Question

Describe the mechanism underlying the gravitropic response of inflorescence stem.

Answer 1

Gravitropism is a response that triggers asymmetric cell elongation in the plant organs in response to gravity.

The mechanism underlying the gravitropic response of inflorescence stem are:

The roots grow downward and the shoots grow upward, showing positive and negative gravitropic responses, respectively.

In higher plants, gravitropism proceeds through three sequential steps:

• perception of gravity signals,
• signal transduction and
• asymmetric cell elongation.

Light and temperature also influence the gravitropic orientation of plant organs.

Under red and far‐red light conditions, the phytochrome photoreceptors suppress the negative gravitropic response of hypocotyls by inhibiting the function of a subset of phytochrome‐interacting factors (PIFs), causing random directional growth

At low temperatures, the gravitropic curvature of inflorescence stems is reduced.

The starch‐statolith theory underlies the perceprion step of gravity signals. It depicts that starch‐filled amyloplasts, existing in the gravity‐sensing cells (statocytes), such as the endodermal cells of the shoots and the columella cells of the roots, sediment in the direction of gravity.

The sedimentation of amyloplasts perhaps triggers downstream signalling events that eventually lead to organ curvature.

So endodermis is essential for shoot gravitropism and functions as the gravity-sensing cell layer in dicotyledonous plant shoots.

The Cholodny‐Went hypothesis illustrates that gravitropic stimuli induce lateral auxin redistribution, resulting in differential cell elongation in the responding organs.

The auxin efflux proteins PIN‐FORMED 3 (PIN3) and PIN7 are rapidly relocalized to the lower side of the columella cells in the roots upon gravity stimulation, suggesting that they mediate lateral auxin transport.

It is thus evident that starch metabolism and/or transport are closely associated with asymmetric auxin transport in the gravitropic respons

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