Abiotic Stress

Abstract

The conditions which allow plants to attain maximal growth and reproductive potential, as determined by their total biomass (comprising of plant height, weight, and seed number), can be considered as the ideal growth conditions for the particular plant. Since plants grow and reproduce in complex environmental conditions composed of a multitude of abiotic and biotic factors, they are frequently exposed to stress conditions. Stress can be described as environmental conditions which prevent plants from attaining their full genetic potential, and, hence, it adversely affects plant growth, development, and productivity. Environmental factors which result in stress may be divided into biotic and abiotic. Biotic stress is imposed by direct or indirect interactions with other organisms, whereas abiotic stress originates from excess or deficit in the physical, chemical, and energetic conditions to which plants are exposed. Environmental conditions which have deleterious effect on plants include drought, flood, excessive soil salinity, high or low temperature, excess or insufficient light, and inadequate mineral nutrients. Phytotoxic molecules, like ozone, can also cause damage to plant tissues. Stress affects numerous plant responses ranging from changes in cellular metabolism and gene expression to modulation of growth rate and crop yield. The response of a plant is influenced by the severity, duration, and rate at which stress is imposed. A single stress or a combination of varied stress conditions can result in different stress responses. Moreover, plant responses can be elicited directly by stress or indirectly through stress-induced injury. Various factors, such as genotype, developmental stage, species, and organ or type of tissue, influence the sensitivity or resistance of plants to stress condition(s).

Multiple-Choice Questions

• 1. Example of stress avoidance mechanism represented by desert plants:

  • (a) Presence of deep root system

  • (b) Crassulacean acid metabolism

  • (c) Presence of spines

  • (d) Presence of succulent tissues

• 2. A catastrophic response is observed when:

  • (a) System bounces back and regains its former state.

  • (b) System is deformed and settles on a new stable configuration.

  • (c) System is deformed and leads to decrease in entropy and ultimately system dies.

  • (d) System enters into a stage of incoherence, entropy enhances, and the living system dies.

• 3. Evolutionary improvements, which enhance the fitness of the organism and occur over many generations and across entire populations, are termed as:

  • (a) Adaptations

  • (b) Acclimation

  • (c) Gene alterations

  • (d) Both b and c

• 4. What happens to GSH concentration under stressed condition?

  • (a) GSH concentration usually increases, and redox state becomes more reduced.

  • (b) GSH concentration usually declines, and redox state becomes more oxidized.

  • (c) GSH concentration usually declines; thus, redox state becomes more reduced.

  • (d) GSH concentration remains the same though GSSG concentration increases.

• 5. Why Na⁺ and K⁺ ions compete for uptake via transporters under saline conditions?

  • (a) Both have similar ionic radii and ion hydration energies.

  • (b) Both have same transporters.

  • (c) Na⁺ ions have small ionic radii compared to K⁺ ions.

  • (d) Both b and c.

• 6. Compartmentalization of Na⁺ into vacuoles is carried out by?

  • (a) Nonselective cation channels (NSCCs)

  • (b) SOS3-SOS2 complex

  • (c) Na+/H+ exchangers (NHXs)

  • (d) P-type ATPases

• 7. Cellular osmolarity in the shoots of halophytes is 2–3 times higher than the osmolarity of soil solution however the cytoplasmic concentration of ions is maintained at nontoxic levels. How?

  • (a) Action of tonoplast-localized Na+ and Cl− importers

  • (b) Accumulation of organic solutes in the cytoplasm

  • (c) Active sequestration of Na+ into the vacuoles by Na+-H+ antiporters

  • (d) All of the above

• 8. Bladder cell is characteristic feature of:

  • (a) Desert ephemerals

  • (b) Saprophytes

  • (c) Halophytes

  • (d) None of the above

• 9. In which categories of plants minimum thermal death point has been observed?

  • (a) Desert plants

  • (b) Hydrated organs of temperate plants

  • (c) Aquatic and shade plants

  • (d) Both b and c

• 10. Biosynthesis of heat shock proteins (HSPs) is induced in response to:

  • (a) High temperature stress

  • (b) Cold stress

  • (c) Drought stress

  • (d) All of the above

• 11. In plants molecular chaperons are:

  • (a) Histidine kinase Hik33

  • (b) HSPs

  • (c) LEA proteins

  • (d) HSPs and LEA proteins

• 12. Role of antifreeze proteins (AFPs) under freezing stress:

  • (a) Prevent protein denaturation

  • (b) Act as a osmoprotectants

  • (c) Prevent the nucleation of ice crystals

  • (d) Prevent electrolyte leakage by stabilizing plasma membrane

• 13. miRNAs and siRNAs play important role in certain plant responses against environmental stressors via:

  • (a) Post-translational gene silencing

  • (b) RITS (RNA-induced transcriptional silencing) formation

  • (c) Enhanced gene expression by ribonuclease complex formation

  • (d) Both a and b

• 14. ABA and cytokinins exhibit opposite effects with respect to:

  • (a) Stomatal closing and photosynthesis

  • (b) Nutrient deficiency

  • (c) Stomatal opening, transpiration, and photosynthesis

  • (d) Photosynthesis

• 15. Flood-sensitive plants get injured in response to anoxia due to absence of:

  • (a) Cell division

  • (b) Aerenchyma

  • (c) Ion transport

  • (d) Protein synthesis

• 16. Both epinasty and hyponasty are triggered by enhanced production of:

  • (a) ABA

  • (b) GA

  • (c) Ethylene

  • (d) Jasmonic acid

Answers

1. a	2. d	3. a	4. b	5. a	6. c
7. d	8. c	9. c	10. d	11. d	12. c
13. b	14. c	15. b	16. c