Question

Pigment phytochrome is involved in ..............
A. Hydrotropism
B. Photorespiration
C. Photoperiodism
D. Geotropism

Answer 1

Phytochrome is a homodimer, which means it is made up of two identical protein molecules that are each attached to a light-absorbing molecule (compare rhodopsin). Plants produce five phytochromes: Phy-A, B, C, D, and E. There is considerable redundancy in the functions of the several phytochromes, although some appear to be unique to one or the other. The absorption spectra of phytochromes differs as well, indicating which wavelengths (e.g., red vs. far-red) they absorb best.

Complete answer:
Let us solve this question by analyzing each option and the tropic movements in plants
Option:A - Hydrotropism is a plant's reaction to a stimulus or gradient in water concentration that determines the direction of growth. Phytochromes have no involvement in hydrotropism.
So, Option:A is not correct.
Option:B – Phytochromes do not play any role in photorespiration. Chloroplasts, Peroxisomes and Mitochondria are involved in photorespiration.
So, Option:B is not correct.
Option:C - Many blooming plants (angiosperms) detect seasonal variations in night length, or photoperiod, via photoreceptor proteins like phytochrome or cryptochrome, which they interpret as signals to blossom.
So, Option:C is correct.
Option:D - Plant growth in response to the gravity of earth is known as geotropism. Negative geotropism describes the upward growth of plant shoots, whereas positive geotropism describes the downward growth of roots. Geotropism is not affected by phytochromes.
So, Option:D is also not correct.

So, option C. Photoperiodism is the correct answer.

Note:
Photoperiodism is an organism's functional or behavioural reaction to changes in duration in daily, seasonal, or annual light-dark cycles. Although photoperiodic responses may be anticipated, temperature, nutrition, and other external variables influence how an organism responds. As the days get shorter in the autumn, photoperiodism not only regulates blooming in some trees, but it also slows vegetative development and encourages the formation of winter buds.