Plant Hormones

Flashcards covering plant hormones and their functions, including auxin, gibberellins, and cytokinins.

Air Layering

A technique for rooting woody plants without detaching them, involving stripping bark, wrapping in moist sphagnum moss, and planting the rooted segment separately.

Parthenocarpy

Also known as virgin fruit, this is the formation of seedless fruit, often induced by applying auxin to unfertilized ovaries.

Abscission

The natural detachment of plant parts, such as leaves or fruit, prevented by high levels of IAA (auxin) and triggered by increased ethylene levels as the organ ages.

2,4-D and Dicamba

Examples of synthetic auxins used as selective herbicides that kill dicots by accumulating within them, while being metabolized by monocots.

Agent Orange

A herbicidal mix of synthetic auxins (2,4-D + 2,4,5-T) used in the Vietnam War for defoliation, but contaminated with dioxin, leading to health issues and bans.

Gibberellins (GA)

A group of over 125 plant hormones identified by Kurosawa in 1926 via the Foolish Seedling Disease, promoting cell elongation and division.

Foolish Seedling Disease (Baka-nae)

A disease in rice caused by Gibberella fujikuroi, a fungus that produces gibberellic acid (GA), leading to excessive growth.

Internode Elongation

GA promotes this, restoring normal height in dwarf plants by causing the sections between plant nodes to grow.

Bolting

The process of flowering in rosette plants (e.g., cabbage, lettuce) promoted by increased GA levels during long days (summer).

Seed Germination

Reactivated by GA in dormant embryos, triggering α-amylase production to convert starch into glucose for the embryo's use.

Cytokinin (CK)

A plant hormone derived from adenine, stimulating cytokinesis (cell division) and made in root tips, transported acropetally (root → shoot).

Cytokinesis

Cell division that is stimulated by Cytokinin.

Axillary Bud Growth

Promoted by High CK, overriding apical dominance.

Senescence

Aging, which is delayed by Cytokinins

Chloroplast Development

Initiated by CK + light which leads to proplastid, chlorophyll + protein, and photosynthetically active chloroplast.