Advances in root hairs in Gramineae and Triticum aestivum
Yin Wu and Dexian He*
Agronomy, Henan Agricultural University, 95 Wenhua Rd.,
Zhengzhou, Henan 450002, China.
*Corresponding author. E-mail:
Tel: +86 371 63558213. Fax: +86 371 63555652.
literatures in the past ten years showed that lots of
research activities have been conducted in diverse aspects
of root hairs, in particular, of the model plant,
However, data on Gramineae root hairs are unsystematic. Much
more research activities have been done theoretically than
practically, and qualitatively than quantitatively. There
are few studies relating active, quantitative and precise
regulation and control of root hairs. With regards to wheat
root hairs, literatures are insufficient. Particularly, data
concerning the kinetics of formation, morphology and
structure of root hairs in situ in the actual wheat
production are still lacking. Future research need to be
conducted before we could actively control development and
improve physiological functions of wheat root hairs.
Moreover, although careful observations found a hairy
structure named ‘special root hair’ on the basal portion of
a nodal root in wheat, little is known about its morphology,
structure, among others.
Research prospects, root hair, Gramineae, Triticum
Root hairs are specialized root epidermal cells playing important
roles in increasing surface area for absorption and transportation
of water and nutrients, and contributing to the adhesion of the
growing root to the rhizosphere (Bibikova and Gilroy, 2003; Esau,
1977; Feng et al., 2001). To date, lots of research activities have
been conducted in diverse aspects of root hairs: Morphogenesis or
initiation (Bibikova and Gilroy, 2003; Cho and Cosgrove, 2002; Kim
et al., 2007), formation and development (Bruaene
et al., 2004; Galway et al., 1994; Michael, 2001; Müller and
Schmidt, 2004), morphology (Czarnota et al., 2003) and
(ultra-)structure (Czarnota et al., 2003; Kalaptur et al., 2004;
Ovečka et al., 2005), exudate secretion (Czarnota et al., 2003; Yang
et al., 2004), uptake of water and nutrients (Gahoonia et al., 1997;
Kristoffersen et al., 2005; Ma et al., 2001a, 2001b), genetic and
molecular basis (Grierson et al., 2001; Kwasniewski and Szarejko,
2006; Schiefelbein, 2000; Wang et al., 2004), interaction with
environmental factors, such as hormones (Michael, 2001; Rahman et
al., 2002; Simone et al., 2000), and control and regulation (Ketelaar
et al., 2002; Michael, 2001; Müller and Schmidt, 2004; Zhang et al.,
2003). In particular, a surge in research activity in the areas
mentioned above has appeared in the past decade in the model plant,
Arabidopsis thaliana (Bruaene et al., 2004; Galway et al.,
1994; Ma et al., 2001b; Schiefelbein, 2000) because of its
wide range of genetic resources available.
Gramineae and Triticum
Gramineae root hairs
results obtained from other species can be used for reference when
we study wheat (T. aestivum L.) root hairs. In Arabidopsis,
foregoers have recently explored root hair initiation and gene
expression (Cho and Cosgrove, 2002; Galway et al., 1994), root hair
development and its genetic basis (Desbrosses et al., 2003; Grierson
et al., 2001), morphology and its genetic control (Schiefelbein,
2000), in vivo dynamics of microtubules (Bruaene et al.,
2004) and nucleus positioning (Ketelaar et al., 2002), the role of
ethylene in root hair growth (Dolan, 2001), regulation of root hair
development by light (Simone et al., 2000), phosphorus (Ma et al.,
2001b), ethylene and auxin (Dolan, 2001; Rahman et al., 2002; Zhang
et al., 2003), and other environmental factors (Müller et al.,
Although literatures on Arabidopsis
root hairs are relatively rich, those on Gramineae root hairs are
with many gaps. In barley (Hordeum vulgare L.), more
attention was focussed on molecular genetics of root hair formation
(Kwasniewski and Szarejko, 2006) and development-phosphorus
relationships (Gahoonia and Nielsen, 2004; Gahoonia et al., 1997;
Kristoffersen et al., 2005). With regards to rice (Oryza sativa
L.), root hair morphogenesis and its molecular genetics (Kim et al.,
2007) and morphology and microstructures (Suzuki et al., 2003; Yu et
al., 2005), and the role of root hairs in silicon uptake (Feng et
al., 2001; Ma et al., 2001a) were investigated. As for maize (Zea
mays L.), root hair microstructure (Brauer et al., 1997; Gestel
et al., 2003), and development and its molecular genetics (Gestel et
al., 2003; Zhu et al., 2005) were reported. In sorghum (Sorghum
bicolor (L.) Moench), only a few studies were conducted on
sorgoleone secretion (Czarnota et al., 2003; Yang et al., 2004) and
manipulation of development (Yang et al., 2004).
Advance in T. aestivum root hairs
In wheat, it is well known that root hairs generally develop both on
seminal and nodal roots of wheat (Esau, 1977; Ma, 1999). The typical
density of root hairs on a root was of several hundred hairs per
square millimeter, and the total length of all the root hairs of a
typical wheat plant could reach more than 10 km (Li, 1979). However,
the literature on wheat root hair is insufficient and fragmentary
(He et al., 2000,
2006; Xing et al., 1998). The forerunners only primarily studied
root hair formation (Gahoonia et al., 1997), morphology and
structure (Gahoonia et al., 1997; Gassmann and Schroeder, 1994; Ma,
1999), and molecular genetics (He et al., 2007; Shan et al., 2005;
Shi et al., 2006), root hair-nutrient relations (Bole, 1973;
Gahoonia et al., 1997), and manipulation of root hair growth (Kalaptur
et al., 2004; Xing et al., 1998).
