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Publications

2019
Cinnamon, Y. ; Genin, O. ; Yitzhak, Y. ; Riov, J. ; David, I. ; Shaya, F. ; Izhaki, A. High-resolution episcopic microscopy enables three-dimensional visualization of plant morphology and development. Plant Direct 2019, 3. Publisher's VersionAbstract
The study of plant anatomy, which can be traced back to the seventeenth century, advanced hand in hand with light microscopy technology and relies on traditional histologic techniques, which are based on serial two-dimensional (2D) sections. However, these valuable techniques lack spatial arrangement of the tissue and hence provide only partial information. A new technique of whole-mount three-dimensional (3D) imaging termed high-resolution episcopic microscopy (HREM) can overcome this obstacle and generate a 3D model of the specimen at a near-histological resolution. Here, we describe the application of HREM technique in plants by analyzing two plant developmental processes in woody plants: oil secretory cavity development in citrus fruit and adventitious root formation in persimmon rootstock cuttings. HREM 3D models of citrus fruit peel showed that oil cavities were initiated schizogenously during the early stages of fruitlet development. Citrus secretory cavity formation, shape, volume, and distribution were analyzed, and new insights are presented. HREM 3D model comparison of persimmon rootstock clones, which differ in their rooting ability, revealed that difficult-to-root clones failed to develop adventitious roots due to their inability to initiate root primordia. © 2019 The Authors. Plant Direct published by American Society of Plant Biologists, Society for Experimental Biology and John Wiley & Sons Ltd.
Meir, S. ; Philosoph-Hadas, S. ; Riov, J. ; Tucker, M. L. ; Patterson, S. E. ; Roberts, J. A. Re-evaluation of the ethylene-dependent and-independent pathways in the regulation of floral and organ abscission. Journal of Experimental Botany 2019, 70, 1461-1467. Publisher's VersionAbstract
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. A recent review on plant organ abscission signaling highlighted the IDA-HAE-HSL2 components as the regulators of organ abscission, while the role of auxin and ethylene in this process was hardly addressed. After a careful analysis of the relevant abscission literature, we propose that the IDA-HAE-HSL2 pathway is essential for the final stages of organ abscission, while ethylene plays a major role in its initiation and progression. We discuss the view that the IDA-HAE-HSL2 pathway is ethylene independent, and present recent evidence showing that ethylene activates the IDA-HAE-HSL2 complex. We conclude that the ability of an organ to abscise is tightly linked to cell turgidity in the abscission zone, and suggest that lack of cell turgidity might contribute to the failure of floral organ abscission in the ida mutants. © 2019 The Author(s).
2018
Cohen, O. ; Gamliel, A. ; Katan, J. ; Kurzbaum, E. ; Riov, J. ; Bar, P. Controlling the seed bank of the invasive plant Acacia saligna: comparison of the efficacy of prescribed burning, soil solarization, and their combination. Biological Invasions 2018, 20, 2875-2887. Publisher's VersionAbstract
Reducing the seed bank of invasive plants is a prerequisite for successful restoration of invaded ecosystems. The Australian legume tree Acacia saligna is one of the worst invasive plants in Mediterranean climate regions. This fire-adapted species possesses a large persistent seed bank characterized by physical dormant seeds. The present research was aimed to compare the efficacy of prescribed burning, soil solarization by solar heating of moist soil, and their use in combination on A. saligna seed bank reduction, using the buried seed method, and on seedling emergence from the natural seed bank, as a model of controlling fire-adapted plants. The data obtained show that the direct effect of prescribed burning on the buried seed dynamics was highly variable, and it only reduced seed viability from 98% to about 56%. Soil solarization, particularly in combination with prescribed burning, was much more effective than prescribed burning alone, reducing seed viability to about 29 and 4%, respectively. These results were confirmed by recording seedling emergence from the natural seed bank during two successive germination years following the treatments. Only a relatively very small number of seedlings emerged in the soil solarization treatment and none in the combined treatment. Based on the above data, it is recommended to apply prescribed burning as a pretreatment for soil solarization, or to utilize wild fires followed by soil solarization to reduce the seed bank of invasive fire-adapted plants. In situations in which fire cannot be used as a pretreatment, soil solarization alone is reasonably effective. © 2018, Springer International Publishing AG, part of Springer Nature.
