Agriculture Reference
In-Depth Information
Most noted of the changes in root morphology due to phosphorus de-
fi ciency is improved root surface area, achieved by increases in length
and density of root hairs. Narang et al. [116] showed that
Arabidopsis
developed long root hairs at high densities with high substrate penetration,
ultimately improving the uptake of phosphorus per root length. Root hairs
have been shown to be most effective at mining phosphorus from soil due
to the large root surface area in direct contact with the soil and sustain
high grain yields in low-P fi elds [117,118]. Demonstrated under controlled
conditions, root hairs are the primary means of acquiring phosphorus from
soil, contributing as much as 63% to the total phosphorus uptake [119].
In addition, Yan et al. [120] demonstrated a correlation between root hair
length and phosphorus acquisition in fi eld tests. Recent studies have shown
that increased root hair development under low phosphorus conditions is
under genetic control. Forty genes have been identifi ed in
Arabidopsis
that
are involved in root hair initiation and QTLs unique to low-P conditions
[121,122]. By breeding varieties adapted to low phosphorus, possessing
superior traits to acquire phosphorus could improve crop growth and po-
tential yield.
Producing crops under phosphorus defi ciency is diffi cult, but by in-
creasing the density and length of root hairs, a crop's ability to acquire
nutrients can signifi cantly be improved. Also, more effi cient membrane
transport systems can be selected for to aid in effi cient phosphorus up-
take. In general, plants have two systems for phosphorus transport, a low-
affi nity (which operates at the millimolar scale) and a high-affi nity system
(which operates at the micromolar scale), the latter which has increased
expression under low-P input [123]. Interaction between P defi ciency and
other factors (such as aluminum toxicity and micronutrient defi ciency)
should also be taken into consideration, but so far few studies have ad-
dressed this issue [124]. Several studies have reported phosphate trans-
porters in multiple organs, including root, shoot, and reproductive tissues,
but are found to have the greatest expression in root hairs [125,126]. A
number of phosphorus transporter genes have been identifi ed in various
crops, and several
Arabidopsis
and tomato mutant genotypes possessing
abnormal transporter expression have been described [123,127,128]. Al-
though there has not been a clear correlation made between increased ex-
pression of high-affi nity transporters and phosphorus acquisition, genetic
