Surface charge on isolated maize-coleoptile amyloplasts

Area of Science:

• Plant Biology
• Biophysics
• Cell Biology

Background:

• Amyloplasts, key organelles in plant graviperception, are starch-filled plastids.
• Their role in sensing gravity is linked to their movement within specialized cells called statocytes.
• The biophysical properties of amyloplasts, such as surface charge, are hypothesized to influence their behavior.

Purpose of the Study:

• To quantify the surface charge of whole amyloplasts isolated from Zea mays L. coleoptiles.
• To investigate the relationship between amyloplast surface charge and plant age/light exposure.
• To explore the potential role of amyloplast surface charge in plant graviperception.

Main Methods:

• Isolation of whole amyloplasts from Zea mays L. coleoptiles.
• Electron microscopy to confirm amyloplast envelope integrity.
• Electrokinetic measurements (cataphoresis) to determine zeta potential.
• Ultrastructural analysis using cationized ferritin binding.

Main Results:

• Isolated amyloplasts consistently exhibited negative zeta potentials (mean of -19.4 mV).
• Negative surface charge was observed across different plant ages and light exposure durations.
• Isolated starch granules showed comparable negative surface charge.
• Cationized ferritin binding confirmed the net negative surface charge on amyloplasts and starch grains.

Conclusions:

• Amyloplasts and starch granules possess a net negative surface charge.
• This charge may play a role in the sedimentation and interaction of amyloplasts within statocytes.
• The findings support a hypothesized role for statolith charge in the mechanism of plant graviperception.