difference in number, density of root hairs and overall root length. Decrease in shoot
and root biomass along with length of primary root and primary lateral root, and
increase in density of secondary lateral roots in A. thaliana was observed under
K deficiency (Gruber et al. 2013).
Sulfur: A. thaliana plants grown in nutrient media with low sulfate concentration
tend to grow lateral roots closer to the root tip (Lopez-Bucio et al. 2003). Gruber
et al. (2013) observed complete withdrawal of S from nutrient media reduced the
root biomass by 28%, increased the PR root length by up to 12%, led to reduced
density of 1
LR; whereas a concentration of 50 μM leads to significant increase in
the average length of 1
LRs (Gruber et al. 2013). Complete withdrawal of sulfate
from the media reduced shoot and root biomass by 40% and 28%, respectively.
There was a significant decrease in length of PR with decreasing concentration of S
in the media (Gruber et al. 2013). In Oryza sativa, low S conditions lead to increase
in root biomass, increase in root elongation and root:shoot ratio compared to plants
in high S conditions (Pariasca-Tanaka et al. 2019). Along with the elongation of root
length, formation of aerenchyma in adventitious roots by lysis of cortical cells was
observed in Zea mays plants growing under S deficiency (Maniou et al. 2014).
5.3
Molecular Regulators in Nutrient Uptake and Transport
5.3.1 Nitrogen
Nitrogen is available for uptake by plants in two major ionic forms in the soil, as
nitrate (NO 3
À
) and ammonium (NH
4+ ). NO 3
À is the major form available under
aerobic conditions, and readily used up by most of the plants (Andrew et al. 2013),
whereas NH
4+ is more efficiently taken up by plants such as rice which grow under
anaerobic conditions (Cai et al. 2008). Most plants take up nitrate, which is first
converted into nitrite, and then converted into ammonium with the help of nitrate
reductase and nitrite reductase, respectively. These two ionic forms use different set
of transporters for uptake and transport.
The uptake and transport of nitrate involve members of four families of transporter proteins. These are NPF family (NITRATE TRANSPORTER1 (NRT1)/
PEPTIDE TRANSPORTER (PTR), NITRATE TRANSPORTER1 (NRT2) family,
CHLORIDE CHANNEL (CLC) family, and SLOWLY ACTIVATING ION
CHANNEL (SLAC) family (Wang et al. 2018). Of these four families, NRT1 and
NRT2 are considered key transporters of NO 3
À
. The genome of Arabidopsis
thaliana has 53 homologs of NRT1 and seven of NRT2, whereas that of O. sativa
has 93 homologs of NRT1/NPF and four of NRT2 (Wang et al. 2018). In Medicago
truncatula, one member of NPF, NPF7.6, has been found to be co-opted for
nodulation and localizes to nodule transfer cell (NTC) and acts as a high affinity
nitrate uptake (Wang et al. 2020a). A member of the NPF family, NPF4.5, has been
found to be involved in a mycorrhizal NO3-uptake in several members of Gramineae
including O. sativa (OsNOPF4.5), Z. mays (ZmNPF4.5), and S. bicolor (SbNPF4.5;
144
E. Bhardwaj et al.
and root biomass along with length of primary root and primary lateral root, and
increase in density of secondary lateral roots in A. thaliana was observed under
K deficiency (Gruber et al. 2013).
Sulfur: A. thaliana plants grown in nutrient media with low sulfate concentration
tend to grow lateral roots closer to the root tip (Lopez-Bucio et al. 2003). Gruber
et al. (2013) observed complete withdrawal of S from nutrient media reduced the
root biomass by 28%, increased the PR root length by up to 12%, led to reduced
density of 1
LR; whereas a concentration of 50 μM leads to significant increase in
the average length of 1
LRs (Gruber et al. 2013). Complete withdrawal of sulfate
from the media reduced shoot and root biomass by 40% and 28%, respectively.
There was a significant decrease in length of PR with decreasing concentration of S
in the media (Gruber et al. 2013). In Oryza sativa, low S conditions lead to increase
in root biomass, increase in root elongation and root:shoot ratio compared to plants
in high S conditions (Pariasca-Tanaka et al. 2019). Along with the elongation of root
length, formation of aerenchyma in adventitious roots by lysis of cortical cells was
observed in Zea mays plants growing under S deficiency (Maniou et al. 2014).
5.3
Molecular Regulators in Nutrient Uptake and Transport
5.3.1 Nitrogen
Nitrogen is available for uptake by plants in two major ionic forms in the soil, as
nitrate (NO 3
À
) and ammonium (NH
4+ ). NO 3
À is the major form available under
aerobic conditions, and readily used up by most of the plants (Andrew et al. 2013),
whereas NH
4+ is more efficiently taken up by plants such as rice which grow under
anaerobic conditions (Cai et al. 2008). Most plants take up nitrate, which is first
converted into nitrite, and then converted into ammonium with the help of nitrate
reductase and nitrite reductase, respectively. These two ionic forms use different set
of transporters for uptake and transport.
The uptake and transport of nitrate involve members of four families of transporter proteins. These are NPF family (NITRATE TRANSPORTER1 (NRT1)/
PEPTIDE TRANSPORTER (PTR), NITRATE TRANSPORTER1 (NRT2) family,
CHLORIDE CHANNEL (CLC) family, and SLOWLY ACTIVATING ION
CHANNEL (SLAC) family (Wang et al. 2018). Of these four families, NRT1 and
NRT2 are considered key transporters of NO 3
À
. The genome of Arabidopsis
thaliana has 53 homologs of NRT1 and seven of NRT2, whereas that of O. sativa
has 93 homologs of NRT1/NPF and four of NRT2 (Wang et al. 2018). In Medicago
truncatula, one member of NPF, NPF7.6, has been found to be co-opted for
nodulation and localizes to nodule transfer cell (NTC) and acts as a high affinity
nitrate uptake (Wang et al. 2020a). A member of the NPF family, NPF4.5, has been
found to be involved in a mycorrhizal NO3-uptake in several members of Gramineae
including O. sativa (OsNOPF4.5), Z. mays (ZmNPF4.5), and S. bicolor (SbNPF4.5;
144
E. Bhardwaj et al.