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The phenomenon of excessive flower abscission in yellow lupine is a process of substantial interest to the agricultural industries, because it substantially affects the yield. The aim of this work was to provide an analysis of the changes taking place precisely in the abscission zone (AZ) during early stages of flower separation. We put particular emphasis on mRNA accumulation of BOP (BLADE ON PETIOLE) gene encoding a transcriptional factor so far considered to be essential for AZ formation. Our results show that the AZ displays a particular transcriptional network active in the specific stages of its function, as reflected by the expression profile of LlBOP. Noteworthy, spatio-temporal LlBOP transcript accumulation in the elements of pedicel vascular tissue reveals divergent regulatory mechanism of its activity. We have also found that AZ cells accumulate reactive oxidative species following abscission and what is more, become active due to the increasing amount of uridine-rich small nuclear RNA, accompanied by poly(A) mRNA intensive synthesis. Our paper is a novel report for BOP involvement in the AZ functioning in relation to the whole transcriptional activity of AZ and overall discussed regarding BOP role as a potential mobile key regulator of abscission. [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]

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. [ABSTRACT FROM AUTHOR]

We recently showed that yellow lupine is highly sensitive to soil water deficits since this stressor disrupts nodule structure and functioning, and at the same time triggers flower separation through abscission zone (AZ) activation in the upper part of the plant. Both processes require specific transformations including cell wall remodeling. However, knowledge about the involvement of particular cell wall elements in nodulation and abscission in agronomically important, nitrogen-fixing crops, especially under stressful conditions, is still scarce. Here, we used immuno-fluorescence techniques to visualize dynamic changes in cell wall compounds taking place in the root nodules and flower AZ of Lupinus luteus following drought. The reaction of nodules and the flower AZ to drought includes the upregulation of extensins, galactans, arabinans, xylogalacturonan, and xyloglucans. Additionally, modifications in the localization of high- and low-methylated homogalacturonans and arabinogalactan proteins were detected in nodules. Collectively, we determined for the first time the drought-associated modification of cell wall components responsible for their remodeling in root nodules and the flower AZ of L. luteus. The involvement of these particular molecules and their possible interaction in response to stress is also deeply discussed herein. [ABSTRACT FROM AUTHOR]

Drought causes the excessive abscission of flowers in yellow lupine, leading to yield loss and serious economic consequences in agriculture. The structure that determines the time of flower shedding is the abscission zone (AZ). Its functioning depends on the undisturbed auxin movement from the flower to the stem. However, little is known about the mechanism guiding cell–cell adhesion directly in an AZ under water deficit. Therefore, here, we seek a fuller understanding of drought-dependent reactions and check the hypothesis that water limitation in soil disturbs the natural auxin balance within the AZ and, in this way, modifies the cell wall structure, leading to flower separation. Our strategy combined microscopic, biochemical, and chromatography approaches. We show that drought affects indole-3-acetic acid (IAA) distribution and evokes cellular changes, indicating AZ activation and flower abortion. Drought action was manifested by the accumulation of proline in the AZ. Moreover, cell wall-related modifications in response to drought are associated with reorganization of methylated homogalacturonans (HG) in the AZ, and upregulation of pectin methylesterase (PME) and polygalacturonase (PG)—enzymes responsible for pectin remodeling. Another symptom of stress action is the accumulation of hemicelluloses. Our data provide new insights into cell wall remodeling events during drought-induced flower abscission, which is relevant to control plant production. [ABSTRACT FROM AUTHOR]

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]

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]

• The process of natural flower separation in lupine involves extensive lipid changes in the abscission zone. • Specific upregulation of oxidative processes related to ascorbate peroxidase are initiated in the abscission zone during flower detachment. • The combined action of lipase and lipoxygenase is triggered during abscission zone activation. • Natural activation of abscission zone cells is closely correlated with the accumulation of jasmonates including methyl jasmonate, which is a stronger accelerator of abscission in lupine than free jasmonic acid. Yellow lupine is an economically important crop. This species has been used as a great model for abscission processes for several years due to extreme flower abortion, which takes place in the abscission zone (AZ). AZ activation involves modifications of cell walls, membranes, and cellular structure. In this paper, we applied physiological, molecular, biochemical, and instrumental methods to explore lipid-associated changes and the possible involvement of lipid-derived phytohormones – jasmonates (JAs) - in flower AZ activation. Our comprehensive analyses revealed that natural abscission is accompanied by the upregulation of peroxidase, which reflects a disruption of redox balance and/or lipids peroxidation in AZ cell membranes. Redox imbalance was confirmed by appearance of malondialdehyde. Lipid-related processes involved the specific localization and increased level and activity of lipase and LOX, enzymes associated with cell membrane rupture, and JA biosynthesis. Lipid-hydrolyzing phospholipase D, implicated previously in abscission, is also found in naturally active AZs. Observed changes are accompanied by the accumulation of jasmonates, both free jasmonic acid and its methyl ester. The JA derivative exhibited higher biological activity than the nonconjugated form. Overall, our study shed new light on the lipid and phytohormonal regulation of AZ functioning supporting a role of JAs during abscission-associated events. [ABSTRACT FROM AUTHOR]