The Growth Oscillator and Plant Stomata: An Open and Shut Case

Area of Science:

• Plant Biology
• Cellular Physiology
• Biochemistry

Background:

• The precise mechanism of oscillatory plant growth has remained elusive since Darwin's observations.
• A hypothetical growth oscillator regulating phenomena like circumnutation and pollen tube growth is sought.
• Arabinogalactan glycoproteins (AGPs) were recently identified as a key missing component.

Purpose of the Study:

• To elucidate the molecular mechanism of a universal plant growth oscillator.
• To propose a new model integrating AGPs, Ca2+ signaling, and auxin transport.
• To challenge the established "acid growth" theory.

Main Methods:

• Identification of four key components: auxin-activated proton pumps, AGPs, Ca2+ channels, and auxin efflux PIN proteins.
• Modeling the interaction of these components in the plasma membrane to generate Ca2+ oscillations.
• Reinterpreting experimental data in light of the proposed molecular PINball machine model.

Main Results:

• A four-component molecular PINball machine model for oscillatory growth was proposed.
• Demonstrated how Hechtian adhesion and proton pumps release Ca2+ stored in AGPs.
• Showed that proton pumps, AGPs, Ca2+ channels, and PIN proteins generate cytosolic Ca2+ oscillations.
• Proposed an alternative to the acid growth theory, linking proton pumps to Ca2+ signaling and auxin transport.

Conclusions:

• Arabinogalactan glycoproteins (AGPs) are crucial for dynamic Ca2+ storage at the cell surface.
• The proposed model offers a new paradigm for understanding plant oscillatory growth, challenging the acid growth theory.
• Further research is needed to validate the universal growth oscillator model, especially for marine plants and stomatal regulation.