Reevaluation of ethylene role in Arabidopsis cauline leaf abscission induced by water stress and rewatering.

It was previously reported that cauline leaf abscission in Arabidopsis is induced by a cycle of water stress and rewatering, which is regulated by the complex of INFLORESCENCE DEFICIENT IN ABSCISSION (IDA), HAESA (HAE), and HAESA-LIKE2 (HSL2) kinases. However, the involvement of ethylene in this process was ruled out. Because this conclusion contradicts the well-established role of ethylene in organ abscission induced by a cycle of water stress and rewatering, our present study was aimed to reevaluate the possible involvement of ethylene in this process.

Role of the KNOTTED1-LIKE HOMEOBOX protein (KD1) in regulating abscission of tomato flower pedicels at early and late stages of the process.

The KNOTTED1-LIKE HOMEOBOX PROTEIN1 (KD1) gene is highly expressed in flower and leaf abscission zones (AZs), and KD1 was reported to regulate tomato flower pedicel abscission via alteration of the auxin gradient and response in the flower AZ (FAZ). The present work was aimed to further examine how KD1 regulates signaling factors and regulatory genes involved in pedicel abscission, by using silenced KD1 lines and performing a large-scale transcriptome profiling of the FAZ before and after flower removal, using a customized AZ-specific microarray. The results highlighted a differential expression of regulatory genes in the FAZ of KD1-silenced plants compared to the wild-type.

Characterization of Two Ethephon-Induced Genes from Mango, and Elucidation of Their Involvement in Regulating Organ Abscission.

In mango ( L.), fruitlet abscission limits productivity. The INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) peptide acts as a key component controlling abscission events in Arabidopsis.

Expression Kinetics of Regulatory Genes Involved in the Vesicle Trafficking Processes Operating in Tomato Flower Abscission Zone Cells during Pedicel Abscission.

The abscission process occurs in a specific abscission zone (AZ) as a consequence of the middle lamella dissolution, cell wall degradation, and formation of a defense layer. The proteins and metabolites related to these processes are secreted by vesicle trafficking through the plasma membrane to the cell wall and middle lamella of the separating cells in the AZ. We investigated this process, since the regulation of vesicle trafficking in abscission systems is poorly understood.

Raising the pH of the Pulsing Solution Improved the Acropetal Transport of NAA and 2,4-D and Their Efficacy in Reducing Floret Bud Abscission of Red Cestrum Cut Flowers.

The use of auxins to improve the vase life of cut flowers is very limited. Previous studies demonstrated that a pulse treatment of Red Cestrum ( Schlecht.) cut flowers with 2,4-dichlorophenoxyacetic acid (2,4-D) significantly reduced floret bud abscission, whereas 1-naphthaleneacetic acid (NAA) was ineffective.

Ethylene Induces a Rapid Degradation of Petal Anthocyanins in Cut 'Sansai Blue' Orchid Flowers.

Ethylene plays a major role in the regulation of flower senescence, including in the ethylene-sensitive 'Sansai Blue' orchid flowers. This cut flower is popular in Thailand due to its light blue big size florets possessing a beautiful shape pattern. In the present study, we further examined the rapid ethylene-induced process of active anthocyanin degradation in cut 'Sansai Blue' flowers, which occurred much before detection of other typical senescence-related symptoms.

Re-evaluation of the ethylene-dependent and -independent pathways in the regulation of floral and organ abscission.

Abscission is a developmental process with important implications for agricultural practices. Ethylene has long been considered as a key regulator of the abscission process. The existence of an ethylene-independent abscission pathway, controlled by the complex of INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) peptide and the HAESA (HAE) and HAESA-like2 (HSL2) kinases, has been proposed, based mainly on observations that organ abscission in ethylene-insensitive mutants was delayed but not inhibited.

The Tomato Hybrid Proline-rich Protein regulates the abscission zone competence to respond to ethylene signals.

The Tomato Hybrid Proline-rich Protein () gene was specifically expressed in the tomato () flower abscission zone (FAZ), and its stable antisense silencing under the control of an abscission zone (AZ)-specific promoter, , significantly inhibited tomato pedicel abscission following flower removal. For understanding the THyPRP role in regulating pedicel abscission, a transcriptomic analysis of the FAZ of -silenced plants was performed, using a newly developed AZ-specific tomato microarray chip. Decreased expression of in the silenced plants was already observed before abscission induction, resulting in FAZ-specific altered gene expression of transcription factors, epigenetic modifiers, post-translational regulators, and transporters.

