Root growth responses to soil physical conditions.
Scottish Crop
Research Institute
Tracy A. Valentine, Kirsty Binnie, Joachim Hans, Blair M. McKenzie and A. Glyn Bengough
Scottish Crop Research Institute, Dundee.
Background
• Roots experience a range of physical constraints including mechanical impedance, water stress and oxygen deficiency.
• We are linking studies of soil physical properties to root responses invitro and in the field.
Soil physical environment
Root responses to soil conditions
Soil strength depends on soil type, water
potential, and structure.
Computer visualisation of root growth
Aims: Quantify cell expansion and root growth over short time intervals to study control of root responses
under stress.
5
No till
Compact
4
3
Deep plough
Min till
2
Particle Image Velocimetry (P.I.V.) tracks pixel patches between images to measure growth, with a 2 min
resolution.
1
A
0
0.7% (w/v) agar
D
2% (w/v) agar
G
200
Genes: Arabidopsis At3g54890 (to monitor extraction
efficiency); Barley GAPDH (root internal standard); Barley
BPW (target gene associated with water transport).
Barley root RNA from 3 tillage treatments: Graphs show
PCR using Light cycler for AtSPIKE (A), GAPDH (B) and BPW
(C) sequences.
300
400
5 pixels
2
1
1.0
0.8
0.8
0.6
0.6
0.4
0.4
0.2
F
C
3
1.2
1.0
0.2
100 200 300 400 500 600
x coordinate
4
H 1.4
1.2
I
-0.004
-0.004
-0.003
-0.003
-0.002
-0.002
-0.001
-0.001
Strain rate (/min)
We are developing methods for studying
expression of root genes in relation to soil
physical conditions.
E
1.4
200
Strain rate (/min)
Root gene expression in field soil
B
100
0.000
0
Velocity (µm/min)
Soil strength (penetrometer resistance) increases as soil
dries, and is greatest in compacted soil. Roots can
experience large mechanical impedance even at field
capacity
y coordinate
25
50
Water tension (kPa)
Velocity (µm/min)
10
Velocity (µm/min)
Penetrometer resistance (MPa)
6
Mechanically impeded roots are shorter and fatter with more border cells.
200
400
600
800
Distance from quiescent centre (µm)
P.I.V. process (A-C). A: Patch placement on
confocal image. B: Displacement vector field
showing direction and relative movement of
patches. C: Calculated velocity of patches
verses distance from quiescent centre.
0.000
100200300400500600700
100200300400500600700
Distance from quiescent centre (µm)
D-I: Arabidopsis growth on 0.7% agar (D-F) and 2%
agar (G-I) using P.I.V. Confocal images of roots (D,G).
Root tissue velocity as related to position along the
root length (E,H) Strain rate calculated from velocity
curves (F, I).
A
More border cells are associated with nutrient stress and mechanical impedance.
Effect of nutrient availabiity on border
cell numbers
Border cell counts
B
18
16
14
12
10
8
6
4
2
0
C24
N60000
0.1MS
0.5MS
Nutrient stress induces border cell production in Arabidopsis.
C
We are screening for mutants that have altered border cell responses under nutrient and physical stress.
Future work
1. Quantify soil physical stresses experienced in field throughout season
2. Measure variation in root gene expression (including border cell genes), for in vitro, and soil grown roots.
3. Computer visualisation - development of a model to track cell features and extract cell expansion data, so that gene function can be related to growth
in soil environment.
Acknowledgements - SCRI receives grant-in-aid from SEERAD. Computer visualisation and modelling of plant morphogenesis is funded by BBRSC. Dr. D. White (Cambridge University) for
access to P.I.V. code.