Plant Phyisiol. (1968) 43, 345-350
Inhibition of Water Uptake in Sugar Beet Roots by Ammonia'
Darrel M. Stuart2 and Jay L. Haddock
Southwest Branch, Soil and Water Conservation Research Division,
Agricultural Research Service, United States Department of Agriculture, Logan, Utah
Received September 25, 1967.
Abstract. Ammonium sulfate, ammonium carbonate or ammonia gas inhibited water
uptake in sugar beet roots whenever the pH was sufficiently high to cause the production of
ammonia. When ammonia was removed by aeration, inhibition of the water uptake by roots
was rapidly reversed. ATP at 0.2 mm appeared to either wholly or partially prevent the
ammon,ia-induced inhibition of water uptake by roots. ATP may be involved in maintaining
the structure of water pathways through the root. In roots lacking epidermis, ammonia did
not inhibit water uptake by the roots. This may indicate that the site of the inhibition lies
within the root epidermis.
During a previou,s study we observed that sugar
beets grown in the greenhouse or out-of-doors in a
nutrient solution (pH 7.6-8.0) using ammonium
suilfate as the ni,trogen source wilited severely on h,o,t
summer days. Sugar beets ireceiving poitassium
nlitraite as a nitrogen soturce sthowed little, if any,
wiliting. On ciloudy days or ait night, no difference
in wiilting wa's observed between the treatments.
lit appeared that amimonia may have been interfering
with the movement of water thrrotugh the sugar
beeit plant.
Several investigators have reported that respiration inhibitor's anid/o,r un!oouplers such as cyanide
(2, 3, 15,16, 17, 19), aziide (2,13, 19), 2,4-dinitrophen,ol (16), fluoiride (2), i'odoacetate (2), arrsenate
(2), phenylurethiane (2), and lack of oxygen (15,
20) decrease the movement oif w,alter int'o or oult of
coleolptille segmenits, root segments 'or initact roots.
Ammonia (NH3) and/or undi ssocia'ted ammonium
hydroxide, hereinafter called ammonia, mlay also act
as respi,ration inhibitors. AlItschuil et al. (1) showed
that treating cotton seed wiitih ammonia inhibited
respiration in boith mature and immature seeds.
V:nes and Wedd:n,g (24,26) found that ammon.a
inhbted resp.rat.on in excised bar'ey roots, garclen
bee't di,skq, leaf d.sks of sp:nach antd sugiar beets
and garden beet root m:toc'hondr.a. They fouiind
that the degree o,f inh'b tion was related to pH,
since pH controls the amount of ammon:a present
in solutitons contan:ng ammon um ion's (NH,').
Since ammoni(a acts as a 'respiration inhibitor,
oeii might expecit that ammonia would also reduice
or inhibilt wiater uptake by sugar beet roots.
Materials and Methods
Materials. Suga,r beet (Betal vulgaris L. var.
ilonlogerim) seeld was germinated in moiist vermiiculiite and mo'istened with one-hialIf strength Hoagland
Illo. 1 nutrient solution as neeided. Ait the 3- to
4-leaf stage the seedlings were transferred t'o 4-liter
polyethylene containers fi'lled with one-half strength
Hoagliand no. 1 nutrient solution with fulll strengthl
n-inor elements and iron added as sodium ferric
ethylenedi'am'ine di- (o-hydroxyphenylacetate) (8).
One seedling wa's pliaced in each conitaiiner. The
solutions were aerated conisitanitly land renewed
weekly. Dei,onized, water was used for all solutions.
Plants oif the same age varied in size; therefore,
the pl4ants were used fior experimental purposes
when the top of the main rooit reached 8 to 12 mm
in diameter.
Methods. A modific,ati,on of Kramer's apparatus
(10) was used to measure water uptake by the
sugar beet rooit (fig 1). An experimenit was initiated by removing a plant from the nutrient solution
3-way stopcock
-1
1 In cooperation with the Utah Agricultural Experiment Station, Logan. Utah. Approved as Utah Agricultural Experiment Station Journal Paper No. 648.
2 Present address: Soil and Water Conservation
Research D,ivision, Agricultural Research Service,
USDA, Box 8858 University Station, Reno, Nevada
89507.