Izhaki, A. ; Yitzhak, Y. ; Blau, T. ; David, I. ; Rotbaum, A. ; Riov, J. ; Zilkah, S. Rooting of cuttings of selected Diospyros virginiana clonal rootstocks and bud growth in rooted cuttings. Scientia Horticulturae 2018, 232, 13-21. Publisher's VersionAbstract
Diospyros virginiana is a common rootstock in several countries growing commercial plantations of persimmon. However, trees grafted on this rootstock, which is exclusively propagated from seeds, are not uniform in both vegetative and reproductive growth. The aim of the present research was to study the effect of various factors on the rooting of D. virginiana cuttings, in order to develop an efficient rooting procedure for selected clonal rootstocks. The clone genotype had a significant effect on the rooting rate, which ranged from zero to close to 100% in the various clones examined. Cuttings collected from different positions on the mother plant shoots did not differ significantly in their rooting rate, suggesting that juvenility does not play an important role in rooting of D. virginiana cuttings. Collecting cuttings at the early stage of the growing season yielded the highest rooting rate, which gradually decreased as the growing season progressed. Using three to 4-node cuttings and treatment with 6000 mg L−1 indole-3-butyric acid (IBA) by quick-dip in solution led to a relatively high rooting rate. Anatomical analysis demonstrated that adventitious root primordia were initiated at the phloem side of the fascicular cambium, with no relationship to the callus tissue that was formed on the cut surface of the cutting base. Out of the examined clones, rooted cuttings of only one clone exhibited a high rate of bud growth, a phenomenon which was also found to be genotype-dependent. Increasing the applied IBA concentration to cuttings of a clone with a high bud growth rate inhibited bud growth, whereas increasing the length of cuttings of clones with a low bud growth rate promoted bud growth. These observations suggest that the IBA applied to promote rooting is transported acropetally and inhibits bud growth. No cutting mortality was observed during rooting and above 90% of the rotted cuttings which exhibited bud growth survived after transplanting into the growing pots. © 2017 Elsevier B.V.
Sundaresan, S. ; Philosoph-Hadas, S. ; Ma, C. ; Jiang, C. - Z. ; Riov, J. ; Mugasimangalam, R. ; Kochanek, B. ; Salim, S. ; Reid, M. S. ; Meir, S. The Tomato Hybrid Proline-rich Protein regulates the abscission zone competence to respond to ethylene signals. Horticulture Research 2018, 5. Publisher's VersionAbstract
The Tomato Hybrid Proline-rich Protein (THyPRP) gene was specifically expressed in the tomato (Solanum lycopersicum) flower abscission zone (FAZ), and its stable antisense silencing under the control of an abscission zone (AZ)-specific promoter, Tomato Abscission Polygalacturonase4, significantly inhibited tomato pedicel abscission following flower removal. For understanding the THyPRP role in regulating pedicel abscission, a transcriptomic analysis of the FAZ of THyPRP-silenced plants was performed, using a newly developed AZ-specific tomato microarray chip. Decreased expression of THyPRP 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. Our data demonstrate that the effect of THyPRP silencing on pedicel abscission was not mediated by its effect on auxin balance, but by decreased ethylene biosynthesis and response. Additionally, THyPRP silencing revealed new players, which were demonstrated for the first time to be involved in regulating pedicel abscission processes. These include: gibberellin perception, Ca2+-Calmodulin signaling, Serpins and Small Ubiquitin-related Modifier proteins involved in post-translational modifications, Synthaxin and SNARE-like proteins, which participate in exocytosis, a process necessary for cell separation. These changes, occurring in the silenced plants early after flower removal, inhibited and/or delayed the acquisition of the competence of the FAZ cells to respond to ethylene signaling. Our results suggest that THyPRP acts as a master regulator of flower abscission in tomato, predominantly by playing a role in the regulation of the FAZ cell competence to respond to ethylene signals. © 2018 The Author(s).
