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Questions and Answers
What is defined as environmental factors that can potentially hinder plant growth?
What is defined as environmental factors that can potentially hinder plant growth?
Which type of drought occurs primarily due to low atmospheric humidity and high temperatures?
Which type of drought occurs primarily due to low atmospheric humidity and high temperatures?
What happens to stomata during severe drought conditions?
What happens to stomata during severe drought conditions?
During drought, which metabolic change occurs in plant leaves?
During drought, which metabolic change occurs in plant leaves?
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How does drought affect photosynthetic activity in plants?
How does drought affect photosynthetic activity in plants?
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What happens to osmotic pressure in plant cells during water stress?
What happens to osmotic pressure in plant cells during water stress?
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Which biochemical effect is NOT caused by water shortage in plants?
Which biochemical effect is NOT caused by water shortage in plants?
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What is the primary impact of drought on the carbohydrates metabolism in green leaves?
What is the primary impact of drought on the carbohydrates metabolism in green leaves?
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What happens to plants in water logged soils due to oxygen deficiency?
What happens to plants in water logged soils due to oxygen deficiency?
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Which of the following plants is typically tolerant to water logging conditions?
Which of the following plants is typically tolerant to water logging conditions?
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How does flooding affect stomatal behavior in C3 plants?
How does flooding affect stomatal behavior in C3 plants?
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What effect do reduced levels of auxins have on plants under flooding stress?
What effect do reduced levels of auxins have on plants under flooding stress?
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Which plant growth regulator is primarily responsible for promoting stem elongation?
Which plant growth regulator is primarily responsible for promoting stem elongation?
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What impact does increased ABA have on the shoots of plants under flooding stress?
What impact does increased ABA have on the shoots of plants under flooding stress?
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What is a consequence of decreased cytokinin (CK) levels in plants experiencing flooding stress?
What is a consequence of decreased cytokinin (CK) levels in plants experiencing flooding stress?
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What change occurs to the levels of Aminocyclopropane-1-Carboxylic Acid (ACC) in response to flooding stress?
What change occurs to the levels of Aminocyclopropane-1-Carboxylic Acid (ACC) in response to flooding stress?
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What are ephemerals known for in terms of drought resistance?
What are ephemerals known for in terms of drought resistance?
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Which adaptations are primarily seen in succulent plants to cope with drought?
Which adaptations are primarily seen in succulent plants to cope with drought?
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What characterizes non-succulent plants in relation to drought?
What characterizes non-succulent plants in relation to drought?
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Which of the following is NOT a method to overcome drought stress?
Which of the following is NOT a method to overcome drought stress?
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What does the term 'xeromorphy' refer to?
What does the term 'xeromorphy' refer to?
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How do osmotic adjustment mechanisms help plants during drought?
How do osmotic adjustment mechanisms help plants during drought?
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What is the main consequence of water logging in plants?
What is the main consequence of water logging in plants?
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Which characteristic is specific to the adaptations of non-succulent plants?
Which characteristic is specific to the adaptations of non-succulent plants?
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What is a consequence of increased abscisic acid (ABA) in plants?
What is a consequence of increased abscisic acid (ABA) in plants?
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What phenomenon is characterized by uneven cell growth resulting in leaf distortion under increased ethylene?
What phenomenon is characterized by uneven cell growth resulting in leaf distortion under increased ethylene?
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How can high moisture stress be mitigated effectively?
How can high moisture stress be mitigated effectively?
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Which factor characterizes saline soil?
Which factor characterizes saline soil?
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What effect does frequent foliar spray of salicylic acid have under high moisture stress?
What effect does frequent foliar spray of salicylic acid have under high moisture stress?
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Which treatment is used to prevent premature fall of buds and young fruits?
Which treatment is used to prevent premature fall of buds and young fruits?
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What is the primary effect of excess salt accumulation in soil?
What is the primary effect of excess salt accumulation in soil?
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Which combination of nutrients is recommended for foliar spray during critical stress stages?
Which combination of nutrients is recommended for foliar spray during critical stress stages?
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What is the primary characteristic that defines alkaline soils?
What is the primary characteristic that defines alkaline soils?
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Which type of plants can tolerate extreme salt stress?
Which type of plants can tolerate extreme salt stress?
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During which growth stage is plant response to salt stress maximally severe due to environmental conditions?
During which growth stage is plant response to salt stress maximally severe due to environmental conditions?
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How does salt stress primarily affect seed germination?
How does salt stress primarily affect seed germination?
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Which process is negatively impacted by salinity, causing damage to thylakoids?
Which process is negatively impacted by salinity, causing damage to thylakoids?
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What mechanism do some plants use to mitigate the effects of salt stress?
What mechanism do some plants use to mitigate the effects of salt stress?
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Which of the following crops is classified as sensitive to salt stress?
Which of the following crops is classified as sensitive to salt stress?
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What is one suggested method for mitigating salt stress in plants?
What is one suggested method for mitigating salt stress in plants?
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Study Notes
Environmental Stresses
- Environmental stresses are unfavorable conditions like water deficit/excess, high radiation, extreme temperatures, salinity, nutrient deficiencies, and pollution.
- Stresses affect crop growth in terms of morphology, physiology, metabolism, and yield.
- Stress is the action, and strain is the reaction.
Drought (Water Stress)
- Drought is a severe water deficiency that inhibits plant growth.
- Drought is categorized into soil drought and atmospheric drought.
- Soil drought leads to atmospheric drought.
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Physiological changes due to drought:
- Stomata: Lose function and may die, wilting denatures starch in guard and mesophyll cells.
