Two Distinct Signaling Pathways Participate in Auxin-Induced Swelling of Pea Epidermal Protoplasts

• Published in: Plant physiology (Bethesda) Vol. 134; no. 2; pp. 735 - 747
• Main Authors: Mutsumi Yamagami, Haga, Ken, Napier, Richard M., Iino, Moritoshi
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Biologists 01.02.2004; American Society of Plant Physiologists; The American Society for Plant Biologists
• Subjects: Acetic acid; Agronomy. Soil science and plant productions; Antibodies; Auxins; Biological and medical sciences; Calcium - pharmacology; Cell membranes; Cell physiology; Chemical agents; Chlorides - pharmacology; Coleoptiles; Development and Hormone Action; Dose response relationship; Dose-Response Relationship, Drug; Economic plant physiology; Epidermis; Fundamental and applied biological sciences. Psychology; Growth and development; Growth regulators; Indoleacetic Acids - pharmacology; Molecular and cellular biology; Naphthalene; Naphthaleneacetic Acids - pharmacology; Peas; Pisum sativum - drug effects; Pisum sativum - growth & development; Plant Epidermis - drug effects; Plant Epidermis - growth & development; Plant Growth Regulators - pharmacology; Plant physiology and development; Plant Proteins - metabolism; Plants; Potassium - pharmacology; Protoplasts; Protoplasts - drug effects; Protoplasts - physiology; Receptors; Receptors, Cell Surface - metabolism; Signal transduction; Signal Transduction - drug effects; Signal Transduction - physiology; Swelling; Vegetative apparatus, growth and morphogenesis. Senescence; Auxin; Calcium; Growth; 1-Naphthaleneacetic acid; Binding protein; Signal transduction; Dicotyledones; Indoleacetic acid; Chlorides; Protoplast; Angiospermae; Plant growth substance; Mechanism of action; Swelling; Epidermis; Extracellular; Biological activity; Grain legume; Leguminosae; Pisum sativum; Second messenger; Perception; Spermatophyta; Phytohormone; Potassium
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.103.031294

Protoplast swelling was used to investigate auxin signaling in the growth-limiting stem epidermis. The protoplasts of epidermal cells were isolated from elongating internodes of pea (Pisum sativum). These protoplasts swelled in response to auxin, providing the clearest evidence that the epidermis can directly perceive auxin. The swelling response to the natural auxin IAA showed a biphasic dose response curve but that to the synthetic auxin 1-naphthalene acetic acid (NAA) showed a simple bell-shaped dose response curve. The responses to IAA and NAA were further analyzed using antibodies raised against ABP1 (auxin-binding protein 1), and their dependency on extracellular ions was investigated. Two signaling pathways were resolved for IAA, an ABP1-dependent pathway and an ABP1-independent pathway that is much more sensitive to IAA than the former. The response by the ABP1 pathway was eliminated by anti-ABP1 antibodies, had a higher sensitivity to NAA, and did not depend on extracellular Ca2+. In contrast, the response by the non-ABP1 pathway was not affected by anti-ABP1 antibodies, had no sensitivity to NAA, and depended on extracellular Ca2+. The swelling by either pathway required extracellular K+ and Cl-. The auxin-induced growth of pea internode segments showed similar response patterns, including the occurrence of two peaks in the dose response curve for IAA and the difference in Ca2+ requirements. It is suggested that two signaling pathways participate in auxin-induced internode growth and that the non-ABP1 pathway is more likely to be involved in the control of growth by constitutive concentrations of endogenous auxin.