2023-10-17-BIOL254-W14-Notes .docx

LECTURE 9: PRINCIPLES OF PLANT PHYSIOLOGY Lecturer: Dr Claudia Meisrimler ABA-induced stomatal closure is extremely rapid and involves changes in ion channel activities ABA is one of the positive regulators initiators for opening and closing of stomata. Increase amount of aba will lead to opening of...

LECTURE 9: PRINCIPLES OF PLANT PHYSIOLOGY Lecturer: Dr Claudia Meisrimler ABA-induced stomatal closure is extremely rapid and involves changes in ion channel activities ABA is one of the positive regulators initiators for opening and closing of stomata. Increase amount of aba will lead to opening of stomata and decrease amount of ABA will lead to closing of stomata. Hormonal responses to biotic stress Salicylic acid and jasmonates are the key regulators for this. These 2 are the opposing hormones associated with biotic stress. Salicylic acid is associated with biotrophic organisms and jasmonic is associated with necrotrophic organisms. Biotrophic organisms are the organisms that live on the plant tissue and keep them alive even though they are still pathogenic which necrotrophic organisms kill the plant material and feed on the plant material. Jasmonates They are associated with necrotrophic pathogens. They induce antiherbivore responses. Production of herbivore-induced volatile to prime other tissues and attract predatory insects. JA biosynthesis This happens in different organelles of the cells. First are the plastids, then the peroxisomes and then the cytoplasm. Jasomonic acid is strongly associated with lipid metabolism in plants. E.g. the carotenoids are coming from a similar pathways as jasmonic acid. JA is known to be associated with defence mechanisms and immunity but when knocked out it will impact plant growth as well. JA in its active state is conjugated to isoleucine. JA signalling contributed to defense against herbivory When exposed to hungry fly larvae, plants unable to produce JA have low rates of survival. JA induce the expression of anti-herbivory chemicals Protease inhibitors are induced not only when something is feeding on plants but also induced by wounding or by cutting the plants. JA contribute to systemic defense responses Defense responses are activated in distant tissues. JA is a known systemic signal that warn the other plant of the plant that there is a feeding occurring in another plant of the plant. This will cause the amount of JA in the plant to go up making the plant deterrent for other insects to eat it. This is also associated to ethylene and other type of primers. Herbivore-induced volatiles are recognized by carnivorous and parasitic insects. Salicylic acid – plant hormone and painkiller It is responsible for response to biotrophic pathogens. It induced defence response and systemic acquired resistance. Salicylic acid is named for the willow salix whose analgesic properties were known long before the chemical was found. How it works in plants has been known only 20 to 30 years, so it is relatively new hormones in plants. Salicylic synthesis is induced upon pathogen attack Isochorismate synthase (ICS) is induced by pathogen infection. ICS give rise to salicylic acid and pyruvate. Increase of SA leads to an increased pathogenesis related protein and other defense genes. SA contributes to systemic acquired resistance SA is associated to long distance signalling. An attack by microbe will lead to increase in SA in that leaf and the conjugated form (MeSA) will be transported and get to another leaf and get deconjugated and becomes SA again. Plants recognise PAMPS (pathogen-associated molecular patterns) Recognition of PAMPs by a plant cell triggers a set of immune responses that are mediated by salicylic acid. Plants cannot recognise a beneficial microbe and pathogenic microbe and induce the same reaction to all bacteria.