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Understanding the mechanisms underlying the activation of the abscission zone (AZ) responsible for organ separation from plant body in crop species will help improve their yielding and economic importance. Special attention has been given recently to the role of the INFLORESCENCE DEFICIENT IN ABSCISSION protein, particularly its functional fragment, EPIP peptide. Its stimulatory effect on abscission in different crops has been demonstrated. Recently we described the role of EPIP in the redox, lipid, and pectin-related events taking place in AZ of Lupinus luteus flowers, which undergo massive abscission in natural conditions. To further examine EPIP contribution in AZ functioning, here, we analyze its impact on the ultrastructural changes, synthesis of two hormonal abscission stimulators – abscisic acid (ABA) and ethylene (ET), and the appearance of phosphoproteins. As our results show, the response of flower AZ to exogenous EPIP involves the induction of distinct modifications related to the one hand with upregulation of cell activity but on the other hand degradation processes and possible autophagy. Furthermore, the EPIP stimulated biosynthesis pathways of ABA and ET precisely in AZ cells. In addition, progressive phosphorylation of proteins has been observed under EPIP influence. The highly accumulated ones were identified as those, related to primary metabolism and reactive oxygen species homeostasis, and their role in abscission has been discussed. To summarizing, the presented detailed description of EPIP action in AZ cells in combination with our previous data offers new insights into its regulatory function and provides opportunities to counteract excessive flower abscission in lupine. • EPIP peptide evokes ultrastructural modifications of AZ related to its activation • Biosynthetic pathways of abscisic acid and ethylene are induced in AZ cells by EPIP • The emergence of phosphoproteins in flower AZ in response to EPIP was stimulated [ABSTRACT FROM AUTHOR]

The abscission zone (AZ) is a specialized tissue that usually develops at the base of an organ and is highly sensitive to phytohormones, e.g., abscisic acid (ABA), ethylene (ET), and gibberellins (GAs). A current model of organ abscission assumes that the formation of an auxin gradient around the AZ area determines the time of shedding; however, that thesis is supported by studies that are primarily concerned with auxin transporters. To better understand the events underlying the progression of abscission, we focused for the first time on indole-3-acetic acid (IAA) distribution following AZ activation. We performed a series of immunolocalization studies in proximal and distal regions of floral AZ cells in yellow lupine, which is an agriculturally important legume. The examined phytohormone was abundant in natural active AZ cells, as well as above and below parts of this structure. A similar gradient of IAA was observed during the early steps of abscission, which was induced artificially by flower removal. Surprisingly, IAA was not detected in inactive AZ cells. This paper is also a consequence of our comprehensive studies concerning the phytohormonal regulation of flower abscission in yellow lupine. We present new data on interactions between IAA and ET, previously pointed out as a strong modulator of flower separation. The detailed analysis shows that disruption of the natural auxin gradient around the AZ area through the application of synthetic IAA had a positive effect on ET biosynthesis genes. We proved that these changes are accompanied by an accumulation of the ET precursor. On the other hand, exposure to ET significantly affected IAA localization in the whole AZ area in a time-dependent manner. Our results provide insight into the existence of a spatio-temporal sequential pattern of the IAA gradient related to the abscission process; this pattern is maintained by interactions with ET. We present new valuable evidence for the existence of conservative mechanisms that regulate generative organ separation and can help to improve the yield of agronomically significant species in the future. [ABSTRACT FROM AUTHOR]

Flower abscission is a highly regulated developmental process activated in response to exogenous (e.g. changing environmental conditions) and endogenous stimuli (e.g. phytohormones). Ethylene (ET) and abscisic acid (ABA) are very effective stimulators of flower abortion in Lupinus luteus , which is a widely cultivated species in Poland, Australia and Mediterranean countries. In this paper, we show that artificial activation of abscission by flower removal caused an accumulation of ABA in the abscission zone (AZ). Moreover, the blocking of that phytohormone’s biosynthesis by NDGA (nordihydroguaiaretic acid) decreased the number of abscised flowers. However, the application of NBD – an inhibitor of ET action – reversed the stimulatory effect of ABA on flower abscission, indicating that ABA itself is not sufficient to turn on the organ separation. Our analysis revealed that exogenous ABA significantly accelerated the transcriptional activity of the ET biosynthesis genes ACC synthase ( LlACS ) and oxidase ( LlACO ), and moreover, strongly increased the level of 1-aminocyclopropane-1-carboxylic acid (ACC) – ET precursor, which was specifically localized within AZ cells. We cannot exclude the possibility that ABA mediates flower abscission processes by enhancing the ET biosynthesis rate. The findings of our study will contribute to the overall basic knowledge on the phytohormone-regulated generative organs abscission in L. luteus . [ABSTRACT FROM AUTHOR]

Summary: 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. [Copyright &y& Elsevier]

How auxin transport regulates organ abscission is a long-standing and intriguing question. Polar auxin transport across the abscission zone (AZ) plays a more important role in the regulation of abscission than a local concentration of this hormone. We recently reported the existence of a spatiotemporal sequential pattern of the indole-3-acetic acid (IAA) localization in the area of the yellow lupine AZ, which is a place of flower detachment. In this study, we performed analyses of AZ following treatment with an inhibitor of polar auxin transport (2,3,5-triiodobenzoic acid (TIBA)). Once we applied TIBA directly onto the AZ, we observed a strong response as demonstrated by enhanced flower abscission. To elucidate the molecular events caused by the inhibition of auxin movement, we divided the AZ into the distal and proximal part. TIBA triggered the formation of the IAA gradient between these two parts. The AZ-marker genes, which encode the downstream molecular components of the inflorescence deficient in abscission (IDA)-signaling system executing the abscission, were expressed in the distal part. The accumulation of IAA in the proximal area accelerated the biosynthesis of abscisic acid and ethylene (stimulators of flower separation), which was also reflected at the transcriptional level. Accumulated IAA up-regulated reactive oxygen species (ROS) detoxification mechanisms. Collectively, we provide new information regarding auxin-regulated processes operating in specific areas of the AZ. [ABSTRACT FROM AUTHOR]