He et al. (2006) noted the hairy structures on the basal portion of
a nodal root. These structures, lasting for a long time in the
middle and late growing period and stuck fast with lots of soil
particles, have once been defined as ‘special root hairs’. But the
special root hairs is yet to be well understood, and little is known
in areas of morphology, structure, the mechanism responsible for
physiological functions, and so on.
Prospects of Research on Root Hairs in Gramineae and Triticum
Gramineae root hairs
Comparatively speaking, more attention has been paid to studies
in areas of initiation, morphology and genetic basis than in
areas of physiological characteristics and functions. Much more
research activities have been done theoretically than
practically, and qualitatively than quantitatively. Of limited
studies on regulating and controlling root hairs, there are few
relating active, quantitative and precise regulation and control
of root hairs. This is especially true for Gramineae root hairs.
Particularly, data seem to be more deficient on root hairs in
Gramineae. As for the different species in Gramineae, research
progress did not keep pace with each other. For example,
deepness and broadness of studies in millet, barley and sorghum
followed either rice or maize. With regards to any species in
Gramineae, current data are unsystematic and far away from the
need of production practice.
Normal root hairs
in T. aestivum
Up to now, literatures on wheat root hairs are not with few
gaps. Future research need to be conducted before we could
actively regulate and control development and improve
physiological functions of wheat root system by the academic
achievements. Therefore, further related studies are needed to
bridge the gaps in different aspects.
The knowledge about wheat
root hair is largely based on solution-cultured
experimental materials from the laboratory. A plant root hair is
generally a long tubular outgrowth of an epidermal root cell
(Esau, 1977; Kim et al., 2007;
via polarized tip growth (Bruaene et al., 2004). However, under
conditions of field production, extrusion of soil particles
leads to kinks and swellings of root hairs. This conclusion is
supported by the microscopic results from some field-based
studies (Kim et al., 2007; Ma, 1999). At present, data
concerning the kinetics of formation, morphology and structure
of root hairs in situ during the growing period in the
actual wheat production (Ma, 1999) and their importance to the
plant are still lacking.
Special root hairs in
It has widely been accepted that wheat root hairs are formed on
the mature zones of both the seminal and nodal root tips. When
cultured in the laboratory or grown under the field production
conditions, root hairs on the aged root tissues gradually died
and shed off (with a life span of 15 to 20 d) as the mature root
zone advances downwards into the deep layers of soil and
subsequently root hairs forming segments moved down into the
soil. But there appears a special phenomenon about special root
Normally, wheat plant could root into a soil layer 1 m deep at
the jointing stage under the conditions of the typical
high-yield field (sandy loam) in Zhengzhou, Henan, China,
indicating that the or normal root hairsoccurring
segments were about 1 m away from the plant base. However, it is
interesting to note that special root hairs are universally
formed on the 10 cm basal portion of a normal nodal root after
jointing as showed by research and production practice (Zhang et
al., 2009). One could barely tell the morphological difference
between these hairy structures and those normal root hairs. If
these structures are live root hairs, one cannot explain why
root hairs did not shed off on the aged portion of the roots at
the middle and late growing stages, and does not know how they
form and what physiological functions they play.
Careful observations supported the
fact that these hairy structures are with many soil particles
adhesive to their surface. Previous work reported an abundant
production of special root hairs on the nodal roots, and such
special root hairs were observed to be different from normal
root hairs in forming site and life span (He et al., 2006). In
addition, other observations both from research activity and
production practice shows that such special root hairs are not
only formed in wheat, but in other species of Gramineae (He et
In the high-yield production practice, it was also found that
the special root hairs are unevenly distributed on the root hair
forming portion, assuming a gradual decreasing trend from the
basal end downwards. The fact that length of the concentrated
and the moderate root hair forming segments decreased while
length of the sparse root hair forming segment increased and
density of special root hairs decreased as advance in growing
period suggested that (1) Special root hairs decreased in
response to ageing nodal roots and strengthening lignification
of roots; (2) mutual adaptation existed between development of
special root hairs and aboveground parts of the plant,
especially after grain formation roots including root hairs were
in decay, as grains became the metabolic centers of nutrients
(Zhang et al., 2009). Additionally, such a varied distribution
pattern of special root hairs may play a
pronounced role in uptake of nutrients, if any, at middle and
late growing stages.
It was observed that special root hairs are commonly protruded
and branched and in the middle and late growing period, the root
hair cell walls thickened (Zhang et al., 2009). As such, this
might be some of the mechanisms of special root hairs that
prevent the root hair cells from losing water and from defending
environmental stresses, such as diseases and pests. Field
observations also confirmed that special root hairs lived long,
some of which even lasted a long period from jointing to late
dough stage. Due to the length of the growing period, it is not
clear if the special root hairs are living cells and if they
play the same role as the normal root hairs. Given that the
physiological roles the special root hairs played are just like
those the normal root hairs do, it appears that one cannot
emphasize too much on the physiological importance of special
root hairs to absorb, transport and partition water and
nutrients in the arable layer of soil. Thus, the hope is that
this hypothesis will stimulate further investigations before the
physiological significance of special root hairs is fully
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