Quantification of Cauline Leaf Abscission in Response to Plant Pathogens

ABSTRACTPatharkar and Walker (2016) 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, they stated without presenting experimental results that ethylene is not involved in this process. Since this statement 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 re-evaluate the possible involvement of ethylene in this process. For this purpose, we examined the endogenous ethylene production during water stress and following rewatering, as well as the effects of exogenous ethylene and 1-methylcyclopropene (1-MCP), on cauline leaf abscission of Arabidopsis wild type. Additionally, we examined whether this stress induces cauline leaf abscission in ethylene-insensitive Arabidopsis mutants. The results of the present study demonstrated that ethylene production rates increased significantly in cauline leaves at 4 h after rewatering of stressed plants, and remained high for at least 24 h in plants water-stressed to 40 and 30% of system weight. Ethylene treatment applied to well-watered plants induced cauline leaf abscission, which was inhibited by 1-MCP. Cauline leaf abscission was also inhibited by 1-MCP applied during a cycle of water stress and rewatering. Finally, no abscission occurred in two ethylene-insensitive mutants, ein2-1 and ein2-5, following a cycle of water stress and rewatering. Taken together, these results clearly indicate that ethylene is involved in Arabidopsis cauline leaf abscission induced by water stress.One sentence summaryUnlike Patharker and Walker (2016), our results show that ethylene is involved in Arabidopsis cauline leaf abscission induced by water stress and rewatering, similar to leaf abscission in other plants.

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Leaf shedding as a bacterial defense in Arabidopsis cauline leaves

10.1101/189720 ◽

2017 ◽

Author(s):

O. Rahul Patharkar ◽

Walter Gassmann ◽

John C. Walker

Keyword(s):

Innate Immunity ◽

Salicylic Acid ◽

Pseudomonas Syringae ◽

Defense Mechanism ◽

Threshold Model ◽

Abscission Zone ◽

Leaf Abscission ◽

Long Distance ◽

Cauline Leaf ◽

Physiological Level

AbstractPlants utilize an innate immune system to protect themselves from disease. While many molecular components of plant innate immunity resemble the innate immunity of animals, plants also have evolved a number of truly unique defense mechanisms, particularly at the physiological level. Plant’s flexible developmental program allows them the unique ability to simply produce new organs as needed, affording them the ability to replace damaged organs. Here we develop a system to study pathogen-triggered leaf abscission in Arabidopsis. Cauline leaves infected with the bacterial pathogenPseudomonas syringaeabscise as part of the defense mechanism.Pseudomonas syringaelacking a functional type III secretion system fail to elicit an abscission response, suggesting that the abscission response is a novel form of immunity triggered by effectors.HAESA/HAESA-like 2, INFLORESCENCE DEFICIENT IN ABSCISSION, andNEVERSHEDare all required for pathogen-triggered abscission to occur. Additionallyphytoalexin deficient 4, enhanced disease susceptibility 1, salicylic acid induction deficient 2, andsenescence-associated gene 101plants with mutations in genes necessary for bacterial defense and salicylic acid signaling, and NahG transgenic plants with low levels of salicylic acid fail to abscise cauline leaves normally. Bacteria that physically contact abscission zones trigger a strong abscission response; however, long distance signals are also sent from distal infected tissue to the abscission zone, alerting the abscission zone of looming danger. We propose a threshold model regulating cauline leaf defense where minor infections are handled by limiting bacterial growth, but when an infection is deemed out of control, cauline leaves are shed. Together with previous results our findings suggest that salicylic acid may regulate both pathogen‐ and drought-triggered leaf abscission.Author SummaryPlants have a flexible development program that determine their form. We describe an organ level defense response in Arabidopsis to bacterial attack where plants simply shed heavily infected leaves. The genetics regulating this defense mechanism are comprised of both classical defense genes and floral organ abscission genes working together. Long distance signals are transmitted from infected areas to abscission zones which activate the abscission receptor. Salicylic acid, a defense hormone, signaling is necessary for cauline leaf abscission.

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Zoospore Density-Dependent Behaviors of Phytophthora nicotianae Are Autoregulated by Extracellular Products

Phytopathology ◽

10.1094/phyto-100-7-0632 ◽

2010 ◽

Vol 100 (7) ◽

pp. 632-637 ◽

Cited By ~ 10

Author(s):

Ping Kong ◽

Chuanxue Hong

Keyword(s):