IF
meter
I
111
stick|
I 1
rl
.I.I.
(
capillary tubing7
to vacuum
IO
I
I
-41rc
screw
..InC
lmrn
gum rubber
beaker.o.
FIG. 1. Apparatus for measuring the rate of water
uptake by excised sugar beet roots.
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345of Plant Biologists. All rights reserved.
Copyright © 1968 American Society
346
PLANT PHYSIOLOGY
and placing the roots inito a liter beaker filled with
deionized aeratted waiter, nuatrient solution, or a
dilute buffer solution. By using this open beaker
arrangement, solutions could be changed and ammontia or ammonium salts convenienitly added.
Aeration was accomplished by buibbling air through
an aquarium stone directly into the beaker. Temperaiture varied firom 21° to 24° during the course
of all the experiments.
The planit was topped just below the last leaf
scar, and the root was gently slipped into the gum
rubber tubing an(d ,sealled by tightening a piece of
so-fit wiire a-round the tubing. Thirty centimeters
of mercury suction or, in some experiments, no
suction wats applied ito the enid of the capilillary tube
and afiter a few minutes the system was checked
for leaks 'and cleared of bbubbles. A drop of mercu,ry was introduced into ithe capidllary tutbe through
the right-hiand stopcock and the irate of its movement was recorded. Readings were taken every 20
minuites unltil the rate of waiter uptake became
steiady, usu.ally tabouit 1 htour. The roots were then
lifted 'out of the water and an ammonium salt or
ammonia gas was added to the scolution. Tihe roots
w'ere repliaced in the soluition and readings were
continued.
The roots utsed va'ried in size, weiight, sulrface
area, and amounit of wa;ter moved per roolt per unit
of time; lbecautse olf this, all movement of the
mercury droplet was recorided as percenit initia:al rate.
The initial rate was (taken as the rate of movement
jlsit before the itreiatmenit was tapplied.
In measuring water uptake in Hoagiland's onehalf strength nutrient solution with added lammonium carbonate anid ditlute buffers with added
amimonium chl'oride, aeration was stopped just before ,the ammonium salt was added and was not
resumed for 20 minutes. This prevented the removial of amm'onia from the nutrientt solution until
aeration was resumed.
Wihen ammonia gas rather than ammonium
carbonate or ammonium chloride was used the ammoniia gas was introduced 'into ithe aeration stream
b)y 'plaicinig 'a sol1ution 'of about 0.5 M ammonlium
hydroxide into a flask an'd passing air over the top
of 'the solution. The regular aeration stream was
wilth'drawn 'from the water containing the roots,
anid the .air containing the ammonia was introduced
into 'the water until the pH )reacheid 8.4 't'o 8.5. The
ai'r containing the ammonia was then withdrawn
from 'the fsollu'tion and the 'regular aeratiion stream
was again introduced.
Aidding ammonia to pH 9.0 injured some of the
roots, causing them 'to iturn dark. Wlhen the roots
tuirned dark water uptake greatly increased and then
becanme erratic. At greater t!han pH 9.0 all roots
were damaged when aimmonia and/or ammonium
salts were present in the concentrations we used.
Roots that had been broken or mechanically damaged showed water uptake similar to the ammoniadamaged roots.
Results
InhiUition of Water Uptake by Ammonia. In
each of the experimen'ts 'the 'addition of ammonium
carbonate or NH3 raised the pH to 8.2 to 8.4 and
wate.r uptake dropped to less than 5 % of the
initial rate ('fi'g 2, 3, 4, 6, 7). A's ammonia wa's removed from the water or nuttrien't solution by the
aeration stream, (tihe pH dropped to 7.5 (to 7.7, or
when NH3 was added to 7.3 to 7.4, and water uptake
aga'in resumed. After restumption, 'the ra(te of water
uptake reached a peak and then decreased (fig 2, 3).
In nutnienit solution this decrease was not noted
(fiig 4). Results with 0.5 and 0.25 mM ammonium
carbonate, noit shown, were 'similar. R'oo.ts p1aced
in water without added ammonium carbonate s'howed
a general decrease in wlater .uptake wi'th time.
When isuction wias not applied, 'the initial 'rajtes
were much 'lower 'than when suction was applied.