- Carbohydrates metabolism: Drought depletes starch in wilted leaves and accumulates sugar.
- Photosynthesis: Reduced stomatal openings inhibit CO2 diffusion, decreasing photosynthesis.
- Osmotic pressure: Reduced water leads to increased osmotic pressure in plant cells, helping utilize soil moisture better.
- Permeability: Water and urea permeability increase during drought.
- Biochemical effects: Starch converts to sugar, nitrate nitrogen increases, and protein synthesis is negatively affected.
Adaptation to Drought
- Drought resistance: Plants' capacity to survive drought with minimal damage.
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Drought-resistant plant types:
- Ephemerals: Short-lived plants that complete their life cycle during the rainy season and survive as seeds in dry periods.
- Succulent plants: Store large amounts of water for use during dry periods, adapting with features like thick cuticles, reduced leaf areas, and sunken stomata to minimize transpiration.
- Non-succulent plants: True drought-tolerant plants that endure drought without water-supplying mechanisms. They exhibit xeromorphy (greyish color, reflective surfaces, smaller leaves, extensive root systems, leaf fall, sunken stomata, thick cuticles, and more).
Methods to Overcome Drought
- Selection of drought-tolerant species.
- Adjusting sowing time to ensure completion of the crop cycle before drought onset.
- Seed hardening with KCl, KH2PO4, CaCl2, or Thiourea.
- Thinning of poorly established plants.
- Mulching to reduce evaporation.
- Foliar spray of antitranspirants like Kaolin, PMA, Waxes, and Silicone oils.
- Foliar spray of KCl.
- Foliar spray of growth retardants like CCC and MC.
High Moisture Stress - Flooding/Waterlogging
- Waterlogging occurs when excessive water saturates the soil, creating anaerobic conditions in the rhizosphere.
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Effect of waterlogging:
- Oxygen deficiency inhibits plant growth and survival.
- Flood-sensitive plants die, while tolerant plants can withstand waterlogging for some time.
- Continuous submergence can be detrimental.
Plant Water Relations in Flooding Stress
- Flooding triggers stomatal closure in C3 plants.
- Reduced root permeability leads to leaf dehydration and wilting.
- Toxic substances (acetaldehyde/alcohol) produced under anaerobic conditions in roots are transported to shoots, affecting plant functions.
Levels of Endogenous PGRs under Flooding Stress
- Flooding stress reduces GA and CK levels in roots.
- ABA and ethylene levels increase in shoots, causing stomatal closure and senescence, respectively.
- Auxin levels decrease, while ACC (ethylene precursor) levels increase.
Mitigation of High Moisture Stress (Waterlogging)
- Providing drainage to remove excess water.
- Spraying cycocel growth retardant to reduce apical dominance and promote lateral growth.
- Foliar spray of 2% DAP + 1% KCl.
- Nipping terminal buds to promote sympodial branches (e.g., in cotton).
- Spraying NAA to control premature fruit/pod fall.
- Spraying brassinolide to increase photosynthetic activity.
- Foliar spray of salicylic acid to increase stem reserve utilization.
- Foliar spray of Boric acid + ZnSO4 + FeSO4 + urea.
Salt Stress
- Salt stress arises from excessive salt accumulation in the soil, decreasing soil solution water potential and leading to exosmosis and wilting.
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Classification of saline soil:
- Saline soil: Electrical conductivity > 4 dS/m, exchangeable sodium percentage < 15%, pH < 8.5, dominated by Cl- and SO2-4 ions.
- Alkaline soil (sodic soil): Electrical conductivity < 4 dS/m, exchangeable sodium percentage > 15%, pH > 8.5, dominated by CO-3 and HCO-3 ions.
Classification of Plants Based on Salt Tolerance
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Halophytes: Grow in high salt concentrations:
- Euhalophytes: Tolerate extreme salt stress.
- Oligohalophytes: Tolerate moderate salt stress.
- Glycophytes: Sensitive to high salt concentrations.
Effect of Salt Stress on Plant Growth and Yield
- Seed germination: Salt stress delays germination due to reduced α-amylase activity.
- Seedling growth: Early seedlings are more sensitive. Root growth and length are significantly reduced.
- Vegetative growth: Salt injury is more severe at high temperatures and low humidity.
- Reproductive stage: Salt affects panicle initiation, spikelet formation, fertilization, and pollen germination.
- Photosynthesis: High salt concentrations damage thylakoids and reduce chlorophyll b content.
Mechanism of Salt Tolerance
- Maintaining high water potential by reducing transpiration.
- Salt accumulation in older leaves and stems with slower metabolic rates.
- Accumulation of K+ ions to avoid Na+ toxicity.
- Accumulation of toxic ions in the vacuole but not the cytoplasm.
- Accumulation of proline and abscissic acid, linked to salt tolerance.
Relative Salt Tolerance of Crops
- Tolerant: Cotton, sugarcane, barley.
- Semi-tolerant: Rice, maize, wheat, oats, sunflower, soybean.
- Sensitive: Cowpea, beans, groundnut, grams.
Mitigation of Salt Stress
- Seed hardening with NaCl (10 mM concentration).
- Application of gypsum (50% Gypsum Requirement).
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Other options:
- Improving drainage to leach salts.
- Using salt-tolerant varieties.
- Modifying irrigation practices.
- Applying organic matter.
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Description
This quiz covers various environmental stresses that affect crop growth, including drought and its physiological impacts on plants. Learn about how factors like water deficit, salinity, and temperature extremes influence crop morphology and yield. Test your knowledge on these critical agricultural challenges.
