FILLING IN THE GAPS: MODELING AS A SPUR TO
RESEARCH IN SUNFLOWER
A.J. Hall, J.E. Cantagallo, C.A.Chimenti, M.C. Rousseaux and N. Trápani
IFEVA, Facultad de Agronomía (Univ. Buenos Aires)/CONICET. e-mail: [email protected]
INTRODUCTION
Formulation and testing of OILCROP-SUN (Villalobos et al., Agron. J. 88:403-415, 1996) served to expose a number of missing links in information about how the sunflower crop responds to the environment.
Much of the work with this crop carried out in Buenos Aires over the subsequent years focused on these knowledge gaps. This poster summarizes four case studies.
Problem: How does radiation during the critical period (floret initiation to end seed setting period) affect grain number?
Approach: Experiments involving short periods of shading (80 %, 7-10 days) during floral initiation (Exp.1 and 2) or at intervals between floral initiation and [anthesis+20d]
(Exp. 3).
Conclusions: Shading reduced floret primordia number per capitulum (Fig. 1) without altering grain set (filled grains/floret, data not shown). Shading after floret
differentiation was completed altered grain set differentially according to floret position and timing of shading (Fig. 2). Floret differentiation and the immediate post-anthesis
periods exhibited maximum sensitivity to shading (Fig. 3). Reference: Cantagallo, J., Hall, A.J., 2000 – Reduction in the number of filled seed in sunflower (Helianthus
annuus L.) by light stress. - 15th International Sunflower Conference – Toulouse – France, pp. D-35-40
Radiation and grain number determination.
FIG. 1
e
-x / -5,261
(r 2=0,85)
shading Exp. 1
2000
control Exp. 1
1500
shading Exp. 2
1000
control Exp. 2
Floral stage 8
500
Exp.1
Exp. 2
Middle
2
4
6
8
Center
0.6
Control
0.4
Periphery
Middle
0.2
0
0
Periphery
0.8
FIG. 2
10
0
FS8
2
4
6
8
10
12
14
2
,
0
0
FIG. 4
1
,
8
0
p
e
r
i
p
h
e
r
a
l
i
n
t
e
r
m
e
d
i
a
t
e
1/Embryo-growth duration (d)
Embryo-growth rate (mg d -1)
1
9
9
7
1
9
9
8
1
9
9
9
FIG.5
5
0
1
0
1
5
2
0
2
5
3
0
3
5
4
0
4
5
o
T
e
m
p
e
r
a
t
u
r
e
(
C
)
3
Specific leaf nitrogen
30
FIG. 8
FIG. 7
FIG. 7
LD (days)
+FR
40
35
+R
25
20
10.0
15
0.0
12.5
0.1
Mean daily radiation (mol m )
CASE 4.
0.3
0.4
0.5
FIG. 9
2
D1
D2
D3
1
0
0.00
0.6
Fig. 8. Leaf duration (days after full expansion) as
a function of mean daily fractional radiation
measured 197 °Cd after full expansion in basal
leaves of a canopy for leaves exposed to additional
R (triangles), additional green (circles [equivalent
dose of PAR to R]) and controls (squares).
Full symbols: Exp. 1 - empty symbols: Exp. 2
Fig. 9. Specific leaf nitrogen /mean daily R/FR
relationship for basal leaves in canopies of varying
density.
0.25
0.50
0.75
1.00
1.25
R/FR
Problem: The effects of nitrogen on sunflower leaf photosynthesis had been described, but its effects on sunflower leaf expansion had not been studied in great detail.
Approach: Experiments involving variations in nitrogen supply or reciprocal exchanges between high and low levels of N were used to examine expansion of leaves at
various levels of insertion and the effects of N on cell division (before and after leaf emergence) and expansion.
Conclusions: Leaf expansion rates in the quasi-linear phase of growth varied between levels of leaf insertion and with specific leaf nitrogen (SLN) (Fig. 10). The threshold
SLN for leaf expansion was considerably greater than that of maximum photosynthesis, rather closer to the SLN at which Pmax saturates (Fig. 11). Changes between levels
of N availability at various stages of the growth of emerged leaves did not produce significant changes in cell division if the changeover ocurred later than 10% of final leaf
size, cell expansion continued to respond to changeovers until the leaf had achieved at least 60% of its final size (data not shown). N availability did, however, produce
important changes (by a factor of ca. x2) in cell number per leaf primordium at the stage of leaf appearance (Fig. 12). References: Trápani and Hall, Plant Soil 184: 331-40,
1996; Trápani et al., Ann. Bot. 84: 599-606, 1999.
50
40
30
20
0
3
4
2
Specific leaf nitrogen (gNm )
FIG. 11
80
80
Pmax'
60
60
LERlg
LEGlg
40
40
20
20
0
0
0
1
2
3
4
5
-2
Specific leaf nitrogen (g N m )
6
-2 -1
10
12
16
20
25
22
8
LERlg (cm d )
leaf
leaf
leaf
leaf
leaf
leaf
Pmax'(  mol CO2m s )
FIG. 10
2 -1
Nitrogen effects on leaf expansion
(cm d )
0.2
Fig. 7 . Leaf duration (days after full expansion) as
a function of mean daily incident PAR for leaves of
isolated plants without (squares) or with (triangles)
FR enrichment.
