen attack. We put emphasis on induced resistance functioning both locally and systemically and involvement of phytohormones signaling networks. Systemic acquired resistance (SAR) involved the action of salicylic acid and H202 and accumulation of pathogenesis-related proteins. In turn, jasmonates and ethylene are signaling molecules in the induced resistance (SIR). All these substances play a crucial role in the forest management and can be applied in the tree protection strategies based on the natural and synthetic active compounds.

Ent-kaurene oxidase (EKO) catalyze three sequential oxidations in the early steps of gibberellin biosynthesis pathway. In this research, a cDNA sequence of InEKO1 gene in the model short-day plant Ipomoea nil was identified. Our studies revealed that inductive conditions for flowering caused an increase in the transcriptional activity of the examined gene in the cotyledons–the main organs for the perception of the photoperiodic stimulus. In contrast, in the second half of the 16 h long inductive night and after that, a decreased amount of InEKO1 mRNA in the apexes was detected. What is more, ethylene, the key inhibitor of flower induction in I. nil, elevated the InEKO1 expression exclusively in the cotyledons between 10 and 14 h of the inductive night.

The involvement of gibberellins (GAs) in the control of flower induction in the short-day plant Ipomoea nil has been investigated. To clarify the molecular basis of this process, we identified the full-length cDNAs of the InGA20ox3 and InGA2ox1 genes, which encode enzymes responsible for GA biosynthesis and catabolism, respectively. We studied the expression patterns of both genes and determined the tissue and cellular immunolocalisation of gibberellic acid (GA3) in the cotyledons of 5-day-old seedlings growing under inductive and non-inductive photoperiodic conditions. In the second half of the inductive night, which is crucial for flower induction in I. nil, InGA20ox3 expression decreased, whereas InGA2ox1 mRNA accumulated, which indicates that photoperiod regulates the activity of both genes. Furthermore, these changes are correlated with GA3 level. Thus, our results support the thesis that the proper balance between the expression of the InGA20ox3 and InGA2ox1 genes and low GA3 content correlate with photoperiodic flower induction in I. nil.

Aktywność strefy odcinania (AZ, ang. abscission zone) warunkuje separację organów od rośliny macierzystej. U Lupinus luteus AZ kwiatów powstaje u podstawy szypułek tych organów. Zmiany na poziomie komórkowym są skorelowane ze zmieniająca się ekspresją BLADE-ON-PETIOLE (LlBOP). Poziom mRNA tego genu regulowany jest także przez hormonalne stymulatory odcinania kwiatów — etylen (ET) i kwas abscysynowy (ABA) — co wskazuje, że LlBOP jest zaangażowany nie tylko w powstawanie AZ, ale także w późniejsze etapy jej funkcjonowania. Kwas abscysynowy wpływając na akumulację transkryptów genów kodujących enzymy biosyntezy etylenu ET (syntazę i oksydazę kwasu 1-aminocyklopropano-1-karboksylowego (ACC) i jednocześnie powodując wzrost poziomu prekursora tego fitohormonu w AZ, pośrednio reguluje czas odcinania kwiatów L. luteus.

Twenty days-long stratification of Scots pine seeds results in the seeds germinating in similar high percentage in darkness as in light. The period of stratification enough to overcome the "barrier" of light is connected with simultaneous increase of gibberellin contents, especially with the appearance of the new groups of gibberellins qualitatively similar to those occurring in pine tissues under the influence of red and white light. It was also found that seedlings grown from stratificated pine seeds produce the increased amounts of gibberellins.

Flower sex differentiation in Scots pine is correlated with endogenous balance of auxins to gibberellins. Male flower primordia initiation is connected with high amounts of gibberellins whereas the initiation of female ones is associated with a high level of auxins and a low content of gibberellins.

The increase of gibberellin content and decrease of amount of inhibitors in light irradiated pine seedlings were found. It was also stated that stimulating effect of light on pine seeds germination is correlated with the increase of gibberellin and simultaneous decrease of the inhibitor content. The inhibitor isolated from pine seeds proved to be a compound similar in some properties to abscisic acid.

The investigations were conducted on the embryonic shoots which were taken at the stage just before the start of the elongation of the last year formed embryonic shoot; it means long time before male and female cone primordia initiation. The results point out to the existence of distinctive balance of auxins to gibberellins in apical meristems oi potentially female and male shoots for about a month before the initiation of new embryonic shoots. These results confirm our previous suggestions that femaleness and maleness in Scots pine is correlated with a high amount of auxins and gibberellins, respectively.

The initiation of Scots pine male flower primordia is connected with a high content of gibberellins and a low level of auxins, whereas the initiation of female flower primordia is correlated with a high content of auxins and a low level of gibberellins. There is lack of direct correlation between the content of cytokinins or abscisic acid and flower sex differentation.