• Drought stress decreased water content directly in nodules and caused degradation of symbiosome. • Hormonal changes evoked by water deficit are reflected by the affection of ET and ABA biosynthesis pathway. • The stress factor negatively regulated the expression of LlBOP and LlLbl genes responsible for the proper functioning of the nodules. • We provide several potential molecular and hormonal markers related to the response on soil drought. The ability of symbiosis with Rhizobium bacteria is an extremely important trait of Lupinus luteus L. Its cultivation increases soil fertility and reduces the necessity of using chemical fertilizers, thus makes lupine an excellent proecological and agronomical species. Nevertheless, nodule functioning associated with nitrogen fixation can be strongly affected by soil drought. On the face of changing climatic conditions, the emphasis should be given to get the knowledge concerning the phytohormonal and molecular markers of early response on water deficit in soil. In this paper, we have shown that soil drought stress, by causing water loss in nodules and affecting their structure, evokes degradation of symbiosome and leads to hormonal and molecular changes. The stress factor modulated abscisic acid (ABA) and ethylene (ET) biosynthesis pathways. It was reflected by increased expression of LlZEP (ZEAXANTHIN EPOXIDASE) involved in ABA biosynthesis and strong accumulation of this phytohormone. At the same time, the mRNA of synthase (LlACS) and oxidase (LlACO) of 1-aminocyclopropane-1-carboxylic acid (ACC) were elevated, while ACC accumulated significantly. Moreover, drought stress negatively influenced the expression of LlBOP (BLADE-ON-PETIOLE) and LlLbI (LEGHEMOGLOBIN), previously pointed out as regulators of nodule functioning. Simultaneously the iron and nitrogen content drastically decreased in the stressed nodules. Presented novel information describing phytohormonal changes during drought stress directly in the nodules can help to elucidate the hormonal and molecular mechanisms that control plant response to water loss. [ABSTRACT FROM AUTHOR]

The drought is a crucial environmental factor that determines yielding of many crop species, e.g., Fabaceae, which are a source of valuable proteins for food and feed. Herein, we focused on the events accompanying drought-induced activation of flower abscission zone (AZ)—the structure responsible for flower detachment and, consequently, determining seed production in Lupinus luteus. Therefore, detection of molecular markers regulating this process is an excellent tool in the development of improved drought-resistant cultivars to minimize yield loss. We applied physiological, molecular, biochemical, immunocytochemical, and chromatography methods for a comprehensive examination of changes evoked by drought in the AZ cells. This factor led to significant cellular changes and activated AZ, which consequently increased the flower abortion rate. Simultaneously, drought caused an accumulation of mRNA of genes inflorescence deficient in abscission-like (LlIDL), receptor-like protein kinase HSL (LlHSL), and mitogen-activated protein kinase6 (LlMPK6), encoding succeeding elements of AZ activation pathway. The content of hydrogen peroxide (H2O2), catalase activity, and localization significantly changed which confirmed the appearance of stressful conditions and indicated modifications in the redox balance. Loss of water enhanced transcriptional activity of the abscisic acid (ABA) and ethylene (ET) biosynthesis pathways, which was manifested by elevated expression of zeaxanthin epoxidase (LlZEP), aminocyclopropane-1-carboxylic acid synthase (LlACS), and aminocyclopropane-1-carboxylic acid oxidase (LlACO) genes. Accordingly, both ABA and ET precursors were highly abundant in AZ cells. Our study provides information about several new potential markers of early response on water loss, which can help to elucidate the mechanisms that control plant response to drought, and gives a useful basis for breeders and agronomists to enhance tolerance of crops against the stress. [ABSTRACT FROM AUTHOR]

The appropriate timing of organ abscission determines plant growth, development, reproductive success, and yield in relation to crop species. Among these, yellow lupine is an example of a crop species that loses many fully developed flowers, which limits the formation of pods with high-protein seeds and affects its economic value. Lupine flower abscission, similarly to the separation of other organs, depends on a complex regulatory network functioning in the cells of the abscission zone (AZ). In the present study, genetic, biochemical, and cellular methods were used to highlight the complexity of the interactions among strong hormonal stimulators of abscission, including abscisic acid (ABA), ethylene, and jasmonates (JAs) precisely in the AZ cells, with all results supporting that the JA-related pathway has an important role in the phytohormonal cross-talk leading to flower abscission in yellow lupine. Based on obtained results, we conclude that ABA and ET have positive influence on JAs biosynthesis and signaling pathway in time-dependent manner. Both phytohormones changes lipoxygenase (LOX) gene expression, affects LOX protein abundance, and JA accumulation in AZ cells. We have also shown that the signaling pathway of JA is highly sensitive to ABA and ET, given the accumulation of COI1 receptor and MYC2 transcription factor in response to these phytohormones. The results presented provide novel information about the JAs-dependent separation of organs and provide insight and details about the phytohormone-related mechanisms of lupine flower abscission. • ABA and ET stimulate jasmonic acid accumulation in the flower abscission zone. • Manifestation of lipid metabolism initiation is the induction of LOX by ABA and ET. • COI1 is sensitive to hormonal stimulators of flower abscission. • ABA- and ET-mediated abscission of flowers is linked with MYC2 transcription factor. • ABA and ET act via jasmonates to promote flower abortion in lupine. [ABSTRACT FROM AUTHOR]