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Potassium (K+) is an important macronutrient for plant growth and productivity. It fulfills important functions and it is widely included in fertilization management strategies to increase crop production. Although K+ is one of the most abundant elements of the earth crust, its availability to plants is usually limited leading to severe reduction in plant growth and yield. In plants, K+ shortage induces several responses at different levels: morphological, physiological, biochemical, and molecular. Activation of signaling cascades including reactive oxygen species, phytohormones (ethylene, auxin, and jasmonic acid), Ca2+, and phosphatidic acid is also triggered. In this review, we summarize the main of these adaptive responses evolved by plants to cope with K+ deficiency in the rhizosphere.
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Potassium deficiency in plants: effects and signaling cascades
Chokri Hafsi Ahmed Debez Chedly Abdelly
Received: 16 February 2013 / Revised: 3 January 2014 / Accepted: 8 January 2014 / Published online: 24 January 2014
ÓFranciszek Go
´rski Institute of Plant Physiology, Polish Academy of Sciences, Krako
´w 2014
Abstract Potassium (K
) is an important macronutrient
for plant growth and productivity. It fulfills important
functions and it is widely included in fertilization man-
agement strategies to increase crop production. Although
is one of the most abundant elements of the earth crust,
its availability to plants is usually limited leading to severe
reduction in plant growth and yield. In plants, K
induces several responses at different levels: morphologi-
cal, physiological, biochemical, and molecular. Activation
of signaling cascades including reactive oxygen species,
phytohormones (ethylene, auxin, and jasmonic acid), Ca
and phosphatidic acid is also triggered. In this review, we
summarize the main of these adaptive responses evolved
by plants to cope with K
deficiency in the rhizosphere.
Keywords K
deficiency Plants Tolerance Signaling
is one of the essential macronutrients playing an
important role in plant growth and development (Leigh and
Wyn Jones 1984; Marschner 1995; Schachtman and Shin
2007; Wang and Wu 2013). It is the most abundant cation
in plants and is associated or involved in several physio-
logical processes supporting crop growth and development
(Pettigrew 2008). The importance of K
in photosynthesis,
osmoregulation, enzyme activation, protein synthesis, ion
homeostasis, and the maintenance of anion–cation balances
in plants is well documented (Bhandal and Malik 1988;
Marschner 1986; Zhao et al. 2001; Kanai et al. 2007).
Uptake of this cation by plant roots has been found to be
accomplished by at least two distinct kinetic systems
(Epstein et al. 1963): (1) high-affinity systems with
apparent affinities (Km) for K
in the range of about
4–35 lM and operating at low external K
usually within 0.2 mM K
(Epstein et al. 1963; Maathuis
and Sanders 1994), showing saturation at about 300 lM
external K
and (2) constitutive low-affinity components,
which have an average Km of about 3–19 mM and oper-
ating when the external K
concentration is higher than
1 mM. The high-affinity K
uptake is mediated by K
transporters whereas K
absorption in the low-affinity
range of concentrations is mediated by K
channels (Ma-
athuis and Sanders 1996). More recently, molecular, elec-
trophysiological, and reverse genetics approaches in plants
identified genes encoding K
transporters and K
´guez-Navarro 2000;Ve
´ry and Sentenac 2003; Gierth
and Ma
¨ser 2007). K
channels are classified into three
groups according to their structural features: shaker-type
channels, two-pore channels, and cyclic nucleotide-gated
channels (reviewed by Ashley et al. 2006). K
are present in three families of membrane proteins: the K
uptake permeases (KT/HAK/KUP), the K
(Trk/HKT) family, and the cation proton antiporters (CPA)
(Gierth and Ma
¨ser 2007).
Although K
is not assimilated into organic matter, it is
well documented that K
deficiency severely impacts plant
metabolism. In K
-deficient rice roots, gene ontology
analysis identified the expression of several genes which
were classified into 13 functional categories including
metabolic process, membrane, cation binding, kinase
Communicated by P. Wojtaszek.
C. Hafsi (&)A. Debez C. Abdelly
Laboratoire des Plantes Extre
ˆmophiles, Centre de
Biotechnologie a
`la Technopole de Borj Ce
BP 901, Hammam-Lif 2050, Tunisie
Acta Physiol Plant (2014) 36:1055–1070
DOI 10.1007/s11738-014-1491-2
activity, transport, protein modification, and response to
stress (Ma et al. 2012). Although plant responses to K
deficiency are well documented at the physiological and
transcriptional levels, the regulatory mechanisms underly-
ing these changes are poorly understood (Ashley et al.
2006). To cope with K
deficiency, plants must sense
changes in its availability and transmit the signals to
modulate their metabolism. Recent works have clarified
sensing and signaling pathway that involve components
like ROS, ethylene, Ca
, auxin, jasmonic acid, and
phosphatidic acid (Shin and Schachtman 2004; Armengaud
et al. 2004; Li et al. 2006; Jung et al. 2009; Hafsi et al.
2008,2009). This article discusses soil K availability and
dynamics, physiological roles of K
, plant’s responses to
conditions, and signaling cascades regulating
responses to K
Potassium in the rhizosphere
K is abundant in the earth crust but in the soil solution K
is present at relatively low concentrations (Grattan and
Grieve 1992). It represents the fourth most abundant ele-
ment of the lithosphere. However, only a low fraction
(1–4 %) on the surface of clay humus particles of the soil is
bioavailable. The major fraction is part of mineral com-
positions and is unavailable to plants (Mengel and Kirkby
1982). Sparks (1987) distinguished four principal forms of
potassium in the soil: potassium as ionic form K
(in soil
solution, 0.1–0.2 %), exchangeable K (1–2 %), not
exchangeable K (fixed in 2:1 clays 1–10 %), and unavail-
able form of K (90–98 %). In the soil, the latter form is
found in primary aluminosilicate minerals, which include
muscovite micas, K-feldspars and biotite (Bertsch and
Thomas 1985). The first two forms of soil K are considered
to be labile and meet the immediate requirements of
growing plants, while the last two forms are considered
non-labile and are responsible for the long-term supply of
K to plants (Askegaard et al. 2003). As shown in the K
cycle (Fig. 1), K is in perpetual transformation. The dif-
ferent forms of K in soils are dynamically interconverted
by fixation and release processes (Yawson et al. 2011). A
balance exists between the different forms. The exchange is
defined as a balance maintained between soil solution K
and exchangeable K through fixation and release processes.
The amount of K that is made available depends on the
intensity of weathering, time of deposition, and the pro-
portion and the type of clay minerals that are present in the
soil (Sparks and Huang 1985). The release of K from the
exchangeable pool is often much lower than K
uptake by
plants (Sparks and Huang 1985) and consequently K
concentration in certain soils is a limiting factor for plant
growth (Johnston 2005).
Potassium roles and K
deficiency effects on plants
is a vital macronutrient for plant growth and develop-
ment (Schachtman and Shin 2007). It is the most abundant
cation in plants, with up to 6 % of the plant dry weight
(Raven et al. 1976). The physiological roles of K
in plants
are often divided in to biophysical and biochemical func-
tions (Fig. 2). As proposed by Leigh and Wyn Jones (1984)
these might be distinct in different cellular compartments.
Unavailable K in primary
minerals (muscovite
micas, K-feldspars
Non-echangeable K+
Soil solution K+
Plants and animals residues
Echangeable K+
Fig. 1 Potassium cycle in the
1056 Acta Physiol Plant (2014) 36:1055–1070
In the cytoplasm, K
plays important biochemical func-
tions and it cannot be replaced by other solutes. In the
vacuole, it is mainly involved in the regulation of osmotic
potential and turgor. K
has several functions in plants. In
phanerogams, both pollen germination after reaching the
stigma and the development of pollen tube depend on the
transport of inorganic ions like Ca
and K
plasma membrane of the pollen and/or the pollen tube
´et al. 1995; Taylor and Hepler 1997). K
flux into
non-germinated pollen can initiate an osmotic influx nec-
essary for germination suggesting that K
can serve as an
osmoticum thus maintaining the turgescence pressure of
pollen cells (Obermeyer and Blatt 1995). It was demon-
strated that the inward-rectifying K
channel SPIK, a
Shaker-type channel, is involved in K
uptake into pollen
tubes across the plasma membrane and then regulates
pollen tube growth and development (Mouline et al. 2002).
is the most abundant cation in the cytoplasm of a
plant cell (as well as cells in other organisms), typically
reaching 100–200 mM (Walker et al. 1996). Considering
its high concentration in the cytoplasm and chloroplasts,
neutralizes soluble anions (e.g., acid organic anions,
inorganic anions) and the macromolecular insoluble anions
and stabilizes the pH between 7 and 8, which is the optimal
pH for most enzymatic reactions in the cytosol (Marschner
plays important role in the secretion of mugineic
acid family phytosiderophores (MAs). In fact, under iron
deficiency conditions, the secretion of these compounds
from the roots to the rhizosphere represents an important
step in the acquisition of sparingly soluble iron (Fe) in
strategy II plants (Ro
¨mheld 1987; Marschner and Ro
1994). Iron is then taken up in the form of a MAs-iron
complex. Sakaguchi et al. (1999) demonstrated that MAs
are secreted from iron-deficient barley roots together with
in an almost equimolar ratio suggesting that MAs are
secreted in the form of monovalent anions via anion
channels using the K
gradient between the cytoplasm and
the extracellular medium.
activates more than 50 enzymes (Bhandal and Malik
1988). Protein synthesis needs high K
(Blaha et al. 2000) because of its intervention in the syn-
thesis of ribosomes and aminoacyl-tRNA, protein synthesis
from charged tRNA transfer and messenger RNA turnover
(Evans and Wildes 1971). K
stimulates the uptake and
transport of NO
within the plant, as K
serves as the
accompanying counter cation (Blevins et al. 1978). K
deficiency inhibits nitrogen assimilation. In two cultivars of
cotton (Liaomian 18 and NuCOTN99
) differing in their
tolerance to K
deficiency, Wang et al. (2012) observed a
reduction in nitrate reductase activity and protein content,
whereas the content of amino acids increased. In maize
plants exposed to K
deficiency for 5 weeks, Qu et al.