Increasing the number of flowers and pods set, as well as reducing the intensity of their abortion, is of crucial importance for the yielding of leguminous plants. This study examined the effects of the type of soil used and mineral fertilization applied on the generative development of the traditional and self-completing (restricted branching) cultivars of white lupin (Lupinus albus L.), yellow lupin (L. luteus L.) and narrow-lafed lupin (L. angustifolius L.) cultivated under controlled phytotron conditions. Experiments carried out under such conditions allow for the elimination of variable environmental factors affecting the course of plant ontogenesis in field cultivation, and enable unambiguous interpretation of the biochemical and molecular influence of a selected factor on the physiological process studied. For the first time, the influence of different cultivation factors on generative development of traditional and selfcompleting (restricted branching) cultivars of lupins under phytotrone was examined. The research results presented here indicate that each of the selected lupin cultivars has its own characteristic cultivation conditions that are optimal for its generative development. The largest number of flowers were formed by the traditional cultivars of L. luteus and L. angustifolius, as well as the self-completing (restricted branching) cultivars of L. luteus and L. albus grown in class IIIa soil material. The lowest flower abortion rate was observed in L. albus grown in class V soil material, in L. luteus grown in class IIIa soil material, and in L. angustifolius grown in class IVa soil material. Regardless of the cultivation conditions applied, in all of the lupin cultivars examined the first pods to be set were characterized by the lowest abortion rate. The results obtained allowed for the development of lupin phytotron cultivation models for the purposes of research on generative development control.

Te abscission of certain organs from the plant is part of the fulfilment of its developmental programs. Te separation process occurs in a specialized abscission zone usually formed at the base of detached organ. Te changing level of phytohormones, particularly ethylene, is the element responsible for coordinating anatomical and physiological transformation that accompanies organ abscission. Te application of ethylene (ET) on Lupinus luteus stimulates flower abortion. However, the treatment with 1-aminocyclopropane-1-carboxylic acid (ACC) - direct ET precursor - does not cause such a strong physiological response. In turn, when applied on the pedicels both ET biosynthesis (2-aminoethoxyvinylglycine; AVG) and action (norbornadiene; NBD) inhibitors reversed the stimulatory effect of ET on generative organ separation. In order to determine ET role in the flower abscission process in L. luteus, we identified the sequences coding for synthase (LlACS) and oxidase (LlACO) of ACC and measured their expression levels. Abscission zone activation is accompanied by a considerable increase both in LlACS and LlACO cDNAs and also ACC content, which is specifically localized in the dividing cells at the base of the flower being detached. Obtained results suggest that ET is a strong stimulator of flower abortion in L. luteus., This project was supported by the funds provided by Polish Ministry of Agriculture and Rural Development grants Nos. 149/2011, 222/2016 and funds provided by Nicolaus Copernicus University (Toruń, Poland) for the research program of the Chair of Plant Physiology and Biotechnology. AK thanks the eidA3-ceiA3 consortium for funding throughout the program for PhD cosupervision for foreign students.

The study examined the influence of light and auxin on the transcription level of PnACO3, a gene involved in ethylene production, in relation to the inhibitory effect of ethylene on flower induction in the short-day plant Pharbitis nil (=Ipomoea nil). Exogenous auxin was shown to increase the level of PnACO3 mRNA, with the effect depending on the experimental conditions. Light did not affect the level of PnACO3 mRNA. Applying auxin to seedling cotyledons at the beginning of inductive night boosted PnACO3 transcriptional activity even threefold during the next few hours, supporting our previous suggestion that the inhibitory effect of auxin on P. nil flowering results from its stimulatory effect on ethylene production.

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 plant hormone auxin plays a critical role in regulating plant growth and development. Recent advances have been made that having improved our understanding of auxin response pathways, primarily by characterizing the genes encoding auxin response factors (ARFs) in Arabidopsis. In addition, the expression of some ARFs is regulated by microRNAs (miRNAs). In Arabidopsis thaliana, ARF6 and ARF8 are targeted by miR167, whereas ARF10, ARF16 and ARF17 are targeted by miR160. Nevertheless, little is known about any possible interactions between miRNAs and the auxin signaling pathway during plant development. In this study, we isolated the miR167 target gene InARF8 cDNA from the cotyledons of the short day plant (SDP) Ipomoea nil (named also Pharbitis nil). Additionally, the In-miR167 precursor was identified from the I. nil EST database and analyses of InARF8 mRNA, In-pre-miR167 and mature miR167 accumulation in the plant's vegetative and generative organs were performed. The identified cDNA of InARF8 contains a miR167 complementary sequence and shows significant similarity to ARF8 cDNAs of other plant species. The predicted amino acid sequence of InARF8 includes all of the characteristic domains for ARF family transcription factors (B3 DNA-binding domain, AUX/IAA-CTD and a glutamine-rich region). Quantitative RT-PCR reactions and in situ hybridization indicated that InARF8 was expressed primarily in the shoot apices, leaf primordia and hypocotyls of I. nil seedlings, as well as in flower pistils and petals. The InARF8 transcript level increased consistently during the entire period of pistil development, whereas in the stamens, the greatest transcriptional activity occurred only during the intensive elongation phase. Additionally, an expression analysis of both the precursor In-pre-miR167 molecules identified and mature miRNA was performed. We observed that, in most of the organs examined, the InARF8 expression pattern was opposite to that of MIR167, indicating that the gene's activity was regulated by mRNA cleavage. Our findings suggested that InARF8 and InMIR167 participated in the development of young tissues, especially the shoot apices and flower elements. The main function of MIR167 appears to be to regulate InARF8 organ localization.

