Download The role of ammonia in plant physiology

The role of ammonia in plant
physiology
Ineke Stulen, Ana Castro, and Luit J. De Kok
Laboratory of Plant Physiology
University of Groningen
The Netherlands
N is essential – amino acids and
proteins
N uptake and assimilation
NH3
nitrate
ammonium
N assimilation - root
{
nitrate
ammonium
NO3- and NH4+
actively taken up
by transporters
N assimilation - root
{
{
nitrate
ammonium
NO3- and NH4+
actively taken up
by transporters
NO3- reduced, and
transported
N assimilation - root
{
{
{
nitrate
ammonium
NO3- and NH4+
actively taken up
by transporters
NO3- reduced, and
transported
NH4+ attached to a
C skeleton (GS)
N assimilation - root
{
{
{
{
{
nitrate
ammonium
NO3- and NH4+
actively taken up
by transporters
NO3- reduced, and
transported
NH4+ attached to a
C skeleton (GS)
amino acids
formed
used in protein
synthesis
N assimilation - leaf
{
{
NO3- reduced
NH4+ attached to a
C skeleton
N assimilation - leaf
{
{
{
{
NO3- reduced
NH4+ attached to a
C skeleton
amino acids
formed
used in protein
synthesis
Atmospheric NH3 deposition
NH3 taken up
dissolved in apoplast
NH4+ formed
NH4+ assimilated by
glutamine synthetase(s)
Atmospheric NH3 deposition
NH3 taken up
dissolved in apoplast
NH4+ formed
NH4+ assimilated by
glutamine synthetase(s)
M. Pérez-Soba, 1995
Atmospheric NH3 as N source
NH3
proteins
amino acids
substomatal
cavity
mesophyll
GOGAT
GS
NH4+
GS - glutamine synthetase – high affinity for NH4+
Atmospheric NH3 as N source
underlying physiological processes
series of experiments with
Brassica oleracea (curly kale)
exposed to a range of NH3
concentrations (0 - 8 µl l-1) for
one week
controlled environmental
conditions
in nutrient solution, with and
without nitrate
Atmospheric NH3 as N source
underlying physiological processes
{
{
contribution to the
N requirement for
growth?
effect on root
NO3+ uptake ?
A. Castro, 2006
Atmospheric NH3 as N source
underlying physiological processes
Total nitrogen content
[N] μmolg FW
Increase in total N and amino
acids up to the highest [NH3]
d
1250
c
-1
1000
b
750
b
a
500
b
a
250
a
a
a
Plants grown with nitrate in the
nutrient solution
0
0.0
-1
4.0
6.0
“Metabolic detoxification” –
capacity of the GS/GOGAT
system to assimilate NH4+ -
d
100
c
75
b
50
25
8.0
Free amino acid content
125
μmol g FW
2.0
a
is high over the whole range
a
a
a
a
a
a
0
0.0
2.0
4.0
-1
[NH3] μl l
6.0
8.0
Atmospheric NH3 as N source
underlying physiological processes
Increase in fresh weight / 7 days
Total nitrogen content
b
d
1250
[N] μmolg FW
7.5
c
c
b
750
gFW
-1
1000
b
a
500
a
250
a
a
a
5.0
2.5
b
b
b
b
a
a
b
a
a
0.0
0
0.0
2.0
4.0
6.0
8.0
0.0
2.0
4.0
6.0
8.0
-1
[NH3] μl l
-1
μmol g FW
d
100
c
75
b
50
25
growth (increase in fresh
weight) is reduced at 6 and
8 µl l-1 NH3
Free amino acid content
125
a
a
a
a
a
a
a
0
0.0
2.0
4.0
-1
[NH3] μl l
6.0
8.0
although “detoxification” is
still possible, shoot and root
growth are reduced!
Atmospheric NH3 as N source
contribution to N nutrition
Control
4 μl l-1 NH3
+ NO3-
- NO3-
+ NO3-
- NO3-
Biomass S
1.19c
0.29a
1.17bc
1.03c
Biomass R
0.24b
0.35cd
0.10a
0.35abcd
DW %
S
8.9a
17d
12bc
12a
Total N
S
618c
414a
917e
803d
AA
S
14b
9a
73d
64d
Total N
R
317c
202a
348c
339c
AA
R
11a
13a
24c
25c
Experiments with B. oleracea, grown in nutrient solution,
+ and – NO3-, fumigated with 4 µl l-1 NH3 (Castro, 2006)
S shoot; R root; biomass production in g; N and amino acids (AA) in µmol g-1 FW
Plants can grow well with NH4+ as sole N source
Atmospheric NH3 as N source
contribution to N requirement for growth
N requirement for growth can be defined as
Nrequirement = (RGR) x Ncontent
in which RGR is the relative growth rate
g g-1 day-1
4 µl l-1 NH3 as sole N source can contribute
considerably (70-80%) to the N requirement
for growth
in agreement with theoretical calculations (Stulen et al, 1998) and
Raven (1998)
Atmospheric NH3 as N source
effect on root uptake
Does fumigation with
4 µl l-1 NH3 reduce root
NO3- uptake?