(2011) observed a reduction in the activities of important
nitrogen metabolism enzymes (nitrate reductase, glutamate
dehydrogenase, glutamate synthase, urease, glutamic–
pyruvic transaminase, and glutamic–oxaloacetic transami-
nase). In Arabidopsis, Armengaud et al. (2004) demon-
strated that the expression of three nitrate transporter genes
(AtNRT2;1,AtNRT2;3, and AtNRT2;6) was reduced by K
deficiency and increased after K
resupply. Similar results
have been observed by Ma et al. (2012). These authors
observed a decrease in the expression of two nitrate
transporter genes (Os02g0112600 and Os02g0689900)in
rice roots subjected to K
starvation for 5 days.
Furthermore, K
is important for the fixation of
molecular nitrogen by root nodules. Mengel et al. (1974)
studied the effect of K
supply on Vicia faba growth and
fixation based on experiments adding
gas to the
growth compartment. Control plants showed higher con-
tents of
N in the soluble amino fraction and in the protein
fraction of various plant organs as compared with K
deficient plants. This was explained by a better supply of
nodules with carbohydrates in plants optimally supplied
with K
, resulting in a higher carbohydrate turnover in the
nodules. More recently, in Trifolium repens, Høgh-Jensen
(2003) observed that K
deprivation induced changes in
the relative growth of roots, nodules, and shoots rather than
changes in N and/or carbon uptake rates per unit mass or
area of these organs. In this context, it is important to
conduct experiments to clarify in more detail the effects of
deficiency on nitrogen uptake and metabolism.
is also implicated in carbohydrate accumulation
since its deficiency was found to result first in an accu-
mulation followed by a strong decrease of these
Regulation of
stomatal movement
Protein synthesis
Maintenance of
cation-anion balances
Fig. 2 Major roles of K
: inside the plant, K
has a wide range of
functions/reactions including (1) the generation of turgor as it
constitutes the main cation in the vacuole, (2) photosynthesis, (3)
control of stomatal aperture, (4) protein synthesis, (5) maintenance of
cation–anion balances, and (6) enzymes activation by acting as a
cofactor in enzymatic reactions
Acta Physiol Plant (2014) 36:1055–1070 1057
compounds (Fageria et al. 1997; Cakmak 2005). It also
plays an important role in transport of solutes through the
phloem including sucrose movement from shoot to root
and to the sink tissues such as fruits (White and Karley
2010). The carbon flow may be stopped because of the
inhibitory effect of K
-deficiency stress on sink activity by
disturbing the water status of the plant (Kanai et al. 2007).
More recently, Kanai et al. (2011) reported that K
ciency may reduce aquaporin activity, consequently sup-
pressing root hydraulic conductance and water supply to
the growing stem for diameter expansion and leaf for
transpiration suggesting the existence of close coupling
between aquaporins and K
-channel transporters. K
important role in maintenance of photosynthesis too.
Indeed, it influences this physiological process mainly
through ATP synthesis, the activation of the enzymes
involved in photosynthesis, CO
uptake, the balance of the
electric charges required for photophosphorylation in
chloroplasts, and acts as the counter ion to light-induced
flux across the thylakoid membranes (Marschner 1986).
deficiency leads to a reduction of photosynthetic
activity in a number of ways. Zhao et al. (2001) reported
that K
deficiency modifies the chloroplast ultrastructure
of cotton leaves. The control had more well-defined grana
stacks and extensive stroma lamellae with very small
amounts of starch granules. In K
-deficient plants, chlo-
roplasts were filled with large starch granules and con-
tained significantly more plastoglobuli together with fewer
grana. It was demonstrated that guard-cell osmoregulation
is mediated by K
and its counter-ions malate and Cl
(Talbott and Zeiger 1996) in addition to sucrose which
plays important role in regulating stomatal opening (Tal-
bott and Zeiger 1996; Kang et al. 2007;Ni2012). The
negative impact of K
deficiency on photosynthesis, tran-
spiration, and stomatal conductance is well documented
(Degl’Innocenti et al. 2009; Kanai et al. 2011), whereas
photorespiration and respiration are rather stimulated
(Bottrill et al. 1970; Singh and Blanke 2000). Biochemical
factors may explain the reduced photosynthesis observed
especially under severe K
deficiency (Bednarz et al. 1998;
Tester and Blatt 1989) such as the need for K
in the
photosynthetic transfer of radiant energy into chemical
energy through the production of ATP (Havlin et al. 2005).
The energy that is derived from ATP is required to power
metabolic processes in plants that produce carbohydrates,
proteins, and other compounds essential for crop produc-
tivity and quality. In addition to reduced photosynthesis
under plant K
starvation, the transport of photoassimilates
away from the source tissues is also restricted (Cakmak
2005; Gerardeaux et al. 2010; Kanai et al. 2011). Zhao
et al. (2001) observed in cotton plants that reduction in leaf
photosynthesis by K
deficiency was mainly associated
with low chlorophyll content, poor chloroplast
ultrastructure, and restricted photoassimilates transport,
rather than limited stomata conductance.
In plants, K
deficiency-related symptoms include
brown scorching and curling of leaf tips as well as chlo-
rosis between leaf veins, which is directly bound up with
chlorophyll degradation (Xiao-Lei et al. 2012). Often, K
deficiency symptoms first appear on the older leaves
(Fageria et al. 2001). This may represent a survival strategy
adopted by plants exposed to K
-shortage stress consisting
in the mobilization of K
from mature and senescing
organs to make it available for the youngest ones (Hewitt
1963; Cochrane and Cochrane 2009). Cakmak (2005)
suggested that those signs could be associated with the
oxidative degradation of chlorophyll by reactive oxygen
species (ROS), whose production is enhanced by K
deficiency. The reduction in photosynthetic activity and the
restriction in sucrose export from the source to the sink
organs result in a strong accumulation of carbohydrates in
the source leaves leading to an over-reduction of the pho-
tosynthetic electron transport chain that enhances the pro-
duction of ROS (Cakmak 2005) (Fig. 3).
Several authors have described a reduction in leaf area
under K
deficiency (Zhao et al. 2001; Degl’Innocenti
et al. 2009; Gerardeaux et al. 2010). Jordan-Meille and
Pellerin (2004) demonstrated in maize plants that the
limitation of leaf elongation by K
deficiency was not
related to restricted carbohydrates availability in leaf
growing zones, suggesting that this restriction was proba-
bly due to altered plant–water relations. More recently,
Gerardeaux et al. (2010) suggested that the occurrence of
organ size (leaves, internodes) reduction in cotton was not
directly caused by lack of photoassimilates and cell turgor
but can be due to sugar starvation of sink tissues probably
through sugar signaling.
Plant responses to K
Morphological responses
The plant root system is characterized by a high level of
plasticity. This plasticity is possible due to a continuous
production of new meristems (Williamson et al. 2001). The
root morphology is influenced by the plant environment
and especially by the availability of nutrients (Thaler and
Pages 1998). Root morphological and physiological traits
are important for absorbing nutrients from the soil (Satt-
elmacher et al. 1994). Yang et al. (2003) showed that the
-efficient rice genotypes had a longer root system than
the inefficient ones under low-K
conditions. Chen and
Gabelman (2000) in tomato and Hafsi et al. (2011)in
Hordeum maritimum and Catapodium rigidum species
showed that K
deficiency increases root length, hence
1058 Acta Physiol Plant (2014) 36:1055–1070
contributing to the increase of exploring surface to enhance
the K
uptake. In cotton, Xiao-Li et al. (2008) indicated
that K
accumulation was positively correlated with two
features of the root architecture: the root length and the
root surface area. The genetic variation in root traits and
nutrient acquisition of 10 lentil genotypes was investigated
by Gahoonia et al. (2006). These authors suggested that the
ability of the most performing genotype (Barimasur-4) in
acquiring K
could be partly ascribed to its ability to
produce a longer root system covered with longer and
denser root hairs. Finally, in cotton, Brouder and Cassman
(1990) and Han-Bai et al. (2009) found that the K-efficient
cultivar had more root surface area than the K-sensitive
The reduction in the number and the growth of lateral
roots was observed in barley (Drew 1975) and Arabidopsis
thaliana (Shin and Schachtman 2004) grown under low-K
concentrations. This was related to an increase in ethylene
concentration in response to K
deficiency (Shin and
Schachtman 2004). Yet, this response was found to be not
necessarily accompanied by gene activation related to
ethylene signalization and metabolism (Armengaud et al.
