Question

Which bioassay is used to detect the presence of auxin?

• A. Only tobacco pith culture
• B. Tobacco pith culture and Avena curvature test
• C. Tobacco pith culture and Split pea stem curvature test
• D. Split pea stem curvature test and Avena curvature test

Hint:

Remember:
• Auxin $\rightarrow$ Avena curvature test, Split pea stem curvature test.
• Cytokinin $\rightarrow$ Tobacco pith culture. These are frequently asked matching questions in biotechnology and plant physiology.

Answer 1

The Correct Option is D

Concept: Auxins are plant growth hormones that regulate cell elongation, apical dominance, root initiation, and tropic responses. Since auxins promote differential growth of plant tissues, special biological tests called bioassays are used to detect and estimate their activity.
• A bioassay measures the biological response produced by a hormone.
• Auxin causes unequal cell elongation, resulting in bending or curvature of plant organs.
• The Avena curvature test is the classical bioassay for auxin.
• The Split pea stem curvature test is another widely used bioassay for auxin activity.
• Tobacco pith culture is mainly used for studying cytokinins rather than auxins.

Step 1: Understand the Avena curvature test.
The Avena curvature test was developed using oat (Avena) coleoptiles. When auxin is applied to one side of the coleoptile, cells on that side elongate more rapidly than the opposite side. This unequal growth causes the coleoptile to bend. \[ \boxed{\text{Auxin} \longrightarrow \text{Differential cell elongation} \longrightarrow \text{Curvature}} \] Hence, the amount of curvature produced is directly related to the concentration of auxin.

Step 2: Understand the Split pea stem curvature test.
In this bioassay, a pea stem is split longitudinally into two halves. When auxin is applied to one side, that side elongates faster than the other, producing a characteristic curvature. This curvature serves as an indicator of auxin activity and concentration.

Step 3: Eliminate the incorrect options.

• Tobacco pith culture is primarily used for cytokinin studies.
• Both the Avena curvature test and Split pea stem curvature test are standard bioassays for auxin. Therefore, \[ \boxed{Option (D) is the correct answer. \]