Polymerization of Actin from Maize Pollen.

Area of Science:

• Plant Biology
• Biochemistry
• Cytoskeleton Research

Background:

• Actin, a crucial cytoskeletal protein, is essential for cell structure and motility.
• While actin is well-characterized in muscle cells, its properties in plant systems are less understood.

Purpose of the Study:

• To investigate the in vitro polymerization of actin isolated from maize (Zea mays) pollen.
• To compare the biochemical and structural characteristics of maize pollen actin with known muscle actin.

Main Methods:

• Purification of actin from maize pollen.
• In vitro polymerization assays using ATP, KCl, and MgCl2.
• Spectrophotometric analysis of absorbance changes.
• Viscosity measurements.
• Ultraviolet difference spectroscopy.
• Enzyme activity assays with rabbit muscle myosin ATPase.
• Electron microscopy for filament visualization.
• Treatment with cytochalasin B and rabbit heavy meromyosin.

Main Results:

• Purified maize pollen actin is biologically active and polymerizes into filaments in vitro.
• Polymerization is accompanied by increased absorbance at 232 nm and solution viscosity.
• Ultraviolet difference spectra of pollen actin closely resemble those of rabbit muscle actin.
• Polymerized pollen actin (F-actin) activates rabbit muscle myosin ATPase activity sevenfold.
• Electron microscopy reveals 7 nm diameter filaments, exhibiting arrowhead structures upon decoration with heavy meromyosin, and are disrupted by cytochalasin B.

Conclusions:

• Maize pollen actin exhibits functional and structural similarities to vertebrate muscle actin.
• These findings suggest conserved properties of actin across diverse eukaryotic kingdoms.
• The study provides evidence for the presence of functional actin cytoskeletons in plant cells.