2004). Interestingly, lesser export of photoassimilates from
leaves under K
lacking conditions, thereby inhibiting root
growth has been also reported (Cakmak et al. 1994;
Degl’Innocenti et al. 2009; Gerardeaux et al. 2010). Nat-
ural variation of root traits such as primary root length,
lateral root length, and total root size within 26 Arabidopsis
accessions was observed by Kellermeier et al. (2013)
which reveals different strategies to adapt to K
Quantitative trait loci (QTLs) analysis using Col-
09Catania-1 populations revealed several loci determin-
ing specific subsets of root architectural traits (Kellermeier
et al. 2013).
Reduced photosynthesis
Restricted transport
of sucrose into roots
Inhibition of phloem
accumulation Over-reduction of
electron transport
Increased ROS
Reduced leaf surface area
Increased uptake of
Mg, Na, and Ca
Regulation of root architecture and K+ uptake
systems leading to increased K+ uptake efficiency
Recirculation of K+ from older
leaves to younger ones
Increased K+ utilization efficiency
Fig. 3 Schematic representation of possible consequences of K
deficiency on various processes in plants. In K
-deficient plants, the
decline in photosynthetic activity and restricted phloem export of
photoassimilates out of the leaves led to an oxidative stress, which has
deleterious effects on plants. This resulted in growth and productivity
reductions. To cope with K
deficiency, plants develop some
tolerance strategies including increased K
uptake and utilization,
increased uptake of other cation like Na
, and Ca
to replace
in some physiological and biochemical functions, and recircula-
tion of K
from older leaves to youngest ones
Acta Physiol Plant (2014) 36:1055–1070 1059
One of the early reactions of K
deficiency stress in
plants is its impact on dry matter partitioning between roots
and shoots. The root/shoot DW ratio under K
depends on the species and conditions of culture (Andrews
et al. 1999). An increase in this parameter was observed in
wheat (Andrews et al. 1999), mulberry (Tewari et al.
2007), Brassica oleracea (Singh and Blanke 2000), and H.
maritimum (Hafsi et al. 2011). In contrary, Cakmak et al.
(1994) and Marschner et al. (1996) reported a decrease in
root/shoot DW ratio in K
-deficient plants whereas no
statistically significant effect was found in maize (Tewari
et al. 2004), C. rigidum (Hafsi et al. 2011) and A. thaliana
(Gruber et al. 2013) plants. More works are needed to
explain this variation in dry matter partitioning between
roots and shoots under K
-deficient conditions.
Physiological responses
It is well established that K
deficiency induces the acid-
ification of extracellular medium. Minjian et al. (2007)
demonstrated that root K
absorption depends on the
activity of the proton pumps (H
-ATPases) and the
occurrence of K
transporters on the cellular membrane.
The degree of H
expulsion can be used as a criterion of
tolerance to K
deficiency. Chen and Gabelman (2000)
observed in tomato strains that K
uptake efficiency is
associated with high net K
influx coupled with low pH
around root surfaces. The proton-electrochemical gradient
may energize K
uptake, and indeed it is used by some KT/
KUP/HAK transporters, which co-transport K
and H
´guez-Navarro 2000). Under K
-deficient conditions,
Arend et al. (2004) observed in young stems of poplar
plants, an up-regulation of specific isoforms of the plasma
membrane (PM) H
-ATPase in the vessel-associated cells
of the wood ray parenchyma suggesting a key role for these
-ATPases in unloading K
from the xylem stream.
In addition, in response to mineral deficiency, a change
in membrane potential is a spectacular effect. For instance,
deficiency triggers a membrane hyperpolarization of
root cells; which appears within just a few minutes after the
decrease in external K
(Spalding et al. 1999; Nieves-
Cordones et al. 2008; Wang and Wu 2010). It is not clear
how plant cells detect the changes in membrane potential
(Schachtman and Shin 2007). The hyperpolarization of
plasma membrane following K
deficiency may activate
channels and enhance K
uptake (Sentenac et al. 1992;
Gambale and Uozumi 2006). Nieves-Cordones et al. (2008)
demonstrated that the expression of the gene (LeHAK5)
encoding the tomato high-affinity K
transporter HAK5 in
tomato root cells correlated with the steady-state plasma
membrane potentials of plants but not with their cyto-
plasmic K
concentrations nor with the concentrations of
in the external medium.
Under a severe K
deficiency, cytosol K
is maintained constant at the expense of its vacuolar pool
(Leigh and Wyn Jones 1984; Walker et al. 1996; Ottow
et al. 2005). This can be due to a cytosol acidification
(Walker et al. 1996) and a high increase of putrescine
concentration (up to 10 mM) (Bruggemann et al. 1998;
Dobrovinskaya et al. 1999), which inhibits the tonoplast
fast-activating vacuolar canal under K
deficiency pre-
venting its reabsorption from the cytosol to the vacuole
(Pottosin and Este
´vez 2003). K
mobilization from the
vacuole into the cytosol is much higher in K
barley genotypes than inefficient ones (Memon et al. 1985).
Under moderate K
deficiency, Leigh and Wyn Jones
(1984) have suggested that plants maintain the K
centration in the cytoplasm in the range of 100–200 mM to
ensure biochemical processes at the expense of the K
concentration in the vacuole. Recently, it has been reported
in Arabidopsis that a tonoplast-located calcineurin B-like
protein (CBL2 or CBL3) may form a complex with their
target CBL-interacting protein kinase (CIPK9) which
phosphorylates an unknown tonoplast-located K
porter or channel like the tandem-pore K
channel 1
(TPK1), leading to K
efflux from the vacuole into the
cytoplasm (Pandey et al. 2007; Liu et al. 2013). This
phenomenon is important to regulate K
between these two compartments under K
The presence of Na
, and Ca
is important in
alleviating the effects of K
deficiency. Increased con-
centrations of Na
, and Ca
in response to K
deficiency and decreased concentrations of these cations
under high concentrations of K
have been reported (Diem
and Godbold 1993; Pujos and Morard 1997; Jordan-Meille
and Pellerin 2008; Gerardeaux et al. 2009; Hafsi et al.
2011; Hernandez et al. 2012). The occurrence of such
antagonisms may contribute to maintain constant the cation
balance for a given organ irrespective of K
changes. K
and Mg
have in part similar roles such as
osmoregulation, enzyme activation, and cellular pH control
(Marschner 1986). Na
could replace K
in non-specific
physiological and biochemical functions (Flowers and
¨uchli 1983) (Fig. 3).
Under K
-deficient conditions, an early decrease of K
concentration in barley roots was detected (Hafsi et al.
2008,2009) which may be due to its translocation from
roots to shoots during K
deprivation period. Hafsi et al.
(2011) demonstrated that the lower K
requirement of H.
maritimum to express its optimal growth compared to C.
rigidum can be attributed to its higher efficiency to acquire
and transfer K
to shoots.
Species and genotypes tolerant to nutrient deficiency
have also developed specific morphological and physio-
logical mechanisms allowing them to acquire sufficient
1060 Acta Physiol Plant (2014) 36:1055–1070
quantities of a specific nutrient (uptake efficiency) (Satt-
elmacher et al. 1994; Xiao-Lei et al. 2012). K
efficiency determines the ability of plants to take up K
under low soil K
availability (Samal et al. 2010). Chen
and Gabelman (1995) showed that the tomato genotype
576 responded morphologically to K
deficiency by pro-
liferating root length thereby increasing root surface areas
to capture K
whereas in the genotype 483 a physiological
response was demonstrated by high net K
influx. Chen and
Gabelman (2000) concluded that the mechanism for strain
483 in acquisition of K
in comparison to 320 and 525
strains was due to a high absorption capacity.
Variation among plants in the capacity to take up K
from the external medium has been investigated in several
works (Guoping et al. 1999; Xiao-Li et al. 2008; Han-Bai
et al. 2009; Xiao-Lei et al. 2012). Under K
conditions, a potato K-efficient genotype had about a
twofold higher K
uptake rate than a K-inefficient one
(Trehan and Sharma 2002). Under K
starvation, plant
survival depends not only on its uptake efficiency, but also
on its utilization efficiency (KUE), i.e., the quantity of
biomass produced per unit of absorbed K
et al. 1994; Rengel and Damon 2008). This parameter is
commonly measured in relation to vegetative growth,
particularly in forage crops (Woodend and Glass 1993).