Cohen, O. ; Bar Kutiel, P. ; Gamliel, A. ; Katan, J. ; Kurzbaum, E. ; Weber, G. ; Schubert, I. ; Riov, J. Rain-based soil solarization for reducing the persistent seed banks of invasive plants in natural ecosystems - Acacia saligna as a model. Pest Manag Sci 2018.Abstract
BACKGROUND: The large persistent seed bank of invasive plants is a significant obstacle to restoration programs. Soil solarization was demonstrated to be an effective method for reducing the seed bank of Australian acacias. However, the use of this method in natural habitats might be limited due to the requirement to moisten the soil by irrigation. The present study examined the possibility of replacing irrigation by trapping the soil moisture caused by the last rainfall, i.e. rain-based soil solarization (RBS). RESULTS: Exposure of Acacia saligna seeds to 57 C at 20 % soil moisture for 68 h caused an almost complete loss of seed viability. Similarly, RBS treatment significantly reduced the viability of A. saligna seeds buried at a soil depth of 1-19 cm as well as the seed density in the natural seed bank, and almost completely eliminated seedling emergence from the natural seed banks of A. saligna and other environmental weeds. CONCLUSION: Our results indicate that RBS is an effective method for reducing the seed bank of invasive plants in natural habitats located in various climate regions characterized by different soil types. This is the first demonstration of a successful application of RBS for soil disinfestation. This article is protected by copyright. All rights reserved.
2017
Bernstein, N. ; Shushan, S. ; Shargil, D. ; Perzelan, Y. ; Salim, S. ; Zadka, T. ; Riov, J. ; Sacks, M. ; Spiegel, E. ; Tamari, Y. ; et al. Seasonal variation in leaf damage symptoms, mineral contents, and postharvest attributes of cut foliage of Eucalyptus silver dollar (E. cinerea). Israel Journal of Plant Sciences 2017, 64, 63-79. Publisher's VersionAbstract
Eucalyptus silver dollar (Eucalyptus cinerea) is cultivated under intensive agronomic practices for production of cut foliage branches for the floriculture industry. A range of damage symptoms, suspected to be related to unoptimized mineral nutrition, routinely occur in the leaves at the production plantations and reduce yield quality. No information is available about the nutritional requirements of Eucalyptus silver dollar, or of any other Eucalyptus species under intense cultivation for cut foliage branches production. In this study we evaluated the hypotheses that: (1) leaf damage symptoms in the Eucalyptus silver dollar plantations might be related to the nutritional status of the leaves; and (2) they are affected by environmental and growing conditions, and will therefore differ between seasons and location of the plantations. To test these hypotheses we studied the seasonal and location variations in the ionomics of damaged and healthy leaves, physiological parameters, and postharvest attributes of cut foliage branches during vase life in four plantations of Eucalyptus silver dollar in Israel. The observed leaf symptoms were also characterized anatomically. The range of concentrations for individual macronutrients in the leaves was (in g kg-1): N (18-40); P (1.2-3.0); K (5.5-17.0); Ca (3.5-14.0); Mg (1.1-2.8); S (1.3-2.6). The concentrations range for micronutrients was (in mg kg-1): B (10-100); Fe (30-170); Zn (14-27); Mn (38-190); Cu (3.5-5.9). None of the identified leaf symptoms correlated with a consistent increase or decrease of the content of a specific mineral nutrient or heavy metal compared to the healthy leaves, suggesting that they were not caused by mineral deficiency or toxicity. The leaf ionomics was affected by season and varied between locations. The main damage symptoms observed in the four examined plantations during the four harvests were red and purple spots, and oil stains. Postharvest experiments showed that the quality of branches was reduced during 7-15 days of vase life following transport simulation to the local market. The degree of reduced quality during vase life was also dependent on the location of the plantation and the season of harvest. The oil stains appeared in the two most southern locations during summer, suggesting that this symptom might be derived from the summer conditions such as the high temperatures and high light intensities occurring in the southern part of Israel. © 2017 by Koninklijke Brill NV, Leiden, The Netherlands.
