Plant Growth and Hormones

The mobilization of reserve material from endosperm to the developing embryo is brought about by gibberellin through synthesizing hydrolysing enzyme (e.g., amylase and protease) which cause the breakdown of starch and proteins respectively. Sugar and amino acids so formed are transferred to the developing embryo.

Abscisic acid (ABA) is sometimes called the stress hormone because it initiates and maintains seed and bud dormancy and brings about the closure of stomata.

Monocots and herbaceous dicots typically exhibit only primary growth.The important factors affecting plant growth and development include heredity, hormones, nutrition, and environment.

Coconut water (liquid endosperm) is rich in cytokinins, which promote cell division. It's widely used in tissue culture media. Gibberellins promote stem elongation, ethylene controls fruit ripening, and auxin regulates cell elongation and apical dominance.

IAA (Indole-3-Acetic Acid), the natural auxin, is primarily responsible for apical dominance - where the main shoot tip suppresses lateral bud growth. ABA (abscisic acid) is a stress hormone, GA3 promotes elongation and flowering, and C2H4 is ethylene (ripening hormone).

Long-day plants flower when the day length exceeds their critical photoperiod.

Zeatin is a cytokinin-like substance isolated and crystallized by Letham (1964) from milky endosperm of corn (Zea mays). He named this substance as zeatin.

 It is also present in coconut water.

Cytokinins delay the senescence of plant organs by controlling protein synthesis and mobilisation of resources.

Gibberellins induce production of male flowers on genetically female plants.

Abscisic acid (ABA) is the plant hormone responsible for inducing and maintaining seed dormancy. It inhibits growth and helps seeds survive unfavorable conditions. IAA (auxin) promotes growth, gibberellic acid breaks dormancy, and cytokinins promote cell division.

Kinetin (a cytokinin) is formed from the degradation products of DNA, specifically from the adenine base. It was discovered as a compound that promotes cell division. It is not derived from RNA, proteins, or carbohydrates.

Skoog and Miller (1957) discovered the critical balance between auxin and cytokinin in plant tissue culture. High cytokinin with low auxin promotes shoot formation, while high auxin with low cytokinin promotes root formation. This was a fundamental discovery in plant developmental biology.

Leaf abscission occurs when auxin production decreases, which happens naturally as leaves age or under stress conditions. The drop in auxin triggers the formation of the abscission layer at the leaf base, weakening the connection and causing leaf fall.

IAA (Indole-3-acetic acid) is the primary natural auxin produced by plants. NAA (naphthaleneacetic acid) and 2,4-D are synthetic auxins used in agriculture. Aviton appears to be an incorrect or obscure term.