extra reading citations Flashcards
Arms race talk about plant-insect interactions and the Genetic host race formation, where insects adapt to new host plants, often occurs between closely related plants with similar chemistry, also optimal defence theory
(Feeny, 1976)
If mention inconspicuous flower e.g hakeas in Unapparent plants invest in “low-cost” defenses, such as specific toxins, to deter specialized herbivores, while apparent plants deploy “high-cost” defenses, such as digestibility-reducing compounds, to defend against both generalist and specialist herbivores.
The theory predicts that herbivore pressure selects for both intra- and interspecific variation in defenses among unapparent plants, while apparent plants exhibit interspecific convergence of defenses with some intraspecific variation. Ultimately, defense theory offers insights into the coevolutionary dynamics between plants and herbivores and provides a framework for understanding the ecological implications of plant defenses at the community level.
Tannins: Tannins are broadly categorized into two main groups:
hydrolyzable tannins and condensed tannins.
1. Hydrolyzable Tannins: These are esters of gallic or ellagic acid with glucose or other polyols. They are found in fruits, seeds, and leaves of various plant species. Hydrolyzable tannins are water-soluble and can be easily broken down by hydrolysis into simpler phenolic compounds and sugars.
2. Condensed Tannins (Proanthocyanidins): Condensed tannins are polymers of flavonoid units, primarily catechin or epicatechin. They are found in the bark, wood, and fruits of plants and are insoluble in water. Condensed tannins are often responsible for the astringent taste in foods like tea and red wine.
Alkaloids: Alkaloids are nitrogenous organic compounds produced by plants as secondary metabolites. They often have pronounced physiological effects on animals and humans. Examples of alkaloids include:
Cyanide: Cyanide is a highly toxic compound that inhibits cellular respiration by blocking the cytochrome c oxidase enzyme in mitochondria. It is found in various plants, particularly those in the Rosaceae family like apple seeds and cherry pits.
Cardiac Glycosides: These are compounds that affect the heart by inhibiting the sodium-potassium ATPase pump, leading to increased intracellular sodium levels and decreased potassium levels. Cardiac glycosides are found in plants like foxglove (Digitalis) and oleander.
Glucosinolates: Glucosinolates are sulfur-containing compounds found in cruciferous vegetables like broccoli, cabbage, and mustard greens. When plant tissues containing glucosinolates are damaged (e.g., by herbivores), enzymes called myrosinases break them down into various biologically active compounds, including isothiocyanates, which have insecticidal properties.
Step-wise coevolution describes reciprocal evolutionary changes between interacting species, like plants and herbivores, where each influences the other’s gene pool. It suggests specific, discrete adaptations in response to changes in the partner species’ traits. This pattern is more likely in communities with short-lived plants, where rapid turnover and frequent herbivore interactions drive swift evolutionary changes. In contrast, persistent plants, with longer lifespans, exhibit gradual adjustments to diffuse herbivory over time. This distinction offers alternative explanations for observed patterns in plant-herbivore interactions, emphasizing different mechanisms and assumptions based on plant life history traits.
(Fox, 1981)
cyanogenesis may be harmful to the plant, impairing the action of other defence mechanisms
(Lieberei, 1986)
Herbivore-induced plant volatiles (HIPVs) not only communicate between the infested plant and natural enemies of the attacking insects, but also warns the neighboring undamaged plants of the forthcoming danger, besides communicating between different parts of the same plant (inter-plant and intraplant signaling, respectively).7,10 -13 The HIPVs also act as feeding and/or oviposition deterrents to insect pests.4 , 7, 8HIPVs are released from leaves, flowers and fruits into the atmosphere. Jasmonic acid (JA) and its precursors serve as the potential stimulators of HIPVs that activate distinct set of genes, which in turn leads to terpenoid synthesis. plants exposed to GLVs emitted increased quantities of sesquiterpenes as compared with the non-exposed plants
(War et al., 2011)
Different defense hypothses
Optimal Defence
Growth Rate
Carbon:Nutrient
Growth/Differentiation
OD=Feeny (1976)
GR=Coley et al (1985)
C:N=Bryant et al (1983)
GD=Herms & Matson (1992)
Chemical Ecology of Plant-Ant Interactions: Plant–ant association evolved quite early, as already several ferns have various adaptations to ants, including rhizomes riddled with tunnels used as nesting site. Although EFN has been found to attract different species of insects and arthropods (e.g. parasitoids, predatory mites, spiders), in most cases it seems to be specially designed to attract ants, whose feeding ecology and behaviour fit very well the plant’s defensive needs.
Beneficial Effect of Mutualistic Ants on Plant Health: In plants inhabited by mutualistic ants, it was observed that these ants substantially reduced damage inflicted by pathogens on plant leaves and decreased the abundance of epiphytic bacteria. This suggests that mutualistic ants play a protective role for the plants they inhabit, potentially through behaviors such as removing pathogens or maintaining a cleaner plant surface. This beneficial effect was found to be associated with the presence of specific bacterial communities on the ants’ legs, including bacteria from genera such as Bacillus, Lactococcus, Pantoea, and Burkholderia. These bacteria may contribute to the ants’ ability to suppress pathogenic microbes on the plant surface.
Increase in Aggressiveness Due to Consumption of EFNs: However, it has also been observed that the consumption of carbohydrate-rich Extra Floral Nectaries (EFNs) by ants can lead to an increase in their predatory behavior.
Grasso et al. (2015)
Plant pathogen evolution and climate change. Maybe mention how due to climate change this could lead to plastic genomes and phenotypic plasticity and therefore pathogens may ‘jump’ host plants.
Santini and Ghelardini (2015)
Plant-Microbe Interactions: Another form of plant immune response extensively observed in crops and natural plant populations confers partial resistance to pathogens and is usually referred to as quantitative disease resistance (QDR).
Peyraud et al.,(2017)
Anthracnose appressorium: A gene called CMK1, similar to genes in yeast, controls how the fungus grows and penetrates the leaves. scientists studied a similar gene called CST1. They found that when CST1 is missing, the fungus can’t cause disease on healthy leaves but can still infect wounded ones. Although CST1-deficient fungi can start growing on both natural and artificial surfaces, they struggle to penetrate the host’s tissues. Additionally, these fungi have fewer fat droplets, which they need for successful invasion. This suggests that CST1 plays a crucial role in helping the fungus penetrate plant tissues effectively.
Tsuji et al. (2003)
Evolution of Plant Immunity effector: phytopathogenic bacteria often secrete proteins into the plant cell to alter host processes in a way favourable to the pathogen. The most important ones are effectors secreted through the type III secretion system. Type III effectors interfere with host immunity but also elicit disease resistance upon recognition by specific resistance proteins in the host cell. first effector gene from the soybean bacterial pathogen Pseudomonas syringae pv. glycinea. This gene was named avrA (avirulence A) because bacterial isolates carrying this gene fail to cause disease on soybean cultivars carrying a cognate resistance (R) gene.
(Cui et al., 2009)
Phytohormone Signaling in Plant Defense: he phytohormones such as auxins, cytokinins (CKs), gibberellins (GAs), salicylic acid (SA), jasmonic acid (JA), ethylene (ET), abscisic acid (ABA), and brassinosteroids (BRs) respond to stress via synergistic and antagonistic actions often referred to as signaling cross talk. These phytohormones coordinate with each other in a harmonious manner and respond to developmental and environmental cues.
(Checker et al., 2018)
