1 1 Responses to stress Katerina Dadakova, Department of Biochemistry Figures adopted from Buchanan et al., Biochemistry & molecular biology of plants 2 Responses to stress Pathogens and pests 3 Plant-microbe interactions Responses to stress 4 Pathogens Responses to stress •Necrotrophy •Biotrophy •Hemibiotrophy Biotrophic fungi usually form haustoria Pathogenic bacteria often enter the leaves through stomata, and produce effector molecules only at higher density of bacterial population, leading to the death of plant cells. 5 Pests Responses to stress Plant-nematode interaction Aphids locate and penetrate the phloem sieve elements, and remove the sap 6 Preformed defenses Responses to stress Saponin Glucosinolate Benzoxazinoid metabolite 7 Plant immunity Responses to stress 8 Plant immunity Responses to stress Zig-zag model of the plant defense response The hypersensitive cell death response Induced defenses Responses to stress Responses to stress Induced defenses Medicarpin Capsidiol Camalexin Resveratrol Responses to stress Induced defenses Responses to stress Systemic defenses Defensin accumulation is controlled by a combination of JA and ethylene. Responses to stress Abiotic stress Responses to stress Water deficit Responses to stress Compatible solutes Responses to stress Flooding and oxygen deficit Aerenchyma Responses to stress Low temperatures Detrimental effects •membrane solidification •reductions in enzymatic reaction rates •dehydration (freezing) •mechanical stress (freezing) Acclimation •membrane stabilization •compatible solutes Responses to stress High temperatures Protein classes Size (kDa) Major functions HSP 100 100-114 Protein disaggregation, unfolding, degradation HSP90 80-94 Maturation of signaling molecules HSP70 69-71 Prevention of aggregation, assisting refolding, protein import and translocation, signal transduction, transcriptional activation HSP60 60 Folding, assisting refolding Small HSP 15-30 Prevention of aggregation, stabilization of nonnative proteins Responses to stress Oxidative stress H2O2, O2.-, HO.- Responses to stress Ascorbate-glutathione cycle