Question

State whether the following statements are true or false.
Plant growth is stimulated by the presence of auxins, ethylene and abscisic acid

Answer 1

Phototropism is the growth movement exhibited by plants in the response to light. The higher concentration of auxins in the shaded part of the stem results in the higher rate of cell elongation in this part than the cells present on the side exposed to the light. It causes bending of the stem in towards the light.

Complete step by step answer: Plants secrete chemical signals called hormones that affect their growth and development. Plant hormones are small molecules and affect different aspects of their development. The five main hormones synthesized by the plants are auxins, gibberellins, cytokinins, ethylene, and abscisic acid.
Auxins are the plant growth hormones synthesized mainly in shoot apical meristem, young stem, and leaves. Auxins promote stem elongation, stimulate the development of roots in the stem cuttings, and mediate the fruit development in flowering plants. Auxins are also responsible for apical dominance. It prevents the abscission of immature fruits and leaves.
Ethylene is the only gaseous hormone synthesized by stem nodes, ripened fruits, and the aging plant tissues. Ethylene promotes horizontal growth of seedlings, ripening of fruits, seed germination, and root initiation. It also promotes the elongation of internodes or petioles in some plants such as rice.
Abscisic acid is the plant hormone that is secreted by almost all the plant cells. It inhibits plant growth and development. Abscisic acid promotes seed dormancy and inhibits seed germination. It allows the seeds to cope up with the unfavorable growth conditions such as desiccation.
So, the given statement is “false”.

Note: Abscisic acid is also called the plant stress hormone. It triggers the closure of stomata during water stress and helps the plant to withstand the abiotic stress conditions. The effects of abscisic acid on plant growth are antagonistic to gibberellic acid.