Download presentation
Presentation is loading. Please wait.
1
Plant Response to biotic and abiotic stresses
Nabil Killiny Associate Professor Citrus Research and Education Center
2
What is Stress
3
Stresses External conditions that adversely affect growth, development, or productivity. Stresses can be abiotic or biotic Stresses trigger a wide range of plant responses: Altered gene expression Cellular metabolism Changes in growth rates and crop yields
4
Plants respond to stresses as individual cells and as whole organisms Stress induced signals can be transmitted throughout the plant, making other parts more ready to withstand the stress..
5
Adaptation versus Acclimation
Adaptation - evolutionary changes that enable an organism to exploit a certain niche. These include modification of existing genes, as well as gain/loss of genes. e.g., thermo-stable enzymes in organisms that tolerate high temperature Acclimation – inducible responses that enable an organism to tolerate an unfavorable or lethal change in their environment. e.g., heat shock response
6
Types of Stress Abiotic Biotic
Arising from an excess or deficit in the physical or chemical environment Heat Cold Drought Salt Wind Oxidative Anaerobic Heavy metals Nutrient deprivation Excessive light Biotic Arising from another organism Pathogens Herbivores
7
Abiotic stresses
8
I-Plant Responses to abiotic stress
Resistance or sensitivity of plants to stress depends on: The species The genotype Development age How plant response to environmental stress? Stress resistance mechanisms Avoidance mechanisms – prevents exposure to stress Tolerance mechanisms – permit the plant to withstand stress Acclimation – alter their physiology in response stress
9
Stress resistance plants must adapt to stresses because of their sedentary lifestyle
10
Changes in gene expression to stress
A stress response is initiated when plants recognizes stress at the cellular level Stress recognition activates signal transduction pathways that transmit information within the individual cell and throughout the plant Changes in gene expression may modify growth and development and even influence reproductive capabilities
11
Plants vary in ability to tolerate flooding
Flooding causes anoxia and an anaerobiotic response in roots. Plants can be classified as: Wetland plants (e.g., rice, mangroves) Flood-tolerant (e.g., Arabidopsis, maize) Flood-sensitive (e.g., soybeans, tomato) Involves developmental/structural, cellular and molecular adaptations. - Shift carbohydrate metabolism from respiration to anaerobic glycolysis Protein synthesis affected: results in selective synthesis of ~ proteins mRNAs for other proteins there but not translated well! Most of the ANPs are enzymes associated with glycolysis and fermentation.
12
Aerobic Anoxic Protein synthesis in aerobic versus anoxic maize root tips. 5-hour labeling with 3H-leucine and 2-D gel electrophoresis. Enzymes that are up-regulated by anaerobiosis Fig
13
2- Water deficit Stresses involving water deficit
Water related stresses could affect plants if the environment contains insufficient water to meet basic needs Tolerance to drought and salinity Osmotic adjustment – a biochemical mechanism that helps plants acclimate to dry and saline conditions Many drought-tolerant plants can regulate their solute potentials to compensate for transient or extended periods of water stress by making osmotic adjustments, which results in a net increase in the number of solutes particles present in the plant cell Environmental conditions that can lead to water deficit Drought hypersaline conditions low temperatures transient loss of turgor at midday Factors that can affect the response of a plant to water deficit duration of water deficiency if the plant was acclimated to water stress
14
Osmotic adjustment Osmotic adjustment Osmotic adjustment occurs when the concentrations of solutes within a plant cell increases to maintain a positive turgor pressure within the cell The cell actively accumulates solutes and as a result the solute potential (s) drops, promoting the flow of water into the cell
15
Solutes that contribute to osmotic adjustments
Compatible solutes (osmolytes) Compatible solutes tend to be neutrally charged at physiological pH, either non-ionic or zwitterionic, and are excluded from hydration shells of macromolecules. – In contrast, many ions can enter the hydration shells of a protein and promote its denaturation Membrane-associated carriers and transporters are probably involved in differentially distributing osmolytes within the cell and throughout the plant Compatible ions Increasing synthesis rate of: Proline Glycine betaine Mannitol D-Pinitol
16
Osmotin abundant alkaline protein discovered in cultured tobacco cells that had been acclimated to 428 mM NaCl molecular size of 26-kDa localized in the vacuole classified as a pathogenesis-related (PR) protein Osmotin Transcription of an osmotin gene is induced by at least 10 signals: – ABA, ethylene, auxin, infection by TMV, salinity, lack of water, cold, UV light, wounding, and fungal Infection Many of the stress-induced genes are regulated by ABA ABA plays a role in stomata closure and induction of gene expression
