LS302 Plant Defense Mechanisms PDF

LS302 DEFENSE MECHANISMS IN PLANTS AND ANIMALS  TOPICS: UNIT 3 Stress metabolism in plants – Environmental stresses, salinity, water stress, heat, chilling, anaerobiosis, pathogenesis, heavy metals, radiation and their impact on plant growth and metabolism, crite...

LS302 DEFENSE MECHANISMS IN PLANTS AND ANIMALS  TOPICS: UNIT 3 Stress metabolism in plants – Environmental stresses, salinity, water stress, heat, chilling, anaerobiosis, pathogenesis, heavy metals, radiation and their impact on plant growth and metabolism, criteria of stress tolerance. Antioxidative defense system in plants – reactive oxygen species and their generation, enzymic and non-enzymic components of antioxidative defense mechanism.  Stress Physiology Stress: Any change in environmental conditions that might reduce or adversely change a plant’s growth or development. Freeze, chill, heat, drought, flood, salty, pest and air pollution etc. Resistance: The ability adaptive or tolerant to stresses.  ENVIRONMENTAL STRESSES Water stress Salinity Heat Chilling Anaerobiosis Pathogenesis Heavy metals Radiation Resistance includes adaptation, avoidance and tolerance. Adaptation is permanent resistance to stress in morphology and structure , physiology and biochemistry under long-term stress condition. Ex: A well-developed aerenchyma in hydrophytes A pattern for stomata movement in CAM plant (CAM pathway is adapted to minimize water loss and photorespiration) Avoidance is a manner to avoid facing with stress using neither metabolic process nor energy Very short lifecycle in desert plants. Dormancy during the cool, hot, and drought conditions Tolerance is a resistant reaction to reduce or repair injury with morphology , structure, physiology, biochemistry or molecular biology, when plant counters with stresses Hardening is a gradual adaptation to stress when the plant is located in the stress condition WATER STRESS FLOODING/WATERLOGGING DROUGHT WATERLOGGING/FLOODING Waterlogging: saturation of the soil pores with water, and with a very thin – or even without - a layer of water above the soil surface. In waterlogged conditions, only the root system of plant is under the anaerobic conditions imposed by the lack of oxygen, while the shoot is under atmospheric normal conditions. Flooding is the situation in which there is a water layer above the soil surface. This water layer can be shallow or deep, so that it can provoke partial or complete submergence of plants.  Eh=reduction potential Reference: Parent, C., Capelli, N., Berger, A., Crèvecoeur, M., & Dat, J. F. (2008). An overview of plant responses to soil waterlogging. Plant stress, 2(1), 20-27.  Suberization Aerenchyma Hypertrophied lenticels Adventitious roots Anaerobiosis Flooding stress leads to anaerobic conditions i.e. oxygen stress. The decreased supply of oxygen limits respiration, nutrient uptake and other root functions. DROUGHT STRESS Water scarcity resulting in low soil moisture content and low water potential. The rate of loss of water through transpiration from leaves surpasses the water uptake rate through roots in dry environments. The roots strive to uptake more water through their expansion adapting plants to minimize stomatal loss of water when there is a water deficit. Typical drought stress symptoms in plants include leaf rolling, stunting plants, yellowing leaves, leaf scorching, permanent wilting.  https://youtu.be/o-QfPNVBCbw?si=S0mZax_FBJTqSqQD : Plant adaptation to water stress https://youtu.be/qZQiwlCs18M?si=zVI7AGQR6FsBN5kK : How trees prevent flooding How flooding effects can be reduced: https://youtu.be/j_f9muYtyR0?si=whZjrymwkYxxh7c5 https://youtu.be/A6Tks2O-2cM?si=RSnfJPJREaPRCnrN : How to treat drought. https://youtu.be/1yT8jpZ09TU?si=oA7MXtW6AzmqxCUd: Drought stress https://youtu.be/uj_meyFYGSI?si=ZqBpRO_5ud12Clvt : Drought stress in plants SALT STRESS  Improper use of water resources in irrigation that contain a significant amount of salts Faulty agronomic practices such as improper fertilization Climate change Aggravated by natural environment deterioration There is accumulation of Na+ and Cl− ions in the soil, causing hyperosmotic and hyperionic conditions, which obstruct plant retention of water and supplements from the soil. EFFECTS OF SALINITY Reference: Muchate, N. S., Nikalje, G. C., Rajurkar, N. S., Suprasanna, P., & Nikam, T. D. (2016). Plant salt stress: adaptive responses, tolerance mechanism and bioengineering for salt tolerance. The Botanical Review, 82, 371-406.  