Root cap influences root colonisation by Pseudomonas fluorescens SBW25 on maize

Area of Science:

• Plant-microbe interactions
• Root biology
• Soil microbiology

Background:

• Root border cells are specialized cells at the root tip.
• These cells secrete mucilage, forming a protective layer.
• Understanding microbial colonization is crucial for agriculture and biocontrol.

Purpose of the Study:

• To investigate the role of root border cells in Pseudomonas fluorescens colonization of Zea mays roots.
• To determine how soil bulk density affects this interaction.

Main Methods:

• Zea mays seedlings were grown in sandy loam soil at two densities (1.0 and 1.3 mg m(-3)).
• Intact and decapped roots were inoculated with Pseudomonas fluorescens SBW25.
• Bacterial colonization was quantified by colony forming units (CFU) on root sections.
• Confocal microscopy was used to visualize bacteria on root tips.

Main Results:

• Pseudomonas fluorescens colonization was highest on the root section below the seed, decreasing towards the tip.
• Decapped roots showed significantly higher P. fluorescens colonization at the root tip (100-fold in loose, 30-fold in compacted soil) compared to intact roots.
• Confocal imaging confirmed P. fluorescens presence only on the tips of decapped roots.

Conclusions:

• Root border cells and their mucilage act as a barrier, limiting Pseudomonas fluorescens colonization of the root tip.
• This suggests border cells may function as a disposable sheath, preventing deeper microbial penetration.
• The findings have implications for biocontrol strategies using Pseudomonas fluorescens in agriculture.