Regulating Growth Plant Hormones Plant Growth, Structure & Function Regulating Growth Plant Hormones

Hormones Hormones are organic substances produced in small amounts that regulate and coordinate metabolism, growth, and morphogenesis.

Plant Hormones: 5 Classes Auxins Young leaves, developing seeds. Polar (unidirectionally) and nonpolarly. Cytokinins Root tips. From roots to shoots via xylem. Ethene Most tissues in response to stress. Diffusion from site of synthesis. Abscisic acid Mature leaves and roots, seeds. From leaves in phloem and from the roots in the xylem. Gibberellins Young tissues of the shoot and developing seeds. Xylem and phloem.

Auxin is the only plant hormone known to be transported polarly. Polar transport is toward the base Promotes cell elongation

Auxins Produces in the apical meristems at the tips of shoots Auxin builds up on shaded sided of seedling and stimulates growth beneath the tip

Auxin Plays a Role in the Differentiation and Regeneration of Vascular Tissue

Auxin Promotes Fruit Development

Auxin Promotes the Formation of Lateral and Adventitious Roots

Synthetic Auxins - Herbicides

Ethene Plays a Role in Fruit Ripening

Ethene Promotes Leaf Drop Ethene concentration increases and auxin concentration decreases in response to autumn’s shorter days and cooler temperatures

Cytokinins Promote Cell Division

Cytokinins Promote the Growth of Lateral Buds

Abscisic Acid (ABA) ABA promotes seed dormancy and prevents early germination ABA halts primary and secondary growth in plants ABA acts as a stress hormone ABA easily washes out during rainfall

Abscisic Acid is Responsible for Stomata Closure

Gibberellin (GA) Gibberellin (GA) causes dwarf mutants to grow tall. Gibberellin causes hyperelongation of shoots by stimulating cell division and elongation.

Gibberellin Plays Multiple Roles 1) Breaking seed dormancy 2) In germination

Gibberellin Affects Fruit Development