Sauerbeck and Helal (1990) defined nutrient use efficiency
as plant yield per unit of nutrient supply. In both H.
maritimum and C. rigidum, KUE for shoot biomass pro-
duction increased as K
concentration in the culture
medium decreased (Hafsi et al. 2011). Mahmood et al.
(2001) showed that wheat genotypes differed considerably
in terms of their growth response, K
uptake and utiliza-
tion efficiency under different K
treatments. Damon et al.
(2007) reported a genotypic variation between canola
genotypes in response to changes in K
availability in the
external medium which was due to differences due to
genotypic differences in both the uptake and the utilization
of K
Regulation of K
transport systems
Plants have a wide variety of transport systems that play
crucial roles in K
uptake, redistribution, and homeostasis
(see, e.g., the reviews by Ve
´ry and Sentenac 2003; Britto
and Kronzucker 2008; Alema
´n et al. 2011; Wang and Wu
2013) which may be related to the fact that most plants are
sessile organisms and must be able to adapt to the varia-
tions of K
concentration in the medium as suggested by
Fairbairn et al. (2000). In A. thaliana,71K
and channels were identified (Chen et al. 2008). The wheat
High-Affinity K
transporter1 (HKT1), which is mainly
expressed in roots and permeable to both K
and Na
represents the first plant K
transporter to be cloned
(Schachtman and Schroeder 1994). Functional character-
ization in oocytes demonstrated that EcHKT1 and EcH-
KT2, two K
transporters from Eucalyptus camaldulensis,
are implicated in K
and Na
uptake as has been shown for
HKT1 (Fairbairn et al. 2000). In Arabidopsis, the High-
Affinity K
Transporter5 (AtHAK5) and the K
Arabidopsis K
Transporter1 (AtAKT1) have been iden-
tified as the two major systems involved in K
uptake in
the high-affinity range (Gierth et al. 2005; Rubio et al.
2008; Pyo et al. 2010; Kim et al. 2012). A lesion of either
AtHAK5 or AKT1 significantly impairs the high-affinity
) uptake (Hirsch et al. 1998; Gierth et al. 2005;
Pyo et al. 2010). Furthermore, a reduction in the ability of
akt1-1 Arabidopsis mutant to grow in K
-deficient condi-
tions was observed by Hirsch et al. (1998). In addition to
mediating primary K
uptake, these transport systems play
important role in K
redistribution between different plant
organs. The outward-rectifying K
channel (SKOR), a
Shaker-type efflux channel found in stellar parenchyma,
mediates K
secretion from root cells into the xylem sap
for transport toward shoots (Gaymard et al. 1998). These
authors observed a 50 % reduction in shoot K
content in
SKOR-deficient A. thaliana mutants, while root content
was unaffected (Gaymard et al. 1998). K
recirculation in
the phloem was conducted by another Shaker-type channel,
AKT2, which was identified in phloem cells using b-glu-
curonidase reporting and in situ hybridization (Lacombe
et al. 2000; Deeken et al. 2000; Che
´rel et al. 2002; Ga-
jdanowicz et al. 2011). Stomatal regulation is also con-
trolled by the function of some other channels. The inward-
rectifying channels, KAT1 and KAT2, mediate K
into guard cells during stomatal opening (Schachtman et al.
1992; Pilot et al. 2001), while the outward-rectifying K
channel GORK is responsible for K
release from guard
cells during stomatal closure (Hosy et al. 2003).
Several works demonstrated that K
deficiency induces
quantitative and qualitative changes of K
uptake systems
(Benlloch et al. 1989; Maathuis and Sanders 1995). The
high-affinity uptake mechanism has been shown to be
inducible, whereas the low-affinity system may be consti-
tutive (Glass and Dunlop 1978; Fernando et al. 1990).
Transcriptome analysis of rice roots during the response to
starvation, Ma et al. (2012) revealed that several genes
in ion transporter families were markedly up-regulated,
suggesting that they may play important roles in rice
responses to K
Regulation of K
Gene response to nutrient starvation has been characterized
as early responsive genes, responding rapidly and often
non-specifically, and late responsive genes, induced by
long-term stress conditions, which is considered to be more
Acta Physiol Plant (2014) 36:1055–1070 1061
specific for nutrient deprivation (Hammond et al. 2004;
Schachtman and Shin 2007). Shin and Schachtman (2004)
demonstrated that K
deficiency provokes an increase in its
absorption. This activation is generally associated with an
induction of high-affinity transporters and is considered as
the main adaptation mechanism to K
deficiency (Ashley
et al. 2006). Wang et al. (1998) demonstrated, in a work on
barley and wheat roots, that K
deficiency is accompanied
by a fast up-regulation at transcriptional level of high-
affinity transporters HKT1 which is suppressed following
resupply. Similar results were observed in the Arabi-
opsis AtHAK5 transporter (high-affinity K
(Armengaud et al. 2004, Shin and Schachtman 2004;
Gierth et al. 2005) and in Oryza sativa OsHAK1 (Ban
et al. 2002) and Capsicum annuum CaHAK1 (Martı
Cordero et al. 2004) transporters. According to Shin and
Schachtman (2004), AtHAK5 is rapidly and transiently
(after 6 h of K
deficiency) activated whereas Gierth et al.
(2005) indicate that this transporter is only activated after
48 h and this activation is maintained at least 5 days after
deficiency. In Nicotiana rustica roots, the expression
level of the gene NrHAK1 was higher in the root tip and
was up-regulated when exposed to K
starvation (Guo
et al. 2008). In Arabidopsis, Qi et al. (2008) demonstrated
that AtHAK5, a plasma membrane uptake mechanism,
plays a role during severe K
deprivation. In Arabidopsis,
Kim et al. (2012) identified a transcription factor RAP2.11
as a component in the response to low K
through regu-
lation of the high-affinity K
uptake transporter AtHAK5
and other components of the low-K
signal transduction
pathway. More recently, Hong et al. (2013) demonstrated
that the expression of four transcription factors [dwarf and
delayed flowering 2 (DDF2), jagged lateral organs (JLO),
basic helix-loop-helix 121 (bHLH121), and transcription
initiation factor II_A gamma chain (TFII_A)] was up-
regulated by K
deficiency suggesting that these factors
can bind to the HAK5 promoter and then activate HAK5
In K
-deficient rice roots, Ma et al. (2012) observed an
up-regulation of three OsHAK genes. These authors sug-
gested that the increase in expression levels of genes
encoding K
transporters may be a rapid and direct strat-
egy for plants to increase K
-uptake and overcome K
Regulation of K
Electrophysiological studies on Arabidopsis roots revealed
an activation of inwardly rectifying K
channels in
response to K
deficiency (Maathuis and Sanders 1995;
Hirsch et al. 1998). The Arabidopsis AtAKT1 channel,
which localized to the plasma membrane, is involved in K
uptake in the high-affinity range of concentrations (Hirsch
et al. 1998; Gierth et al. 2005). In this species, no tran-
scriptional activation of AKT1 channel was observed (Pilot
et al. 2003; Hampton et al. 2004) suggesting a posttran-
scriptional activation of this channel (Li et al. 2006). In the
calcium section, the regulation of AKT1 by CBLs and
CIPK23 is described. Other works demonstrated a down-
regulation of transcription of SKOR and AKT2 in Arabi-
dopsis (Maathuis et al. 2003; Pilot et al. 2003). These
channels are involved in long distance transport of K
Therefore, it was suggested that the decrease in their
expression is important to limit its recirculation between
plant tissues and organs. Such alteration of long distance
transport can be also important to insure a communi-
cation between shoots and roots concerning K
(Pilot et al. 2003). In Triticum aestivum roots, an up-reg-
ulation of the mRNA level of the TaAKT1 gene was
observed in response to K
starvation (Buschmann et al.
2000). More recently, it was demonstrated that AKT1
channel is regulated by some other regulators, such as
AtKC1 and SNARE. AtKC1 is identified as a-subunit that
negatively regulates the Arabidopsis inward Shaker chan-
nel (AKT1) activity (Duby et al. 2008; Wang et al. 2010;
Jeanguenin et al. 2011). Alone, AtKC1 is unable to form a
functional homotetrameric K
channel (Reintanz et al.
2002) but its interaction with AKT1 leads to the formation
of the heterotetrameric AKT1-AtKC1 complex K
whose activation results in inhibition of AKT1-mediated
currents by negatively shifting the voltage dependence
of the Shaker-type K
channel (Duby et al. 2008; Geiger
et al. 2009; Wang et al. 2010) (Fig. 4). As a consequence,
loss through AKT1 can be limited in Arabidopsis roots
under K
- conditions (Geiger et al. 2009; Wang et al.
2010). In addition, Honsbein et al. (2009) demonstrated in
Arabidopsis that AtKC1 selectively interacts with a
SNARE (soluble N-ethylmaleimide—sensitive factor pro-
tein attachment protein receptor) protein SYP121 leading
to the formation of a tripartite K
channel complex which
plays a pivotal role in plant K
nutrition under low-K
stress (Fig. 4).
