Question

briefly describe the mechanism underlying the gravitropic response of inflorescence stem

Answer 1

Gravitropism refers to the response towards gravity. It is seen in both roots and the stems. Roots show positive gravitropism while shoots show negative gravitropism.Stems if placed horizontally show curvature and grow in upward direction thereby indicating response of the cells to gravitropism. The mechanism underlying this response of the stem is understood majorly by studying the organelles called amyloplasts which are responsible for the production of starch. The response mechanism is carried out in 3 steps i.e., perception, signal transduction and growth. Statoliths are specialized form of amyloplasts present in cells called statocytes which have the ability to sense gravity in both roots and shoot. Statoliths get deposited on the bottom of the cells due to gravity and hence they help on graviperception. They interact with the endoplasmic reticulum of the cell activating the calcium signaling pathway which deposits the hormone Indole Acetic Acid (IAA) at the bottom of the cells causing growth of axis in the shoot by promoting cell elongation(in roots it promotes lateral expansion causing them to swell and but grow in the doirection of gravity). Hence if you position a plant horizontally the hormone gets deposited in the cells that are present at the lower bottom and then asymmetric distribution of the plant hormone occurs leading to axial growth causing curvature thereby showing negative gravitropic effect.