Stress physiology MCQ Quiz - Objective Question with Answer for Stress physiology - Download Free PDF
Last updated on May 7, 2025
Latest Stress physiology MCQ Objective Questions
Stress physiology Question 1:
Plants perceive effector molecules of a pathogen and mount a series of events that lead to the activation of a defense response. Following statements are made with respect to events that occur within a few minutes of the effector perception.
A. Transient change in the ion permeability of the plasma membrane.
B. Efflux of K+ and Cl- ions from the cell.
C. Influx of Ca2+ and H+ ions into the cell.
D. Influx of K+ and Cl- ions into the cell and efflux of Ca2+ and H+ ions from the cell.
Which one of the following options represents the combination of all correct statements?
Answer (Detailed Solution Below)
Stress physiology Question 1 Detailed Solution
The correct answer is A, B and C.
Explanation:
When plants perceive effector molecules from pathogens, they initiate a cascade of responses that involve rapid ion fluxes across the plasma membrane.
A. Transient change in the ion permeability of the plasma membrane.
- Correct. One of the earliest responses in plant defense is a transient change in the ion permeability of the plasma membrane. This is part of the plant's recognition of pathogen-associated molecular patterns (PAMPs) and effectors, triggering ion fluxes.
B. Efflux of K+ and Cl- ions from the cell.
- Correct. In response to effector perception, potassium (K⁺) and chloride (Cl⁻) ions often move out of the cell. This efflux is part of the early defense response and helps to maintain ionic balance during defense signaling.
C. Influx of Ca2+ and H+ ions into the cell.
- Correct. Upon effector recognition, there is typically an influx of calcium ions (Ca²⁺), which plays a key role in signaling. The influx of H⁺ ions (proton movement) is also part of the ionic changes that occur during defense responses, contributing to the acidification of certain compartments and signaling.
D. Influx of K+ and Cl- ions into the cell and efflux of Ca2+ and H+ ions from the cell.
- Incorrect. This statement is incorrect because, during the early stages of plant defense, K⁺ and Cl⁻ typically move out of the cell (efflux), and Ca²⁺ typically moves into the cell (influx). The reverse movement mentioned in this statement does not align with the typical defense response.
Conclusion: A, B, and C are correct statements describing the early events that occur in plant cells after perceiving pathogen effectors.
Stress physiology Question 2:
Which of the following compatible solutes does NOT contribute to osmotic adjustment within plant cells under drought or salinity stress?
Answer (Detailed Solution Below)
Stress physiology Question 2 Detailed Solution
The correct answer is Glucose
Explanation:
Compatible solutes are small organic molecules that plants and other organisms accumulate in response to stress conditions such as drought or high salinity to maintain cell turgor and protect cellular components. These molecules are typically non-toxic at high concentrations and do not interfere with normal biochemical processes of the cell. They contribute to osmotic adjustment, helping cells to retain water, stabilize proteins and membranes, and scavenge free radicals.
- Proline - Proline is one of the most common compatible solutes in plants. It accumulates in various plant tissues under stress conditions like drought and salinity. Proline acts as an osmoprotectant that helps in osmotic adjustment, protects cellular structures, and scavenges free radicals.
- Glycine betaine - Another well-known osmoprotectant, glycine betaine, helps protect the plant cells under stress by contributing to osmotic balance. It is found in many organisms and plays a crucial role in protecting plants from the damaging effects of drought and salinity.
- Mannitol - Mannitol is a sugar alcohol that serves as a compatible solute in some plant species. Like other compatible solutes, it contributes to osmotic adjustment under stress conditions. Mannitol can help stabilize proteins and membranes, and its accumulation in cells is a common response to osmotic stress.
- Glucose - While glucose is a fundamental sugar and energy source for plants, it is not typically accumulated in high concentrations as an osmoprotectant or compatible solute in response to stress conditions like drought or salinity. Plants may convert excess glucose into other forms (like sucrose or starch) for storage or use it directly for energy and structural components rather than as a primary means of osmotic adjustment.
Conclusion:
Glucose does not primarily contribute to osmotic adjustment within plant cells under conditions of drought or salinity stress in the same way that specialized compatible solutes like proline, glycine betaine, and mannitol do.
Stress physiology Question 3:
Which one of the following is the correct function of JAZ (JASMONATE ZIM-DOMAIN) protein family, a key regulator of Jasmonic Acid (JA) signalling response?
Answer (Detailed Solution Below)
Stress physiology Question 3 Detailed Solution
The correct answer is Binds to MYC2 and represses the JA dependent genes.
Explanation:
- JAZ (Jasmonate ZIM-domain) proteins are crucial repressors in the JA (jasmonic acid) signaling pathway. Under conditions where JA is not present or its levels are low, JAZ proteins bind to transcription factors such as MYC2, inhibiting their activity and thus repressing the expression of JA-responsive genes.