Signaling cascades
concentration varies widely in time and space. To
ensure an adequate supply of this element, plants possess
many absorption and transport mechanisms (Ve
´ry and
Sentenac 2003; Ahn et al. 2004). However, despite inten-
sive works, it is still not very clear how plants detect and
respond to changes in K
concentrations in media where
they live (Shin and Schachtman 2004; Li et al. 2006;
Schachtman and Shin 2007; Wang and Wu 2010). Recent
studies suggested the involvement of several compounds
considered as signaling molecules, including hydrogen
1062 Acta Physiol Plant (2014) 36:1055–1070
peroxide (H
) (Shin and Schachtman 2004; Shin et al.
2005; Hafsi et al. 2008,2009; Hernandez et al. 2012),
ethylene (Shin and Schachtman 2004), phytohormones
such as auxin and jasmonic acid (Armengaud et al. 2004),
and phosphatidic acid (Hafsi et al. 2008,2009) in response
to K
deprivation. These changes are summarized in
Fig. 4.
Reactive oxygen species (ROS)
Although ROS are conventionally known as toxic mole-
cules for cellular metabolism, recent works suggest that
they can act as messenger molecules. Because of its rela-
tively long life and high permeability across membranes
hydrogen peroxide is considered as a signaling molecule in
plants that mediates responses to abiotic and biotic stresses
(Neill et al. 2002). In roots, H
plays a role in the
signaling cascade involved in the response to K
ciency. These compounds are necessary for the growth of
root hairs and are implicated in root elongation and gene
expression under low-K
conditions. Shin and Schachtman
(2004) and Shin et al. (2005) demonstrated that H
implicated in the regulation of plant response to K
vation. They showed that H
is rapidly accumulated in
response to short-term K
deprivation, triggering the
expression of some genes. In addition, these authors
demonstrated that changes in the kinetics of K
uptake are
due to H
, whose production is localized in a specific
region of the roots that has been shown to be active in K
uptake and translocation. More recently, Hernandez et al.
(2012) observed that H
accumulation under short-term
starvation in tomato was located mainly in the epi-
dermal cells of the elongation zone and the meristematic
cells of the root tip and the epidermal cells of the mature
Sensor ?
CBL 1/9 CPIK23
HAK transcript
surface area ?
Fig. 4 Generic pathway for plant sensing and signaling to K
deficiency. K
deficiency is first perceived by the membrane
receptors and then activates complex intracellular signaling cascade.
The external K
deficiency activates ethylene and calcium signals to
regulate ROS production and the CBL-CIPK23 network, respectively.
CIPK23 phosphorylates and then activates the potassium uptake
channel AKT1. AKT1 activity is also regulated by AtKC1 (a
regulatory K
channel subunit) and SYP121 (a SNARE protein)
leading to the formation of a tripartite complex which plays a pivotal
role in K
uptake. ROS production up-regulates the expression of
potassium transporter HAK5, to enhance K
uptake. Furthermore,
ROS activates phospholipase D (PLD), which hydrolyzes structural
phospholipids to generate phosphatidic acid (PA). PLD may be is also
activated by Ca
. The generated PA can be implicated in the up-
regulation of the expression of HAK5 transporter and/or increased
root hair elongation and primary root growth leading to increased root
surface area and consequently increasing K
Acta Physiol Plant (2014) 36:1055–1070 1063
zones of K
-starved roots. The induction of high-affinity
transporters by K
deficiency was accompanied by an
increase (twofold) of H
production. More interestingly,
triggers a high-affinity K
transporter even for
control plants (Shin and Schachtman 2004). The expression
of RHD2 gene was up-regulated in response to K
ciency, which provides an evidence for the implication of
NADPH oxidase (Foreman et al. 2003)inH
This was confirmed by Shin and Schachtman (2004) using
rhd2 mutant. More recently, Hafsi et al. (2008,2009)
observed an increase in H
production with a maximum
after 6 h of K
deprivation in H. maritimum and H. vulgare
species. The early and transient increase in H
in roots
supports the idea that this molecule could play a signaling
role in response to short-term K
The accumulation of phytohormones like ethylene, jas-
monic acid, and auxin in response to K
deficiency has
been often cited. In Arabidopsis roots, after 6–30 h of K
starvation, the expression of genes coding the enzymes
implicated in the biosynthesis and the production of eth-
ylene increased following K
deprivation (Shin and
Schachtman 2004). The role of ethylene as a messenger
hormone is confirmed by measuring the quantities released
in the atmosphere by plants subjected to K
deficiency and
control plants. An increase (about twofold) in ethylene
production was observed which has been implicated in
regulating gene transcription in response to low-K
centrations (Shin and Schachtman 2004). More recently,
Jung et al. (2009) demonstrated that ethylene is important
for changes in both root hair and primary root growth in A.
thaliana and for the expression of AtHAK5, suggesting
that ethylene signaling acts upstream of ROS when plants
are deprived of K
Although auxin can control the expression of K
channels (Philippar et al. 1999), the mechanisms explain-
ing the changes in the content of this hormone in Arabi-
dopsis plants subjected to K
deficiency are still unknown.
DR5-GUS gene expression, which is marker of auxin
localization, changes in K
-deprived roots. It has been
reported that auxin is accumulated in central cylinder cells
in the distal elongation zone of Arabidopsis roots after K
deficiency (Vicente-Agullo et al. 2004).
The changes in auxin localization, its concentration, and
its sensibility can lead to a restriction of lateral roots
growth under prolonged K
shortage. In Arabidopsis,K
deficiency induced a higher expression of genes implicated
in the biosynthesis and signaling of this phytohormone
(Shin and Schachtman 2004). Ma et al. (2012) indicated
that several auxin-related genes responded to K
ciency in rice.
Jasmonic acid (JA) is considered a member of the signal
transduction pathway in plant responses to environmental
stresses (Kramell et al. 2000; Vigliocco et al. 2002). JA
biosynthesis occurs through the octadecanoid acid path-
way, which starts from the oxidation of polyunsaturated
fatty acids by lipoxygenase and produces a number of
intermediate oxylipins (Stintzi et al. 2001; Howe and
Schilmiller 2002). Several transcripts for proteins involved
in the biosynthesis of JA responded to K
starvation and
resupply indicating that JA levels increase during starva-
tion and rapidly decrease after K
resupply (Armengaud
et al. 2004). A 1.8-fold increase of shoot JA (Troufflard
et al. 2010) and a threefold increase (Cao et al. 2006) are
determined in K
-deficient Arabidopsis plants. The regu-
lation of K
channels by JA (Evans 2003) and polyamines
(Liu et al. 2000) was established and may contribute to K
redistribution between the different cellular compartments
(Amtmann et al. 2004).
Besides its important role in plant growth and develop-
ment, calcium (Ca
) is one of the most important ubiq-
uitous intracellular secondary messengers involved in
signal transduction in plants (Tuteja and Mahaja 2007;
Kudla et al. 2010). It has been documented that low-K
availability increases H
production, which can play a
role as signaling molecule triggering the expression of
certain genes (Shin and Schachtman 2004). This produc-
tion is concomitant with changes in intracellular Ca
concentration (Foreman et al. 2003). More recently, tran-
scriptome analysis of rice root (Ma et al. (2012) identified
nine calcium sensor protein genes showing changes in
expression levels during K
starvation; five were up-reg-
ulated and four were down-regulated.
The increase of Ca
concentration in the cytoplasm can
stimulate NADPH oxidase-mediated ROS production
(Yang and Poovaiah 2002) which then activates some
-permeable ion channels leading to further Ca
influx (Demidchik et al. 2007). Therefore, it was suggested
that Ca
may act as a secondary messenger in response to
deficiency. In Arabidopsis, Xu et al. (2006) and Li et al.
(2006) identified three genes critical for plant growth under
-deficient conditions since encoding two Ca
including calcineurin B-like protein (CBL1 and CBL9) and
their target CBL-interacting protein kinase (CIPK23). The
same authors showed that the protein kinase CIPK23
phosphorylated a voltage-gated inward K
(AKT1). Activation of the CBL–CIPK pathway by Ca
triggers the activation of the AKT1 channel, enhancing K
uptake by roots. The interaction between the CIPKs and
AKT1 involves the kinase domain of the CIPK component
and the ankyrin repeat domain of the channel (Lee et al.
1064 Acta Physiol Plant (2014) 36:1055–1070
2007). An A-type protein phosphatase 2C (PP2C) that
physically interacts and inactivates the AKT1 channel was
also identified by the same authors. Recently, Lan et al.