17
3- Oxidative stress Oxidative stress results from conditions promoting the formation of active oxygen species (ROS) that damage or kill cells Environmental factors that cause oxidative stress air pollution (increased amounts of ozone or sulfur dioxide) oxidant forming herbicides e.g. paraquat dichloride heavy metals Drought heat and cold stress Wounding UV light intense light that stimulate photoinhibition Pathogens ROS
18
Reactive oxygen species (ROS)
Formed during certain redox reactions and during incomplete reduction of oxygen or oxidation of water by the mitochondrial or chloroplast electron transfer chain Singlet oxygen, hydrogen peroxide, superoxide anion, hydroxyl and perhydroxyl radicals
19
Ozone and oxidative stress
Hydrocarbons and oxides of nitrogen (NO, NO2) and sulfur (SOx) react with solar UV radiation to generate ozone (O3). Ozone is a highly reactive oxidant The negative effects of ozone on Plants decreased rates of photosynthesis Leaf injury reduced growth of shoots and roots accelerated senescence reduced crop yield Ozone Damage alters ion transport increases membrane permeability inhibits H+-pump activity collapses membrane potential increases Ca2 + uptake from the apoplasm Oxidative damage to biomolecules Resistance to ozone Utilizes either avoidance Avoidance involves physically excluding the pollutant by closing the stomata, the principal site at which ozone enters the plant Tolerance - biochemical responses that induce or activate the antioxidant defense system and possibly also various repair mechanisms
20
Tolerance to oxidative stress
Antioxidant or antioxidant enzyme Stress condition Anionic peroxidases Chilling, high CO2 Ascorbate peroxidase Drought, high CO2, high light intensity, ozone, paraquat Catalase Chilling Glutathione Chilling, drought, -irradiation, heat stress, high CO2, ozone, SO2 Glutatione reductase Chilling, drought, high CO2, ozone, paraquat Polyamines Deficiency of K, P, Ca, Mg, Mn, S, or B; drought, heat, ozone Superoxide dismutase Chilling, high CO2, high light, increased O2, ozone, paraquat, SO2 Salicylic acid and ethylene Ozone exposure results in increased amounts of H2O2, which stimulate the production of SA Results in a transient increase in the number of transcripts that encode defense-related secondary metabolites e.g. phytoalexins, cellular barrier molecules e.g. lignins, callose, and extensins, PR proteins e.g. (13) -glucanase, chitinase, gluthatione S-transferase and phenylalanine ammonia lyase Increases ethylene production by inducing increases in ACC synthase and ACC oxidase gene transcription
21
Most organisms are adapted to environmental temperature:
4- Heat/cold stress The typical response to heat stress is a decrease in the synthesis of normal proteins, accompanied by an accelerated transcription and translation of new proteins known as heat shock proteins (HSPs) Heat shock may arise in leaves – When transpiration is insufficient – when stomata are partially or fully closed and irradiance is high may arise in germinating seedlings – When the soil is warmed by the sun may arise in organs with reduced capacity for transpiration e.g. fruits Resistance or sensitivity of plants to heat/cold stress Duration Severity of the stress Susceptibility of different cell types Stage of development Most organisms are adapted to environmental temperature: Psychrophiles (< 20 °C) Mesophiles (~ °C) Thermophiles ( ~35-70 °) Hyperthermophiles ( °C) Groups 1,3 & 4 are a.k.a. “Extremophiles” But can also acclimate to “extreme” shifts, if they are not permanent, and not too extreme. Two well studied acclimation responses are: 1. the Heat Shock response 2. Cold acclimation
22
1- Heat Stress (or Heat Shock) Response
Induced by temperatures ~10-15oC above normal Ubiquitous (conserved), rapid & transient Dramatic change in pattern of protein synthesis induction (increase) of HSPs most HSPs are chaperones (chaperonins) that promote protein re folding & stability Protein class Size (kDa) Location HSP Cytoplasm HSP Cytoplasm, ER HSP ER, cytoplasm, mitochondria HSP Chloroplasts, mitochondria smHSP Cytoplasm, chloroplast, ER, mitochondria
23
Thermotolerant growth of soybean seedlings following a heat shock.
28oC oC 45oC oC Soybean seedlings.
24
2- Cold Acclimation (CA) response
Increased accumulation of small solutes retain water & stabilize proteins e.g., proline, glycine betaine, trehalose Altered membrane lipids, to lower gelling temp. Changes in gene expression [e.g., antifreeze proteins, proteases, RNA-binding proteins (?)] Activated by CBF1 transcription factor ABA – Abscisic acid, phytohormone induced by wilting, closes stomata by acting on guard cells Positive correlation between CA and [ABA] Treat plants with ABA, and they will be somewhat cold hardened There are ABA-regulated and non-ABA regulated changes that are induced by cold.