Gibberellins (GA4+7) and gibberellin-like substances isolated from generatively induced black henbane (Hyoscyamus niger L.) bring about the growth of shoots and a partial differentiation of axillary meristem in black henbane plants grown under non-inductive light conditions. Long-lasting application of gibberellins, however, did not result in full development of flowers in the majority of the plants investigated. Thus, it seems, that gibberellins are not specific flowering hormones in black henbane - a long-day plant.

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 Pharbitis nil 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 P. nil. On the other hand, applying these substances on the cotyledons of P. nil 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.

The endogenous content of IAA in the cotyledons of Pharbitis nil is low before and during the first half of the inductive 16-h-long dark period. From the 8th to the 12th hour the level of IAA increased and then again was going down at the end of a dark period. Exogenous IAA applied to the cotyledones before and during the first half of the inductive dark period inhibits flower bud formation. The application of IAA to shoot apex also resulted in the inhibition of flowering. Experiments with TIBA, an auxin polar transport inhibitor, and PCIB, an auxin action inhibitor, have shown that auxin polar transport in cotyledones and long-distance auxin transport from cotyledones to shoot apex play an important role in IAA inhibition of flower bud formation. It suggests that auxins play their role not only at the level of floral induction in cotyledones, but also in the later events of floral evocation and differentiation in shoot apex.

The photoconversion of phytochrome PR into the PFR form causes at the same time the destruction of the initial large fraction of phytochrome found in the coleoptiles of etiolated oat seedlings. Factors such as low temperature, light of different wavelengths or growth substances are not capable of preventing the progressive destruction and restore the synthesis of phytochrome. Thus an abnormally high level of phytochrome is found only in etiolated seedlings. Such seedlings, on the other hand, are characterized by a very high rate of elongation growth. The role of phytochrome in the control of deetiolation of seedlings is discussed.

Irradiation with red light leads to the formation of an unstable, undergoing gradual destruction, physiologically active PFR form of phytochrome in the coleoptiles of oat seedlings. Growth substances: IAA, GA3, kinetin, ABA, ethrel as well acetylcholine do not influence the nature and rate of phytochrome dark transformation. Inhibitors of energy-producing processes such as KCN, 2,4-DNP, DCCD and antimycin A inhibit the process of dark destruction of the PFR form of phytochrome.

Investigations were carried out on embryonic shoots of lateral and terminal buds of Scots pine (Pinus silvestris L.) of different age. at various stages of seasonal devclopment. The results show that there is a correlation between gibberellins content and apical dominance in pine. More are found in terminal buds than in lateral ones. The transition from a juvenile phase into a mature one in Scots pine is accompanied by a lowering of the gibberellin content. The formation of male inflorescences is accompanied by an increased amount of endogenous gibberellins and the appearence of a new group of non-polar gibberellin-like substances. The formation of female cones is connected with the lowering of endogenous gibberellin content.

The aim of this work was to determine if there is any relationship between an endogenous phyA level and photoperiodic flower induction. The level of phyA was characterised with polyclonal antibodies directed to phyA from pea. At first it was detected that phyA level is predominant in cotyledons, whereas in roots and stems the concentration of labile phytochrome is rather low. So cotyledons were used for later experiments. In these cotyledons exposed to light illumination a rapid destruction of phyA has been observed. The loss of extractable phyA chromoprotein occurs already after 60 min of irradiation. Pharbitis nil is a short-day plant and a single 16-hours-long dark period is fully inductive. We assessed that phyA level is extremely low during a long inductive night and an immunodetectable phytochrome appears only after 24 hours of darkness. The obtained results suggest that labile phytochrome is not taking part in the direct control of the photoperiodic flower induction.

Night-breaks caused both stimulated shoot growth and caused formation of flowers as well as a general increase in the content of phytohormones in leaves of the long-day plant Hyoscyamus niger L. At the time of flower formation in night-break treated plants, new gibberellin-like substances also appear. The results show that night-breaks cause similar changes in the phytohormones content as a long inductive photoperiod. It may be assumed that independently of the way of induction, the generative differentiation of long-day plants is always accompanied by a general increase in the amount of endogenous hormones and the appearance of new gibberellins. These results suggest the possibility of a morphogenetic role of hormones, especially gibberellins, in the phenomena of flower formation and differentiation.