(2011) documented that PP2Cs interacts with the PPI motif
and the kinase domain to inhibit AKT1 activation by
CIPK-CBL complex through physical binding and
dephosphorylation. Furthermore, these authors identified
that specific CBLs interact with and reduce PP2Cs phos-
phatase activity to recover the CIPK-dependent AKT1
channel activity. More recently, using a transcriptomic
approach on K
-starved rice roots, Ma et al. (2012)
observed that the most genes were identified as kinases
(68 %) and phosphatases (9 %), suggesting that phos-
phorylation and dephosphorylation may be an important
regulatory mechanisms in plant responses to K
Phosphatidic acid
As a selective barrier between cells and their environments,
plasma membrane plays a crucial role in both the perception
and transmission of external information. Recently, it has
been shown that phospholipase D (PLD, EC, in
addition to its catabolic function, has critical roles in cell
signaling cascades (Meijer and Munnik 2003; Navari-Izzo
et al. 2006; Russo et al. 2007). This enzyme hydrolyzes
structural phospholipids (PL) at the terminal phosphate
diester bond, leading to the formation of phosphatidic acid
(PA) and a free head group (Zhang et al. 2003). PA is a
secondary messenger in response to multiple environmental
stresses, including hyperosmotic stress (Munnik et al. 2000),
copper excess (Navari-Izzo et al. 2006), and P deficiency
(Russo et al. 2007). In vivo and in vitro studies on suspen-
sion-cultured rice cells revealed that PLD is activated by
and that this activation involves a protein tyrosine
kinase (Yamaguchi et al. 2004). It has also been suggested
that H
directly modulates the reactive cysteine residues
of protein tyrosine kinase (Meng et al. 2002) and glycer-
aldehyde-3-phosphate dehydrogenase (G3PDH; EC, inhibiting their activities (Schuppe-Koistinen et al.
1994). These authors suggested that in addition to its role in
the inactivation of the dehydrogenase activity of G3PDH on
its catalytic site, H
may also endow G3PDH with the
ability to bind PLD, and the resulting association is involved
in the regulation of PLD activity by H
. In addition, it was
demonstrated that plant PLDs contain a Ca
phospholipid-binding C2 domain and require Ca
activity (Wang 2000). The Arabidopsis genome contains 12
PLD genes, ten of which have the Ca
ing C2 structural fold, whereas the two PLDf proteins con-
tain phosphoinositide interacting pleckstrin homology and
Phox homology domains (Qin and Wang 2002). Knockout of
PLDedecreases root growth and biomass accumulation,
whereas over-expression (OE) of PLDeenhances root hair
elongation and primary root growth and biomass accumu-
lation under severe nitrogen deprivation suggesting that
PLDeand PA play a role in nitrogen signaling (Hong et al.
2009). These authors showed also that under P- and K
deficient conditions, PLDe-OE roots elongated faster than
those of wild type, but the difference was not as great as that
under N-deprived conditions. In two barley species subjected
to a short K
deprivation, a clear relationship among H
production, G3PDH inhibition, and PLD activation was
demonstrated (Hafsi et al. 2008,2009) suggesting a possible
involvement of these three compounds in an early response
to K
starvation. Further works are needed to clarify in more
detail the implication of PLD and PA in plant response to K
Conclusion and perspectives
is an important macronutrient and the most abundant
cation in plants. It accomplishes important functions in
plants including photosynthesis, osmoregulation, enzymes
activities, maintaining the plasma membrane potential, and
protein synthesis. K
deficiency is an abiotic stress that
leads to plant growth and productivity depressions as a
consequence of a wide of perturbations that trigger in
plants. To cope with this constraint plants develop numer-
ous tolerance strategies involving morphological and
physiological modifications and regulation of K
systems which is important for K
uptake and homeostasis
in plant cells under low-K
conditions. However, although
several works are conducted to understand these mecha-
nisms, much remains to be known about the physiological
and molecular mechanisms by which plants detect and
respond to changes in K
concentrations in the external
media (Schachtman and Shin 2007; Wang and Wu 2010).
Hence, it is of major importance to deeply investigate the
complex sensing and signaling pathway in response to K
deficiency. The identification and further examination of the
signaling cascade and valorization of natural variation in
uptake and utilization efficiencies between genotypes
will be essential for an eventual breeding program.
Author contribution Chokri HAFSI designed and wrote
the review. Ahmed DEBEZ checked the English. Chedly
ABDELLY provided scientific advices and supported the
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... Potassium (K + ) is a major nutrient necessary for plant growth and development, accounting for approximately 2-10% of the total dry weight of plants (Leigh and Wyn Jones, 1984). K + plays important roles in enzyme activation, protein synthesis, photosynthesis, turgor, osmotic adjustment, ion homeostasis, and electric neutralization (Römheld and Kirkby, 2010;Kanai et al., 2011;Hafsi et al., 2014), and more than 60 enzymes and several cofactors play direct or indirect roles in these processes (Hawkesford et al., 2012;Vasǎḱ and Schnabl, 2016). K + levels affect the levels of primary and secondary metabolites in plants (Armengaud et al., 2009;Coskun et al., 2017;Chatterjee et al., 2020). ...
... The soil K + content in farmlands is low in large areas of the world, and crops cannot effectively use soil mineral elements (Perry et al., 1972;Hafsi et al., 2014). Coconut trees are grown in acidic soils in southern China, where K + supply is insufficient (Lu et al., 2021). ...
... K + deficiency causes abiotic stress in crops, limiting their yield (Zorb et al., 2014;Qin et al., 2019). Plants respond to K + deficiency at the morphological, physiological, biochemical, and molecular levels (Hafsi et al., 2014). In maize, low K + levels induce lateral root growth, inducing genes related to nutrient utilization, hormones, and transcription factors Ma et al., 2020). ...
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Potassium ions (K+) are important for plant growth and crop yield. However, the effects of K+ deficiency on the biomass of coconut seedlings and the mechanism by which K+ deficiency regulates plant growth remain largely unknown. Therefore, in this study, we compared the physiological, transcriptome, and metabolite profiles of coconut seedling leaves under K+-deficient and K+-sufficient conditions using pot hydroponic experiments, RNA-sequencing, and metabolomics technologies. K+ deficiency stress significantly reduced the plant height, biomass, and soil and plant analyzer development value, as well as K content, soluble protein, crude fat, and soluble sugar contents of coconut seedlings. Under K+ deficiency, the leaf malondialdehyde content of coconut seedlings were significantly increased, whereas the proline (Pro) content was significantly reduced. Superoxide dismutase, peroxidase, and catalase activities were significantly reduced. The contents of endogenous hormones such as auxin, gibberellin, and zeatin were significantly decreased, whereas abscisic acid content was significantly increased. RNA-sequencing revealed that compared to the control, there were 1003 differentially expressed genes (DEGs) in the leaves of coconut seedlings under K+ deficiency. Gene Ontology analysis revealed that these DEGs were mainly related to “integral component of membrane,” “plasma membrane,” “nucleus”, “transcription factor activity,” “sequence-specific DNA binding,” and “protein kinase activity.” Kyoto Encyclopedia of Genes and Genomes pathway analysis indicated that the DEGs were mainly involved in “MAPK signaling pathway-plant,” “plant hormone signal transduction,” “starch and sucrose metabolism,” “plant-pathogen interaction,” “ABC transporters,” and “glycerophospholipid metabolism.” Metabolomic analysis showed that metabolites related to fatty acids, lipidol, amines, organic acids, amino acids, and flavonoids were generally down-regulated in coconut seedlings under K+ deficiency, whereas metabolites related to phenolic acids, nucleic acids, sugars, and alkaloids were mostly up-regulated. Therefore, coconut seedlings respond to K+ deficiency stress by regulating signal transduction pathways, primary and secondary metabolism, and plant-pathogen interaction. These results confirm the importance of K+ for coconut production, and provide a more in-depth understanding of the response of coconut seedlings to K+ deficiency and a basis for improving K+ utilization efficiency in coconut trees.
... Potassium (K) is one of the most essential macronutrients for plant growth and development, and it has essential physiological functions, such as plant osmoregulation, photosynthesis, protein synthesis, ion homeostasis, and enzyme activation (Kanai et al., 2011;Hafsi et al., 2014). Four forms of K exist in the soil, namely, exchangeable K, soluble K, lattice K, and fixed K. ...
... Combined transcriptome metabolome analysis showed that the DEGs and DAMs were associated with biological processes, such as carbohydrate metabolism and photosynthesis. Hafsi et al. (2014) revealed that K stress limits plant leaf growth, which may be due to sugar starvation in stems and leaves. In the present study, genes involved in the TCA cycle, such as CS, IDH, and TCA, were downregulated in apple leaves under LK ( Figure 5), which may induce apple plant growth restriction. ...
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Potassium (K) is one of the most important macronutrients for plant development and growth. The influence mechanism of different potassium stresses on the molecular regulation and metabolites of apple remains largely unknown. In this research, physiological, transcriptome, and metabolite analyses were compared under different K conditions in apple seedlings. The results showed that K deficiency and excess conditions influenced apple phenotypic characteristics, soil plant analytical development (SPAD) values, and photosynthesis. Hydrogen peroxide (H2O2) content, peroxidase (POD) activity, catalase (CAT) activity, abscisic acid (ABA) content, and indoleacetic acid (IAA) content were regulated by different K stresses. Transcriptome analysis indicated that there were 2,409 and 778 differentially expressed genes (DEGs) in apple leaves and roots under K deficiency conditions in addition to 1,393 and 1,205 DEGs in apple leaves and roots under potassium excess conditions, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment showed that the DEGs were involved in flavonoid biosynthesis, photosynthesis, and plant hormone signal transduction metabolite biosynthetic processes in response to different K conditions. There were 527 and 166 differential metabolites (DMAs) in leaves and roots under low-K stress as well as 228 and 150 DMAs in apple leaves and roots under high-K stress, respectively. Apple plants regulate carbon metabolism and the flavonoid pathway to respond to low-K and high-K stresses. This study provides a basis for understanding the metabolic processes underlying different K responses and provides a foundation to improve the utilization efficiency of K in apples.