T'h'e heights of the waiter uptake peaks after ammonia ha'd been removed were somewhat and unaccountably variable (fig 3). When 'ammonia was
added instead of ammonium carbonate the peak was
much smaller and returned to only 25 t'o 50 % of
the initial rate (fig 7).
To eliminate the possibility that high pH alone
inf,hibilted water upitake by sugar beet roots, 0.25 mm
potassium carbonate was us;ed instead of amtmonium
carbonate (,fig 5). Upon 'addition of the pota(ssium
carbonaite, the pH of the water 'increased to 9.4 and
remained above 9.0 for the remainder of the experimen't. Instead of inhibiting the uptake o-f water,
as did am'monium carbonate, the rate of water
up'take flurctuated unaccountably, but did not fall
below 50 % of the initial rate. Restoration of
aeration had little or no effect on water uptake.
Wilth the dillute 'buffeers, the added ammonium
sulfate had 'little, 'if any, effecot on the rate of water
uptake at pH 6 and 7 (fig 8, 9). At these pH's
the water uptake was similar to that with water at
pH 6.3 or with potasslium carbonate at pH 9.4.
However, when the piH was raised ito 8.0 or 9.0 the
added ammonium sulfate acted in ithe 'same m'anner
as ammonium carlbonate o'r ammonia gas, rapidly
reducin,g water uptake to 'less 'than 5 % of the initia.l
rate. Water uptake returned Ito the intitial rate or
greater when ammonia wias 'removed by 'the aeration
stream. In contras,t to the phosphate buffers
(fig 8), 'the tris ibuffers (,fig 9) showed a much
increased water uptake rate after the removal of
the ammonia.
Water Uptake in Response to Added Adenosinetriphosphate (ATP) and Ammonium Carbonate.
Ammonia has been shown to inhibit both the photosynthetic formation (11) and the oxidative formation (6,18, 24, 26) of ATP. Perhaps, ATP is
involved in maintaining the structure of water pathways in varilous tissues. Kramer (10) and Slatyer
(21) both emphasize that respiration is closely
connected with 'the uptake of water by various
plant tissues.
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347
STUART AND HADDOCK-INHIBITION OF WATER UPTAKE BY AMMONIA
The ef fecot of ATP on water uaptake was determined in much ,the same manner as the other experimenits. The sugar beet roots were immersed
in 0.1 mM ATP (disodium salit) at the beginning
of the experiment and anotheir (increment of 0.1 mm
ATP was added 40 minutes later. Ammonium
caribonate was added 20 minuites after the qast addition of ATP. Aeratiion was continuous except for
add 1.0mM
10
a 20-minuite periold after the addition of ammonim
carbonate. Suction was applied ait 30 cm Hg.
The paittern of water uptake by sugar beet roots
wiith added ATP and aimimonium cairbonate is quite
unlike the pattern where ammonia was added and
ATP was not (fig 10). However, it doeis resemble
the pafttern of water uptake iin experiments witth
buffers at pH 6 and 7, Where ammonia was ex-
add 0.25mM
2
O
0NH4)2C03
100
-0
S
o
K2C03
pH9.2
100
pH2
remove
add
air
pH77
0~~~~~~~~~~~~
O75-
:D0
:D
H20
50
w
:t
DH~7 a4.
aH7
pH
pH9.4J
6.3-
~0
25-
D)H 84
0
25~
pH77
10
20
30
40
50
MINUTES
add l.OmM
:
a
H-
75
146
* 3
NHl4pHO3 -H
,
;
oo
-H
Cl-
O~~~
pH6.3
:D
0~~~~~~~~~~
WC
~:oD25
pH
pH
LJ
w
e ,)
< 4-'
LLH
'
w
0
10
20
30
MI NUTES
4050
0
10
2030
MINUTES
FIG. 2. (top, left) Ammonium carbonate and the rate of water uptake by sugar beet roots in water at 30 cm
Hg suction. Continuously aerated. A typical replication.
FIG. 3. (middle,left) Ammonium carbonate and the rate of water uptake by sugar beet roots in water at 0.0
cm Hg suction. Continuously aerated. A typical replication.
