Download Root border cells in the rhizosphere

®
Scottish Crop
Research Institute
Root border cells in the rhizosphere
A.G. Bengough, D. Cooke, B.S. Griffiths, S. Humphris, K. Killham1, O.G.G. Knox1, D.B.
Standing1, S. Rodger2, V.E.C. Stubbs, T.Valentine, I.M. Young2
Scottish Crop Research Institute, Dundee; 1Department of Plant and Soil Science,
University of Aberdeen; 2SIMBIOS Centre, University of Abertay Dundee.
Border cell release into the rhizosphere
• Root caps of most plant species are tipped with a fringe of border cells that can
remain viable in the rhizosphere for several days
Cultivar effects
Rheology of
root cap
mucilage
Mean no.
border
cells/root
• There was an eight-fold variation in the rate of border cell release between maize
cultivars. Rheological properties of the mucilage of the different cultivars affected
border cell release.
700-1600
• Decapping decreased border cell numbers by an order of magnitude for 2-3 days
until the cap regenerated. We tested the hypothesis that the rate of border cell
release influences rhizosphere colonisation.
Border cells
within mucilage
network
3200-3500
Border cells and rhizosphere carbon flow
6
Glucose exudation
(ug/cell)x10-3
• Border cells actively take-up and release
small quantities of glucose-C.
• Root exudate contains much more
bacteria-utilisable carbon than is released
from border cells after they detach.
20 mM glucose
5
2 mM glucose
4
3
2
Border cell and
associated
mucilage
1
0
0
2
20
30
s.e.d.
Time (h)
Border cells influence colonization of the rhizosphere by (micro-) organisms
Soil bacteria
7
-1
lo g C F U c m r o o t
• Colonization of the root tip by Pseudomonas
fluorescens (GFP-labelled) was increased in
decapped roots
• Concept that border cells and their associated
mucilage act as a disposable sleeve around
the root.
Inta ct-loos e
De ca p-compa ct
Nematodes
• Weak long-range attraction to border cells.
4
3
2
• Large and significant effects on movement at
the local scale. Signal molecules involved?
1
0
Ne xt-to-tip
Ne xt-to-s e e d
Seed
Root s e ction
Tip
Next-to-tip
Next-to-seed
Seed
10 mm
Decapped root
0.025
0.020
Average speed (mm/s)
Intact root cap
Inta ct-compa ct
5
Tip
• The border cell sleeve decreases root-soil
friction and decreases root colonisation by
biocontrol bacteria - with implications for
biocontrol strategies in the field.
De ca p-loos e
6
0.015
0.010
0.005
0.000
Treatment
Nematodes + border cells
Acknowledgements
This work was funded by the BBSRC. SCRI receives grant-in-aid from SEERAD.
Nematodes + beads
Nematodes only