... Furthermore, K + indirectly affects plant growth and development (Lu 2016c). All these events can be disrupted by K + deficiency which is a type of plant abiotic stress that induces a wide range of responses, including oxidative stress, and results in limited crop growth and productivity (Hafsi et al. 2014;Waqas et al. 2021;Houmani et al. 2022;Johnson et al. 2022). K + starvation makes various responses at different stages, viz., morphological, physiological, biochemical, and molecular (Hafsi et al. 2014). ...
... All these events can be disrupted by K + deficiency which is a type of plant abiotic stress that induces a wide range of responses, including oxidative stress, and results in limited crop growth and productivity (Hafsi et al. 2014;Waqas et al. 2021;Houmani et al. 2022;Johnson et al. 2022). K + starvation makes various responses at different stages, viz., morphological, physiological, biochemical, and molecular (Hafsi et al. 2014). K + deficiency, also called potash deficiency, leads to decreased chlorophyll content, reducing photosynthetic activity and thus minimizing overall agricultural productivity (Hartt 1969;Pier and Berkowitz 1987;Zhao et al. 2001). ...
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Potassium (K⁺) plays a crucial role in plant homeostasis, and its deficiency significantly impacts photosynthesis, triggering a decrease in growth and crop production. K⁺ starvation induced a significant reduction in the net photosynthetic rate, and the drop is associated with resistance of CO2 diffusion through stomatal conductance, mesophyll conductance, and lowered carboxylase activity of Rubisco, electron transport rate of PSII, and with many biochemical limitations. The complex interaction of all the above factors contributed to limiting photosynthesis under K⁺ starved conditions. Low chlorophyll content and poor chloroplast structure may also define photosynthetic processes and causes a decrease in crop growth and productivity under K⁺ starvation. Under abiotic stresses such as drought, waterlogging, temperature, salinity, and heavy metal, the application of exogenous K⁺ promotes plant tolerance by activating the antioxidant system, which limits the overproduction of reactive oxygen species (ROS), avoiding the associated oxidative damages where other signaling molecules such as nitric oxide (NO) and hydrogen sulfide (H2S) may involve. The review highlights the decisive role of exogenous and endogenous K⁺ in modulating diverse physiological and biochemical processes in a healthy and stressful environment. Furthermore, this review appraises the involvement of K⁺ with another signaling molecule in enhancing abiotic stress tolerance in plants. Therefore, this review provides a comprehensive update on the relevance of K⁺ in higher plants. Its exogenous application should be a potential tool, especially in crops under adverse environmental conditions.
... Potassium in liquid fertilizer comes from two primary sources: coconut husk and chicken excreta (Gbenou et al., 2017). The K element in liquid fertilizers is one of the quality parameters because the K element for plants is a regulatory function in several biochemicals related to energy metabolism, protein synthesis, enzyme activation, photosynthesis, and active transport (Hasanuzzaman et al., 2018), deficiency of K mineral in plants resulting in brown leaf edges, shortening of internodes, root stress, and stunted plants (Hafsi et al., 2014;Hasanuzzaman et al., 2018). ...
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Indonesia is an agricultural country that certainly has the potential for agricultural waste and by-products. Some of those in Indonesia are livestock manure, coconut husk, and sugarcane molasses. Utilization of this waste is limited, which is causing various environmental problems such as environmental pollution. The study is aimed to determine the quality of organic liquid fertilizer made by raw material from goat feces-chicken excreta-coconut husk with various sugarcane molasses concentrations (P0= 0%; P1= 5%; P3= 15%; P4= 20%; P5= 25%). The fermentation was carried out anaerobically for 21 days. The parameters of temperature, pH, organoleptic (color and odor), levels of C-organic, nitrogen (N) total, phosphorus (P) total, potassium (K) total, and biological tests were observed. Biological tests were conducted in the growth of mung bean (Vigna radiata) and spinach (Amaranthus tricolor). Data were analyzed using one-way ANOVA. Variations in the addition of molasses sugarcane did not affect the liquid fertilizer's temperature and pH during fermentation. However, the treatments had positive effect on organoleptic test, C-organic, N total, P total, K total, and biological tests. The addition of 15% sugarcane molasses (P3) showed a dominating performance toward most of the parameters tested. The P3 treatment produced liquid fertilizer with a pleasant smell, and the contents of C-organic, total N, total P, and total K were 2.12%, 0.25%, 0.13%, and 0.13%, respectively. and produce spinach as a biological test with plant height, number of leaves, leaf width, stem diameter, and root length were 21.82 cm, 6.66 sheets, 3.59 cm, 4.09 mm, and 14.67 cm, respectively.
... Phosphorus is a commonly limited Plants 2023, 12, 400 6 of 27 macronutrient in soils; deficiencies can lead to impairments in several phosphate-involved metabolic pathways, such as membrane synthesis, nucleic acid synthesis, and enzyme activation [63]. Potassium is another macronutrient in soils and is necessary for the activity of a plethora of enzymes involved in photosynthesis, carbon synthesis, and protein synthesis [64,65]. ...
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In this literature review, we discuss the various functions of beneficial plant bacteria in improving plant nutrition, the defense against biotic and abiotic stress, and hormonal regulation. We also review the recent research on rhizophagy, a nutrient scavenging mechanism in which bacteria enter and exit root cells on a cyclical basis. These concepts are covered in the contexts of soil agriculture and controlled environment agriculture, and they are also used in vertical farming systems. Vertical farming-its advantages and disadvantages over soil agriculture, and the various climatic factors in controlled environment agriculture-is also discussed in relation to plant-bacterial relationships. The different factors under grower control, such as choice of substrate, oxygenation rates, temperature, light, and CO 2 supplementation, may influence plant-bacterial interactions in unintended ways. Understanding the specific effects of these environmental factors may inform the best cultural practices and further elucidate the mechanisms by which beneficial bacteria promote plant growth.
... Asterisks indicates the statistical significance among replicate samples with p-value as *p < 0.05, **p < 0.01 and ***p < 0.005. enzymes which are involved in important cellular processes, such as protein synthesis, starch synthesis, osmoregulation and photosynthesis (Hafsi et al., 2014). Association of several DEGs with important enzymatic functions indicates that K + deficiency may have altered the functional behavior and activities of different enzymes that could lead to modulation of important cellular processes in chickpea. ...
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Potassium (K +) is an essential macronutrient for plant growth and development. K + deficiency hampers important plant processes, such as enzyme activation, protein synthesis, photosynthesis and stomata movement. Molecular mechanism of K + deficiency tolerance has been partly understood in model plants Arabidopsis, but its knowledge in legume crop chickpea is missing. Here, morphophysiological analysis revealed that among five high yielding desi chickpea cultivars, PUSA362 shows stunted plant growth, reduced primary root growth and low K + content under K + deficiency. In contrast, PUSA372 had negligible effect on these parameters suggesting that PUSA362 is K + deficiency sensitive and PUSA372 is a K + deficiency tolerant chickpea cultivar. RNA-seq based transcriptome analysis under K + deficiency revealed a total of 820 differential expressed genes (DEG's) in PUSA362 and 682 DEGs in PUSA372. These DEGs belongs to different functional categories, such as plant metabolism, signal transduction components, transcription factors, ion/ nutrient transporters, phytohormone biosynthesis and signalling, and root growth and development. RNA-seq expression of randomly selected 16 DEGs was validated by RT-qPCR. Out of 16 genes, 13 showed expression pattern similar to RNA-seq expression, that verified the RNA-seq expression data. Total 258 and 159 genes were exclusively up-regulated, and 386 and 347 genes were down-regulated, respectively in PUSA362 and PUSA372. 14 DEGs showed contrasting expression pattern as they were up-regulated in PUSA362 and down-regulated in PUSA372. These include somatic embryogenesis receptor-like kinase 1, thaumatin-like protein, ferric reduction oxidase 2 and transcription factor bHLH93. Nine genes which were down-regulated in PUSA362 found to be up-regulated in PUSA372, including glutathione S-transferase like, putative calmodulin-like 19, high affinity nitrate transporter Frontiers in Plant Science
... K + ions are essential for the optimal growth of plants, given their involvement in cell homeostasis and photosynthesis [12,13]. Deficiencies of this ion have been correlated with lower productivity yields [14], and higher susceptibility to diseases [15]. In addition, sap pH has been proven to be a powerful biomarker in the diagnosis of diseases such as the ones caused by Fusarium Oxysporum in Arabidopsis [16]. ...