FIG. 4. (bottom, left) Ammonium carbonate and the rate of water uptake by sugar beet roots in one-lhalfstrength Hoagland no. 1 nutrient solution at 30 cm Hg suction. Average of 2 replications.
FIG. 5. (top, right) Potassium carbonate and the rate of water uptake by sugar beet roots in water at 30
cm suction.
Average of 4 replications.
FIG. 6. (middle. right) Ammonia (NH3) and the rate of water uptake by sugar beet roots in water at 30 cm
suction. Continuouisly aerated. Ammonia (NH,) added until pH 8.3 to 8.5 was attained. A typical replication.
FIG. 7. (bottom, right) Ammonia (NH3) and the rate of water uptake by sugar -beet roots in water at 0.0
cm suction.
Continuously aerated. Ammonia (NH) added until pH 8.3 to 8.5 was attained. A typical replication.
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Copyright © 1968 American Society of Plant Biologists. All rights reserved.
34
PLANT PHYSIOLOGY
<
~~~~~add
air
H
50
LU
7
pH6 0
25H
4
H
Z
add i.OmM
\(NH4)2S 4
100
remc,
w
U
0
0'air
air
c-j
------
-
air
75-
LLJ
0
LU
a-
CL
F--
LLI50pH
7O0
LL
U
atl
25
100
F-
add10mM
'~(NH SO
\0 H4)2S 44---_-_-_
o
75removet
75-air
50pH80
25
add
air
0
10
20 30
MINUTES
40
50
MINUTES
FIG. 8. (left) Anmmonium sulfate anid the rate of iwater ul)take bv sugar beet roots in 10 mAr poit;ssiuiiuu puhosphate buffer at pH 6, 7, and 8 and at 30 cm Hg sucttion. Average of 4 replications.
FIG. 9 (right) Ammonium sulfate aand the rate of i vater uptake by sugar beet roots iu 50 i-n\i tris lufuttr at
pH 7, 8, and 9 at 30 cm11 Hg suction.
treinely lo\v because o,f the low pH, alud with
potassiuim carbonate (compiare fig 10 with fig 5,
8, 9). ATP, alone, did not increase the initial rate
of water uptlake, buit it did appear to have reversed,
partially at least, the ammonia inidulce(d in'hibition of
vwater illtake in suigar beet roots.
ff(Vter Uptakc in Roots Lacking Epidermis.
Veldstra and Bo-oy (23) observed tha,t ni-dilamyl
acetic acid (DAA) has a pronouinced synergistic
actioIn wilth auxins, causing root cells to swell and
bturst. Burstrom (4) found that 10 juM DAA ruptuire(l epidermal cells of wvheat roots xvithotut any
appat rent (lamage to the eiidodermiiis. Santdstroi
(21), uising wheat roots w-ith their epidermis eCmove(d by DAA, foundicl the concent,raltio-n ot tht
xylemii sal) to be abovtt the samle .is the nutrie nt.
solltttion in which they were placed. It inay be that
the roo,t epidermis contains the site 4 the ammld
induced inhibition of water utptake.
Stugar beets wx ere growii as previou si, delscribed
and(1 Sandstrom's method (21) xarxs tised( to remiove
the ep"idernis wxith 20 JlM DAA. WVIater uptake oft
roots wax nimasured as befo,re in the lpresence ot
0.25 milAI amimilloinitim carbonate xvithi and wvithout
the DAA treatmleilt. .\Iicroscopic and(l visuial observatioins sho,wed that 40 1oo DAA treatment had
damaged the sugar beet roots, caLusing tlark necrotic
slpots to appear oli the small rootlets. Becatise of
this damage, resuilts of tIle 40 MM DAA treatmeint
are i)Ot incltl(ued in this report. Damage in the
20 Mm DAA treatment was noit apparent but this
loes Ilot elinlia<te the possibility of daInage.
A:\mmilonlitiui carbonate did nlot ilahibit water uiptake by DAA treated roots (fig 11). In the
untreatedl roots, however, ammon'iu1m carbonate nhlibitedl wat(-r ipl)take as in the other experiments.
Ro.t, treated with 20 MiM DAA behaved very illuch
like roots that had been treated with ammonium
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Copyright © 1968 American Society of Plant Biologists. All rights reserved.