Sacks, M. ; Kafkafi, U. ; Ziv, O. ; Salim, S. ; Meir, S. ; Philosoph-Hadas, S. ; Kenig, E. ; Tamari, Y. ; Natan, R. ; Shlomo, E. ; et al. Effects of nutrient supply on production and quality of cut flowering branches of Grevillea "spiderman". Israel Journal of Plant Sciences 2017, 64, 114-123. Publisher's VersionAbstract
The irrigation and fertilization regime of different varieties of Grevillea in Israel are based on existing knowledge for growing various varieties of the Proteaceae family for production of cut flowering branches. However, growers face problems in cultivating Grevillea "Spiderman," such as leaf chlorosis, prolonged growth until flowering, and reduced quality of cut flowering branches. The present study aimed to examine whether these problems stem from deficiency or excess of Fe, Mn, Zn, P, and Mg, focusing on the effect of these nutrients on growth, flowering, and appearance of visual leaf symptoms and on yield, quality, and vase life longevity of cut flowering branches. The nutrient treatments significantly affected plant development and flowering. Increasing the Fe concentration from 1 to 2 or 3 mg l-1 resulted in improved leaf color, from slightly yellow to dark green. The combination of 2 mg l-1 Fe + 1.8 mg l-1 Mn resulted in early flowering, highest yield, and development of long lateral branches. Low levels of P caused in the first year of treatment leaf chlorosis, which was intensified during the third year, resulting in severe yellowing of the flowering branches. Leaf necrosis and tip burn appeared in treatments with high concentrations of Zn, Mn, and Mg. Deficiency of Fe and Mn and high concentration of P and Mg led to the development of a large number of branches without flowers. The optimal fertilization treatment that yielded the highest quality of flowering branches after harvest was 2 mg l-1 Fe. Branches of this treatment had green foliage at harvest and the longest vase life (10 days) following the recommended postharvest treatment and air transport simulation. Based on the findings of the present research, it can be concluded that the problems in the cultivation of G. "Spiderman," such as leaf chlorosis, delayed flowering, and reduced quality of flowering branches, result from improper fertilization. © 2017 by Koninklijke Brill NV, Leiden, The Netherlands.
2016
Sundaresan, S. ; Philosoph-Hadas, S. ; Riov, J. ; Mugasimangalam, R. ; Kuravadi, N. A. ; Kochanek, B. ; Salim, S. ; Tucker, M. L. ; Meir, S. De novo transcriptome sequencing and development of abscission zone-specific microarray as a new molecular tool for analysis of tomato organ abscission. Frontiers in Plant Science 2016, 6. Publisher's VersionAbstract
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. RNA-Seq was performed on a pool of total RNA extracted from tomato FAZ and LAZ, at different abscission stages, followed by de novo assembly. The assembled clusters contained transcripts that are already known in the Solanaceae (SOL) genomics and NCBI databases, and over 8823 identified novel tomato transcripts of varying sizes. An AZ-specific microarray, encompassing the novel transcripts identified in this study and all known transcripts from the SOL genomics and NCBI databases, was constructed to study the abscission process. Multiple probes for longer genes and key AZ-specific genes, including antisense probes for all transcripts, make this array a unique tool for studying abscission with a comprehensive set of transcripts, and for mining for naturally occurring antisense transcripts. We focused on comparing the global transcriptomes generated from the FAZ and the LAZ to establish the divergences and similarities in their transcriptional networks, and particularly to characterize the processes and transcriptional regulators enriched in gene clusters that are differentially regulated in these two AZs. This study is the first attempt to analyze the global gene expression in different AZs in tomato by combining the RNA-Seq technique with oligonucleotide microarrays. Our AZ-specific microarray chip provides a cost-effective approach for expression profiling and robust analysis of multiple samples in a rapid succession. © 2016 Sundaresan, Philosoph-Hadas, Riov, Mugasimangalam, Kuravadi, Kochanek, Salim, Tucker and Meir.
2015
Sundaresan, S. ; Philosoph-Hadas, S. ; Riov, J. ; Belausov, E. ; Kochanek, B. ; Tucker, M. L. ; Meir, S. Abscission of flowers and floral organs is closely associated with alkalization of the cytosol in abscission zone cells. Journal of Experimental Botany 2015, 66, 1355-1368. Publisher's VersionAbstract
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. Similarly, 1-MCP pre-treatment of tomato inflorescence explants abolished the pH increase in AZ cells and pedicel abscission induced by flower removal. Examination of the pH changes in the AZ cells of Arabidopsis mutants defective in both ethylene-induced (ctr1, ein2, eto4) and ethylene-independent (ida, nev7, dab5) abscission pathways confirmed these results. The data indicate that the pH changes in the AZ cells are part of both the ethylene-sensitive and -insensitive abscission pathways, and occur concomitantly with the execution of organ abscission. pH can affect enzymatic activities and/or act as a signal for gene expression. Changes in pH during abscission could occur via regulation of transporters in AZ cells, which might affect cytosolic pH. Indeed, four genes associated with pH regulation, vacuolar H+-ATPase, putative high-affinity nitrate transporter, and two GTP-binding proteins, were specifically up-regulated in tomato flower AZ following abscission induction, and 1-MCP reduced or abolished the increased expression. © The Author 2014. Published by Oxford University Press on behalf of the Society for Experimental Biology.