De novo Transcriptome Sequencing and Development of Abscission Zone-Specific Microarray as a New Molecular Tool for Analysis of Tomato Organ Abscission.

Abscission of flower pedicels and leaf petioles of tomato (Solanum lycopersicum) can be induced by flower removal or leaf deblading, respectively, which leads to auxin depletion, resulting in increased sensitivity of the abscission zone (AZ) to ethylene. However, the molecular mechanisms that drive the acquisition of abscission competence and its modulation by auxin gradients are not yet known. We used RNA-Sequencing (RNA-Seq) to obtain a comprehensive transcriptome of tomato flower AZ (FAZ) and leaf AZ (LAZ) during abscission.

Examination of the Abscission-Associated Transcriptomes for Soybean, Tomato, and Arabidopsis Highlights the Conserved Biosynthesis of an Extensible Extracellular Matrix and Boundary Layer.

Abscission zone (AZ) development and the progression of abscission (detachment of plant organs) have been roughly separated into four stages: first, AZ differentiation; second, competence to respond to abscission signals; third, activation of abscission; and fourth, formation of a protective layer and post-abscission trans-differentiation. Stage three, activation of abscission, is when changes in the cell wall and extracellular matrix occur to support successful organ separation. Most abscission research has focused on gene expression for enzymes that disassemble the cell wall within the AZ and changes in phytohormones and other signaling events that regulate their expression.

Flowering shoots of ornamental crops as a model to study cellular and molecular aspects of plant gravitropism.

Flowering shoots offer a very convenient and excellent model system for in-depth study of shoot gravitropism in regular stems rather than in special aboveground organs, showing how plants cope with the force of gravity on Earth and change in orientation. Regarding the emerging notion that roots and shoots execute their gravitropic bending by different mechanisms, the use of flowering shoots offers additional confirmation for the suggested shoot-sensing mechanisms initially found in Arabidopsis. As a part of confirming this mechanism, studying this unique model system also enabled elucidation of the sequence of events operating in gravity signalling in shoots.

Abscission of flowers and floral organs is closely associated with alkalization of the cytosol in abscission zone cells.

In vivo changes in the cytosolic pH of abscission zone (AZ) cells were visualized using confocal microscopic detection of the fluorescent pH-sensitive and intracellularly trapped dye, 2',7'-bis-(2-carboxyethyl)-5(and-6)-carboxyfluorescein (BCECF), driven by its acetoxymethyl ester. A specific and gradual increase in the cytosolic pH of AZ cells was observed during natural abscission of flower organs in Arabidopsis thaliana and wild rocket (Diplotaxis tenuifolia), and during flower pedicel abscission induced by flower removal in tomato (Solanum lycopersicum Mill). The alkalization pattern in the first two species paralleled the acceleration or inhibition of flower organ abscission induced by ethylene or its inhibitor 1-methylcyclopropene (1-MCP), respectively.

Programmed cell death occurs asymmetrically during abscission in tomato.

Abscission occurs specifically in the abscission zone (AZ) tissue as a natural stage of plant development. Previously, we observed delay of tomato (Solanum lycopersicum) leaf abscission when the LX ribonuclease (LX) was inhibited. The known association between LX expression and programmed cell death (PCD) suggested involvement of PCD in abscission.

Identification of defense-related genes newly-associated with tomato flower abscission.

The current abscission model suggests the formation of a post-abscission trans-differentiation of a protective layer as the last step of the process. The present report expands the repertoire of genes activated in the tomato flower abscission zone (AZ), which are likely to be involved in defense responses. We identified four different defense-related genes, including: Cysteine-type endopeptidase, α-Dioxygenase 1 (α-DOX1), HopW-1-1-Interacting protein2 (WIN2), and Stomatal-derived factor-2 (SDF2), that are newly-associated with the late stage of the abscission process.

Actomyosin mediates gravisensing and early transduction events in reoriented cut snapdragon spikes.

We investigated the involvement of the actomyosin network in the early events of the gravitropic response of cut snapdragon (Antirrhinum majus L.) spikes. The effects of the actin-modulating drug, cytochalasin D (CD) and/or the myosin inhibitor, 2,3-butanedione-2-monoxime (BDM) on amyloplast displacement, lateral auxin transport and consequently on stem bending were examined.

Microarray analysis of the abscission-related transcriptome in the tomato flower abscission zone in response to auxin depletion.

The abscission process is initiated by changes in the auxin gradient across the abscission zone (AZ) and is triggered by ethylene. Although changes in gene expression have been correlated with the ethylene-mediated execution of abscission, there is almost no information on the molecular and biochemical basis of the increased AZ sensitivity to ethylene. We examined transcriptome changes in the tomato (Solanum lycopersicum 'Shiran 1335') flower AZ during the rapid acquisition of ethylene sensitivity following flower removal, which depletes the AZ from auxin, with or without preexposure to 1-methylcyclopropene or application of indole-3-acetic acid after flower removal.