REFERENCE VIDEOS https://youtu.be/Q2ZVav3Cr8Y?si=3aZtYnFpRYKa_6WY https://youtu.be/TiFuzO0p_Fg?si=uVX478vZiw_H29Ls https://youtu.be/rvqcTrS-24c?si=GhH4gxHDzyyeUFnl: Lettuce tackling salt stress-time lapse images TEMPERATURE STRESS  “Heat stress” often refers to a period in which plants are subjected to high temperatures for long enough to permanently alter their ability to function or grow normally. HEAT STRESS The ideal range for most crops is between 68-86 degrees Fahrenheit (20 and 30°C). Temperatures outside this range, whether in the air or the soil, during the day or the night, are harmful to plants. EFFECT OF COLD STRESS Freeze-induced production of reactive oxygen species contributes to membrane damage and that intercellular ice can form adhesions with cell walls and membranes and cause cell rupture. Protein denaturation occurs in plants at low temperature which could potentially result in cellular damage.  Cold stress is perceived by receptor proteins, triggering signal transduction, and Inducer of CBF Expression (ICE) genes are activated and regulated, consequently upregulating the transcription and expression of the C-repeat Binding Factor (CBF) genes. The CBF protein binds to the C-repeat/Dehydration Responsive Element (CRT/DRE), a homeopathic element of the Cold Regulated genes (COR gene) promoter, activating their transcription. Transcriptional regulations and post-translational modifications regulate and modify these entities at different response levels by altering their expression or activities in the signaling cascade. These activities then lead to efficient cold stress tolerance.  The accumulation of sucrose and other simple sugars that typically occurs with cold acclimation also seems likely to contribute to the stabilization of membranes as these molecules can protect membranes against freeze-induced damage Reference: Ali, S., Rizwan, M., Arif, M. S., Ahmad, R., Hasanuzzaman, M., Ali, B., & Hussain, A. (2020). Approaches in enhancing thermotolerance in plants: an updated review. Journal of Plant Growth Regulation, 39, 456-480. COLD STRESS Cold stress adversely affects the plants leading to necrosis, chlorosis, and growth retardation. Various physiological, biochemical, and molecular responses under cold stress have revealed that the cold resistance is more complex than perceived which involves multiple pathways. STRESS BY INFECTION AND WOUNDING  Pathogen attack triggers many responses. Constitutive defenses include morphological and structural barriers, chemical compounds, proteins and enzymes. Plants produce toxic chemicals, pathogen-degrading enzymes. WOUNDING STRESS  Heavy metals Heavy metals reduce plant development and productivity all over the world Anthropogenic activities cause negative effects on plant development by accumulating HMs, and an increase in their concentration is immensely dangerous because HMs are toxic and mostly non- degradable in nature In soil, HMs get accumulated after leaching or being released after the oxidation process, making them easier to uptake by plants and ultimately affecting public health via the food chain.  Heavy metal stress Heavy metals exert toxicities in plants through four proposed mechanisms. These include (i) similarities with the nutrient cations, which result into a competition for absorption at root surface For example, As and Cd compete with P and Zn, respectively, for their absorption (ii) direct interaction of heavy metals with sulfhydryl group (-SH) of functional proteins, which disrupts their structure and function, and thus, renders them inactive (iii) displacement of essential cations from specific binding sites that lead to a collapse of function (iv) generation of reactive oxygen species (ROS), which consequently damages the macromolecules Radiation and their impact on plant growth and metabolism Differences in the number of leaflets on leaves of the right and left side of the symmetry axis, and differences in the variance in right and left characters of plants. Associated with reduced viability and reproductive success in other organisms.  