STUART AND HADDOCK-INHIBITION OF WATER UPTAKE BY AMMONIA
349
sugar rbeet roots. However, both the experiments
using potassium carbonate and buffers indicate thait
this was not 'the clause since the high pH obtained
with potassium carbonate or buffers, in -the absence
77 -w °of ammonia, did not inhibit water utptake. Many
workers (5, 22, 25) have shown thalt as pH increases above pH 7, the toxicity of ammonium
compounds increases and that this is due to an
increase in the percent of ammonia present. AmIATP
monia because of its small size, diffuses very rapidcly
across cell membranes and into the cytoplasm, while
the ammonium ion (NH4,) diffu,ses much morc
slowly (7, 9, 14, 25).
-pH76
ATP
io
50
MI NUTES
FIG. 10. Ammonium carbonate an.d the rate of
water uptake by sugar beet roots in vvater at 30 cm
Hg suction. Average of 4 replications.
add 0.25mM
w
I-
a
+
XoSNH4)2CO3
100
remove
\.
air
\\l
75
"0-
'ad
---------
--- -+
reated
D
c)
|
50.
LLI C
o:
pH
o
0
/untrteated
pH
8.4
25
ad
air
7.7
10
).02 mM DAA
C
20 30
MI NUTES
FIG. 1 1. WVater uptake in sugar beeet roots treated
with 20 jaM n-diamylacetic acid and 0.25 mM ammonium
carohonate in water at 30 cm Hg suctiotn. Average of
4 replications.
sulfate buffered at pH 6 or 7 or ppotassium carbonate, except that the initial rate was higher.
Again, water uptake varied somewh;at over short
periods of time, but there wasn't the! almost complete inhibition that occurred in the un ntreated roots.
Discussion
T'lhe experiments with ammonium. carbonate and
ammonia gas would not eliminate p1 H, per se, as
the cause of the inhibition of water movement in
Ammonia appears to be the cause of the inhibition of water uptake in sugar 'beet roots since at
a pH greater than 7 water uptake was inhibited in
less than 5 minutes, whereas NH4, did not cause
any inhibition of water uptake at pH 7 or less.
At thils pH the concentration of NH4, is very high
and that of ammonia extremely low. Vines and
Wedding (24) reported that ammonia increased
rather than decreased the permeability of the red
beet roo.t disks as measured by 'the 'loss of anthocyanin. However, owing to the high concentration's of ammonia 2.0 to 8.0 mM that they used,
damage to the
undoubtedly occurred. At a
pH of about 9.2, half 'of the ammonia is in the
NH3 form. In this study sugar beet roots were
damaged w'ith 1.0 mii ammonium sulfate at pH 9.0
and some roots still showed damage with 0.5 mWI
ammonium sulfate at pH 9.0.
-0
It wou.ld appear that ATP successfully reversed
'the ammlonlia-induced inhibition oif water uptake in
sugar beet roots. However, we cannot eliminate
the possibilifty that ATP may have damaged 'the
sugar beet roots. Damaged roots had a pabtern of
water uptake simillar to the ATP-treated roots in
that ammonia did not reduce water uptake in eilther
case, but (the inibia,l rate -of uptake was much
slower with ATP-treated roo,ts than with damagefd
roots. The ATP-trealted 'roots appeared to be
normal and showed no visible damage.
Barring any injury by ATP, it appears that
ATP can overcome, at least partially if not completely, the ammonia-induced inhibition of water
uptake. Admittedly, the evidence 'is not overwhelming, buit it may indicate that A'TP or similar
compounds are directly involved in maintaining the
porosity of various tissues to water.
Ammonium carbonate dAd not inhibit water uiptake by DAA-treated roots (fig 11). Roots treated
wi'th 20 /LM DAA behaved very much like roots
that had been treated with ammonium sulfate bulffered at pH 6 and 7 or potassium carbonate, except
the initial rate was greater. Since ammonia did
not inhibit water uptake in roots lacking epidermis,
it is possible that the site of the ammonia-induced
inhibition of water uptake lies within the root
epidermis, if DAA did not damage the 1root other
than by.the removal of the ep.dermis.
'tissue
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350
PLANT PHYSIOLOGY
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