- Upon perceiving JA signals, especially the bioactive form jasmonoyl-isoleucine (JA-Ile), JAZ proteins are targeted for degradation.
- This degradation releases the transcription factors, like MYC2, allowing them to activate the transcription of JA-responsive genes.
- This mechanism is critical for plant responses to biotic stress (such as herbivore attack or pathogen infection) and abiotic stress.
Stress physiology Question 4:
Which one of the following statements about the guardee protein, that plays an important role during plant-pathogen interactions is correct?
Answer (Detailed Solution Below)
Stress physiology Question 4 Detailed Solution
The correct answer is Option 4 i.e.Degradation of guardee protein can activate the defense response.
Explanation-
In plant-pathogen interactions, plants rely on their immune system to defend against invading pathogens. The guardee model is an important part of understanding this interaction. According to this model, certain plant proteins, known as R proteins, guard or monitor other key host (plant) proteins, named guardees, that are targets of pathogen effectors. When a pathogen effector modifies the guardee protein, the R protein 'notices' this change and initiates a defense response, often leading to a form of programmed cell death called the hypersensitive response that prevents the pathogen from spreading.
Key Points "Guardee" is a term used in plant immunology to describe a plant protein that is monitored or 'guarded' by a resistance (R) protein. The R protein is a part of the plant's immune system and may also be referred to as a 'guard.'
- The guardee and guard proteins play significant roles in protecting the plant during pathogen infections, particularly in the context of Pathogen-associated molecular pattern (PAMP)-triggered immunity and effector-triggered immunity (ETI).
- PAMP-triggered immunity: PAMPs are molecules associated with groups of pathogens recognized by cells of the innate immune system. In response to PAMP recognition, a signaling cascade triggers defensive measures like the production of antimicrobial compounds.
- Effector-triggered immunity: While PAMP-triggered immunity provides a generic defense, it's often overcome by pathogens that deliver effectors into host cells to manipulate host processes in ways favorable to the pathogen. ETI is then activated wherein specific R proteins recognize these pathogen effectors or their actions on the guardee proteins.The pathogen, which is trying to infect the plant cell, produces specific effector proteins that are delivered into a host cell. Effector proteins interfere with the host's defenses and can bind to, or otherwise modify, the behavior of the guardee proteins.
Fig-Guard hypothesis the plant R proteins (guard) are associated with the endogenous host protein (guardee) which are common target proteins for the pathogens. The interaction of effector pathogen proteins with the host proteins, causes a change in their structure which is then recognized by the guard proteins. As a result, a pathogen response signaling cascade is triggered against the microbial evasion.
This modification to the guardee proteins alerts the R proteins that something is wrong. Upon detection of an effector's action, R proteins initiate the plant's defenses. Such defenses can include a localized inflammation, the production of antimicrobial metabolites, and a form of programmed cell death in the area around the site of infection known as hypersensitive response, which can limit the pathogen's ability to spread.
Conclusion-Thus, when a guardee protein is modified or degraded by the actions of a pathogen, it can activate the plant's defense response, limiting the spread of the pathogen and maintaining the health of the plant as much as possible.
Stress physiology Question 5:
Glycophytes are salt-sensitive plants while halophytes are
Answer (Detailed Solution Below)
Stress physiology Question 5 Detailed Solution
Key Points Halophytes
- Halophytes are a unique group of plant species that are adapted to survive in high-salt environments, where most plant species, known as glycophytes, cannot survive.
- This tolerance to salt is an adaptive trait that has evolved in these species over long periods.
- Halophytes are capable of growing in soils or waters with high salt concentrations, typically 200 mM NaCl or more, which would be lethal to most plant species.
- This high salt concentration can be found in coastal areas, salt pans, and regions with saline groundwater.
- Adaptation to such environments involves both morphological and molecular changes in plant physiology.
- These include modification in roots, leaves, and overall plant structure that allows increased salt tolerance.
- For example, some halophytes can secrete excess salt from special glands in their leaves or stems, while others accumulate salt in their tissues to a level that would be toxic for other plant species.
- On a molecular level, halophytes have developed mechanisms like selective ion transport, production of compatible solutes, and stress-signaling pathways that enable them to mitigate and manage high salt concentration.
- For instance, some halophytes are capable of adjusting their internal salt concentration to match the external environment and maintain osmotic balance.
- The study of halophytes is significant as salinity is a common problem in many agricultural areas worldwide, leading to reduced productivity and economic loss.
- Understanding the mechanisms of salt tolerance in halophytes can have practical applications in developing genetically modified crop varieties to thrive in high salt conditions, improving crop productivity, and ensuring food security.
- However, it's key to remember that continuous exposure to high salt concentrations, like any extreme environmental condition, can still be detrimental to these plants' overall health and growth despite their adaptation.
- The level of tolerance varies among different halophytes, as these adaptations are species-specific.
Hence the correct answer is option 2.