Fractional Irradiance I/Io
-2
lg
Figure 6. Relationship between relative embryo final
weight (25°C final embryo weight = 100%) and
temperature for grains from the peripheral position of
the capitulum.
1
9
9
7
1
9
9
8
1
9
9
9
6
0
25
LER
Figure 5. Relationship between the reciprocal of
embryo-growth duration and temperature for grains
from the peripheral and intermediate position of the
capitulum.
Problem: Crops that generate high (> 4) LAI´s before anthesis begin to senesce so that LAI is actually falling before anthesis. This does not occur in sparser canopies. What
rôle does light [intensity and quality] play in this process?.
Approach: Experiments involving variations in shading, enrichment with red (R) and far red (FR) light and crop density (D) were used to test the hypothesis that light [intensity
and quality] modulates basal leaf senescece in sunflower.
Conclusions: Leaf duration (LD) (time between maximum leaf area and 20% initial chlorophyll content) is dependent on daily PAR receipt and is shortened by enrichment with
FR (Fig. 7) and extended by enrichment with R (Fig. 8). Experiments with tobacco lines overexpressing Phytochrome A confirmed the rôle of phytochrome in controlling leaf
senescence (data not shown). Specific leaf nitrogen of basal sunflower leaves relates more strongly with mean daily R/FR (Fig. 9) than with mean daily PAR (data not shown).
References: Rousseaux et al., Physiol. Plant. 96: 217-224, 1996; Plant Cell Environ. 20: 1551-8, 1997; Crop Sci. 39: 1093-1100,1999; Physiol. Plant. 110: 000-000, 2000.
30
2 -1
FIG.6
7
0
T
e
m
p
e
r
a
t
u
r
e
(
°
C
)
55
45
Figure 4. Relationship between embryo-growth rate
and temperature for grains from the peripheral
position of the capitulum.
8
0
01
02
03
04
0
Control of pre-anthesis leaf senescence
2
30
9
0
0
,
0
0
CASE 3.
1
20
1
1
0
T
e
m
p
e
r
a
t
u
r
e
(
º
C
)
0
10
1
0
0
1
02
03
04
0
60
0
1
2
0
0
,
0
2
1
,
0
0
7.5
-10
1
3
0
0
,
0
4
5.0
-20
Days to anthesis
0
,
0
6
1
,
4
0
2.5
Fig. 3. Number of filled seed (expressed as
percentage of the Control treatment) as a function of
time to anthesis for mid-shade interval. Open circle:
shading treatments from Exp. 2; filled circles:
shading treatment from Exp. 3. LSD: least
significant difference.
FIG. 3
40
-30
Anthesis
0
,
0
8
1
,
6
0
20
0.0
60
Problem: No temperature response functions for sunflower grain growth were available at the time OILCROP-SUN was formulated. Functions for leaf responses were used as
a substitute.
Approach: Plants were grown in controlled temperature glasshouses and embryo growth rates and durations determined.
Conclusions: Embryo growth rate (Fig. 4) and duration (Fig. 5) response functions were determined. The interaction betwen these variables resulted in continuous reductions
of embryo size with temperatures above 20°C (Fig. 6). The cardinal temperatures (Tb, Topt) for grain growth duration ( -1°C and 34°C) were rather different to those for leaves
( 4°C and 24°C). Reference: Chimenti et al., 2000, Field Crops Research (in press).
Temperature effects on grain size.
50
Fig. 2. Proportion of seed setting, in each sector of
the head, as a function of the ontogenetic stage at
the beginning of the shading treatment.
70
Ontogenic stage
CASE 2.
1
,
2
0
80
50
0.0
Days from FS 5
LD (days)
Center
LSD
90
6
Fig. 10 Leaf expansion rate during the quasi-linear
growth phase (LERlg) as a function of SLN for
selected target leaves L8 through L25. Curves
fitted by eye.
Low N
Ncell (millions)
y=-180,3+361,9
(r 2=0,94)
Relative mbryo final weight (%)
2500
-x / -3,976
Shading
(g N m )
e
Fig. 1. Relationship between number of floral
primordia per apex and days from floral stage (FS)
5. (start of floret differentation). Floret differentiation
ceases at FS 8. FS5 occurred 32 days before
anthesis, which, in turn, take place 56 days after
emergence.
100
-2
3000
1.0
Proportion of seed setting
Primordia apex
-1
3500
Filled seeds
(% of control)
CASE 1.
High N
4
Fig. 11 Diagram of envelopes for relationships of
Pmax’ and LERlg with specific leaf nitrogen for
leaves of different positions and N supply levels.
Curves fitted by eye to outlying individual data
points for each variable.
2
Fig. 12 Dynamics of cell number (Ncell) in
unemerged leaves 9 of hydroponically grown
sunflower plants under high () and low ()
nitrogen supply.
FIG. 12
0
-15
-10
-5
Days before leaf appearance
0