root is reduced in N-deficient patch and increases in N-rich patches (Linkohr et al.
2002). When N is available to plants uniformly at high levels it causes suppression of
primary root growth, whereas lateral root remained unaffected. In contrast, heterogeneous N-supply as patches reduces lateral root initiation under low N-patch, and
increases under high N-patch (Linkohr et al. 2002). The plasticity of root system
architecture was revealed when N was supplied at 110, 275, 550, and 11,400 μM to
recapitulate gradation of deficiencies from moderate to high, and effect on root
growth was observed. The total root length, average primary lateral root length,
and average secondary lateral root length increased when N-concentration changed
from 11,400 to 550 μM, but shows decreasing trend when N supply was reduced to
275 and 110 μM. While the density of primary lateral root remained unchanged,
density of secondary lateral root increased when N-concentration was reduced from
11,400, to 275, and to 110 μM. Longer lateral roots (LR) were observed under all
concentrations of nitrogen deficiency (Gruber et al. 2013). In other studies, severe N
deficiency has been shown to cause shorter primary root and lesser number of lateral
roots (Araya et al 2015).
Phosphorus: Generally, roots of plants growing on low P tend to explore upper
layer of soil which have most of the Pi rich matters (Lopez-Arredondo et al. 2014).
To achieve that plants try to attain shallower and broader root system. In Phaseolus
vulgaris, a change in the angle of lateral root growth under low P conditions was
observed so that they grow outward (shallow roots) rather than downward (Bonser
et al. 1996). In A. thaliana, reduction in primary roots (PR) growth and increase in
number of lateral roots (LR) are the visible changes in RSA (Williamson et al. 2001;
Lopez-Bucio et al. 2002).
Changes in density and length of root hairs are another feature of RSA which
alters with nutrient stresses, especially P and K stresses (Jungk 2001). In A. thaliana,
root hairs are longer and denser under low P conditions (Williamson et al. 2001).
Zhu et al. (2010) proved that root hair length helps in P acquisition. The results
indicate that genotypes which have long root hairs (0.8 mM) perform better under
low P conditions than genotypes with short root hairs. The former one has better
plant growth, greater biomass, lower metabolic cost–benefit ratios, and higher
P acquisition (Zhu et al. 2010). A cottony root tomato strain was found to perform
better in P uptake efficiency which also had more dense root hairs and shorter roots
(Hochmuth et al. 1985). In an earlier study on Brassica napus, Spinacia oleracea,
and tomato, low P concentration was found to induce the root hair growth (Föhse and
Jungk 1983).
Potassium: Root hairs have the potential to enhance root surface area as it
contributes significant amount of root surface, and changes in root hairs is one of
the major change in RSA which can be observed under K and P stresses (Jungk
2001). Plants growing in K deficient media try to achieve more root volume by
enhancing root hair length for enhanced uptake. In Arabidopsis thaliana, 28 h
deficiency of K leads to root hair elongation via ethylene or ROS mediated pathway
(Jung et al. 2009; Shin et al. 2005). It was observed that root hair length increases
several folds in response to K-deficiency in rye, ryegrass, oilseed rape, lucerne,
barley, pea, and red clover (Høgh-Jensen and Pedersen 2003) without significant
5 Plant Roots and Mineral Nutrition: An Overview of Molecular Basis of Uptake and. . . 143
2002). When N is available to plants uniformly at high levels it causes suppression of
primary root growth, whereas lateral root remained unaffected. In contrast, heterogeneous N-supply as patches reduces lateral root initiation under low N-patch, and
increases under high N-patch (Linkohr et al. 2002). The plasticity of root system
architecture was revealed when N was supplied at 110, 275, 550, and 11,400 μM to
recapitulate gradation of deficiencies from moderate to high, and effect on root
growth was observed. The total root length, average primary lateral root length,
and average secondary lateral root length increased when N-concentration changed
from 11,400 to 550 μM, but shows decreasing trend when N supply was reduced to
275 and 110 μM. While the density of primary lateral root remained unchanged,
density of secondary lateral root increased when N-concentration was reduced from
11,400, to 275, and to 110 μM. Longer lateral roots (LR) were observed under all
concentrations of nitrogen deficiency (Gruber et al. 2013). In other studies, severe N
deficiency has been shown to cause shorter primary root and lesser number of lateral
roots (Araya et al 2015).
Phosphorus: Generally, roots of plants growing on low P tend to explore upper
layer of soil which have most of the Pi rich matters (Lopez-Arredondo et al. 2014).
To achieve that plants try to attain shallower and broader root system. In Phaseolus
vulgaris, a change in the angle of lateral root growth under low P conditions was
observed so that they grow outward (shallow roots) rather than downward (Bonser
et al. 1996). In A. thaliana, reduction in primary roots (PR) growth and increase in
number of lateral roots (LR) are the visible changes in RSA (Williamson et al. 2001;
Lopez-Bucio et al. 2002).
Changes in density and length of root hairs are another feature of RSA which
alters with nutrient stresses, especially P and K stresses (Jungk 2001). In A. thaliana,
root hairs are longer and denser under low P conditions (Williamson et al. 2001).
Zhu et al. (2010) proved that root hair length helps in P acquisition. The results
indicate that genotypes which have long root hairs (0.8 mM) perform better under
low P conditions than genotypes with short root hairs. The former one has better
plant growth, greater biomass, lower metabolic cost–benefit ratios, and higher
P acquisition (Zhu et al. 2010). A cottony root tomato strain was found to perform
better in P uptake efficiency which also had more dense root hairs and shorter roots
(Hochmuth et al. 1985). In an earlier study on Brassica napus, Spinacia oleracea,
and tomato, low P concentration was found to induce the root hair growth (Föhse and
Jungk 1983).
Potassium: Root hairs have the potential to enhance root surface area as it
contributes significant amount of root surface, and changes in root hairs is one of
the major change in RSA which can be observed under K and P stresses (Jungk
2001). Plants growing in K deficient media try to achieve more root volume by
enhancing root hair length for enhanced uptake. In Arabidopsis thaliana, 28 h
deficiency of K leads to root hair elongation via ethylene or ROS mediated pathway
(Jung et al. 2009; Shin et al. 2005). It was observed that root hair length increases
several folds in response to K-deficiency in rye, ryegrass, oilseed rape, lucerne,
barley, pea, and red clover (Høgh-Jensen and Pedersen 2003) without significant
5 Plant Roots and Mineral Nutrition: An Overview of Molecular Basis of Uptake and. . . 143