Microtubule reorientation in shoots precedes bending during the gravitropic response of cut snapdragon spikes.

The microtubule reorientation during the gravitropic bending of cut snapdragon (Antirrhinum majus L.) spikes was investigated. Using indirect immunofluorescence methods, we examined changes in microtubule orientation in the cortex, endodermis and pith tissues of the shoot bending zone, in response to gravistimulation.

Differential effects of NAA and 2,4-D in reducing floret abscission in cestrum (Cestrum elegans) cut flowers are associated with their differential activation of Aux/IAA homologous genes.

Background And Aims: A previous study showed that the relative effectiveness of 2,4-dichlorophenoxyacetic acid (2,4-D) compared with that of 1-naphthaleneacetic acid (NAA) in reducing floret bud abscission in cestrum (Cestrum elegans) cut flowers was due to its acropetal transport. The aim of the present study was to examine if the differential effect of these auxins on floret abscission is reflected in the expression of Aux/IAA genes in the floret abscission zone (AZ).

Methods: cDNAs were isolated by PCR-based cloning from the floret AZ of auxin-treated cut flowers.

Changes in starch and inositol 1,4,5-trisphosphate levels and auxin transport are interrelated in graviresponding oat (Avena sativa) shoots.

This study was conducted to unravel a mechanism for the gravitropic curvature response in oat (Avena sativa) shoot pulvini. For this purpose, we examined the downward movement of starch-filled chloroplast gravisensors, differential changes in inositol 1,4,5-trisphosphate (IP(3)) levels, transport of indole-3-acetic acid (IAA) and gravitropic curvature. Upon gravistimulation, the ratio for IAA levels in lower halves versus those in upper halves (L/U) increased from 1.

Gravitropic bending and plant hormones.

Gravitropism is a complex multistep process that redirects the growth of roots and various above-ground organs in response to changes in the direction of the gravity vector. The anatomy and morphology of these graviresponding organs indicates a certain spatial separation between the sensing region and the responding one, a situation that strongly suggests the requirement of phytohormones as mediators to coordinate the process. The Cholodny-Went hypothesis suggested auxin as the main mediator of gravitropism.

An auxin-responsive 1-aminocyclopropane-1-carboxylate synthase is responsible for differential ethylene production in gravistimulated Antirrhinum majus L. flower stems.

The regulation of gravistimulation-induced ethylene production and its role in gravitropic bending was studied in Antirrhinum majus L. cut flower stems. Gravistimulation increased ethylene production in both lower and upper halves of the stems with much higher levels observed in the lower half.

Inhibition of the gravitropic bending response of flowering shoots by salicylic acid.

The upward gravitropic bending of cut snapdragon, lupinus and anemone flowering shoots was inhibited by salicylic acid (SA) applied at 0.5 mM and above. This effect was probably not due to acidification of the cytoplasm, since other weak acids did not inhibit bending of snapdragon shoots.

Characterization of the asymmetric growth of gravistimulated snapdragon spikes by stem and cell dimension analyses.

Growth patterns of detached spikes of gravistimulated snapdragon (Antirrhinum majus L.) were analyzed in detail. The length increment of 5-mm marked subsections in the upper and lower flanks of the stem-bending zone was measured during gravistimulation using time-lapse photographs.

The role of actin filaments in the gravitropic response of snapdragon flowering shoots.

The involvement of the actin and the microtubule cytoskeleton networks in the gravitropic response of snapdragon ( Antirrhinum majus L.) flowering shoots was studied using various specific cytoskeleton modulators. The microtubule-depolymerizing drugs tested had no effect on gravitropic bending.

Chilling-induced leaf abscission of Ixora coccinea plants. III. Enhancement by high light via increased oxidative processes.

The role of increased oxidation induced by successive stresses of chilling and high light in the induction of leaf abscission was studied in Ixora coccinea plants in relation to auxin metabolism and oxidative processes. Exposure of plants following dark chilling (7 degrees C for 3 days) to high light (500-700 &mgr;mol m-2 s-1 photosynthetically active radiation) for 5 h at 20-25 degrees C enhanced chilling-induced leaf abscission. This abscission was inhibited by pretreatment with the antioxidant butylated hydroxyanisole, alpha-naphthaleneacetic acid or the ethylene action inhibitor, 1-methylcyclopropene.