25
II-Plant Response to Biotic Stress
Attacked by other organisms Pathogens Insects
26
Pathogen attack strategies
Necrotrophy, in which the plant cells are killed Biotrophy, in which the plant cells remain alive Hemibiotrophy, in which the pathogen initially keeps cells alive but kills them at later stages of infection
27
Plant Defense response
Physical barriers: cuticle, thorns, cell walls Constitutively produced chemicals (e.g., phytoalexins) and proteins (e.g., Ricin) Induced responses (a.k.a., the Plant Defense Response) Compatible interaction disease Incompatible interaction resistance 3 aspects of response: Hypersensitive Local Systemic
28
Failure of a pathogen to cause
Disease The plant species attacked is unable to support the life-strategy of the particular pathogen The plant possesses preformed structural barriers or toxic compounds Defense mechanisms are activated such that the invasion remains localized Environmental conditions change and the pathogen perish Successful pathogen infection & disease occurs: Only if the environmental conditions are favorable If the preformed plant disease defenses are Inadequate If the plant fail to detect the pathogen If activated defense responses are ineffective Preformed defense: Secondary Metabolites Plants possess different secondary metabolites with antimicrobial properties may be present in their biological active form or may be store as inactive precursors that are converted to their active forms by host enzymes in response to pathogen attack or tissue damage Secondary metabolites pre-formed inhibitors are the saponins and the glucosinolates
29
Saponins Glycosylated compounds, classified as either triterpinoids, steroids, or steroidal Glycoalkaloids A biologically active triterpinoid saponin found in the roots of oat plants, avenacin A-1, is highly effective against the root infecting Takeall fungus, a major pathogen of cereal roots This pathogen affects wheat and barley, but not oat plants
30
Responses Immediate responses of invaded cells
Generation of reactive oxygen species Nitric oxide synthesis Opening of ion channels Protein phosphorylation/de-phosphorylation Cytoskeletal rearrangements Hypersensitive cell death (HR) Gene induction Local responses and gene expression Alternations in secondary metabolic pathways Cessation of cell cycle Synthesis of pathogenesis-related (PR) proteins Accumulation of benzoic and salicylic acids Production of ethylene and Jasmonic acid Fortification of cell wall (lignin, PGIPs, HRGPs) Systemic responses and gene activation (1-3) b-Glucanases Chitinases Peroxidases Synthesis of other PR proteins
31
Hypersensitive response
1st line of activated defense, occurs within 24hr Recognition of a genetically incompatible pathogen Creates unfavorable conditions for pathogen growth and reproduction Impair the spread of harmful enzymes & toxins Leads to localized cell and tissue death
32
Reactive oxygen species (ROS)
the production of ROS is often the first response detected, occurring within 5 min superoxide and hydrogen peroxide (H2O2). The mechanism plants have for producing superoxide from molecular oxygen probably involves a plasma membrane-associated NADPH oxidase Role of ROS in plant defense H2O2 maybe directly toxic to pathogens may contribute to the structural reinforcement of plant cell walls, either by cross-linking various hydroxyproline and proline rich glycoprotein to the polysaccharide matrix or by increasing the rate of lignin polymer formation by way of peroxidase enzyme activity make the plant cell wall more resistant to microbial perpetration and enzymatic degradation Role of ROS in cell signaling H2O2 induces benzoic acid 2 hydrolase (BA 2-H) enzyme activity, which is required for biosynthesis of SA H2O2 is known to induce genes for proteins involved in certain cell protection mechanisms e.g. glutathione S-transferase
33
Nitric oxide Nitric oxide synthesis (NO)
In plants, rapid de novo synthesis of NO accompany the recognition of avirulent pathogenic bacteria NO has the capacity to potentiate induction of plant cell death by ROS NO is known to bind heme and could inhibit catalase and ascorbate peroxidase, which detoxifies H2O2 Nitric oxide In the presence of inhibitors of NO production, the HR diminishes, disease symptoms become more severe, and bacterial growth is increased NO and ROS play an important synergistic role in the rapid activation of a wide repertoire of defense responses after pathogen attack
34
Phytohormones Benzoic acid and salicylic acid
Both SA and BA are derived from the phenylpropanoid pathway and have many roles in plant defense responses Accumulate to high concentrations in the vicinity of incompatible infection sites Jasmonic acid Jasmonic acid (JA) is an oxylipin-like hormone derived from oxygenated linolenic acid Increases in JA in response to pathogen/insect attack occur both locally and systematically Spraying methyl-JA onto plants increases their resistance to some (but not all) necrotrophic fungi, but not to biotrophic fungi or bacteria Ethylene Ethylene is frequently synthesized during both incompatible and compatible interactions Ethylene is required to mediate both resistance against necrotrophic fungal pathogens and against soil borne fungal species that are not ordinarily plant pathogens Ethylene and JA are required for activation of proteinase inhibitor (PI) genes and certain PR and chitinase genes
35
Pathogenesis-related (PR) proteins
fungal cell wall-degrading enzymes Chitinases Glucanases Lipoxygenase anti-microbial polypeptides components of signal transduction cascades PR proteins SA-mediated signal transduction cascades regulate the transcriptional activation of many PR genes Ethylene and SA have been shown to act synergistically, further enhancing the expression of PR genes Plant defensins Type of defense-related genes with demonstrated antimicrobial activity small (<7 kDa) cysteine-rich peptides that accumulate in the periphery of the plant plasma membrane induction of the defensin PDF1-2 gene transcript require ethylene or Me-jasmonate
36
Phytoalexins Pytoalexins
Low-molecular-mass, lipophilic antimicrobial compounds that accumulate rapidly at sites of incompatible pathogen infection Biosynthesis occurs only after primary metabolic precursors are diverted into a novel secondary metabolic pathway – e.g. phenylalanine is diverted into the synthesis of various flavonoid phytoalexins by the de novo synthesis of phenylalanine ammonia lyase (PAL).