Plant Pathogens ◽

Phytophthora Species ◽

Threshold Concentration ◽

Phytophthora Nicotianae ◽

Free Fluid ◽

Signal Molecules ◽

Signal Molecule ◽

Cauline Leaf ◽

Density Dependent ◽

Plant Infection

Phytophthora species are destructive fungus-like plant pathogens that use asexual single-celled flagellate zoospores for dispersal and plant infection. Many of the zoospore behaviors are density-dependent although the underlying mechanisms are poorly understood. Here, we use P. nicotianae as a model and demonstrate autoregulation of some zoospore behaviors using signal molecules that zoospores release into the environment. Specifically, zoospore aggregation, plant targeting, and infection required or were enhanced by threshold concentrations of these signal molecules. Below the threshold concentration, zoospores did not aggregate and move toward a cauline leaf of Arabidopsis thaliana (Col-0) and failed to individually attack annual vinca (Catharanthus roseus cv. Little Bright Eye). These processes were reversed when supplemented with zoospore-free fluid (ZFF) prepared from a zoospore suspension above threshold densities but not with calcium chloride at a concentration equivalent to extracellular Ca2+ in ZFF. These results suggest that Ca2+ is not a primary signal molecule regulating these communal behaviors. Zoospores coordinated their communal behaviors by releasing, detecting, and responding to signal molecules. This chemical communication mechanism raises the possibility that Phytophthora plant infection may not depend solely on zoospore number in the real world. Single zoospore infection may take place if it is signaled by a common molecule available in the environment which contributes to the destructiveness of these plant pathogens.

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Freeze substitution fixation of fungal reproductive structures and spores

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100156936 ◽

1989 ◽

Vol 47 ◽

pp. 990-991

Author(s):

C. W. Mims ◽

E. A. Richardson

Keyword(s):

Plant Pathogens ◽

Freeze Substitution ◽

Uranyl Acetate ◽

Chemical Fixation ◽

Dialysis Membrane ◽

Razor Blade ◽

Thin Sections ◽

Reproductive Structures ◽

Dry Down ◽

Diamond Knife

The advantages of freeze substitution fixation over conventional chemical fixation for preservation of ultrastructural details in fungi have been discussed by various authors. As most ascomycetes, basidiomycetes and deuteromycetes do not fix well using conventional chemical fixation protocols, freeze substitution has attracted the attention of many individuals interested in fungal ultrastructure. Thus far most workers using this technique on fungi have concentrated on thin walled somatic hyphae. However, in our laboratory we have experimented with the use of freeze substitution on a variety of fungal reproductive structures and spores with promising results.Here we present data on freeze substituted samples of sporangia of the zygomycete Umbellopsis vinacea, basidia of Exobasidium camelliae var. gracilis, developing teliospores of the smut Sporisorium sorghi, germinating teliospores of the rust Gymnosporangium clavipes, germinating conidia of the deuteromycete Cercosporidium personatum, and developing ascospores of Ascodesmis nigricans.Spores of G. clavipes and C. personatum were deposited on moist pieces of sterile dialysis membrane where they hydrated and germinated. Asci of A. nigricans developed on pieces of dialysis membrane lying on nutrient agar plates. U. vinacea was cultured on small pieces of agar-coated wire. In the plant pathogens E. camelliae var. gracilis and S. sorghi, a razor blade was used to remove smal1 pieces of infected host issue. All samples were plunged directly into liquid propane and processed for study according to Hoch.l Samples on dialysis membrane were flat embedded. Serial thin sections were cut using a diamond knife, collected on slot grids, and allowed to dry down onto Formvar coated aluminum racks. Sections were post stained with uranyl acetate and lead citrate.

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Effect of Homeopathic Preparations on Lettuce, Parasitized or Not by Meloidogyne enterolobii

Homeopathy ◽

10.1055/s-0040-1716402 ◽

2020 ◽

Author(s):

Thais Moraes Ferreira ◽

Mariana Zandomênico Mangeiro ◽

Alexandre Macedo Almeida ◽

Ricardo Moreira Souza

Keyword(s):

Plant Pathogens ◽

Nematode Control ◽

Plant Tolerance ◽

Nematode Reproduction ◽

Meloidogyne Enterolobii ◽

Negative Effect ◽

Meloidogyne Spp ◽

Constant Dose ◽

Lettuce Growth ◽

Complementary Strategy

Abstract Background There are relatively few scientific works on the use of homeopathy to manage plant pathogens, particularly nematodes. A handful of studies focused on Meloidogyne spp. parasitizing vegetables have brought contradictory results on nematode control and enhancement of plant tolerance to parasitism. Objective Our goal was to assess the effect of Cina—a well-known anti-nematode ingredient—on Meloidogyne enterolobii parasitizing lettuce. Methods Cina was applied daily on nematode-inoculated plants, from the seedling stage until harvest. We tested an evenly spaced range of Hahnemannian concentrations (c), which were applied though irrigation with a constant dose of the ingredient. Several absolute and relative controls were employed to allow the assessment of the effect of Cina on nematode reproduction and lettuce growth. Results Cina affected growth of non-parasitized plants, both positively and negatively; this effect was modulated by the c applied and the thermal stress suffered by the plants in one of the assays. The effect of Cina on the growth of nematode-parasitized plants was neutral or negative. Cina reduced nematode reproduction by 25–36%. Conclusion Based on the moderate negative effect of Cina on M. enterolobii reproduction, it seems this ingredient may be useful as a complementary strategy for Meloidogyne control. But Cina did not enhance the tolerance of lettuce to Meloidogyne spp.

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