Long-term acid-induced wall extension in an in-vitro system

Area of Science:

• Plant Biology
• Cell Wall Mechanics
• Growth Physiology

Background:

• Acid-induced cell wall extension is a known phenomenon in plants.
• Understanding the mechanisms of cell elongation is crucial for plant growth.
• Previous studies have characterized acid-extension but not fully elucidated its phases.

Purpose of the Study:

• To analyze the distinct phases of acid-induced extension in plant tissues.
• To mathematically model the acid-extension response.
• To compare the characteristics of acid-extension phases with auxin-induced growth.

Main Methods:

• Acid-treatment of frozen-thawed Avena sativa L. coleoptile and Cucumis sativa L. hypocotyl sections under tension.
• Measurement of rapid elongation (acid-extension).
• Mathematical modeling of extension using the equation: ΔL = a - a · e (kt) + c · t.

Main Results:

• Acid-extension comprises two phases: an exponentially decaying phase (ExE) and a constant rate extension (CE) phase.
• Low pH and high tension enhanced both ExE (a) and CE (c).
• Temperature primarily affected the rate constant (k) of ExE.
• CE showed significant magnitude (over 50% extension/10 h) and a time course similar to auxin-induced growth.

Conclusions:

• The constant rate extension (CE) phase of acid-induced elongation is mechanistically similar to auxin-induced growth.
• CE, with its yield threshold and sustained rate, is a more likely representation of normal cell wall extension during auxin-mediated growth than the exponential phase (ExE).
• The study provides a quantitative model for acid-extension and highlights the significance of the CE phase in plant growth.