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The direct quantification of plant biomarkers in sap is crucial to enhancing crop production. However, current approaches are inaccurate, involving the measurement of non-specific parameters such as colour intensity of leaves, or requiring highly invasive processes for the extraction of sap. In addition, these methods rely on bulky and expensive equipment, and they are time-consuming. The present work reports for the first time a low-cost sensing device that can be used for the simultaneous determination of sap K+ and pH in living plants by means of reverse iontophoresis. A screen-printed electrode was modified by deposition of a K+-selective membrane, achieving a super-Nernstian sensitivity of 70 mV Log[K+]−1 and a limit of detection within the micromolar level. In addition, the cathode material of the reverse iontophoresis device was modified by electrodeposition of RuOx particles. This electrode could be used for the direct extraction of ions from plant leaves and the amperometric determination of pH within the physiological range (pH 3–8), triggered by the selective reaction of RuOx with H+. A portable and low-cost (<£60) microcontroller-based device was additionally designed to enable its use in low-resource settings. The applicability of this system was demonstrated by measuring the changes in concentration of K+ and pH in tomato plants before and after watering with deionised water. These results represent a step forward in the design of affordable and non-invasive devices for the monitoring of key biomarkers in plants, with a plethora of applications in smart farming and precision agriculture among others.
... The availability of plant nutrients is crucial in drought stress adaptation and avoidance. Potassium (K), known as a stress alleviator plant nutrient, controls water losses from the plant (Farahani et al., 2019), delays leaf chlorosis and senescence (Weng et al., 2007), and mitigates the adverse consequences of drought stress by regulating the physio-biochemical characteristics (Hafsi et al., 2014) such as activating enzymes, osmoregulation, and membrane transport in cotton (Zahoor et al., 2017a), corn (Matłok et al., 2022), rice (Weng et al., 2007), and oilseed (Farahani et al., 2019). Drought increases ROS production by chloroplasts, peroxisomes, and mitochondria, and this could be further enhanced in K-deficient plants (Kaushal and Wani, 2016). ...
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Potassium (K) is known for alleviating the negative effects of abiotic stresses on plants. To explore the functions of K in controlling reactive oxygen species (ROS), antioxidant activities, and osmoregulation in sesame under drought stress, a pot experiment was conducted with three K levels (0, 60, and 120 kg ha–1, recorded as K0, K1, and K2, respectively) and exposed to well-watered (WW, 75% ± 5% soil relative water content) and drought-stressed (DS, 50% ± 5% soil relative water content) conditions. The results showed that DS stimulated the production of ROS such as increased hydrogen peroxide (H2O2), leading to lipid peroxidation as characterized by higher malondialdehyde (MDA) and, consequently, resulting in the decline in relative water content (RWC) and photosynthetic pigments as compared with WW plants. These adverse effects were exacerbated when drought stress was prolonged. Concurrently, K application alleviated the magnitude of decline in the RWC, chlorophyll a, and chlorophyll b, and plants applied with K exhibited superior growth, with the optimal mitigation observed under K2 treatment. Additionally, DS plants treated with K exhibited lower lipid peroxidation, higher antioxidant activities, and increased osmotic solute accumulation in comparison with plants under K deficiency, which suggested that exogenous K application mitigated the oxidative damages and this was more prominent under K2 treatment. Noteworthily, proline and soluble protein, respectively, dominated in the osmotic regulation at 3 and 6 days of drought stress according to the analysis of the quantitative comparison among different osmotically active solutes. Based on the correlation of the aforementioned traits and the analysis of variance on the interaction effects of drought stress and potassium, we propose that superoxide dismutase (SOD), glutathione reductase (GR), and MDA could be critical indicators in balancing ROS detoxification and reproduction. In summary, our studies suggest that optimized K application keeps a balance between the production of antioxidants and ROS and simultaneously affects osmoregulation to alleviate the damage from drought stress.
... Potassium (K) is an essential soil nutrient for plants that plays a vital role in plant physiological and biochemical processes including photosynthesis, cell growth, metabolism, assimilation rate, and accumulation of sugars (Sattar et al., 2019;Wang et al., 2013). Potassium deficient plants are more susceptible to drought, frost, high salt content, stunting, spotting, leaf curl, reduced growth, and productivity shortfalls (Hafsi et al., 2014;Zhang et al., 2020). Supplying plants with sufficient quantities of nutrients is critical for increasing agricultural output. ...
This study presents a simple method for determination of potassium in microliter scale using a paper device together with a smartphone. The method begins with the ion-pair extraction of dibenzo-18-crown-6-K+ complex into dichloromethane with an excess amount of calmagite. The aqueous phase containing the remaining calmagite is transferred to the paper device, where a smartphone is used to capture the color and convert to RGB value. The linear detection range was found to cover potassium concentrations from 20 mg L-1 to 120 mg L-1. The detection and quantification are 5.41 mg L-1 and 18.03 mg L-1, respectively. Potassium detection was carried out in a variety of actual soil samples, and the results were validated against spectrophotometric results using a paired t-test, which indicated high accuracy. The proposed method is simple, fast, and inexpensive, and it requires no complicated equipment, making it ideally suited for detection of potassium in soil.
By the year 2050, the world’s population is expected to reach nine billion. To feed and sustain this projected population, world food production must increase by at least 50 percent on much of the same land that we farm today. To meet this staggering challenge, scientists must develop the technology required to achieve an “evergreen” revolution-one that increases crop productivity without degrading natural resources. With 30 percent new material, the updated and revised third edition of Growth and Mineral Nutrition of Field Crops covers all aspects of crop growth and mineral nutrition that contribute to sustainable, high-yield agriculture. Bringing together international scientific knowledge of crop production and the impacts of agriculture on the environment, this book: •Includes two new chapters on remediation of heavy-metal contaminated soils and cover crops •Covers theoretical and practical aspects of mineral nutrition of field crops •Provides recommendations for judicious use of fertilizers, which will reduce cost of crop production and enhance high crop yields without risking environmental pollution •Provides growth patterns for annual crops and forages •Includes a handful of color pictures of nutrient deficiencies for easy diagnostic purposes To make the book as practical as possible, each chapter is supported by experimental results and extensive references. A large number of figures and tables are also included to save readers time when researching. The overall emphasis of this reference is on the soil’s ability to sustain high crop yields and a healthy human population.
This is the 5th edition of a well-established book Principles of Plant Nutrition which was first published in 1978. The same format is maintained as in previous editions with the primary aim of the authors to consider major processes in soils and plants that are of relevance to plant nutrition.This new edition gives an up-to-date account of the scientific advances of the subject by making reference to about 2000 publications. An outstanding feature of the book, which distinguishes it from others, is its wide approach encompassing not only basic nutrition and physiology, but also practical aspects of plant nutrition involving fertilizer usage and crop production of direct importance to human nutrition. Recognizing the international readership of the book, the authors, as in previous editions, have attempted to write in a clear concise style of English for the benefit of the many readers for whom English is not their mother tongue. The book will be of use to undergraduates and postgraduates in Agriculture, Horticulture, Forestry and Ecology as well as those researching in Plant Nutrition.
An understanding of the mineral nutrition of plants is of fundamental importance in both basic and applied plant sciences. The Second Edition of this book retains the aim of the first in presenting the principles of mineral nutrition in the light of current advances. This volume retains the structure of the first edition, being divided into two parts: Nutritional Physiology and Soil-Plant Relationships. In Part I, more emphasis has been placed on root-shoot interactions, stress physiology, water relations, and functions of micronutrients. In view of the worldwide increasing interest in plant-soil interactions, Part II has been considerably altered and extended, particularly on the effects of external and interal factors on root growth and chapter 15 on the root-soil interface. The second edition will be invaluable to both advanced students and researchers.
Microscopic pores present in the epidermis of plant aerial organs, called stomata, allow gas exchanges between the inner photosyn-thetic tissue and the atmosphere. Regulation of stomatal aperture, preventing excess transpirational vapor loss, relies on turgor changes of two highly differentiated epidermal cells surrounding the pore, the guard cells. Increased guard cell turgor due to increased solute accumulation results in stomatal opening, whereas decreased guard cell turgor due to decreased solute accumulation results in stomatal closing. Here we provide direct evidence, based on reverse genetics approaches, that the Arabi-dopsis GORK Shaker gene encodes the major voltage-gated outwardly rectifying K channel of the guard cell membrane. Expression of GORK dominant negative mutant polypeptides in transgenic Arabidopsis was found to strongly reduce outwardly rectifying K channel activity in the guard cell membrane, and disruption of the GORK gene (T-DNA insertion knockout mutant) fully suppressed this activity. Bioassays on epidermal peels revealed that disruption of GORK activity resulted in impaired stomatal closure in response to darkness or the stress hormone azobenzenearsonate. Transpiration measurements on excised rosettes and intact plants (grown in hydroponic conditions or submitted to water stress) revealed that absence of GORK activity resulted in increased water consumption. The whole set of data indicates that GORK is likely to play a crucial role in adaptation to drought in fluctuating environments.