reduced N compound
Root NO3- uptake
Atmospheric NH3 as N source
effect on root uptake
Net nitrate uptake rate
-1
-1
(μmol g FW day )
Does fumigation with
4 µl l-1 NH3 reduce root
NO3- uptake?
150
125
(a)
c
100
75
b
50
a
25
75
60
c
45
b
30
a
15
Net sulphate uptake rate
-1
-1
(μmol g FW day )
15
N Nitrate uptake rate
-1
-1
(μmol g FW day )
0
(b)
30
b
b
24
18
a
12
6
0
0
0
4
8
0
4
8
-1
[NH3] μl l
[NH3] μl l-1
signal – specific AA
Atmospheric NH3 as N source
underlying physiological processes
{
{
{
{
contribution to the N
requirement √
effect on root uptake
√
nutrient vs toxin? both
mechanisms of NH4+
toxicity?
Atmospheric NH3
proposed mechanisms of toxicity – evidence?
1. Insufficient “detoxification” capacity
– no evidence
2. Shortage of sugars?
Atmospheric NH3
shortage of sugars?
Shoot soluble sugar
-1
(μmol g FW)
6
(a)
5
b
4
3
a
2
a
a
a
a
1
0
(b)
Root soluble sugar
-1
(μmol g FW)
2.0
1.5
abc
1.0
abc
c
c
0.5
b
a
0.0
0
4
The impact of NH3 on
soluble sugar content in
shoot (a) and roots (b).
+ NO3- and – NO3treatments are given in
dark and light-grey bars,
respectively.
8
-1
[NH3] μl l
2. “Shortage of sugars? – no evidence
Atmospheric NH3
proposed mechanisms of toxicity
1. Insufficient “detoxification” capacity no evidence
2. Lack of sugars for the assimilation of NH4+ no evidence
3. Cation imbalances – impaired root uptake ?
4. Ethylene response
experiments in nutrient solution
[NH3] 0 – 8 µl l-1
yearly average concentration:
6.6 µg m3 – 9.3 nl l-1
5.1 µg m3 – 8.0 nl l-1
peak concentrations:
> 2 µl l-1
soil/root compartment
Atmospheric NH3 – nutrient or toxin?
nutrient
detoxification
inhibition of growth
toxin
gradual - depending on plant species
The role of NH3 in plant functioning
With the current knowledge on the impact of
atmospheric NH3 on plant functioning it is hard
to establish cause-effects relations.
The physiological basis the phytotoxicity of
atmospheric NH3 is still largely unknown.
There is no clear-cut transition in the level of
metabolism of the absorbed atmospheric NH3
and its phytotoxicity.
The effect of atmospheric NH3 on plants might
be strongly dependent on the soil nutrient
status.
The role of NH3 in plant functioning
With the current knowledge on the impact of
atmospheric NH3 on plant functioning it is hard
to establish cause-effects relations.
The physiological basis of the phytotoxicity of
atmospheric NH3 is still largely unknown.
There is no clear-cut transition in the level of
metabolism of the absorbed atmospheric NH3
and its phytotoxicity.
The effect of atmospheric NH3 on plants might
be strongly dependent on the soil nutrient
status.
The role of NH3 in plant functioning
With the current knowledge on the impact of
atmospheric NH3 on plant functioning it is hard
to establish cause-effects relations.
The physiological basis of the phytotoxicity of
atmospheric NH3 is still largely unknown.
There is no clear-cut transition in the level of
metabolism of the absorbed atmospheric NH3
and its phytotoxicity.
The effect of atmospheric NH3 on plants might
be strongly dependent on the soil nutrient
status.
The role of NH3 in plant functioning
With the current knowledge on the impact of
atmospheric NH3 on plant functioning it is hard
to establish cause-effects relations.
The physiological basis of the phytotoxicity of
atmospheric NH3 is still largely unknown.
There is no clear-cut transition in the level of
metabolism of the absorbed atmospheric NH3
and its phytotoxicity.
The effect of atmospheric NH3 on plants might
be strongly dependent on the soil nutrient
status.