Effect of radiation Plants are able to survive nuclear disasters due to their adaptiveness in replacing cancerous cells, but they are still vulnerable to irreversible damage at high enough exposures. The adaptivity of plants allows flora to survive in radioactive environments, but survival in these radioactive areas often leads to changes in the plant itself. Some plants, such as soybeans, were found to have reduced water uptake and yield smaller fruits when grown in radioactive areas. For plants that do adapt, survival is often accompanied with irregular growth and development of defensive mechanisms in an effort to protect both the plant and its seeds. Plant Growth and Radiation UV-A: UV-A radiation (315–400 nm) can stimulate biomass accumulation in shoots and roots, and can damage photosynthesis. UV-B:UV-B radiation can inactivate light harvesting complex II, and can alter gene expression for synthesis of PS II reaction center proteins. UV-C:UV-C radiation is the most energetic type of UV radiation and is often more effective at killing microorganisms than UV-A or UV-B, but it can also damage plants. DNA damage: UV radiation can damage plant DNA, which can lead to protein polymerization, enzyme inactivation, and increased cell membrane permeability. Photosynthesis: UV radiation can damage the photosystem II (PSII) complex, which can decrease Rubisco activity and impair photosynthesis. Growth regulators: UV radiation can alter the concentrations of plant growth regulators. Morphological changes: UV radiation can cause plants to have a stocky phenotype, and can affect leaf size and rosette diameter. Color changes: UV radiation can change the color of plants. Flowering times: Overexposure to UV radiation can change the flowering times of some plants, which can impact the animals that depend on them. ANAEROBIOSIS Avoidance of self-poisoning: slowing down of ethanolic Roots cannot survive anaerobic fermentation, or its deviation from conditions for more than a short ethanol formation into less toxic time at warm temperatures even compounds, such as malate, was in flooding-tolerant species proposed as the biochemical basis for adaptation and survival. Avoidance of cytoplasmic acidosis: Transient lactate fermentation acidifies the cytoplasm at the start of anaerobiosis thereby triggering the functioning of pyruvate decarboxylase (PDC) thus forming neutral ethanol. Excised maize root tips transferred from aerobic into oxygen-free conditions displayed transient acidosis of the cytoplasm within 20 min. Sustained energy metabolism and sugar supply: The absence of oxygen arrests oxidative phosphorylation This is replaced by fermentation that yields only 2 mol ATP from each mol of glucose rather than 32. When aerobically grown intact rice seedlings were transferred to oxygen-free medium, no evidence of mitochondrial membrane damage was seen unless coleoptiles were first separated from their source of sugar (the seed). Modified gene expression: Many proteins are formed after 5 h anaerobiosis The majority catalyze reactions in glycolysis or sugar-phosphate metabolism Enzymes formed: Examples alcohol dehydrogenase, pyruvate decarboxylase, enolase, glucose-6-phosphate isomerase, glyceraldehyde-3- phosphate dehydrogenase, lactate dehydrogenase (barley) and sucrose synthase  Developmentally passive tolerance: Example- rhizomes of temperate aquatic and wetland plants which Metabolic And Morphological have large energy reserves that Adaptations In Shoots: sustain the apical buds with low metabolic activity through the winter in anaerobic surroundings (anaerobic dormancy). Enhanced shoot elongation: Even a gentle stress imposed by total or partial submergence of the shoot system in aerated water strongly stimulates stem, petiole or leaf extension in a very wide range of aquatic and amphibious species.  Reactive Oxygen Species (ROS) Production ROS can interact with macromolecules such as ROS also act as signaling molecules involved DNA, pigments, proteins, lipids, and other in the regulation of many key physiological essential cellular molecules depending on the processes such as root hair growth, properties like chemical reactivity, redox stomatal movement, cell growth, and cell potential, half-life, and mobility within the differentiation when finely tuned and cellular system, ultimately leading to a series of regulated by an antioxidative defense destructive processes collectively termed as “oxidative stress” system Antioxidative defense system in plants