37
Systemic plant defense responses
Defense responses elaborated in tissues far from the invasion site and even in neighboring plants The type of response is determined by the attacking organism – Responses to fungi, bacteria, and viruses are distinct from the response to insect – Nematodes appear to induce a mixture of responses – Root colonizing non-pathogenic bacteria induce another type of response Systemic acquired resistance (SAR) induced systemic resistance (ISR)
38
Systemic acquired resistance (SAR)
Fungi, bacteria, and viruses activate systemically a specific subset of PR-type gene by a mechanism known as systemic acquired resistance (SAR) in which local necrosis formation at the initial site of pathogen invasion triggers both a local increase in SA accumulation and the formation of a phloem mobile signal SAR For SAR to occur, the initial infection must result in formation of necrotic lesions, either as part of the HR or as symptom of disease SA concentrations increase and volatile methyl-SA is released in distal plant tissue PR proteins in the non-invaded parts of the plants are synthesized resulting in reduction in disease symptoms after subsequent infection of many pathogenic species
39
Induced systemic resistance (ISR)
Non-pathogenic root-colonizing rhizobacteria cause induced system resistance Rhizobacteria that promote specific plant growth, for example P. fluorescens, induce a systemic resistance response that does not depend on SA or PR protein accumulation Instead, ISR requires both JA and ethylene signaling and also the SAR regulatory protein NPRI SAR ISR
40
Plant Communication Plants communicate chemically.
Injured plants send out chemical signals that may signal other plants to prepare for an attack. attract other insects that eat the insects that are attacking the plant.
42
Plant Volatile response
Within plant signaling Allelopathy
43
Volatile compounds are released by plants in response to insect feeding triggered by an interaction of elicitors from the oral secretions of insect herbivores with damaged plant tissues. These volatiles are used by some parasitoid wasps to locate their hosts.
44
Plant Volatile functions
Protect Against Abiotic stress (heat & ozone) Protect Against Biotic stresses insect herbivores Pathogens competitors (allelopathy) Plant Volatile functions Trichomes - Aerial surface hairs Osmophores -scent producing structures Crenulated epidermal cells Stomates Plant Volatile release points Biotic Stress is stress that occurs as a result of damage done to plants by other living organisms, such as bacteria, viruses, fungi, parasites, beneficial and harmful insects, weeds, and cultivated or native plants
45
Plant Volatile interactions
Fineschi, J.Biogeosciences & Forestry, 2012
46
C6 Green Leaf Volatiles Hirao , J. BioSci&BioEng, 2012
47
Green leaf Volatiles Consist of C6 volatiles
Injury product of most terrestrial plants Aldehydes can deter pests alcohols and esters less effective (Z)-3-hexenal (and related) insecticidal, fungicidal, bactericidal When suppressed- increased aphid Green leaf Volatiles
48
Terpene syntheses sites
49
Terpene intermediates
50
Terpene types acyclic bicyclic cyclic
51
Baldwin, Current Biol., 2010
53
Revealing plant response to stress with microarray technology
Global gene expression analysis Signaling pathways, molecules and hormones involved in biotic stress include Jasmonic acid (JA), Salicylic acid (SA), and Ethylene (ET)…….
54
Non-Coding RNA (Junk RNA)
Role of micro RNAs in Plant Stress Response
57
Conclusion Regulation of plant stress responses Abscisic acid (ABA) Jasmonic acid (JA) Salicylic acid (SA) Ethylene Gene expression Increase amounts of specific mRNA Enhance translation Stabilize proteins Altered protein activity A combination of the above miRNA Metabolism Volatiles Could we use the plant response such as volatiles, phytohormones, and metabolites as biomarkers?
58
Reference Buchanan, Gruissem and Jones (2000) Biochemistry and Molecular Biology of Plants. American Society of Plant Physiologists P.M. Dey & J. B. Harborne Plant Biochemistery. Academic press Publications
Similar presentations
