A T.S. of dicot stem is stained with iodine with proper procedure. Which of the following structures are expected to show blue color?

When a transverse section (T.S.) of a dicot stem is stained with iodine, the structures expected to show a blue color are the starch grains.

Iodine solution stains starch blue, and the reaction is known as the iodine-staining test. Starch is a polysaccharide made up of glucose units, and when iodine is applied, it forms a complex with starch, resulting in a blue or blue-black coloration.

Explanation of the staining process:

• Iodine solution (often iodine-potassium iodide) binds to the starch molecules in plant tissues.
• The iodine reacts with the amylose component of starch, producing a characteristic blue color.

Structures in a dicot stem that are likely to show the blue color include:

• Parenchyma cells that store starch in the form of starch grains.
• Cortex: The outer region of the stem, often containing starch-storing parenchyma cells.
• Pith: The central region of the stem, which can also store starch in parenchyma cells.

Structures such as xylem, phloem, or epidermis do not typically contain starch and therefore will not stain blue with iodine.

To summarize:

• Expected to show blue: Starch grains in parenchyma cells of the cortex and pith.
• Not expected to show blue: Xylem, phloem, and epidermis (since they don’t store starch).