Q9 / 180 · AIIMS 2004 · Botany

Assertion : Photomodulation of flowering is a phytochrome - regulated process. Reason : Active form of phytochrome (Pfr) directly induces floral induction in shoot buds.

  • A
    If both assertion and reason are true and reason is the correct explanation of assertion
  • B
    If both assertion and reason are true but reason is not the correct explanation of assertion
  • Correct answer
    C
    If assertion is true but reason is false
  • D
    If both assertion and reason are false.

Solution

Flowering is a phytochrome regulated process. Phytotchrome is a blue protein pigment with a molecular mass of about $125 \mathrm{k} \mathrm{Da}$ (kilodaltons). Phytochrome occurs in two interconvertible form $P_R$ (which absorbs red light) and $\mathrm{P}_{\mathrm{fr}}$ (which absorbs far red light). The studies with mutants of Arabidopsis support and prove that the $\mathrm{P}_{\mathrm{fr}}$ is the active form of phytochrome. When $\mathrm{P}_{\mathrm{R}}$ molecules are exposed to red light, most of them absorb it and converted to $\mathrm{P}_{\mathrm{fr}}$. This causes floral induction in the shoot.

Hence, the correct answer is option: 'C'.

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