Shtein, I. ; Meir, S. ; Shahar-Ivanov, Y. ; Perzelan, Y. ; Philosoph-Hadas, S. ; Riov, J. Ethylene extends the vase life of Dodonaea 'Dana' cut branches: Possible mechanisms. Acta Horticulturae 2015, 1104, 279-286. Publisher's VersionAbstract
Dodonaea 'Dana' is an Israeli hybrid of Dodonaea viscosa L. 'Purpurea' and Dodonaea lobulata (Sapindaceae), characterized by purple tinted decorative foliage and fruits. Cut Dodonaea branches showed seasonal variations in vase life longevity, wilting after one week in winter, and having a vase life of three weeks in summer. The wilting phenomenon resulted from improper water conductance, caused by temperature-induced seasonal anatomical changes. Exposure of cut branches to ethylene (0.5-10 μL L-1, 24 h) improved their longevity in a concentration-dependent manner, expressed in the absence of leaf wilting and a significant increase in fresh weight (FW) during 12 days. Application of the ethylene inhibitor 1-methylcyclopropene (1-MCP) (0.05-0.2 μL L-1, 4 h) resulted in opposite effects. Ethylene improved water uptake of cut branches but did not affect the transpiration rate or the leaf relative water content (RWC), suggesting that the increased FW might have resulted from new growth. Indeed, a significant ethylene-enhanced increase in both elongation and widening dimensions was observed only in immature leaves (3-to 5.5-cm-long), but not in mature leaves (7.5-to 11-cm-long). The aquaporin inhibitor, phloretin, which reduced the branch FW and leaf size, completely abolished the ethylene-induced increase in branch FW and leaf size, suggesting that the positive response of the cut branches and young leaves to ethylene might involve phloretinsensitive aquaporins. The data suggest that the ethylene-induced increase in FW of cut Dodonaea branches is related to young leaf growth and water flow, which seem to be mediated by the activity of aquaporins.
Meir, S. ; Sundaresan, S. ; Riov, J. ; Agarwal, I. ; Philosoph-Hadas, S. Role of auxin depletion in abscission control. Stewart Postharvest Review 2015, 11. Publisher's VersionAbstract
Purpose of review: Abscission is a programmed developmental process initiated by auxin depletion. This review summarizes the mechanisms leading to auxin depletion in the abscission zone (AZ), evaluates the methods for estimation of the spatio-temporal auxin levels, demonstrates how auxin depletion occurs during natural, stressinduced, and artificially-induced organ abscission, and presents new evidence for early and late events resulting from auxin depletion which lead to organ abscission. Findings: Auxin depletion occurs during natural developmental processes which end in organ abscission (leaf and flower senescence, fruit ripening, and self-pruning) and stress-induced abscission, and following artificial organ removal in the tomato model system. Stress-induced auxin depletion is mediated by increased ethylene and reactive oxygen species (ROS) production and carbohydrate starvation. Similar changes in auxin-related genes occurred in both flower AZ (FAZ) and leaf AZ (LAZ) following flower or leaf removal, respectively, suggesting a similar regulation of the abscission process of these organs. Auxin depletion resulted from decreased indole-3- acetic acid (IAA) biosynthesis and transport, as well as from enhanced IAA transport autoinhibition (ATA), conjugation and oxidative IAA catabolism. Functional analyses of several target genes delaying abscission, such as Knotted- Like Homeobox Protein1 (KD1), Tomato Proline Rich Protein (TPRP), Ethylene Responsive Factor52 (ERF52), and Ribonuclease LX (LX), shed light on various events operating in response to auxin depletion in tomato FAZ and/or LAZ. The information gained allows a better understanding of the abscission process driven by auxin depletion, and might lead to development of improved methods for abscission control in horticultural crops. Direction for future research: A better understanding of abscission regulation as it pertains to auxin depletion will require advanced molecular tools such as microarrays, new generation sequencing (NGS), transcriptomic, functional, and proteomic analyses of target genes and proteins found to operate in the abscission process. © 2015 SPS (UK) Ltd.