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Agronomy QUESTION #2093
Question 1
Osmotic adjustment in crops under drought stress is the process by which:
  • Plants shed their leaves to reduce total transpiring surface area
  • Cells actively accumulate compatible solutes (proline, glycine betaine, soluble sugars, K⁺) in the cytoplasm and vacuole, lowering osmotic potential and maintaining turgor pressure and metabolic function at lower soil water potentials — enabling continued growth and gas exchange✔️
  • Roots lose their selective permeability, allowing free water movement into depleted cells
  • Stomata permanently close to prevent any further water loss
Correct Answer Explanation
Osmotic adjustment (osmoregulation) is an active cellular response to water deficit: solutes accumulate without causing toxicity, lowering \(\psi_s\) (osmotic potential) and maintaining positive turgor pressure (\(\psi_p = \psi_w - \psi_s\)) at lower leaf water potentials. This sustains stomatal opening, photosynthesis, root elongation into dry soil, and metabolic processes — a key drought tolerance mechanism quantified by the Pressure-Volume curve.