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Difficulty: EasyHormonal Coordination in Plants and Animals

During seed germination in cereal grains, gibberellin plays a vital role in mobilizing food reserves stored in the endosperm. Arrange the following steps of gibberellin-mediated seed germination in the correct physiological sequence from first to last.

  1. 1Water imbibition by the dry seed activates metabolic activity in the embryo.
  2. 2The activated embryo synthesizes and secretes gibberellic acid.
  3. 3Gibberellic acid diffuses across the seed tissue to the aleurone layer.
  4. 4Target cells in the aleurone layer synthesize digestive enzymes, including alpha-amylase.
  5. 5Alpha-amylase hydrolyzes stored insoluble starch in the endosperm into soluble sugars for seedling growth.

Answer

The correct physiological sequence is: Water imbibition by the dry seed activates metabolic activity in the embryo -> The activated embryo synthesizes and secretes gibberellic acid -> Gibberellic acid diffuses across the seed tissue to the aleurone layer -> Target cells in the aleurone layer synthesize digestive enzymes, including alpha-amylase -> Alpha-amylase hydrolyzes stored insoluble starch in the endosperm into soluble sugars for seedling growth.
Seed germination begins with water absorption (imbibition), which stimulates the embryo to synthesize gibberellic acid. Gibberellin then diffuses to the aleurone layer, where it induces gene expression and synthesis of alpha-amylase. Alpha-amylase degrades insoluble endosperm starch into simple sugars that nourish the growing embryo.

Step-by-Step Solution

1
Identify the initial physical stimulus for germination.
Imbibition of water activates the embryo.
Water absorption hydrates seed tissues and initiates metabolic reactions.
2
Determine the initial endocrine signal produced by the embryo.
Embryo produces gibberellic acid.
Gibberellin is the primary plant growth regulator that triggers mobilization of reserve food.
3
Trace the pathway of hormone transport.
Gibberellin diffuses to the aleurone layer.
The aleurone layer consists of target tissue surrounding the endosperm.
4
Determine the response of the target aleurone cells.
Aleurone cells synthesize digestive enzymes like alpha-amylase.
Gibberellin stimulates the synthesis of hydrolytic enzymes needed for starch digestion.
5
Identify the final biochemical outcome of enzyme activity.
Starch is converted into soluble sugars to feed the growing seedling.
Soluble glucose and maltose supply energy for respiration and cell elongation in the developing shoot and root.

Key Concept

Gibberellin-Induced Mobilization of Endosperm Reserves
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Topics

Hormonal Coordination in Plants and Animals

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