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Stress Responses & Gene Expression. plants must adapt to stresses because of their sedentary lifestyle. Fig. 22.2, Buchanan et al. Adaptation versus Acclimation. - PowerPoint PPT Presentation
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Stress Responses & Gene Expression
• plants must adapt to stresses because of their sedentary lifestyle
Fig. 22.2, Buchanan et al.
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
Types of Stress
Abiotic 1. heat
2. cold 3. drought 4. salt
5. wind 6. oxidative 7. anaerobic 8. heavy metals 9. nutrient deprivation10. excessive light
Biotic 1.pathogens2.herbivores
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..
Fig. 22.3, Buchanan et al.
Most organisms are adapted to environmental temperature:
1. Psychrophiles (< 20 °C)2. Mesophiles (~ 20-35 °C)3. Thermophiles ( ~35-70 °)4. Hyperthermophiles (70-110 °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 response2. Cold acclimation
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• HSP induction mediated by a bZIP factor, HSF
Fig. 22.43, Buchanan et al.
28oC 40oC 45oC 45oC
Fig. 22.42, Buchanan et al.Soybean seedlings.
Thermotolerant growth of soybean seedlings following a heat shock.
Heat stress effects on protein synthesis in soybean seedlings (J. Key).
Joe Key
Cold Acclimation (CA) involves:• 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 (?)]• Many cold-regulated promoters have DRE/C-elements
• Activated by CBF1 transcription factor
Role of ABA (stress hormone)• 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
However, ABA does not induce all genes that cold will.
Conclusion: there are ABA-regulated and non-ABA regulated changes that are induced by cold.
Plants vary in ability to tolerate flooding
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.
Pneumatophores in mangrove
Flooding causes anoxia and an anaerobiotic response in roots.
Maize (corn)
Fig. 22.23
- Shift carbohydrate metabolism from respiration to anaerobic glycolysis
- Protein synthesis affected: results in selective synthesis of ~10-20 proteins
-mRNAs for other proteins there but not translated well!
Most of the ANPs are enzymes associated with glycolysis and fermentation.
Fig. 22.30
Protein synthesis in aerobic versus anoxic maize root tips.5-hour labeling with 3H-leucine and 2-D gel electrophoresis.
Aerobic Anoxic
Enzymes that are up-regulated by anaerobiosis
Biotic Stress and Plant Defense Responses
Pathogen Strategies1. Necrotrophic – plant tissue killed and then colonized;
broad host rangee.g., rotting bacteria (Erwinia)
2. Biotrophic – plant cells remain alive, narrow host range (1 plant species)
e.g., viruses, nematodes, fungal mildews
Major PathogensViruses - most are RNA viruses w/small
genomes, which always encode: 1. Coat protein2. RNA-dependent RNA polymerase 3. Movement protein(s)
Viroids – naked, single strands of RNA; discovered by T.O. Diener
Bacteria- e.g., Xanthomonas
Fungi - 4 major groups
Nematodes - root parasites, also increase infection by microorganisms
ds DNA virus:Cauliflower Mosaic Virus
SS RNA virus: Tobacco Mosaic Virus
Fig. 21.10, Buchanan et al.
Plant Defenses
1) Physical barriers: cuticle, thorns, cell walls
2) Constitutively produced chemicals (e.g., phytoalexins) and proteins (e.g., Ricin)
3) Induced responses (a.k.a., the Plant Defense Response)
The Plant Defense Response
3 aspects of response:1. Hypersensitive
2. Local
3. Systemic
Compatible interaction diseaseIncompatible interaction resistance
Distribution of Oak Wilt in the US
Fungus - Ceratocystis fagacearum
Leaves from Infected tree
Natural root grafts Sap beetle